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Olaf Schmidt<br />

<strong>Wood</strong> and Tree Fungi<br />

Biology, Damage, Protection, and Use


Olaf Schmidt<br />

<strong>Wood</strong> and Tree Fungi<br />

Biology, Damage,<br />

Protection, and Use<br />

With 74 Figures, 12 in Colors, and 49 Tables<br />

123


Professor Dr. Olaf Schmidt<br />

Universität Hamburg<br />

Zentrum Holzwirtschaft<br />

Abteilung Holzbiologie<br />

Leuschnerstraße 91<br />

21031 Hamburg<br />

Germany<br />

o.schmidt@holz.uni-hamburg.de<br />

Cover: Fruit body of serpula lacrymans and electrophoresis gel demontstrating species-specific priming PCR.<br />

Library of Congress Control Number: 2006920787<br />

ISBN-10 3-540-32138-1 Springer Berlin Heidelberg New York<br />

ISBN-13 978-3-540-32138-5 Springer Berlin Heidelberg New York<br />

This work is subject to copyright. All rights reserved, whether the whole or part of the material is concerned, specifically<br />

the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in<br />

any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the<br />

provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must<br />

always be obtained from Springer. Violations are liable for prosecution under the German Copyright Law.<br />

Springer is a part of Springer Science + Business Media<br />

springer.com<br />

© Springer-Verlag Berlin Heidelberg 2006<br />

Printed in Germany<br />

The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in<br />

the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and<br />

therefore free for general use.<br />

Editor: Dr. Dieter Czeschlik, Heidelberg, Germany<br />

Desk editor: Dr. Andrea Schlitzberger, Heidelberg, Germany<br />

Cover design: design & production, Heidelberg, Germany<br />

Typesetting and production: LE-TEXJelonek,Schmidt& Vöckler GbR, Leipzig, Germany<br />

31/3100/YL – 543210–Printedonacid-freepaper


Foreword<br />

<strong>Wood</strong>, as a raw material and a renewable biomass, has had great importance<br />

for thousands of years. Under suitable conditions, however, it is also easily<br />

degradable as part of the biological cycle. The processes of decomposition<br />

by fungi, and measures for protection against them, have been studied for<br />

quite a long time. The resulting knowledge on the causes and effects of wood<br />

degradation can hardly be overlooked.<br />

For more than 30 years, Olaf Schmidt has investigated the causes and effects<br />

of wood degradation by fungi and bacteria. Pioneering contributions have also<br />

been made in several fields, such as wood-inhabiting bacteria and molecular<br />

methods for fungal identification. Laboratory work is accompanied by teaching<br />

the field of wood deterioration by microorganisms, thus contributing to the<br />

broad spectrum of information accumulated.<br />

“<strong>Wood</strong>andTreeFungi”byOlafSchmidtpresentsthemostcomprehensive<br />

treatise on the fundamentals, causes, and consequences of decomposition of<br />

wood as well as measures for its prevention. The 1,400 references give an<br />

overlook of the vast amount of information evaluated. For a long time to come<br />

this book will be the competent source of knowledge about the fascinating<br />

interactions between wood and microorganisms.<br />

Walter Liese


Preface<br />

This book is the updated revision of the German edition “Holz- und Baumpilze”<br />

from 1994. Errors were corrected and new results were included. Particularly<br />

the chapter “Identification” was supplemented by molecular techniques. I realize<br />

that a one-author book on a relatively broad topic must include errors<br />

and also may have ignored recent literature. Strictly speaking, one should only<br />

write about things that they have experienced themselves, in the case of point<br />

this only concerns some aspects of bacteria and those fungi which inhabit the<br />

xylem of dead wood. Thus, current “secondary literature” was used for those<br />

chapters that are “on the edge” of my own research interest.<br />

For better readability, the authors of fungal names are not mentioned in<br />

the text, but summarized in an appendix. Fungal synonyms are also not given.<br />

These are available from Index Fungorum (www.indexfungorum.org/names/<br />

names.asp). Fungal names cited from (older) publications were transferred to<br />

the current version.<br />

Thanks for general advice go to Prof. Dr. Dr. h.c. mult. Walter Liese, for critical<br />

reading to Prof. Dr. Dirk Dujesiefken (Chap. 8.2), Dr. Hubert Willeitner,<br />

and Dr. Peter Jüngel (Chap. 7.4), to Mrs. Ute Moreth for providing experimental<br />

data, Dr. Tobias Huckfeldt for several photographs, many colleagues for<br />

permission to use their photographs, Mrs. Christina Waitkus for transferring<br />

many pictures in an electronic version, to Springer-Verlag, particularly Mrs.<br />

UrsulaGrammandDr.D.Czeschlik,forco-operation,toMr.JardiMullinaxfor<br />

making my English understandable, and to Mrs. Cornelia Gründer for careful<br />

printing.<br />

Hamburg, December 2005 Olaf Schmidt


Contents<br />

1 Introduction 1<br />

2 Biology 3<br />

2.1 Cytology and Morphology.................................................... 3<br />

2.2 Growth and Spreading ......................................................... 10<br />

2.2.1 Vegetative Growth ..................................................... 10<br />

2.2.2 Reproduction of Deuteromycetes ................................. 16<br />

2.2.3 Sexual Reproduction.................................................. 18<br />

2.2.4 Fruit Body Formation ................................................ 24<br />

2.2.5 Production, Dispersal and Germination of Spores .......... 25<br />

2.3 Sexuality............................................................................ 26<br />

2.4 Identification...................................................................... 31<br />

2.4.1 Traditional Methods .................................................. 31<br />

2.4.2 Molecular Methods.................................................... 33<br />

2.5 Classification...................................................................... 47<br />

3 Physiology 53<br />

3.1 Nutrients ........................................................................... 53<br />

3.2 Air .................................................................................... 58<br />

3.3 <strong>Wood</strong> Moisture Content ....................................................... 60<br />

3.4 Temperature....................................................................... 67<br />

3.5 pH Value and Acid Production by Fungi ................................. 70<br />

3.6 Light and Force of Gravity .................................................... 74<br />

3.7 Restrictions of Physiological Data.......................................... 77<br />

3.8 Competition and Interactions Between Organisms................... 79<br />

3.8.1 Antagonisms, Synergisms, and Succession .................... 79<br />

3.8.2 Mycorrhiza and Lichens ............................................. 82<br />

4 <strong>Wood</strong> Cell Wall Degradation 87<br />

4.1 Enzymes and Low Molecular Agents ...................................... 87<br />

4.2 Pectin Degradation.............................................................. 92<br />

4.3 Degradation of Hemicelluloses.............................................. 93<br />

4.4 Cellulose Degradation.......................................................... 95<br />

4.5 Lignin Degradation ............................................................. 99


X Contents<br />

5 Damages by Viruses and Bacteria 109<br />

5.1 Viruses .............................................................................. 109<br />

5.2 Bacteria ............................................................................. 109<br />

6 <strong>Wood</strong> <strong>Discoloration</strong> 119<br />

6.1 Molding............................................................................. 121<br />

6.2 Blue Stain........................................................................... 125<br />

6.3 Red Streaking ..................................................................... 129<br />

6.4 Protection.......................................................................... 131<br />

7 <strong>Wood</strong> Rot 135<br />

7.1 Brown Rot.......................................................................... 135<br />

7.2 White Rot........................................................................... 138<br />

7.3 Soft Rot ............................................................................. 142<br />

7.4 Protection.......................................................................... 146<br />

8 Habitat of <strong>Wood</strong> Fungi 161<br />

8.1 Fungal Damage to Living Trees.............................................. 161<br />

8.1.1 Bark Diseases............................................................ 163<br />

8.1.2 Wilt Diseases ............................................................ 168<br />

8.2 Tree Wounds and Tree Care .................................................. 173<br />

8.2.1 Wounds and Defense Against <strong>Discoloration</strong> and Decay ... 173<br />

8.2.2 Pruning.................................................................... 177<br />

8.2.3 Wound Treatment...................................................... 178<br />

8.2.4 Detection of Tree and <strong>Wood</strong> Damages .......................... 179<br />

8.3 Tree Rots by Macrofungi ...................................................... 183<br />

8.3.1 Armillaria Species ..................................................... 186<br />

8.3.2 Heterobasidion annosum s.l......................................... 189<br />

8.3.3 Stereum sanguinolentum ............................................ 195<br />

8.3.4 Fomes fomentarius ..................................................... 195<br />

8.3.5 Laetiporus sulphureus ................................................ 197<br />

8.3.6 Meripilus giganteus .................................................... 197<br />

8.3.7 Phaeolus schweinitzii.................................................. 198<br />

8.3.8 Phellinus pini ............................................................ 198<br />

8.3.9 Piptoporus betulinus .................................................. 199<br />

8.3.10 Polyporus squamosus ................................................. 199<br />

8.3.11 Sparassis crispa ......................................................... 200<br />

8.4 Damage to Stored <strong>Wood</strong> and Structural Timber Outdoors......... 200<br />

8.4.1 Daedalea quercina ..................................................... 202<br />

8.4.2 Gloeophyllum Species................................................. 202<br />

8.4.3 Lentinus lepideus ....................................................... 205<br />

8.4.4 Paxillus panuoides ..................................................... 205<br />

8.4.5 Schizophyllum commune............................................. 206


Contents XI<br />

8.4.6 Trametes versicolor .................................................... 206<br />

8.5 Damage to Structural Timber Indoors.................................... 207<br />

8.5.1 General and Identification .......................................... 207<br />

8.5.2 Lesser Common Basidiomycetes in Buildings................. 212<br />

8.5.3 Common House-Rot Fungi ......................................... 214<br />

8.5.4 Prevention of Indoor Decay Fungi and Refurbishment<br />

of Buildings .............................................................. 233<br />

9 Positive Effects of <strong>Wood</strong>-Inhabiting Microorganisms 237<br />

9.1 “Myco-<strong>Wood</strong>”..................................................................... 238<br />

9.2 Cultivation of Edible Mushrooms .......................................... 239<br />

9.3 Biological Pulping ............................................................... 244<br />

9.4 “Palo Podrido” and “Myco-Fodder”....................................... 246<br />

9.5 <strong>Wood</strong> Saccharification and Sulphite Pulping ........................... 247<br />

9.6 Grinding and Steam Explosion.............................................. 248<br />

9.7 Recent Biotechnological Processes and Outlook....................... 249<br />

Appendix 1<br />

Identification Key for Strand-Forming House-Rot Fungi 253<br />

Appendix 2<br />

Fungi Mentioned in this Book 261<br />

References 267<br />

Subject Index 329


1 Introduction<br />

<strong>Wood</strong> is damaged by various agents (Table 1.1).<br />

This book addresses wood damage caused by microorganisms (fungi and<br />

bacteria). <strong>Wood</strong> damage by fungi has also been called “wood diseases” (“Holzkrankheiten”)<br />

and “wood pathology” (“Holzpathologie”). Because it concerns<br />

the substrate “tree” in the majority of dead cells, because all parenchyma cells<br />

in the wood of felled trees are dead after a few weeks, and, thus, because a dead<br />

tissue cannot fall ill, distance was taken to these terms. With regard to the<br />

microbial decomposition of biomass, in the English language there is a welldescribing<br />

differentiation between “biodeterioration”, which means unwanted<br />

biological destruction, and “biodegradation”, which means controlled degradation<br />

by microorganisms or their enzymes and degrading agents. Biodeterioration<br />

corresponds to the German “Holzzerstörung” and “Holzzersetzung”,<br />

and the latter positive aspect of wood biodegradation (“Holzabbau”) belongs<br />

to the area of “biotechnology of lignocelluloses” (Bruce and Palfreyman 1998;<br />

Chap. 9).<br />

Inthefollowingtext,themicrobialdamagetothexylem(wood)ofthetreeis<br />

mainly addressed. Since leaves, bark, and roots are entrance gates for parasites<br />

into the living tree that can lead to reduced tree growth and to lesser wood<br />

quality, some aspects of the area of “forest pathology” are included (Butin<br />

1995; Chaps. 5 and 8.1–8.3). The mechanisms of the decomposition of solid<br />

Table 1.1. Agents for wood damages<br />

– mankind: e.g., paper production, fire for cooking<br />

– conflagrations for agriculture<br />

– weathering, UV light<br />

– acids, bases, corrosion by salts, gases, discoloration by metals<br />

– wood insects: xylophagous beetles, termites, wasps, breeding ambrosia beetles,<br />

wood-colonizing ants<br />

– marine borers<br />

– bacteria: wetwood, discoloration, pit degradation, decay by erosion, tunneling,<br />

cavity bacteria<br />

– fungi:<br />

wood discoloration by molds, blue-stain fungi, red-streaking fungi<br />

wood decay by brown, soft, and white-rot fungi<br />

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2 1 Introduction<br />

wood apply essentially also to wood-based composites (plywood, fiberboard,<br />

particleboard, orientated strand board) (e.g., Chung et al. 1999) and to woodplastic<br />

composites (Simonson et al. 2004). Sutter (2003) and Unger et al. (2001)<br />

report on damages, conservation, and restoration of wood artifacts. Bacterial<br />

and soft-rot attack of archaeological wood is described by Blanchette (1995),<br />

Nelson et al. (1995), and Singh et al. (2003).<br />

The decomposition of biomass, which concerns wood and other lignocelluloses<br />

(annual plants), is a necessary part of the natural material cycle: during<br />

photosynthesis, wood and O2 are formed from CO2 and H2Obymeansoflight.<br />

In counterpart, the wood becomes degraded by fungi and bacteria to CO2,H2O<br />

and energy for microbial metabolism.<br />

In the forests of the earth, about 400 billion t of CO2 are bound. Without<br />

microbial degradation (or burning) of the biomass, the CO2 supply of the<br />

atmosphere necessary for photosynthesis would be used up in 20–30 years<br />

(Schlegel 1992), photosynthesis would grind to a halt, and the earth would be<br />

overfilled with non-decaying biomass.<br />

Humans retard wood degradation by microorganisms for economic reasons<br />

by wood protection measures (Willeitner and Liese 1992; Goodell et al. 2003;<br />

Müller 2005; Chap. 7.4) in order to prolong the use of the raw material wood.<br />

Thus, for example, the service life of a beech sleeper, which would amount to<br />

about 3 years without any protection, extends to about 45 years after impregnation<br />

with coal tar oil.<br />

Until around 1800, rot was considered punishment from God, and fruit<br />

bodies as eczemas. Still, in 1850, v. Liebig attributed decay to a “slow burning”.<br />

In 1874, Robert Hartig recognized the causality between pest and damage and<br />

is thus considered the father of forest and wood pathology (Merrill et al. 1975).<br />

The first pure culture of a wood-degrading fungus was succeeded to Brefeld<br />

(1881).<br />

Research on wood deterioration is done worldwide. The global network for<br />

cooperation in forest and forest products research is the International Union of<br />

Forest Research Organizations (IUFRO), which was created in Eberswalde, Germany,<br />

in 1892, and has 15,000 scientists in almost 700 member organizations<br />

in over 110 countries. Current research results on wood damages, protection,<br />

and investigation methods are introduced at the annual symposia of the International<br />

Research Group on <strong>Wood</strong> Preservation (IRG). Edible mushrooms<br />

cultured on wood are discussed at the meetings of the International Mycological<br />

Society. A recent comprehensive treatise on the various aspects of fungi is<br />

“The Mycota” (Esser 1994 et seq.).<br />

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2 Biology<br />

2.1<br />

Cytology and Morphology<br />

“<strong>Wood</strong> fungi” are eukaryotic and carbon-heterotrophic (free from chlorophyll)<br />

organisms with chitin in the cell wall, reproduce asexually and/or sexually<br />

by non-flagellate spores, filamentous, immovable and mostly land inhabiting.<br />

Damage to wood in water by fungi is described by Jones and Irvine (1971), Jones<br />

(1982) and Kim and Singh (2000). Soft-rot fungi belonging to the Ascomycetes<br />

and Deuteromycetes (Chap. 7.3) destroy wood with high moisture content in<br />

water or soil (e.g., Findlay and Savory 1954; Liese 1955). Fungi associated with<br />

leaf litter in a woodland stream were treated by Suberkropp (1997).<br />

In this book, a fungal cell, the hypha, is defined as one individual cell<br />

of mostly tubular shape that consists of a cell wall, contains a protoplasm<br />

with a nucleus and other organelles, and is in the “higher fungi” separated<br />

from its one or two neighbors by a transverse wall, the septum (Fig. 2.1). In<br />

analogy to the “higher plants”, where nearly every living cell is connected<br />

to its neighbors by cytoplasmic channels, the plasmodesmata, which pass<br />

through the intervening cell walls, also the protoplasms of neighbored hyphae<br />

areconnectedwitheachotherthroughtheporeordoliporesystem(Fig.2.2).<br />

This basic hypha is termed “vegetative hypha” in this book. This definition<br />

contrasts to others where one hypha, also termed generative hypha, is a more<br />

or less long filament consisting of several hyphal “compartments”, a definition<br />

that is hazy because the transition to the next higher unit, the mycelium, is<br />

flowing. The mycelium is thus the filamentous lining up of hyphae, consisting<br />

in young mycelia of only a few vegetative hyphae and in older ones of several<br />

and branched hyphae. Figure 2.1 shows septate hyphae as they occur in the<br />

wood-inhabiting Deuteromycetes, Ascomycetes, and Basidiomycetes.<br />

The diameter of hyphae reaches from 0.1–0.4µm for the microhyphae of<br />

Phellinus pini (Liese and Schmid 1966) to 60µm for the vessel hyphae in the<br />

mycelial strand (cord) of the True dry rot fungus, Serpula lacrymans,withan<br />

average for vegetative hyphae of about 2–7 µm (S. lacrymans: 3µm: Seehann<br />

and v. Riebesell 1988). Their length reaches from about 5µm for round/oval<br />

cells (spores) up to several micrometers. The size of many bacteria is between<br />

0.4 and 5µm.<br />

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4 2Biology<br />

Fig.2.1. Vegetative hyphae. C coenocytic hyphae, S septate hyphae<br />

Due to the smallness of the individual hypha and the use of microscopic and<br />

microbiological methods, fungi are microorganisms. This attachment does not<br />

contrast to the fact that fungi can form large and firm structures such as fruit<br />

bodies of decimeters in size like in the Tinder fungus, Fomes fomentarius (see<br />

Fig. 8.15). Those fruit bodies are, however, also composed of single hyphae. The<br />

main argument is, however, that the “actual fungus” is the vegetative hyphal<br />

system that can grow unlimited by simple mitotic reproduction without ever<br />

fruiting if fresh nutrients (wood, soil, agar) are available, and if growth in<br />

a certain biotope is not inhibited by the own or foreign metabolic products.<br />

Fungi are scientifically examined in microbiological or medical institutes<br />

(predominantly Deuteromycetes and Ascomycetes) and often in botanical institutes.<br />

They do, however, no longer rank among the plants. In multi-kingdom<br />

systems (Whittaker 1969), the “higher fungi” (Ascomycetes, Basidiomycetes)<br />

form the distinct group of fungi beside the Prokaryotes (Bacteria), Protista<br />

(eukaryotic single-celled organisms: slime fungi and “lower fungi”), plants,<br />

and animals (Müller and Loeffler 1992). Based on rDNA sequences, Woese and<br />

Fox (1977) divided the Prokaryotes into the kingdoms Eubacteria and Archaebacteria<br />

and later emphasized three domains, which were renamed Bacteria,<br />

Archaea, and Eucarya (see Fig. 5.1).<br />

The hyphal wall defines the shape of the hypha and provides the mechanical<br />

strength to resist the internal turgor pressure. The wall consists of various<br />

carbohydrates. Some yeast has mannan-β-glucans, while Ascomycetes,<br />

Deuteromycetes, and Basidiomycetes possess chitin-β-glucans, never cellulose.<br />

Chitin [poly–β(1-4)-N-acetoamido-2-deoxy-D-glucopyranose], which occurs<br />

except in fungi also in the exoskeleton of arthropods and crustaceans, and<br />

in some mollusks, is a macromolecule made of β-1,4-glycosidically linked<br />

N-acetylglucosamine units. Chitin synthases (CHS; EC 2.4.1.16) catalyze the<br />

formation of chitin from the precursor UDP-N-acetylglucosamine. In the yeast<br />

Saccharomyces cerevisiae, CHS I acts as a repair enzyme and is involved in the<br />

chitin synthesis at the point where the daughter and mother cells separate. CHS<br />

II participates in septa formation and CHS III in chitin synthesis of the cell<br />

wall (Robson 1999). Ascomycetes have two-layered cell walls, while walls of Basidiomycetes<br />

are multilamellar. The entire structure of the cell wall including<br />

extracellularlayers is complex(Toft1992;Robson1999):The wall offilamentous<br />

fungi may consist for example of an inner wall of about 10–20 nm composed<br />

of chitin microfibrils and an outer wall composed of a protein layer (about<br />

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2.1 Cytology and Morphology 5<br />

10 nm), a layer of glycoprotein (about 50 nm), and a slime layer, also termed<br />

mucilage layer, sheath, extracellular matrix or mycofibrils (about 75–100 nm).<br />

Slimelayersarecommontofungiandhavebeenfoundinbluestain,white,<br />

brown, and soft-rot fungi. They are composed of protein, lipid and carbohydrate<br />

containing material (α-glucan, β-1,3 and β-1,6-glucan) or of crystalline<br />

to membranous and fibrillar structures (Liese and Schmid 1963; Schmid and<br />

Liese 1965; Schmid and Baldermann 1967; Holdenrieder 1982; Green et al.<br />

1989). Various functions have been suggested for the slime layer (Schmid and<br />

Liese 1966; Sutter et al. 1984; Green et al. 1991b; Kim 1991; Abu Ali et al. 1997;<br />

Messner et al. 2003; Table 2.1). In Phanerochaete chrysosporium, the slime layer<br />

is composed of equal amounts of carbohydrates, lipids, and proteins, including<br />

five fractions with molecular weights between 30 and 200 kDa (cf. Messner<br />

et al. 2003). Production of the slime layer was influenced by iron, manganese<br />

and nitrogen concentration, temperature, and pH value (Jellison et al. 1997).<br />

Hyphae may be encrusted and covered with resinous material, oil drops,<br />

and calcium oxalate crystals (e.g., Holdenrieder 1982).<br />

The hyphal wall encloses the cytoplasm with its outer boundary, the plasmalemma.<br />

In the majority of fungi, ergosterol is the chief sterol in the plasma<br />

membrane and is used for fungal quantification (Chap. 2.4). Some antifungals<br />

like polyene and triazole act on this ergosterol (Robson 1999). The cytoplasm<br />

principally resembles that one of plants. There is one too many relatively<br />

small nuclei. Plastides are absent. Growing hyphae of Ascomycetes and Basidiomycetes<br />

show at the hyphal apex a mass of small vesicles, the “Spitzenkörper”.<br />

The tonoplast encloses a vacuolar system. Carbon is stored in glycogen<br />

vesicles and lipid vacuoles. Nitrogen is deposited as amino acids in the vacuolarsystemorasprotein.Phosphorusiscondensedaspolyphosphateinvolutin<br />

grana, often in vacuoles. Some yeast contains starch.<br />

Table 2.1. Possible functions for fungal slime layers<br />

– substrate recognition<br />

– adhesion to and establishing contact<br />

– covering the S3 layer of the wood cell wall during decay process<br />

– conditioning of the substrate for decay<br />

– modification of the extracellular ionic environment and pH-value<br />

– transport vector for low-molecular decay agents and enzymes to the wood (see Fig. 7.3)<br />

– transport vector for degradation products to the hypha<br />

– storage, concentration and retention of decay agents<br />

– regulation of the decay process, e.g., by controlling the glucose level<br />

– microenvironment for H2O2 maintenance needed for lignin degradation<br />

– storage of nutrients<br />

– permitting a film of liquid water to surround the wood cell wall<br />

– protection of the mycelium against dehydration and adverse environmental conditions<br />

– increase of surface area for aerobic respiration<br />

– storage of copper or CCA from attack of impregnated wood<br />

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6 2Biology<br />

The solutes in the cytoplasm and vacuolar system have a certain osmotic<br />

potential. If the potential is lower than that of the substrate, water is adsorbed<br />

across the membranes, increasing the volume of the cytoplasm (Jennings and<br />

Lysek 1999). An internal turgor needs to be generated for the elongation of the<br />

hyphal apex that is that water uptake and wall growth are in balance.<br />

Mycelium is the filamentous, partly branched, and in the wood-inhabiting<br />

Basidiomycetes usually whitish network made from some to numerous, in the<br />

light microscope hyaline to light yellow and in the case of blue-stain fungi<br />

brownish (melanin) hyphae. In Deuteromycetes, the pigmentation of the culture<br />

is manifold due to the various pigments of the conidia, whose color depends<br />

on the species. Mycelium forms the macroscopically visible thallus, the<br />

undifferentiated form of vegetative growth of fungi (thallobionts), which is not<br />

differentiated as it is the kormus of the “higher plants” into the organs, shoot<br />

axis, leaf, and root. Mycelium is the actual fungus with nourishing function and<br />

thus with wood decay ability. Under sufficient nutrient offer, mycelium is theoretically<br />

growable for an unlimited period. Sexuality with fruit body formation<br />

is not necessary for survival. For example, mycelium of an isolate of the Asian<br />

edible mushroom Shiitake, Lentinula edodes, is now maintained since about<br />

1940 exclusively on agar in the refrigerator without ever fructifying, but would<br />

immediately develop fruit bodies (Fig. 9.1) when favorable environmental conditions<br />

are provided (Schmidt 1990). The largest and longest-living wood fungi<br />

are Armillaria species. A clone of A. gallica in a Michigan forest covered 15 ha<br />

and was estimated at an age of about 1,500 years and a total biomass of 1,000 t<br />

(Smith et al. 1992). A clone of A. ostoyae estimated at 400–1,000 years covered<br />

an area of 6 km 2 in the Rocky Mountains (Anonymous 1992a). In Oregon, an<br />

A. ostoyae clone of 2,400 years stretched over an area of about 9 km 2 of forest<br />

soil (Schwarze and Ferner 2003).<br />

Deutero- and Ascomycetes have in the septum a central simple pore. <strong>Wood</strong>inhabiting<br />

Basidiomycetes (Homobasidiomycetes) contain the more complicateddoliporeseptumwithaparenthesomeonbothsides(Fig.2.2).<br />

The protoplasts of neighboring hyphae are connected through pores in the<br />

septa for the longitudinal migration of organelles and even nuclei, and for<br />

the transport of solutes (translocation; Chap. 3.1). Woronin bodies, which are<br />

composed of protein, block the pore when a hypha becomes injured.<br />

Fig.2.2. Septa (S) ofAscomycetes(a)<br />

and Basidiomycetes (b). P simple pore<br />

septum, D dolipore septum, H hyphae<br />

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2.1 Cytology and Morphology 7<br />

The hyphal system expands by extension of individual hyphae that exhibit<br />

apical growth and by branching (Fig. 2.3).<br />

Different zones occur in the growing hypha (Fig. 2.4), which correspond to<br />

different ages and developmental stages (Huckfeldt 2003).<br />

Fig.2.3. Apical growth and hyphal branching system. One branch is sectioned to show<br />

the septum and some features of the protoplasm. N nucleus, ER endoplasmic reticulum,<br />

D dictyosome, V vacuole, M mitochondrion, Woronin bodies (dark) [reproduction with<br />

permission, from Jennings DH, Lysek G (1999) Fungal Biology, 2nd edn. Bios, Oxford,<br />

Fig. 1.1. page 6]<br />

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8 2Biology<br />

Fig.2.4. Ultrastructural features and zonation of growing hyphae of a house-rot fungus in<br />

woody tissue (MP, S1, S2andT wood cell wall layers). G glycogen, N nucleus, L lipid drops,<br />

Mi mitochondrion, MS multivesicles structure, V vacuole, Ve vesicle (from Huckfeldt 2003)<br />

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2.1 Cytology and Morphology 9<br />

Due to the apical growth, the hyphal tip is the most sensitive part of the<br />

mycelium and gets the first contact with the substrate wood. <strong>Wood</strong> preservatives,<br />

unfavorable temperatures, shortage of nutrients, and moisture affect the<br />

tip. The tip contains different vesicles and membranous structures for cell wall<br />

synthesis and transport processes as well as enzymes for nutrient metabolism<br />

(Robson 1999). Like in other Basidiomycetes, the tip in Serpula lacrymans<br />

(Fig. 2.4) consists of three zones:<br />

In the apical zone, material for the structure of the cell wall, slime layer,<br />

and plasmalemma is concentrated and incorporated in the growing mycelium.<br />

Vesicles from the Spitzenkörper merge with the plasmalemma and deliver<br />

cell wall components. In the subapical zone, compartments and ribosomes<br />

are involved in the synthesis of cell wall material and secretion products.<br />

The basal zone contains the nucleus, or in the case of dikaryons, two nuclei.<br />

Vacuoles are involved in internal recycling processes, detoxification, storage,<br />

upkeep of turgor pressure, control of ionic strength as well as metabolization<br />

of compartments and macromolecules. The cytoskeleton, which consists of<br />

actin filaments and microtubuli, serves together with motor proteins to the<br />

upkeep of the zonation of the hyphal tip by changing the position of the<br />

compartments. Thus, the compartments continuously follow the growing tip<br />

to maintain the density of organelles in the subapical zone. Jennings and Lysek<br />

(1999) differentiated the apical growth zone with the extending hyphal tip, the<br />

absorption zone where there is uptake of nutrients, the storage zone in which<br />

nutrients are stored as reserve substances, and the senescence zone where dark<br />

pigments and lysis may occur.<br />

The hyphal system produces a loose network of filaments (aerial mycelium<br />

on the wood surface, substrate mycelium within wood and soil) or solid,<br />

morphologically differentiated units such as the strands of house-rot fungi<br />

and the rhizomorphs of Armillaria species (Chap. 2.2.1), and the fruit bodies.<br />

The mycelia of wood fungi differ considerably in their growth rate. Table 2.2<br />

shows the growth rate of some house-rot fungi.<br />

The growth rate serves as a characteristic for species identification in keys.<br />

Growth rate is also used as a hint of the age of the fungal infestation time of<br />

a building, e.g., in the case of damage by Serpula lacrymans (Chap. 8.5.3.4).<br />

However, mycelial extension depends on environmental conditions like temperature<br />

and nutrients, which differ between stable and favorable laboratory<br />

conditions and fluctuations in buildings. Furthermore, different isolates of<br />

a species commonly differ in growth rate (“strain variation”). In addition,<br />

dikaryons and monokaryons may differ in growth. For example, dikaryons of<br />

Lentinula edodes (Schmidt and Kebernik 1987), Serpula lacrymans (Schmidt<br />

and Moreth-Kebernik 1991a), and Stereum hirsutum (Rayner and Boddy 1988)<br />

grew faster than the monokaryons. Nevertheless, there are so-called “fastgrowing”<br />

wood fungi like the Cellar fungus, Coniophora puteana, withupto<br />

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10 2 Biology<br />

Table 2.2. Growth rate of house-rot fungi at optimum temperature (from Schmidt and<br />

Huckfeldt 2005)<br />

Group Species Number of Maximum radial<br />

investigated increase on agar<br />

isolates per day (mm)<br />

Dry-rot fungi Serpula lacrymans 2 4.0–5.1<br />

S. himantioides 2 7.0–11.0<br />

Leucogyrophana mollusca 6 1.0–3.3<br />

L. pinastri 4 2.4–4.2<br />

Meruliporia incrassata 2 2.8–3.2<br />

Cellar fungi Coniophora puteana 27 2.5–11.3<br />

C. marmorata 2 9.7–12.3<br />

C. arida 1 4.7<br />

C. olivacea 5 3.7–9.0<br />

White polypores Antrodia vaillantii 12 4.3–7.7<br />

A. sinuosa 4 4.0–8.0<br />

A. xantha 3 5.5–8.2<br />

A. serialis 3 3.5–3.9<br />

Oligoporus placenta 4 4.2–9.8<br />

Gill polypores Gloeophyllum abietinum 5 3.8–5.5<br />

G. sepiarium 4 6.8–8.3<br />

G. trabeum 5 7.1–9.1<br />

Oak polypore Donkioporia expansa 1 5.1<br />

11 mm radial increment per day on 2% malt extract agar at 23 ◦ C and “slowgrowing”<br />

species like S. lacrymans with up to 5mm at 19 ◦ C.<br />

Mycelium of wood-decay fungi predominantly grows as substrate mycelium<br />

insideofthesubstrateswood(orsoil)andisoftennotvisiblyontheoutside,<br />

thus, wood rot, particularly at incipient decay, is frequently not recognizable<br />

outwardly. By means of surface mycelium, growth additionally or predominantly<br />

occurs on the substrate surface, e.g., on nutrient agar or in the case of<br />

molds that grow superficially on timber and masonry. Aerial mycelium, e.g., in<br />

the white polypores in buildings (Antrodia spp.), is an intensively developed<br />

surface mycelium. The texture of the mycelial mat is manifold, e.g., flat on the<br />

substrate, crusty, woolly, felty, or zonate (Stalpers 1978).<br />

2.2<br />

Growth and Spreading<br />

2.2.1<br />

Vegetative Growth<br />

Simplistically, wood fungi live through two functionally different phases: the<br />

vegetative stage for mycelial spread and the reproductive stage for the elaboration<br />

of spore-producing structures. Rayner et al. (1985) extended the de-<br />

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2.2 Growth and Spreading 11<br />

velopment of a fungus in arrival, establishment, exploitation, and exit. The<br />

vegetative, asexual stage consists in wood fungi of vegetative hyphae with<br />

some specialized forms. The reproductive stage can both occur asexually or<br />

sexually (Schwantes 1996; Table 2.3).<br />

Functional specialization of the mycelium occurs during the vegetative stage:<br />

germination, infection, spread, and survival. These functions are correlated<br />

with different “fungal organs”. Spores (conidia, chlamydospores, also the sexually<br />

derived asco- and basidiospores) germinate under suitable conditions<br />

(moisture, temperature). The young germ hypha first shows some nuclei before<br />

the young mycelium grows with septation in the monokaryotic condition.<br />

Mycelial growth takes place via mitoses and synthesis of hyphal biomass. Infection<br />

and colonization of new substrates occurs by spores, hyphae, mycelium,<br />

and special forms like bore-hyphae, transpressoria, strands, and rhizomorphs.<br />

Prerequisites for the colonization of a substrate are suitable humidity and nutrient<br />

availability in the substrate or, like in Serpula lacrymans, theability<br />

of a fungus to transport nutrients and water and last, whether and by which<br />

organisms the substrate is already occupied (Rayner and Boddy 1988). Boring<br />

microhyphae of 0.1–0.4µm diameter develop e.g., in Phellinus pini at the<br />

hyphal tip without recognizable septum and produce boreholes of 0.3–3.3µm<br />

diameter probably by enzyme action (Schmid and Liese 1966). The appressorium<br />

is a hypha for the mechanical fixation to the substrate (Fig. 2.5a). The<br />

transpressorium (Fig. 2.5b) of the blue-stain fungi (Chap. 6.2) is a specialized<br />

boring hypha (Liese 1970); it is still unknown whether the penetration<br />

of the woody cell wall is by mechanical and/or enzymatic action. Transpressoriahavealsobeenfoundinthewhite-rotfungusPhellinus<br />

pini (Liese and<br />

Schmid 1966).<br />

Table 2.3. Functional and morphological differentiation of wood fungi (modified after<br />

Müller and Loeffler 1992)<br />

Developmental stage Function “Organ”<br />

Vegetative/asexual Germination Germ hypha<br />

Infection, Hypha, mycelium,<br />

spread boring hypha,<br />

appressorium, transpressorium,<br />

strand, rhizomorph<br />

Survival Chlamydospore, arthrospore,<br />

mycelia with resistance to<br />

dryness and heat<br />

Reproductive/asexual Anamorphic Fruit body, conidiophore,<br />

reproduction conidium<br />

Reproductive/sexual Teleomorphic Fruit body,<br />

reproduction ascus, basidium<br />

ascospore, basidiospore<br />

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12 2 Biology<br />

Fig.2.5. Appressorium and transpressoria of blue-stain fungi in wood. a Hyphae (H) of<br />

Ophiostoma piceae in the luminina (L) of a pine tracheid. A appressorium, T boring canal<br />

through the activity of a transpressorium, C wood cell wall. (LM, from Liese and Schmid<br />

1962); b Two transpressoria (EM, from Liese and Schmid 1966)<br />

Strands (cords) (Fig. 2.6) develop in a number of house-rot fungi and usually<br />

consist of three hyphal types, vegetative hyphae, thin fiber (skeletal) hyphae<br />

with mostly thick walls for strengthening, and broad vessel hyphae for nutrient<br />

transport (Nuss et al. 1991). These hyphae form a distinct mycelium in the longitudinal<br />

direction, which is, however, not so well organized like the tissue-like<br />

structure of the rhizomorphs. Also in contrast to rhizomorphs, strands develop<br />

behind the mycelial growth front. Particularly Serpula lacrymans overgrows<br />

larger distances of non-woody substrates and penetrates through masonry<br />

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2.2 Growth and Spreading 13<br />

Fig.2.6. Hyphae within a strand of Serpula lacrymans. H vegetative hyphae, V vessel hypha,<br />

F fiber hyphae (dark-field photo W. Liese)<br />

(only through the joints) between bricks or through old, crumbly bricks, and<br />

insulation materials. In the laboratory, some house-rot fungi overgrew by<br />

means of strands agar that contained wood preservatives (Liese and Schmidt<br />

1976) as well the fungal partner in dual culture.<br />

In the literature, there is however not always a uniform use of the terms<br />

“strands (= cords)” and “rhizomorphs”. For example, the strands of the American<br />

dry rot fungus, Meruliporia incrassata, have been termed rhizomorphs and<br />

were described as consisting of more or less parallel hyphae, outer (cortical)<br />

hyphae thick-walled and uniform in size (author: = fibers), inner (medullary)<br />

thin-walled hyphae, variable in size, and some differentiated into large conducting<br />

tubes (author: = vessels) (Palmer and Eslyn 1980). According to Burdsall<br />

(1991) “these two (S. lacrymans, M. incrassata) being similar and unique<br />

in forming large water-conducting rhizomorphs”.<br />

By means of his strand diagnosis, Falck (1912) was able to differentiate some<br />

house-rot fungi like S. lacrymans, Coniophora puteana, and Antrodia vaillantii<br />

macroscopically and microscopically. Table 2.4 shows an updated version for<br />

the above tree species based on recent measurements of mycelia in buildings<br />

andonagarculturesofgeneticallyverifiedisolates.<br />

As strand morphology is, after fruit body structure, a main feature to identify<br />

fungigrowingindoorsoranconstructionwood,anidentificationkeyforabout<br />

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14 2 Biology<br />

Table 2.4. Strand diagnosis for some common house-rot fungi (modified from Huckfeldt<br />

and Schmidt 2004, 2006)<br />

Serpula lacrymans<br />

Strands white, silver-grey to brown, more than 5 mm to 3 cm diameter, separable, with<br />

flabby mycelium in between, thick strands when dry breaking with clearly audible<br />

cracking (strands with mold contamination often not cracking any more), often in<br />

masonry; (S. himantioides: strands thinner than 2 mm and fibers 2–3.5 µmin<br />

diameter)<br />

Vegetative hyphae hyaline, partly yellowish, with large clamp connections, 2–4 µmin<br />

diameter<br />

Vessels at least partly numerous (in groups), 5–60 µmindiameter,notorrarely<br />

branched, with bar thickening up to 13 µmhigh<br />

Fibers refractive, 3–5 µm diameter, straight-lined, stiff, septa not visible, no clamps,<br />

lumens often visible<br />

Coniophora puteana, C. marmorata<br />

Strands first bright, then brown to black, up to 2 mm wide, to 1 mm thick, root-like,<br />

hardly removable (not so in C. marmorata), when removed usually fragile, partly<br />

with brighter center, underlying wood becoming black, also in masonry<br />

Vegetative hyphae usually without clamps, rarely multiple clamps (often indistinct<br />

when branched), 2–6 µmindiameter<br />

Vessels surrounded and interwoven by many fine hyphae (0.5–1.5 µm in diameter),<br />

difficult to isolate (preparation with KOH solution); drop-shaped, hyaline to<br />

brownish secretions (1–5 µm in diameter) often on hyphae; vessels due to<br />

preparation irregularly formed or distorted, up to 30 µm in diameter, thin-walled<br />

(slightly thick-walled with C. marmorata), without bars, with septa<br />

Fibers pale to dark brown, 2–4 µm in diameter, somewhat thick-walled, with relatively<br />

broad, usually visible lumen, some also branched, to be confused with generative<br />

hyphae<br />

Antrodia vaillantii, A. serialis, A. sinuosa, A. xantha<br />

Strands white to cream, partly somewhat yellowing or infected by molds, also ice<br />

flower-like, flexible also when dry, up to 7 mm in diameter, possibly also within<br />

masonry<br />

Vegetative hyphae with few clamps, 2–4 µm in diameter, often somewhat thick-walled;<br />

in KOH somewhat swelling<br />

Vessels not rare but in old strands difficult to isolate, up to 25 µm in diameter, thick-walled<br />

with middle lumen, without bars<br />

Fibers hyaline (in Antrodia xantha partly somewhat yellowish), numerous, 2–4 µmin<br />

diameter, hyphal tips with tapering ending cell walls, straight-lined, mostly<br />

unbranched, insoluble in KOH, but partly somewhat swelling, then with “blown up”<br />

hyphal segments<br />

20 strand-forming wood decay fungi based on Huckfeldt and Schmidt (2004,<br />

2006) is given in Appendix 1.<br />

The rhizomorphs of Armillaria mellea (Fig. 2.7) are tissue-like mycelial bundles<br />

with apical growth and consist of a black, gelatinous bark layer, followed<br />

by a pseudoparenchyma, and a central, loosely interwoven pith with vessel and<br />

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2.2 Growth and Spreading 15<br />

Fig.2.7. Rhizomorph of Armillaria mellea. Left: Apex with hair-like microhyphae (A), cortex<br />

(B) andpith(C). (from Hartig 1882); right: cross section (LM; from Schmid and Liese<br />

1970)<br />

fiber hyphae (Hartig 1882). By means of rhizomorphs, Armillaria species grow<br />

in the soil and infect the roots of living trees (Chap. 8.3.1).<br />

Under unfavorable conditions, resistance stages are formed. Spores are more<br />

resistant to heat, dryness, and wood preservatives than their mycelium. The hyphal<br />

cell water content is reduced, nutrients are concentrated, parts of the protoplasts<br />

or storage substances of neighboring cells are translocated in resting<br />

cells, and enzyme activity decreases (“latent life”). Chlamydospores (Fig. 2.8)<br />

are thick-walled spores with a brown cell wall, which occur in many blue-stain<br />

fungi.<br />

Formerly, it was believed that the vegetative mycelium of some wood-decay<br />

fungi is also resistant to dryness (Chap. 3.3) and heat (Chap. 3.4). Recent results<br />

show that this must not be true: When cultured on agar at about 28 ◦ C,<br />

the dikaryotic hyphae of Serpula lacrymans tend to revert to the monokaryotic<br />

condition, which regularly shows abundant arthrospores (Schmidt and<br />

Moreth-Kebernik 1990). In wood samples that were slowly dried or warmed,<br />

the substrate mycelium of S. lacrymans, C. puteana, Donkioporia expansa,<br />

and Gloeophyllum trabeum also formed arthrospores (Huckfeldt 2003). It was<br />

therefore assumed that these arthrospores are the agents for resistance against<br />

drying and heat.<br />

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16 2 Biology<br />

2.2.2<br />

Reproduction of Deuteromycetes<br />

Fungi that reproduce asexually (anamorphic fungi) are either yeasts or Deuteromycetes.<br />

The term “yeast” is descriptive and stands for any fungus that<br />

reproduces by budding.<br />

Deuteromycetes (Fungi imperfecti, colloquially: molds) is an artificial assemblage<br />

of fungi that reproduce asexually by conidia (conidiospores), either<br />

as the only form for propagation (imperfect fungi) or additionally (anamorph)<br />

to a sexual reproduction (teleomorph). When both the anamorph and the teleomorph<br />

are known, the fungus is called a holomorph (the whole fungus). The<br />

teleomorph may have one (mono-anamorphic) or many (pleo-anamorphic)<br />

asexual stages. In other words: Deuteromycetes are the conidia-producing<br />

forms of a fungus and may or may not be associated with a teleomorph.<br />

Many Deuteromycetes are supposed to have a teleomorph in the Ascomycetes,<br />

but they may also have basidiomycetous affinity. Also in the wood-inhabiting<br />

Deuteromycetes, the teleomorph often is of ascomycetous affinity as in the<br />

blue stain and soft-rot fungi, but some are anamorphs of Basidiomycetes<br />

like in the Root-rot fungus, Heterobasidion annosum [anamorph: Spiniger<br />

meineckellus (A.J. Olson) Stalp.; e.g., Holdenrieder 1989]. In the absence of<br />

a teleomorph, taxonomic affinity can be detected by the ultrastructure of<br />

the cell wall: Ascomycetes have two-layered walls, while the walls of Basidiomycetes<br />

are multilamellar. In terms of strict nomenclature, the teleomorph<br />

name takes precedence over the anamorph but in practice, a species is often<br />

identified according to the form in which it was found (Eaton and Hale<br />

1993), like in the case of the wood-inhabiting molds Aspergillus and Penicillium.<br />

The Deuteromycetes are usually divided in Coelomycetes and Hyphomycetes.<br />

Coelomycetes develop conidiophores within fruit bodies (conidiomata).<br />

In Hyphomycetes (or Moniliales), conidia develop on simple or aggregated<br />

hyphae. Conidium formation and conidiophore morphology are criteria to<br />

classify Deuteromycetes (Chap. 2.5). A simplified differentiation for woodinhabiting<br />

Deuteromycetes (Fig. 2.8) distinguishes between conidiospore (free<br />

cell fragmentation at the hyphal tip or a branch) and sporangiospore (development<br />

in a sporangium).<br />

Conidia of wood-inhabiting Deuteromycetes can be defined as mitotically<br />

developed (mitospores), immovable, mononuclear to more-nuclear, unicellular<br />

to more-celled, pigmentless (hyaline) to white, yellow, orange, red, green,<br />

brown, blue, or black colored (depending on the species) spores of different<br />

development, size, shape and surface (Fig. 2.9; Reiß 1997; Kiffer and Morelet<br />

2000). The variety of the spore pigments causes that molded substrates may be<br />

colorful.<br />

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2.2 Growth and Spreading 17<br />

Fig.2.8. Generalized view of conidia according to their development. C conidia, S sporangiospores,<br />

A arthrospores, Ch chlamydospores<br />

Fig.2.9. Conidia. Example of the manifold shapes and structures<br />

Fig.2.10. Developmental cycle of<br />

a deuteromycete. A conidium, B germ<br />

hypha, C development of conidiophore,<br />

D development of vesicle, E vesicle with<br />

conidia<br />

The series of spore germination, hyphal growth, and conidia production represents<br />

the asexual reproduction cycle of a deuteromycete fungus, illustrated<br />

in Fig. 2.10 by an Aspergillus species.<br />

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18 2 Biology<br />

The biological advantage of the conidia production to the Deuteromycetes<br />

(and anamorphs of Asco- and Basidiomycetes) is that these fungi can exit<br />

from an exploited substrate to arrive fresh nutrients by spores (mitospores) in<br />

huge numbers without the need of preceding sexuality. Distributed randomly<br />

by and through the air or by adhering to the surface of animals, spores are<br />

present everywhere. Disadvantageous is that without (para)sexuality clones of<br />

an original hypha are distributed. Conidia can develop independently from<br />

the karyotic stage of the hypha that is anamorphs can occur both on haploid<br />

and dikaryotic mycelium.<br />

2.2.3<br />

Sexual Reproduction<br />

A specific feature of the sexual reproduction of Ascomycetes and Basidiomycetes<br />

is that plasmogamy of haploid cells and karyogamy of two nuclei<br />

(n) to form a diploid nucleus (2n) are separated from each other temporally<br />

as well spatially by the dikaryophase (two-nuclei phase, dikaryon, n + n, ===)<br />

(Fig. 2.11). A dikaryotic hypha is one with two nuclei that derive from two<br />

haploid hyphae, but in which the nuclei are not yet fused by karyogamy.<br />

Particularly in Basidiomycetes, the dikaryotic phase is considerably extended.<br />

By conjugated division of the two nuclei (conjugated mitosis), by<br />

division of the dikaryotic hypha, and by means of a special nucleus migration<br />

connected with clamp formation both daughter cells become again dikaryotic.<br />

Fig.2.11. Generalized scheme of nuclear condition of haplo-dikaryotic Ascomycetes and<br />

Basidiomycetes. → haploid (n), ===> dikaryotic(n+n),=> diploid (2n), P plasmogamy,<br />

K karyogamy, M meiosis<br />

2.2.3.1<br />

Ascomycetes<br />

The life cycle of a typical ascomycete is shown in Fig. 2.12 (also Müller and<br />

Loeffler 1992; Eaton and Hale 1993; Schwantes 1996; Jennings and Lysek 1999).<br />

Haploid (n) spores (A, ascospores or conidia from an anamorph) germinate<br />

to haploid hyphae and after mitoses to haploid mycelium (B), which is<br />

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2.2 Growth and Spreading 19<br />

Fig.2.12. Generalized life cycle of an euascomycete. A ascospores or conidia, B germinated<br />

monokaryons, C plasmogamy of ascogonium (As)-trichogyne (T) and antheridium (An),<br />

D–G section of ascogonium after incorporation of “male” nuclei, D ascogenous hypha, E<br />

hook formation, F karyogamy in the tip hypha, G dikaryon and ascus after meiosis, H ascus<br />

after mitosis with eight ascospores, I anamorph with conidia<br />

the essential ascomycete with nutrition function and theoretically unlimited<br />

growth. Conidia may develop at the haploid mycelium as anamorph (I).<br />

Within the fruit body, hyphae develop to gametangia (“sexual organs”, C)<br />

connectedwithmitosis.Thetrichogyne(T,“copulationhypha”),whichderives<br />

from the ascogonium (As, “female gametangium”), fuses (plasmogamy, gametangiogamy)<br />

with the antheridium (An, “male gametangium”). The nuclei<br />

fromtheantheridiummigrate(therefore:male)throughthetrichogyneintothe<br />

ascogonium. There may be various modifications of the generalized scheme:<br />

Antheridia are absent, and mono-nuclear spermatia (from an anamorph) fuse<br />

with the trichogyne (deuterogamy). Somatogamy of “normal” hyphae takes<br />

place (see Chap. 2.2.3.2). One sex is missing or not functional, and fertilization<br />

occurs between two nuclei of the same sex (automixis).<br />

In the hymenial Ascomycetes (Ascohymeniales, wood-inhabiting Ascomycetes),<br />

the fruit bodies (ascocarps, ascomata) develop after the fertilization of<br />

the ascogonium from basal cells of the gametangia, and thus the fruit bodies<br />

predominantly consist of haploid hyphae (Fig. 2.13).<br />

From the “pollinated” ascogonium, ascogenous hyphae develop, into which<br />

migrates each one pair of two genetically different (compatible) nuclei. In<br />

Ascomycetes, the dikaryotic phase is limited and without nutrition function.<br />

By means of hook formation (Fig. 2.12E) the short-lived hook mycelium and<br />

the ascus (meiosporangium) develop, in which karyogamy and meiosis occur.<br />

Before ascospore formation, there is commonly an additional mitosis, which<br />

bringsthenumberofascospores(meiospores)intheascustoeight.Themature<br />

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20 2 Biology<br />

Fig.2.13. Structure of a fruit body (apothecium) of an ascomycete predominantly consisting<br />

of haploid hyphae (thin lines,onenucleus),somedikaryotichyphae(thick lines,twonuclei)<br />

and differently matured asci within the hymenium. As-, An ascogonium and antheridium<br />

before gametangiogamy, As+ fertilized ascogonium<br />

ascus is usually tube-shaped (“tube fungi”). The non-flagellate ascospores<br />

disper after disintegration of the ascus or via different opening mechanisms.<br />

The ascospores are mono-nuclear or after further mitosis multi-nuclear. They<br />

can be septate and show similar conidia characteristics of size, shape, color<br />

and wall sculpturing.<br />

The relatively small fruit bodies (less than 1 mm in diameter) of the woodinhabiting<br />

Ascohymeniales are the spherically closed cleistothecium, the pear-<br />

Fig.2.14. Fruit body types of Ascomycetes. P perithecium, A apothecium, C cleistothecium<br />

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2.2 Growth and Spreading 21<br />

shapedperithecium, e.g., inseveral blue-stainfungi, orthe disk-shapedapothecium<br />

(Fig. 2.14).<br />

2.2.3.2<br />

Basidiomycetes<br />

ThelifecycleofatypicalbasidiomyceteisschematicallyrepresentedinFig.2.15.<br />

The haploid basidiospore or conidium (A) germinates to the n-mycelium<br />

(B, monokaryon, primary mycelium). There are also asexual anamorphs in<br />

Basidiomycetes. According to Müller and Loeffler (1992), asexual anamorphs<br />

are supposed to occur almost just as frequently as in Ascomycetes: “they are<br />

named however only rarely with an own name, therefore hardly considered in<br />

the system of the Deuteromycetes and would be more frequent in the dikaryotic<br />

phase”. A known example among the wood-decay Basidiomycetes is Heterobasidion<br />

annosum with its anamorph Spiniger meineckellus.<br />

In the laboratory, monokaryons are capable of indefinite growth if they<br />

are regularly subcultured on fresh medium. In nature, characteristically the<br />

dikaryon or secondary mycelium develops. Basidiomycetes do not form sexual<br />

organs for plasmogamy, but monokaryotic hyphae come into contact one with<br />

another and fuse by somatogamy (C). If the nuclei are compatible, the dikaryon<br />

develops (D). This long-lived mycelium (Schwantes 1996) represents the essential<br />

basidiomycete that penetrates the substratum and absorbs nourishment,<br />

inthecaseofwoodfungiwithwood-decayfunction(D–G).Inabouthalfofthe<br />

Basidiomycetes, the dikaryon grows by clamp connections (clamp mycelium):<br />

Fig.2.15. Generalized life cycle of a homobasidiomycete. A basidiospores or conidia, B<br />

monokaryons after germination, C somatogamy, D dikaryon, E–G clamp formation, H–K<br />

basidium development, I karyogamy, J meiosis, K basidium with four basidiospores located<br />

in sterigmata<br />

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22 2 Biology<br />

A short branch arises on the side of the apical hypha and bends over. After<br />

synchronous (“conjugate”) division of the two nuclei (E), two daughter nuclei<br />

remain in the apical cell, one nucleus migrates into the branch (F), the branch<br />

end fuses with the subapical cell, and by septum formation, two dikaryotic<br />

hyphae have developed (G). Repeated conjugate divisions accompanied by<br />

septum formation result in an extensive dikaryotic mycelium (Jennings and<br />

Lysek 1999). Sometimes there are double or multiple (whorl) clamps (maximally<br />

eight) around one septum, e.g., in Coniophora puteana (four clamps). In<br />

a second method of dikaryotization, there is a division of the nuclei in the binucleate<br />

hypha followed by a migration of the daughter nuclei into the primary<br />

myceliumoftheoppositematingtype.Theforeignnucleusineachmycelium<br />

dividesanditsprogenymigratefromhyphatohyphathroughtheseptalpores<br />

until both parent mycelia have been dikaryotized (Alexopolus and Mims 1979).<br />

Depending on external factors, like season (temperature, air humidity), nutrients<br />

and light, large fruit bodies (tertiary mycelium, basidiocarp, basidioma)<br />

develop on the secondary mycelium (Fig. 2.16).<br />

In the fruit body of the hymenomycetes, the hymenium (fertile layer) develops<br />

(Fig. 2.16), in which the formation of basidia occurs (Fig. 2.15H–K). For<br />

Fig.2.16. Life cycle of a wood-decay basidiomycete. A haploid spores, hyphae, somatogamy<br />

and dikaryotic growth in the soil, B infection of the tree through a wound, C tree deterioration<br />

by the dikaryon, D fruit body formation (bracket); in the hymenium: E karyogamy,<br />

F, G meiosis, H mature basidium with four basidiospores<br />

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2.2 Growth and Spreading 23<br />

surface enlargement the hymenium may be e.g., net-like arranged (merulioid,<br />

S. lacrymans), warted (C. puteana), porous (A. vaillantii), or lamellate (Armillaria<br />

mellea). In the young basidium (Fig. 2.15H), karyogamy (I) and meiosis<br />

(J)occur.Fourhaploidnucleimigrateintooutgrowths(sterigmata)atthetop<br />

of the basidium (K) and are discharged as basidiospores.<br />

The spore size (5–20µm), shape (globose, cylindric, ellipsoid etc.), surface<br />

sculpturing (“ornamentation”: warted, crested, etc.), wall-thickness (thinwalled,<br />

double wall) (Ryvarden and Gilbertson 1993) and color (colorless or<br />

pigmented: white, yellow, orange, ochre, pink, brown, green, violet, black)<br />

are taxonomic characteristics. In the microscope, spores appear frequently<br />

bright to colorless (hyaline), e.g., in Daedalea quercina, Fomes fomentarius,<br />

H. annosum, Laetiporus sulphureus, Piptoporus betulinus and Trametes versicolor.<br />

Brownish spores separate e.g., the genus Serpula from other fungi with<br />

merulioid hymenium (Pegler 1991). Further characteristics are the violetstaining<br />

of amyloid spores (e.g., Stereum sanguinolentum)andthebrown-red<br />

staining of dextrinoid spores by JJK as well as the blue-staining of cyanophilic<br />

spores (C. puteana, H. annosum, Oligoporus placenta) by aniline blue (e.g., Erb<br />

and Matheis 1983).<br />

For the differentiation of the various fruit body types serve, e.g., the occurrence<br />

of sterile cells (cystidia) between the basidia (e.g., Antrodia spp.<br />

and Gloeophyllum spp.) and the construction of basidiocarps consisting of<br />

vegetative hyphae (monomitic), additionally of either skeletal or binding hyphae<br />

(dimitic) or of all three hyphal types (trimitic). Monomitic genera are<br />

Coniophora, Meripilus and Phaeolus, dimitic are Antrodia, Heterobasidion,<br />

Hirschioporus, Laetiporus and Phellinus, and trimitic are Daedalea, Fomes and<br />

Trametes.<br />

Most wood-inhabiting Basidiomycetes belong to the Homobasidiomycetes<br />

(formerly Holobasidiomycetes: single-celled basidium) and there to the Aphyllophorales<br />

with gymnocarpous (hymenium exposed while spores are still im-<br />

Fig.2.17. Common types of fruit bodies of wood-inhabiting Basidiomycetes. a Pileate with<br />

central stipe (Lentinula edodes cultured on wood by J. Liese in 1935). b Bracket-like (Piptoporus<br />

betulinus on a birch tree, photo T. Huckfeldt). c Resupinate (Serpula lacrymans in<br />

a building)<br />

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24 2 Biology<br />

mature) and non-lamellate fruit bodies. The Aphyllophorales show a number<br />

of different types of fruit bodies whose attachment to the substrate may also<br />

be rather distinctive: stalked, coral-like, club-like, bracket-like, resupinate, etc.<br />

(Ryvarden and Gilbertson 1993, 1994; Schwantes 1996). Simplistically, fruit<br />

bodies may be grouped into pileate with central stipe, bracket-like, and resupinate<br />

(Fig. 2.17). Fruit bodies may be annual (passing after spore discharge),<br />

biannual or perennial (every year new hymenial layers laid on the preceding<br />

ones).<br />

2.2.4<br />

Fruit Body Formation<br />

Fruit body initiation and development that occurs usually outside of the substrate<br />

are affected by various exogenous factors: humidity, temperature, light,<br />

nutrition, force of gravity, composition of air, and interactions with other<br />

organisms (Schwantes 1996). Endogenous factors cover the participation of<br />

phenol oxidases and other enzymes, cyclic adenosine monophosphate (AMP)<br />

and genes. Fruit body formation is often promoted by conditions, e.g., warmth<br />

in S. lacrymans, which are unfavorable for the vegetative development.<br />

In fungi that are not tolerant to dryness, like Pholiota and Pleurotus species,<br />

the fruit bodies frequently have a fleshy consistency and lose when drying<br />

their function irreversibly, so that in the northern hemisphere many forest<br />

fungi with annual fruit bodies preferentially fructify in damp-cool weather<br />

in the autumn. Dry-tolerant fruit bodies, like in Schizophyllum commune,<br />

continue spore production under humid conditions after dryness for many<br />

years. Others reduce the evaporation by hairy or “varnished” surfaces, like<br />

Inonotus and Ganoderma species. The concentric zonation of the pileus surface<br />

(rough and smooth in the change) of Trametes versicolor is influenced by<br />

humidity variation and the different colors of the individual zones by light and<br />

dark phases (Williams et al. 1981). In Coprinus comatus, fruit body primordia<br />

do not develop further without light (Jennings and Lysek 1999). Short-wave<br />

light (UV, blue) may influence fruit body development (Schwantes 1996). The<br />

Oyster fungus, Pleurotus ostreatus, only fruits below 16 ◦ C (Chap. 9.2), and<br />

the less tasty subspecies P. ostreatus ssp. florida at a higher temperature. Fruit<br />

bodies of the Winter fungus, Flammulina velutipes, appear also after snowfall.<br />

Serpula lacrymans fruits in the laboratory after a stimulating pretreatment of<br />

the mycelium for 3–4 weeks at the submaximal temperature of 25 ◦ C (Schmidt<br />

and Moreth-Kebernik 1991b; Chap. 3.4). Lentinula edodes is stimulated during<br />

its cultivation on wood in Asia by a cooling treatment. Schizophyllum commune<br />

fruits already on simple nutrient agar at room temperature. Gloeophyllum<br />

trabeum (Croan and Highley 1992a) and L. edodes (Leatham 1983) fructified<br />

on defined growth media. AMP was suitable for a Coprinus species (Uno<br />

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2.2 Growth and Spreading 25<br />

and Ishikawa 1973). Yeast extract, vitamin B1, traumatic influences through<br />

physical distortions to the mycelium, and the presence of another fungus or its<br />

mycelial extract or culture filtrate may be favorable (Stahl and Esser 1976; Leslie<br />

and Leonard 1979; Matsuo et al. 1992; Kawchuk et al. 1993). In S. commune,the<br />

development of a fruit-body-inducing substance (FIS) is genetically controlled<br />

(Leslie and Leonard 1979). In a Polyporus species, there are fi+ genes (fruiting<br />

initiation) (Stahl and Esser 1976; Esser 1989). The force of gravity determines<br />

that the yearly hymenial layers in the bracket-like, perennial fruit bodies of<br />

Fomes fomentarius also point to the earth center if the host tree is lying on the<br />

ground (Chap. 3.6).<br />

2.2.5<br />

Production, Dispersal and Germination of Spores<br />

Spores represent in the life cycle of a fungus a state of rest (low water content,<br />

high nutrient content; “latent life”) between the active phase of spore dispersal<br />

and start of new growth.<br />

Serpula lacrymans produces 300,000 (Falck 1912) to 360,000 (Rypáček 1966)<br />

and Piptoporus betulinus 31,000,000 (Kramer 1982) spores per hour and cm 2 of<br />

hymenium. Many forest mycorrhizal fungi fruit at higher air moisture content<br />

and lower temperature in the autumn. Among the tree parasites, Heterobasidion<br />

annosum disperse spores almost over the whole year, Laetiporus sulphureus<br />

in the autumn.<br />

Many Basidiomycetes disperse their spores actively for 0.1–0.2 mm (ballistospores)<br />

so that the spores more easily reach the open air (Schwantes 1996).<br />

In Schizophyllum commune, a liquid drop at the sterigma becomes larger and<br />

hurls the spore into the airflow (Müller and Loeffler 1992). Möykkynen (1997),<br />

using a wind tunnel, measured for the conidia of Heterobasidion annosum that<br />

a threshold speed of an airflow of 1.8 m/s liberates the spores.<br />

Falck (1912) calculated the mass of a spore of S. lacrymans as 171 × 10 −12 g.<br />

Fungal spores exhibit a density of 1.1 dp. In standing air, spores sink with<br />

sedimentation speeds of 0.03–0.55 cm/s (Reiß 1997). A continuously colonized<br />

area can expand 50 km over the year. In an appropriate air stream, spores<br />

can be transported up to 1,000 km (Burnett 1976). Furthermore, spores are<br />

spread by rain and snow. Animals distribute spores that are attached by the<br />

spore surface sculpturing (see Fig. 2.9) or remain indigested. Assumably by<br />

international trade, the causal agent of the Dutch Elm disease, Ophiostoma<br />

ulmi, was imported from Asia to Europe in 1918 (Chap. 8.1.2.1).<br />

The spore content in air is subject to characteristic rhythms. In Central<br />

Europe, it is higher in the summer at warm temperatures and low relative<br />

air humidity than in the winter. Basidiospores and ascospores are numerous<br />

in the air in spring and in autumn. Conidia have a maximum from June<br />

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26 2 Biology<br />

to September. In cities in temperate regions, the spore concentration of Cladosporium,<br />

mainly C. herbarum, often rises up to 10,000–15,000 spores/m 3<br />

air with peaks of more than 50,000 spores/m 3 (Nolard 2004). Air turbulence<br />

during stable areas of high pressure may result in daily rhythms, the concentration<br />

rising during the midday (Reiß 1997). Interiors with high dust content<br />

(e.g., the wood-processing industry) may exhibit increased spore contents. The<br />

lifespan of spores in free air is affected by temperature, air humidity, and sun<br />

exposure. As unpigmented spores are sensitive to UV light, pigmented spores<br />

predominate in the air. Exogenously dormant spores only germinate when the<br />

environmental conditions (nutrients, temperature, pH value) become favorable.<br />

Endogenously dormant spores fail to germinate even under favorable<br />

conditions, which is due to factors within the spore such as nutrient impermeability<br />

or the presence of endogenous inhibitors. Dormancy within these<br />

spores is broken by ageing when nutrients begin to enter or the inhibitors leach<br />

out (Robson 1999).<br />

Priortotheemergenceofoneormoregermtubes,sporesundergoaprocess<br />

of swelling during which they increase in diameter due to the uptake of water.<br />

The metabolic activity, production of protein, DNA and RNA all increase.<br />

The percentage of germinating spores depends on fungal species, spore age,<br />

temperature, available moisture, and substrate. In Serpula lacrymans, only 30%<br />

of sampled spores germinated in vitro (Hegarty et al. 1987). For the conidia of<br />

Heterobasidion annosum, the thermal cardinal points were 0 ◦ C minimum, between<br />

12 and 28 ◦ C optimum and 34 ◦ C maximum (Courtois 1972). Depending<br />

on the species, the duration of the germination ability reaches from a few days<br />

or weeks, like in Stereum species, to several years in Chaetomium globosum,<br />

and can reach up to about 20 years in S. lacrymans (Grosser et al. 2003).<br />

Germination of spores of wood fungi is favored by high air humidity,<br />

warmth, and pH values of 4–6. In Serpula lacrymans, citricacid(Hegarty<br />

et al. 1987) and vitamin B1 (Czaja and Pommer 1959) stimulated germination.<br />

Heartwood compounds may inhibit.<br />

2.3<br />

Sexuality<br />

The wood-inhabiting Ascomycetes and Basidiomycetes are either homothallic<br />

or heterothallic (Ryvarden and Gilbertson 1993).<br />

Homothallic fungi are self-fertile, that is no second mating type is required<br />

for sexual reproduction. Fertilization takes place at the same mycelium. Many<br />

Ascomycetes and about 10% of the Basidiomycetes belong to this type.<br />

Heterothallism includes both bipolar and tetrapolar fungi. In bipolar (unifactorial)<br />

species, incompatibility is controlled by a series of multiple alleles at<br />

one locus. Any dikaryon has two alleles that segregate at meiosis so that half<br />

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2.3 Sexuality 27<br />

the basidiospores have one allele and half the other. Compatible matings occur<br />

between monokaryons with different mating type factors. The inbreeding level<br />

is 50%. The outbreeding level in populations of bipolar polypores is over 90%.<br />

In tetrapolar (bifactorial) species, incompatibility is controlled by two series<br />

of multiple alleles at two loci on different chromosomes. The two pairs<br />

segregate independently at meiosis. Four different mating types rise from one<br />

dikaryon. In a fruit body of an isolate, basidiospores of the mating type AxBx,<br />

AxBy,AyBx and AyBy develop. These spores germinate to monokaryons. Fully<br />

compatible matings of monokaryons (+ in Table 2.5) occur when both factors<br />

are heterozygous (A#B#): AxBx and AyBy as well as AxBy and AyBx. In addition,<br />

there are hemicompatible matings, in which only one factor is different: AxBx<br />

and AxBy as well as AyBy and AxBy.<br />

The inbreeding level is 25%. The outbreeding level is very high. In Schizophyllum<br />

commune 450 A factors and 90 B factors can combine to over 40,000<br />

mating types (Raper and Miles 1958). Many Ascomycetes and about 25% of<br />

the examined Basidiomycetes are bipolar heterothallic (e.g., Oligoporus placenta).<br />

About 65% Basidiomycetes are tetrapolar (Raper 1966). Bipolar mating<br />

predominates among brown-rot fungi and tetrapolar mating among white-rot<br />

fungi (Rayner and Boddy 1988). Of 25 investigated brown-rot polypores, 17<br />

were bipolar, three were tetrapolar, three were heterothallic with type of mating<br />

system undetermined, one was homothallic, and one was reported by different<br />

authors as bipolar and tetrapolar (Ryvarden and Gilbertson 1993). The biological<br />

significance of heterothallism is that inbreeding is limited and outbreeding<br />

is enhanced, promoting gene flow between populations and decreasing the rate<br />

of speciation.<br />

Combination and recombination of the genetic material with plasmogamy,<br />

karyogamy, and haploidization, but without sexual organs, gamets and changes<br />

of generations, can take place by parasexuality, particularly in Deuteromycetes<br />

(Jennings and Lysek 1999). Nuclei of a hypha migrate by anastomosis into<br />

another hypha and multiply and spread there. In the case of a heterokaryon,<br />

Table 2.5. Mating scheme of tetrapolar heterothallic fungi<br />

AxBx AxBy AyBx AyBy<br />

AxBx − A B +<br />

AxBy A − + B<br />

AyBx B + − A<br />

AyBy + B A −<br />

− incompatible (A=B=), + compatible (A#B#)<br />

A common-A heterokaryon (A=B#): conjugate nuclear division and clamp formation<br />

blocked, variable nucleus content per hypha,<br />

B common-B heterokaryon (A#B=): nuclear migration and clamp cell fusion blocked (“false<br />

clamps”)<br />

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28 2 Biology<br />

some nuclear fusions and after haploidization new combinations occur. Usually,<br />

the diploid nuclei are unstable, and their ploidy number is regulated to the<br />

haploid stage by elimination of chromosomes or discharge of sections (Müller<br />

and Loeffler 1992).<br />

Illustrated by the tetrapolar heterothallic Serpula lacrymans,interstockmating<br />

of ten isolates is demonstrated in Table 2.6 (Schmidt and Moreth-Kebernik<br />

1991c). First, the four different mating type monokaryons of each isolate were<br />

obtained after fruit body stimulation (Schmidt and Moreth-Kebernik 1991b)<br />

and subsequent inbreeding according to Table 2.5. Then the 10×4 monokaryons<br />

were paired one with another in all possible combinations on agar. As in S.<br />

lacrymans, like in many Basidiomycetes, only the dikaryon forms clamps, it<br />

can be detected in the light microscope. In contrast, only the monokaryons of<br />

the fungus show abundant arthrospores. The heterokaryons of the type A=B#<br />

and the “false clamps” mycelia (A# B=) can be recognized from the mating<br />

diagram by calculation or by further pairings. The mating types of the isolate<br />

monokaryonsareshownintheuppertablepart.<br />

The mycelium of the F1-dikaryons of S. lacrymans grew faster at about 20 ◦ C<br />

than that of the two parental monokaryons (Schmidt and Moreth-Kebernik<br />

1991a), like this applies also to Lentinula edodes (Schmidt and Kebernik 1987)<br />

and Stereum hirsutum (Rayner and Boddy 1988). Thus, dikaryotic mycelium,<br />

which grows out from compatible monokaryons, looks like a bow tie (Fig. 2.18),<br />

that is, dikaryons can usually be detected macroscopically.<br />

In a sample of ten isolates, theoretically 20 different A and B factors can<br />

occur. In the S. lacrymans sample, there were however only four A and five<br />

B factors. This limited number of mating alleles contrasts with the regular<br />

observation of a high number of mating alleles in other Basidiomycetes (May<br />

et al. 1999) and indicated that S. lacrymans has a narrow genetic base.<br />

Fig.2.18. Bow tie-like outgrowth of the<br />

faster growing dikaryon (D) ofSerpula<br />

lacrymans from the slowly growing<br />

monokaryons (M)<br />

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2.3 Sexuality 29<br />

Table 2.6. Pairings among the four mating types of ten isolates of Serpula lacrymans (from<br />

Schmidt and Moreth 1991b)<br />

The matings in S. lacrymans have also shown some physiological differences<br />

between the mycelia of the different nuclear types. However, there was also consistency<br />

over the generations (parents as well as F1 and F2 generation), namely<br />

with regard to the growth rate, wood decay ability, as well as temperature and<br />

preservative tolerance (Chap. 8.5.3.4).<br />

Interfertility/intersterility tests are a useful criterion for the identification<br />

of unknown isolates and for separation of very similar species. Mating of<br />

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30 2 Biology<br />

a haploid mycelium with defined tester strains whose species affiliation is<br />

known only results in a dikaryotic/diploid mycelium if the isolate belongs to<br />

the same species. Mating is also possible between dikaryotic/diploid mycelium<br />

and monokaryotic/haploid mycelium (Buller phenomenon) in this way that<br />

one nucleus of the dikaryon enters a monokaryon of the same species. Complete<br />

absence of interfertility between monokaryons of the True dry rot fungus, S.<br />

lacrymans, and the Wild dry rot fungus, Serpula himantioides, (Harmsen<br />

et al. 1958) showed that both fungi are independent species. That is the True<br />

dry rot fungus should no more described as domestic variant of the wild<br />

species adapted to buildings, which was later confirmed by DNA techniques<br />

(Chap. 2.4.2.2).<br />

Intersterility must be approached cautiously, however, because intersterile<br />

populations (intersterility groups, ecotypes) occur that cannot be separated<br />

morphologically. For example, in Heterobasidion annosum (Chase and Ullrich<br />

1990), monokaryons isolated from fruit bodies sampled in pine forests<br />

(P-isolates) did not pair with isolates from spruce trees (S-isolates) (Korhonen<br />

1978a), and F-isolates were specialized for fir (Capretti et al. 1990). The different<br />

groups have been recently attributed to three distinct species (Niemelä and<br />

Korhonen 1998). Comparably, the five intersterility groups A, B, C, D, E within<br />

the annulate Armillaria mellea complex (Korhonen 1978b) were assigned to<br />

five biological species (Guillaumin et al. 1993). For edible mushrooms of the<br />

Pleurotus species, three North American, eight European, and five Asian intersterility<br />

groups have been found (Bao et al. 2004a).<br />

Another genetic system referred to as somatic or vegetative incompatibility<br />

restricts plasmogamy between genetically different heterokaryotic dikaryons.<br />

In 1929, Fomitopsis pinicola was the first basidiomycete to be studied by means<br />

of somatic incompatibility (cf. Högberg et al. 1999). The somatic incompatibility<br />

system can be defined as the rejection of nonself mycelia following hyphal<br />

anastomosis (Worrall 1997), thus assuring the isolation of unrelated individuals<br />

in nature. Cultures of the same genotype form a common mycelium, while<br />

cultures of different genotypes of a species or of different species separate themselves<br />

by a demarcation zone. Two isolates are incompatible if they carry different<br />

alleles at one or more vic loci. Self/nonself recognition is normally related<br />

to genetic uniqueness (Hansen and Hamelin 1999). Thus, there is a correspondence<br />

between the delimitation of genets by DNA fingerprints and vegetative<br />

compatibility tests. In some Basidiomycetes, however, vegetatively compatible<br />

isolates are not necessarily genetically identical or similar individuals, clones<br />

or genets, but closely related genets by chance may share similar vegetative<br />

compatibility alleles and do not recognize self from nonself. Kauserud (2004)<br />

grouped the European isolates of S. lacrymans into five widespread vegetative<br />

compatibility groups (VCGs). Due to low genetic variation of the fungus, the<br />

VCGs may not represent clones or inbred lineages, but rather different genets<br />

by chance share similar vic alleles (Kauserud et al. 2004a).<br />

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2.4 Identification 31<br />

In addition to the pairing of compatible monokaryons to insert genetic<br />

material in a fungus from another isolate, fusion of fungal protoplasts can be<br />

performed. Protoplast fusion can be used to make hybrids between cells of the<br />

same mating type, as well as of dikaryotic cells or even between species and genera.<br />

Spheroplasts (cell wall partially removed by lysing enzymes) or protoplasts<br />

(cell wall completely removed) fuse by electric influence or through osmotic<br />

active substances (polyethylene glycol) and some of them regenerate to new<br />

hyphae. Protoplast fusion is used for genetic studies as well as for isolate improvement.<br />

Experiments on wood fungi comprise, e.g., Auricularia polytricha,<br />

Gloeophyllum trabeum, Heterobasidion annosum, Lentinula edodes, Oligoporus<br />

placenta, Ophiostoma piceae, O. ulmi, Phanerochaete chrysosporium, Pleurotus<br />

ostreatus, Trametes versicolor, and Trichoderma spp. (Nutsubidze et al. 1990;<br />

Trojanowski and Hüttermann 1984; Royer et al. 1991; Sunagawa et al. 1992;<br />

Rui and Morrell 1993; Richards 1994; Tokimoto et al. 1998; Bartholomew et al.<br />

2001; Xiao and Morrell 2004). Interspecific fusions (Toyomasu and Mori 1989;<br />

Eguchi and Higaki 1992) and intergeneric fusions (Liang and Chang 1989) were<br />

reported. With increasing genetic distance of the fusion partners, however, the<br />

hybrids are instable, do no fruit, die, or the obtained fruit bodies correspond to<br />

one of the parents, that is, obviously one of the two nuclei has been eliminated<br />

before.<br />

Protoplasts have been produced from O. piceae with the aim of subsequently<br />

inserting genetic material capable of producing fluorescent proteins to allow visualization<br />

of hyphae of that species in wood by using fluorescence microscopy<br />

(Xiao and Morrell 2004).<br />

2.4<br />

Identification<br />

2.4.1<br />

Traditional Methods<br />

Determination keys and descriptions for Deuteromycetes are based on morphology,<br />

color, and development (conidiogenesis) of conidia and conidiogenous<br />

cells (Figs. 2.8–2.10) (Carmichael et al. 1980; Domsch et al. 1980; v. Arx<br />

1981; Wang 1990; Hoog and Guarro 1995; Schwantes 1996; Kiffer and Morelet<br />

2000; Samson et al. 2004).<br />

The fruit bodies of Ascomycetes and Basidiomycetes serve to identify species<br />

on the basis of macro- and microscopic characteristics using keys or illustrated<br />

books: Kreisel 1961; Domański 1972; Domański et al. 1973; Breitenbach and<br />

Kränzlin 1981, 1986, 1991, 1995; Moser 1983; Jülich 1984; Hanlin 1990; Jahn<br />

1990; Wang and Zabel 1990; Ryvarden and Gilbertson 1993, 1994; Huckfeldt<br />

and Schmidt 2005; yeasts: Barnett et al. 1990). There are identification kits<br />

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32 2 Biology<br />

for yeasts that employ assimilation tests of carbohydrates with a specifically<br />

adapted database, and also growth tests on carbon sources that are bound to<br />

a tetrazolium dye (Mikluscak and Dawson-Andoh 2005). An illustrated key for<br />

wood-decay fungi is in the Internet (Huckfeldt 2002).<br />

For wood-inhabiting Basidiomycetes, of which only mycelium is present,<br />

keys are based on microscopic characteristics of the hyphae and on growth parameters<br />

(Davidson et al. 1942; Nobles 1965; Stalpers 1978; Rayner and Boddy<br />

1988; Lombard and Chamuris 1990). Among the physiological characteristics,<br />

the Bavendamm test for the differentiation of brown- and white-rot fungi is<br />

based on the presence/absence of the phenol oxidase laccase (Bavendamm<br />

1928; Davidson et al. 1938; Käärik 1965; Niku Paavola et al. 1990; Tamai and<br />

Miura 1991; Chap. 4.5). Specific reactions to temperature (Chap. 3.4) provide<br />

further information. However, keys for mycelia are unable to differentiate<br />

closely related fungi such as the various Antrodia and Coniophora species. The<br />

strand diagnosis of Falck (1912; Table 2.4, Figs. 8.19–8.21) differentiates few<br />

indoor decay fungi like Serpula lacrymans, Coniophora puteana and Antrodia<br />

vaillantii. As house-rot fungi are the economically most important wood fungi<br />

by destroying wood during its final use within buildings and as not all indoor<br />

fungi fruit, a key including about 20 strand-forming indoor wood decay fungi<br />

(Huckfeldt and Schmidt 2004, 2005, 2006) is given in Appendix 1.<br />

In addition, there are monographs and descriptions of important tree<br />

pathogens (e.g., Ceratocystis and Ophiostoma species: Upadhyay 1981; Wingfield<br />

et al. 1999; Armillaria species: Shaw and Kile 1991; Heterobasidion annosum:<br />

<strong>Wood</strong>ward et al. 1998) and of wood-degrading Basidiomycetes (Cockcroft<br />

1981; Ginns 1982) with data to taxonomy, morphology, ecology, growth behavior,<br />

and wood degradation in the laboratory and outside. A further possibility<br />

for identification is by national institutions against fee (Table 2.7).<br />

A list of collections and institutions with strain collections, compiled by<br />

German Collection of Microorganisms and Cell Cultures, is in the Internet<br />

(www.dsmz.de/species/abbrev.htm). Sixty-one culture collections in 22 European<br />

countries are united in the European Culture Collections’ Organisation<br />

(ECCO; www.eccosite.org). The World Federation of Culture Collections<br />

(WFCC; www.wfcc.info/index.html) is a worldwide database on culture resources<br />

comprising 499 culture collections from 65 countries.<br />

Table 2.7. Examples of institutions for identification, deposition, and purchasing of microorganisms<br />

German Collection of Microorganisms and Cell Cultures (DSMZ), Braunschweig<br />

Centraalbureau voor Schimmelcultures (CBS), Baarn, Netherlands<br />

International Mycological Institute (IMI), Kew, UK<br />

Belgian Coordinated Collections of Microorganisms (BCCM), Gent<br />

American Type Culture Collection (ATCC), Rockville<br />

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2.4 Identification 33<br />

2.4.2<br />

Molecular Methods<br />

Molecular methods to characterize, identify, and classify organisms do not<br />

depend on the subjective judgment of a human being as it might occur using<br />

classical methods, but are based on the objective information (molecules)<br />

deriving from the target organism. Thus, molecular methods are increasingly<br />

used to identify organisms and for taxonomy research (molecular systematic).<br />

In the 1980s, molecular methods were established for wood-decay and staining<br />

fungi. Mainly, the fungal proteins (enzymes) and nucleic acids are used. It is<br />

outside the intention of this book to describe all molecular techniques that are<br />

currently used in the field of biology. The following overview comprises only<br />

some methods and results that are related to the characterization, identification,<br />

and phylogeny of wood-inhabiting fungi, particularly wood-decay fungi.<br />

Genome sequencing (meanwhile over 100 genomes are sequenced), molecular<br />

engineering, cloning, etc. are briefly addressed in other chapters. As an example<br />

of the latter, Lee et al. (2002) transformed the wild-type and the albino<br />

strain of the blue-stain fungus Ophiostoma piliferum with a green fluorescent<br />

protein (GFP) to microscopically differentiate the GPF-expressing fungi from<br />

other fungi in wood.<br />

2.4.2.1<br />

Protein-Based Techniques<br />

SDS polyacrylamide gel electrophoresis (SDS-PAGE)<br />

In SDS-PAGE, the whole cell protein is extracted from fungal tissue, denatured,<br />

and negatively charged with mercaptoethanol and sodium dodecyl sulfate<br />

(SDS). The proteins are separated according to size on acrylamide gels and<br />

visualized by Coomassie blue, amido black, fast green, imidazole-zinc or silver<br />

staining. The banding pattern obtained discriminates at the species level and<br />

slightly below.<br />

SDS-PAGE was used for wood-inhabiting Ascomycetes and Deuteromycetes<br />

like the Cancer stain disease fungus of plane, Ceratocystis fimbriata f. platani,<br />

(Granata et al. 1992) and Trichoderma species (Wallace et al. 1992).<br />

The technique also differentiated a number of wood-decay fungi (Schmidt<br />

and Kebernik 1989; Vigrow et al. 1989, 1991a; Schmidt and Moreth-Kebernik<br />

1991a, 1993; Palfreyman et al. 1991; McDowell et al. 1992; Schmidt and Moreth<br />

1995). For example, the closely related Serpula lacrymans, S. himantioides and<br />

the “American dry rot fungus”, Meruliporia incrassata, weredistinguished<br />

(Schmidt and Moreth-Kebernik 1989a). Figure 2.19 shows that the technique<br />

also detected a misnamed isolate of S. lacrymans.<br />

In addition, monokaryons and F1 dikaryons of S. lacrymans exhibited the<br />

typical species profile (Schmidt and Moreth-Kebernik 1990). There was no need<br />

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34 2 Biology<br />

Fig.2.19. Protein bands of Serpula lacrymans isolates (S) after SDS polyacrylamide gel<br />

electrophoresis. H false naming later identified as S. himantioides (from Schmidt 2000)<br />

to extrapolate on a possible influence of culture age or medium composition<br />

(Schmidt and Kebernik 1989).<br />

SDS-PAGE is fast when the sample originates from a pure culture and can<br />

be performed within 1 day. Reproducible homemade gels require accuracy<br />

and precautions, as acrylamide is carcinogenic in the unpolymerized form.<br />

Prefabricated gels are expensive. At least regarding wood-decay fungi, the<br />

method did not reach a practical application.<br />

Isozyme analyses<br />

Isozyme analyses have been used to distinguish similar and closely related<br />

species and forms, for investigations on the genetical variability and on the<br />

spread of pathogens (e.g., Blaich and Esser 1975; Prillinger and Molitoris 1981;<br />

Micales et al. 1992). Being functional proteins, isozymes are investigated by<br />

native electrophoresis or isoelectric focusing. There are a number of investigations<br />

on mycorrhizal fungi, e.g., Pisolithus and Scleroderma species (Sims<br />

et al. 1999) and on tree parasites, like Armillaria species (Bragaloni et al. 1997)<br />

and Heterobasidion annosum (Karlsson and Stenlid 1991).<br />

Two-dimensional gel electrophoresis, comprising isoelectric focusing and<br />

subsequent SDS-PAGE, is able to separate a sample of a large number of proteins.<br />

Immunological methods<br />

<strong>Wood</strong> fungi can be also detected and identified by immunological (serological)<br />

methods. Immunological assays use polyclonal antisera or monoclonal<br />

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2.4 Identification 35<br />

antibodies. Antisera produced by animals like mice and rabbits as answer<br />

to the injection of mycelial fragments, extracts or culture filtrates are investigated<br />

by Western blotting, enzyme-linked immunosorbent assay (ELISA)<br />

or immunofluorescence (Clausen 2003). However, the experiments often exhibit<br />

cross-reactions with non-target organisms, even when monoclonal antibodies<br />

after fusion with myeloma cells (hybridomas) are used. Investigations<br />

were performed with e.g., Armillaria spp., Coniophora puteana, Gloeophyllum<br />

trabeum, Lentinula edodes, Lentinus lepideus, Oligoporus placenta, Phellinus<br />

pini, S. lacrymans, Trametes versicolor and with wood-stain fungi (Jellison and<br />

Goodell 1988; Palfreyman et al. 1988; Breuil et al. 1988; Glancy et al. 1990;<br />

Burdsall et al. 1990; Vigrow et al. 1991b, 1991c; Clausen et al. 1991, 1993; Kim<br />

et al. 1991a, 1991b, 1993; Toft 1992, 1993; McDowell et al. 1992; Clausen 1997a;<br />

Breuil and Seifert 1999; Hunt et al. 1999).<br />

The diagnostic potential lies in the identification of species without the<br />

need of preceding isolation and pure culturing and in the detection of fungi<br />

at early stages of decay (Clausen and Kartal 2003). The methods may become<br />

applicable when the producing techniques for hybridomas and diagnostic kits<br />

have been established.<br />

Immunological methods were also used to visualize the distribution of<br />

enzymes of wood-degrading fungi within and around the hypha and in woody<br />

tissue (e.g., Kim 1991; Kim et al. 1991a, 1993; Chap. 4).<br />

2.4.2.2<br />

DNA-Based Techniques<br />

Southern blotting of restriction fragments (RFLPs)<br />

In the RFLP technique, nuclear, mitochondrial or chloroplast DNA is treated<br />

with endonucleases, which each have a short nucleotide recognition site on<br />

the DNA target, and which cut the DNA into fragments. The fragments are<br />

separated on agarose gels and transferred by Southern blotting on nitrocellulose<br />

or nylon membranes. The addition of a special nucleotide probe, which<br />

hybridizes with a fragment, selects fragments from the present bulk (“smear”)<br />

of fragments. The probe may be radioactively labeled ( 32 Por 35 S) showing<br />

the hybridized fragment by autoradiography. Biotin, dioxigenin, or fluorescein<br />

probes visualize the fragment colorimetrically or as chemoluminescence.<br />

The different fragment pattern (restriction fragment length polymorphisms,<br />

RFLPs) differentiate species, intersterility groups and isolates, like as it was<br />

used e.g., for Armillaria spp. (Schulze et al. 1995, 1997).<br />

The technique is exact, but needs time and is methodically longwinded.<br />

Methods using the polymerase chain reaction (PCR)<br />

The procedure of PCR multiplies a part of DNA by a repeated (25–40 times)<br />

three-stage temperature cycle (amplification): the double strand is split into its<br />

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36 2 Biology<br />

single strands at about 94 ◦ C (denaturation), two nucleotide primers (15–30<br />

bases) attach to the complementary nucleic acid region at 35–60 ◦ C (annealing),<br />

and a thermostable polymerase synthesizes two new single strands at<br />

about 72 ◦ C (extension) by starting at the primers and using the four nucleotides<br />

present in the reaction mixture (Mullis 1990), that is the target DNA<br />

is doubled with each cycle.<br />

In real-time PCR techniques, the accumulation of PCR product is detected<br />

in each amplification cycle either by using a dye or a fluorescently labeled<br />

probe. Hietala et al. (2003) quantified Heterobasidion annosum colonization in<br />

different Norway spruce clones using multiplex real-time PCR. Eikenes et al.<br />

(2005) monitored Trametes versicolor colonization of birch wood samples. The<br />

technique of PCR-DGGE was used for arbuscular mycorrhizal fungi. A nested<br />

PCRofvariableregionsofthe18SrDNAwascombinedwithsubsequent<br />

separation of the amplicons using denaturing gradient gel electrophoresis<br />

(DGGE), and the method is intended to be used to discriminate closely related<br />

Glomus species (Vanhoutte et al. 2005). Vainio and Hantula (2000) performed<br />

DGGE analysis of fungal samples collected from spruce stumps.<br />

Randomly amplified polymorphic DNA (RAPD)-analysis<br />

RAPD analysis is based on PCR, but uses only one, short (about ten bases)<br />

and randomly chosen primer, which anneals as reverted repeats to the complementary<br />

sites in the genome. The DNA between the two opposite sites with<br />

the primers as starting and end points is amplified. The PCR products are<br />

separated on agarose gels, and the banding patterns distinguish organisms<br />

according to the presence/absence of bands (polymorphism). It is a peculiarity<br />

of RAPD analyses that they discriminate at different taxonomical level, viz.<br />

isolates and species, depending on the fungus investigated and the primer<br />

used (Annamalai et al. 1995).<br />

RAPD was used for tree parasites, such as Armillaria ostoyae (Schulze et al.<br />

1997) and H. annosum (Fabritius and Karjalainen 1993; Karjalainen 1996),<br />

mycorrhizal fungi (Jacobson et al. 1993; Tommerup et al. 1995) and edible<br />

mushrooms (Lentinula edodes: Sunagawa et al. 1995). Regarding wood decay<br />

fungi, Theodore et al. (1995) showed for S. lacrymans polymorphism among<br />

eight isolates. Another RAPD analysis exhibited similarity within S. lacrymans,<br />

which may be attributed to the low genetic variation of the species, but “normal”<br />

polymorphism in S. himantioides and Coniophora puteana (Schmidt and<br />

Moreth 1998).<br />

The German isolate Eberswalde 15 of C. puteana is obligatory test fungus for<br />

wood preservatives according to EN 113. The isolate is known for its variable<br />

behavior in wood decay tests. RAPD analysis was able to show that some alleged<br />

Ebw. 15 cultures held in different test laboratories are in reality subcultures<br />

from the British facultative test isolate FPRL 11e (Göller and Rudolph (2003),<br />

which explains the varying test results.<br />

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2.4 Identification 37<br />

RAPD analysis does not require information of the target DNA and is fast<br />

when starting from pure cultures. However, at least four primers should be used<br />

to avoid spurious results, because the short primers imply a great sensitivity to<br />

contamination. In addition, the technique is unsuitable for the identification<br />

of unknown samples by comparison, because other not yet investigated fungi<br />

by chance may share a similar banding pattern.<br />

Use of ribosomal DNA<br />

The investigation of the ribosomal DNA (rDNA) has become popular, because<br />

the rRNA genes and spacers are assumed to evolve cohesively within a single<br />

species, to exhibit only very little sequence divergence between rDNA copies<br />

within single individuals, but to show normal levels of sequence divergence between<br />

species. The repetitive units of the nuclear rDNA of Eukaryotes consists<br />

of the conserved coding domains 18S and 28S rDNA. The conserved domains<br />

are interrupted by the non-coding variable internal transcribed spacer ITS I<br />

(between 18S and 5.8S) and ITS II (between 5.8S and 28S) which are informative<br />

for differentiation. The intergenic spacer IGS is located between the 28S<br />

andthe18SofthenextrDNAunit.Inthecaseofapresent5SrRNAgene,<br />

the IGS consists of two parts, IGS I and IGS II (Fig. 2.20). The conserved<br />

regions are preferentially used for phylogenetic analyses of genera, families,<br />

and orders. The rapidly evolving ITS spacers have become a popular choice<br />

for closely related species and at the subspecies level. After amplification by<br />

PCR, the amplicons are either restricted by endonucleases providing restriction<br />

fragments (RFLPs) which are subsequently separated according to size<br />

using agarose or polyacrylamide gel electrophoresis, or the DNA sequence is<br />

determined (“sequencing”).<br />

In addition to the nuclear rDNA, also mitochondrial rDNA was used for<br />

Basidiomycetes, e.g., by Bao et al. (2005a) in view of phylogenetic relationships<br />

among closely related Pleurotus species.<br />

Restriction fragment length polymorphism (RFLP) of rDNA<br />

RFLP analysis based on the rDNA was also called amplified ribosomal DNA<br />

restriction analysis (ARDRA). Depending on the intension, the RNA genes or<br />

the spacers are used. For RFLP analysis of the ITS, the ITS is first amplified,<br />

often using the “universal primers” ITS 1 and ITS 4 (White et al. 1990), which<br />

anneal to the evolutionary stable 18S and 28S rRNA genes. This attachment<br />

Fig.2.20. Schematic diagram of one rDNA unit. The number in the boxes is the size in base<br />

pairs for Serpula lacrymans (supplemented from Moreth and Schmidt 2005)<br />

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38 2 Biology<br />

to conserved rDNA regions allows the ITS amplification from fungi without<br />

prior knowledge of their ITS sequence. The PCR products are then digested<br />

either as single or as double digest by restriction endonucleases, of which some<br />

hundreds of different enzymes are known and each having an own recognition<br />

site on the DNA.<br />

Jonsson et al. (1999) identified mycorrhizal fungi in a spruce forest by ITS-<br />

RFLP comparison to reference material. Similarly, Johannesson and Stenlid<br />

(1998) identified tree parasites like Armillaria borealis and Heterobasidion annosum<br />

from bore core samples or mycelia isolated from wood. Regarding wooddecay<br />

Basidiomycetes, Zaremski et al. (1999) differentiated single isolates of<br />

C. puteana, Gloeophyllum trabeum and Oligoporus placenta by ITS-RFLPs.<br />

Various isolates of the closely related S. lacrymans and S. himantioides exhibited<br />

a distinct fragment profile for both fungi after digestion with HaeIII/TaqI<br />

(Schmidt and Moreth 1999). Restriction with TaqI differentiated S. lacrymans;<br />

S. himantioides, D. expansa, C. puteana, A. vaillantii, O. placenta and Gloeophyllum<br />

sepiarium by specific fragments (Fig. 2.21).<br />

Obviously, ITS-RFLP analysis is able to separate various wood decay fungi.<br />

It also detected misnamed isolates assumed to be S. lacrymans (Horisawa et al.<br />

2004; also Fig. 2.21) and identified unknown samples. The method is currently<br />

to be intended as a database for the identification of wood decay and associated<br />

fungi (Zaremski et al. 1999; Adair et al. 2002; Diehl et al. 2004; Råberg et al.<br />

2004).<br />

Advantageous is that the technique is fast and inexpensive. Limitations are:<br />

First, the use of universal primers implies sensitivity to contamination. Second,<br />

Fig.2.21. Species-specific ITS-RFLP pattern of isolates of Serpula lacrymans (L), S. himantioides<br />

(H), Coniophora puteana (C), Donkioporia expansa (D), Antrodia vaillantii (A),<br />

Oligoporus placenta (O), and Gloeophyllum sepiarium (G) generated by TaqI. M marker<br />

(50–1,000 bp). The culture X had been assumed to be C. puteana and was later identified<br />

by sequencing as C. olivacea<br />

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2.4 Identification 39<br />

in view of a data collection to be used for identification by fragment length<br />

comparison, the limited ITS size of only 600–700 bases prevents a separation of<br />

all relevant fungi in a certain biotope by specific digest pattern. Third, the great<br />

number of possible fungi in a biotope is much greater than the few fragment<br />

patterns that would be present in data collections, that is, a not yet analyzed<br />

species may feign another fungus by exhibiting identical fragments.<br />

RFLP analysis of a 5.8S rDNA/ITS II/28S rDNA fragment was used to characterize<br />

five species of the Phellinus igniarius group (Fischer 1995) and 13 species<br />

of the Phellinus pini group (Fischer 1996). Corresponding DNA digestion of<br />

52 lignicolous European species with HpaII resulted in 44 distinct phenotypes<br />

and additional application of Hin6 IandHinf I in 48 species-specific and<br />

two genera-specific phenotypes (Fischer and Wagner 1999). RFLP patterns<br />

obtained from seven restriction enzymes assigned 34 Pleurotus strains to 11<br />

RFLP types, of which ten corresponded to biological species (Bao et al. 2004b).<br />

The intergenic spacer, either the IGS I alone or both IGS parts, has often<br />

been used for RFLP studies of Armillaria species (e.g., Harrington and Wingfield<br />

1995; Frontz et al. 1998; White et al. 1998; Terashima et al. 1998a; Kim<br />

et al. 2001). IGS I-RFLPs were also used to assign isolates of Heterobasidion<br />

annosum to intersterility groups (Kasuga and Mitchelson 2000) and to investigate<br />

the population structure of five Fennoscandian geographic populations<br />

of Phellinus nigrolimitatus (Kauserud and Schumacher 2002).<br />

rDNA Sequencing<br />

PCR-amplification and subsequent sequencing of parts of the ribosomal DNA<br />

avoid the main limitations of RFLPs because the whole information of hundreds<br />

of nucleotides of the target DNA is used. rDNA sequences may be used for diagnosis<br />

and for phylogenetic analyses (dendrograms) on relationships among<br />

fungi. Sequencing is nowadays the most important tool for molecular systematics<br />

and led to taxonomic rearrangements and changes in nomenclature.<br />

TheITSsequencesofagreatnumberofwoodfungiareknown,e.g.,from<br />

mycorrhizal fungi like Hebeloma velutipes (Aanen et al. 2001), from parasites<br />

like Armillaria species (Chillali et al. 1998) and Laetiporus sulphureus<br />

(Rogers et al. 1999), and from the red streaks producing Trichaptum abietinum<br />

(Kauserud and Schumacher 2003). Regarding wood decay fungi, a data set of<br />

rDNA-ITS sequences of 18 house-rot fungi is shown in Table 2.8 (Schmidt and<br />

Moreth 2002/2003) complemented by the 18S and 28S rDNA sequences of some<br />

important species (Moreth and Schmidt 2005). The ITS of some brown-rot and<br />

white-rot fungi was sequenced by Jellison et al. (2003).<br />

It is normal to deposit sequences in the international electronic databases<br />

for everyone’s use (European Molecular Biology Laboratory EMBL: www.ebi.<br />

ac.uk/embl; American GenBank: www.ncbi.nlm.nih.gov/genbank; DNA Data<br />

Bank of Japan DDBJ: www.ddbj.nig.ac.jp).<br />

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40 2 Biology<br />

Table 2.8. Sequenced and deposited rDNA regions of indoor wood decay fungi. Grey sequence<br />

known, 1–28 number of sequenced isolates, six-digit number EMBL database accession<br />

number (supplemented from Schmidt and Moreth 2002/2003 and Moreth and Schmidt<br />

2005)<br />

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2.4 Identification 41<br />

Sequences of the ITS region (and the 18S and 28S rDNA) may be used to<br />

identify unknown fungal samples through sequence comparison by Basic local<br />

alignment search tool (BLAST) (e.g., www.ncbi.nlm.nih.gov/blast/bast.cgi).<br />

BLAST revealed ITS-sequence identity of a “wild” S. lacrymans isolate from<br />

the Himalayas with indoor isolates (White et al. 2001), identified misnamed<br />

isolates of S. lacrymans (Horisawa et al. 2004), identified Antrodia spp. and<br />

Serpula spp. isolations from fruit bodies and wood samples (Högberg and<br />

Land 2004), and confirmed Coniophora puteana isolates (Råberg et al. 2004).<br />

Kim et al. (2005) used a part of the 28S rDNA for identification of a number<br />

of basidiomycete fungi from playground wood products by BLAST. Partial 18S<br />

rDNA sequence of Sirococcus conigenus isolated from Norway spruce cankers<br />

was used by Lilja et al. (2005) to confirm the identification of the fungus. The<br />

whole IGS was sequenced to investigate intraspecific variation of mycorrhizal<br />

fungi like Laccaria bicolor (Martin et al. 1999). IGS I sequence analysis was<br />

used for Hebeloma cylindrosporum (Guidot et al. 1999) and Xerocomus pruinatus<br />

(Haese and Rothe 2003). IGS I analysis suggested that three different<br />

morphotypes/genotypes of an ectomycorrhizal fungus present in Kenya represent<br />

separate biological species (Martin et al. 1998). The IGS I region grouped<br />

isolates of Armillaria mellea s.s. in Asian, western North American, eastern<br />

North American and European populations (Coetzee et al. 2000).<br />

Sequences are used to construct phylogenetic trees (dendrograms) for phylogenetic<br />

analyses (molecular systematics). It is not unusual for those intentions<br />

to complement own data with sequences downloaded from the databases.<br />

For closely related fungi, like Armillaria species, IGS sequences were used for<br />

phylogenetic analysis (e.g., Terashima et al. 1998b). Also, ITS sequences may be<br />

applied to phylogenetic trees. An example of S. lacrymans and S. himantioides<br />

isshowninFig.2.22.ThetreeshowsthatisolatesofS. lacrymans collected in<br />

nature in Czechoslovakia, India, Pakistan and Russia group in the branch of<br />

indoor isolates (“Domesticus group”) but differ from wild Californian isolates<br />

(“Shastensis group”) (Kauserud et al. 2004b; also White et al. 2001; Palfreyman<br />

et al. 2003), suggesting a North American link between the anthropogenic<br />

isolates and the wild relative S. himantioides. Yao et al. (1999) applied ITS<br />

sequences to a phylogenetic study of Tyromyces s.l.<br />

For phylogenetic analyses of higher groups, genera, families and orders,<br />

often the conserved 18S and 28S rDNA are used. Bresinsky et al. (1999) and<br />

Jarosch and Besl (2001) sequenced 900 bases of the 28S rDNA of S. lacrymans, S.<br />

himantioides, Meruliporia incrassata and of Coniophora and Leucogyrophana<br />

species. Although it is not necessary to sequence the whole rRNA genes to construct<br />

trees, complete 18S and 28S rDNA sequences of a number of important<br />

wood-decay fungi are already known (Table 2.8).<br />

Nuclear and mitochondrial genes have different inheritance. Selosse et al.<br />

(1998) showed intraspecific polymorphism of the large subunit of mitochondrial<br />

rDNA in Laccaria bicolor. A sequence database of several ectomycorrhizal<br />

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42 2 Biology<br />

Fig.2.22. Phylogeny of Serpula<br />

lacrymans and Serpula himantioides<br />

ITS-rDNA sequences<br />

using maximum parsimony and<br />

Meruliporia incrassata as outgroup.<br />

Sequences are labeled<br />

with geographical origin of the<br />

isolate, followed by the isolate or<br />

collection name. Bootstrap support<br />

values (≥50%) are shown<br />

below the nodes. Stripped lines<br />

indicate nodes that collapsed in<br />

the strict consensus tree. Tree<br />

symbols indicate specimens derivedfromnature(otherwise<br />

from buildings), and star symbols<br />

pinpoint sequences derived<br />

from two newly discovered localities<br />

in Russia. Black squares<br />

indicate specimens having double<br />

character nucleotides in one<br />

or several positions, reflecting<br />

a heterozygous state (from<br />

Kauserud et al. 2004b)<br />

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2.4 Identification 43<br />

basidiomycetes based on a portion of the large subunit of mitochondrial rDNA<br />

was assembled in view of identification (Bruns et al. 1998).<br />

rDNA sequencing yields a comprehensive pool of information, but is tedious<br />

and expensive. Further costs emerge if the PCR products are previously cloned.<br />

An automatic sequencer is too expensive for small laboratories. However, specialized<br />

sequencing services are meanwhile inexpensive, providing a sequence<br />

of about 800 bp length for about e10.<br />

Species-specific priming PCR (SSPP)<br />

As an advantage of the sequence divergence among fungi, oligonucleotide sequences<br />

may be used to design species-specific primers for PCR. At first sight,<br />

SSPP seems to be a powerful molecular identification tool for fungi. Subsequent<br />

restriction of the amplicon as well as the use of pure fungal cultures, axenically<br />

obtained samples, and precautions to exclude DNA from the laboratory or<br />

from contaminated field material are not required. Jasalavich et al. (1998) used<br />

primers that detect any basidiomycete fungus present, but not a particular<br />

species. Specific PCR primers were able to detect the aggressive biotypes 2 and<br />

4ofTrichoderma harzianum (T. aggressivum f. europaeum and f. aggressivum),<br />

which are strong parasites in the mushroom production of agarics, Shii-take,<br />

and Pleurotus species (Albert 2003). With regard to the tree-inhabiting Basidiomycetes,<br />

special ITS-primers were used for Heterobasidion annosum and<br />

Armillaria ostoyae (Garbelloto et al. 1996; Schulze and Bahnweg 1998). Specific<br />

primers distinguished A. mellea from the other four annulate European Armillaria<br />

species (Potyralska et al. 2002) and detected Phlebia brevispora (Suhara<br />

et al. 2005).<br />

To identify indoor wood decay fungi, specific oligonucleotide sequences that<br />

are located in the ITS II region of seven fungi and were previously tested for<br />

possible cross-reaction (Moreth and Schmidt 2000; Schmidt 2000) are suitable<br />

as primers for SSPP (Table 2.9).<br />

To make subsequent sample recognition easier, different distances of the<br />

DNA target region to the ITS 1 primer were considered, that is the amplified<br />

ITS regions exhibit a DNA fragment for each fungus of distinct and predictable<br />

length on the agarose gel, ranging from about 385 to 625 bp (Fig. 2.23).<br />

Oh et al. (2003) immobilized specific ITS oligonucleotides of some woodinhabiting<br />

fungi onto membrane filters for subsequent hybridization of DNA<br />

from field samples and detected e.g., Chaetomium globosum.<br />

A specific primer pair targeting the β-tubulin gene was able to distinguish<br />

between the mutant strain of Ophiostoma piliferum used for biocontrol of<br />

woodstain and the European and New Zealand wildtype isolates (Schröder<br />

et al. 2000).<br />

SSPP is precise and fast. The technique is already used in Germany for<br />

commercialfungaldiagnosis.However,SSPPdoesnotworkwithallfungi.The<br />

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44 2 Biology<br />

Table 2.9. Species-specific ITS-PCR primers (reverse) with target area (bp) in the ITS II if the<br />

ITS 1 primer of White et al. (1990) is used as forward primer (complemented from Moreth<br />

and Schmidt 2000)<br />

Species Specific primer (5 ′ → 3 ′ ) Target<br />

area (bp)<br />

Serpula lacrymans ATG TTT CTT GCG ACA ACG AC 567–587<br />

CAG AGG AGC CGA TGA ACA AG 459–478<br />

Serpula himantioides TCC CAC AAC CGA AAC AAA TC 410–429<br />

Coniophora puteana AGT AGC AAG TAA GGC ATA GA 614–633<br />

Antrodia vaillantii CAC CGA TAA GCC GAC TCA TT 498–517<br />

ACT GAC TAC AAA ATG GCG CG 445–464<br />

Oligoporus placenta TTA CAA GCC AGC ATA AAC CT 431–450<br />

Donkioporia expansa TCG CCA AAA CGC TTC ACG GT 525–544<br />

Gloeophyllum sepiarium GTT AAT AAA AAC CGG GTG AG 379–398<br />

Fig.2.23. Electrophoresis gel demonstrating species-specific priming PCR. L–A codes of<br />

specific primers which detected isolates of Serpula lacrymans (L), S. himantioides (H),<br />

Coniophora puteana (C), Donkioporia expansa (D), andAntrodia vaillantii (A). M marker<br />

(200–900 bp) (from Moreth and Schmidt 2000)<br />

closely related annulate European Armillaria species A. borealis, A. cepistipes,<br />

A. gallica, and A. ostoyae, exhibited rather similar ITS sequences and also<br />

intraspecific variation, that is a specific primer was only obtained for A. mellea<br />

(Potyralska et al. 2002; also Chillali et al. 1998). In addition, intraspecific<br />

variation may also occur with regard to the geographic origin of isolates<br />

(Kauserud et al. 2004b). The main limitation is, however, comparable to ITS-<br />

RFLPs, that the limited ITS size of only 600–700 nucleotides prevents the design<br />

of a specific primer for all relevant fungi of a certain biotope. In a practical<br />

view, also the technical effort becomes big on that score that a great number of<br />

specific primer has to be used for the diagnosis of an unknown sample.<br />

Microsatellites<br />

Microsatellites or simple sequence repeats (SSR) are hypervariable genomic<br />

regions characterized by short tandem repeat sequences of up to seven nu-<br />

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2.4 Identification 45<br />

cleotide units that are distributed throughout the genomes of most Eukaryotes<br />

(Powell et al. 1996). The variability of the number of repeat units at a particular<br />

locus and the conservation of the sequences flanking the repeat make<br />

microsatellites valuable genetic markers. They provide information for identification<br />

and on genetic diversity and relationships among genotypes. For<br />

example, DNA fingerprinting with multilocus microsatellite probes suggested<br />

thatCapeTownisolatesofArmillaria mellea s.s. were introduced from Europe<br />

more than 300 years ago (Coetzee et al. 2001).<br />

Amplified fragment length polymorphism (AFLP)<br />

AFLP is a powerful tool for DNA fingerprinting and is based on (1) total genomic<br />

restriction, (2) ligation of primer adapters, and (3) unselective followed<br />

by selective PCR amplification of anonymous DNA fragments from the entire<br />

genome (Vos et al. 1995). AFLP markers are recognized as more reproducible<br />

compared to RAPD analyses and inter-simple sequence repeats (ISSRs), and are<br />

also able to give a higher resolution. AFLP analysis by Kauserud et al. (2004a)<br />

of European isolates of Serpula lacrymans belonging to five somatic incompatibility<br />

groups indicated that the species in Europe is genetically extremely<br />

homogenous by observing that only five out of 308 scored AFLP fragments<br />

were polymorphic. In contrast, S. himantioides as the closest relative to S.<br />

lacrymans possessed 31.3% polymorphic fragments.<br />

2.4.2.3<br />

Further Molecular Methods<br />

DNA-Arrays<br />

DNA-arrays (DNA-chips, microarrays) are tools in medical, pharmaceutical,<br />

and biological diagnosis of pathogens (genotyping, pathotyping) (Beier et al.<br />

2002; Wiehlmann et al. 2004). Basis is the increasing availability of sequence<br />

information of various viruses and bacteria. One chip can carry up to 10,000<br />

different DNA probes (e.g., oligonucleotides), which are raster-like bound on<br />

its surface. Nucleic acid molecules of the sample hybridize specifically with the<br />

corresponding DNA probe, and the hybridized chip areas are detected colorimetrically.<br />

Compared to PCR techniques, the sensitivity of the chip technology<br />

is lower than with species-specific PCR, and the chip techniques need experienced<br />

staff and expensive laboratory equipment. The great miniaturization and<br />

automation, however, allow the analyses of a great number of samples in a short<br />

time. Specific oligonucleotides to be used for arrays are already commercially<br />

available for several pathogenic bacteria and yeasts. A possible future use for<br />

wood fungi using specific oligonucleotides from rDNA sequences (Table 2.8)<br />

could be a new technique for fungal diagnosis.<br />

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46 2 Biology<br />

Fig.2.24. MALDI-TOF mass spectra of mycelia of each two closely related Serpula and<br />

Coniophora species (from Schmidt and Kallow 2005)<br />

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2.5 Classification 47<br />

Fatty acid profiles<br />

Microorganisms synthesize over 200 different fatty acids. The presence of<br />

specific acids and their relative amounts are constant for a particular species.<br />

Since the 1960s, bacteria and fungi are identified by gas chromatographic<br />

analysis of fatty acids, which were previously derivatized to methyl esters. The<br />

technique has also been used to identify wood-decay fungi like Phanerochaete<br />

chrysosporium, P. sordaria, Trametes versicolor, T. hirsuta,andT. pubescens<br />

(Diehl et al. 2003).<br />

MALDI-TOF mass spectrometry<br />

The technique of matrix-assisted laser desorption/ionization time-of-flight<br />

mass spectrometry (MALDI-TOF MS) was developed in the 1980s, and was<br />

used in many fields for peptide, protein, and nucleic acid analyses (Jürgens<br />

2004; Welker et al. 2004). The method was suitable to differentiate and identify<br />

viruses, bacteria, and fungi (yeasts and Deuteromycetes) (e.g., Fenselau and<br />

Demirev 2001). In MALDI-TOF MS, biomolecules and even whole cells are<br />

embedded in a crystal of matrix molecules, which absorb the energy of a laser.<br />

The sample is ionized by means of the matrix, and both the matrix and the<br />

analyte are transferred to the gas phase. The ions are accelerated in an electric<br />

field, and their time of flight is determined in a detector. After calibration of the<br />

instrument with molecules of known mass, the flight time of the analyte ions<br />

is converted to mass-to-charge ratios (m/z). Organism-specific signal patterns<br />

(“fingerprints”) in the mass range 2,000–20,000 Da were obtained. Figure 2.24<br />

shows the first MALDI-TOF MS fingerprints of Basidiomycetes, namely the<br />

closely related sister taxa Serpula lacrymans, S. himantioides and Coniophora<br />

puteana, C. marmorata (Schmidt and Kallow 2005). The obtained spectra may<br />

be used for subsequent diagnosis of unknown fungal samples by comparison.<br />

2.5<br />

Classification<br />

Approximately 120,000 fungal species are described. If the numerical ratio<br />

between vascular plants and fungi of 1:6 in botanically well-examined regions,<br />

like Great Britain, however, is transferred to a global scale of 270,000 vascular<br />

plants, 1.6 million fungi might exist. That is, so far only about 10% of the<br />

actual fungal species are described (Anonymous 1992b). Robson (1999) even<br />

estimated 3 million fungal species.<br />

Nomenclature regulates the constitution of names, their validity, legitimacy<br />

and priority or synonymy, and maintains a single correct name for each taxon<br />

(International Code of Botanical Nomenclature, St. Louis Code 2000). In view<br />

of the author names for fungi, these have to be only abbreviated when more<br />

than two letters are saved. Names are always abbreviated between a conso-<br />

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48 2 Biology<br />

nant and a vowel. The abbreviation should not cause confusion with other<br />

names. Contractions by omission of letters are avoided. Sanctioned names are<br />

indicated with “Fr.” or “Pers.” after the author of the first valid publication.<br />

An example might be shown by Trametes versicolor (L.: Fr.) Pilát (Table 2.10)<br />

(Jahn 1990). “(L.: Fr.) Pilát” means that Linné (L.) described the fungus with<br />

the name Boletus versicolor in “Species plantarum” in 1753. Fries (Fr.) included<br />

it as Polyporus versicolor in “Systema mycologicum” in 1821 that is the epithet<br />

“versicolor” was protected (sanctioned). Pilát placed it in the genus Trametes in<br />

1939. Particularly French mycologists prefer Coriolus versicolor (L.: Fr.) Quélet,<br />

because the French author included the fungus in this genus in 1886. In the<br />

various national colloquial languages and even within a state, different names<br />

are used.<br />

For the classification of fungi, there are different attempts of artificial and<br />

natural systems. The various groups of fungi have little in common, except<br />

the heterotrophy for carbon, that they are Eukaryotes, possess a slightly differentiated<br />

tissue, and exhibit in at least one period of life cell walls as well as<br />

spores as resting and distributing forms. Only for practical reasons they are<br />

nevertheless united. Multi-kingdom systems (Whittacker 1969) consider the<br />

polyphyletic origin of the fungi by attaching the slime fungi and “lower fungi”<br />

totheProtistaandthe“higherfungi”totheFungi,butbreaktherebythetraditional<br />

biological and ecological term fungus. A generally recognized fungal<br />

classification system does not exist, and it was ironically argued that there<br />

might be as many systems as there are systematists. Due to new knowledge,<br />

and depending on the priority, which is attached to a certain characteristic,<br />

taxonomic revisions occur in the classification system as well as changes of<br />

fungal naming (names of wood fungi: e.g., Larsen and Rentmeester 1992; Rune<br />

and Koch 1992). Current names are shown in Appendix 2. The coarse grouping<br />

in Table 2.11 is based on Müller and Loeffler (1992).<br />

About 2,000 described Protista group into six divisions that are independent<br />

from each other as well as from the “higher fungi”. The “higher fungi”<br />

Table 2.10. Naming of fungi, illustrated by Trametes versicolor (L.: Fr.) Pilát<br />

L.: Linné 1753 “Species Plantarum”: Boletus versicolor<br />

Fr.: Fries 1821 “Systema mycologicum”: Polyporus versicolor:<br />

→ sanctioning of the epithet “versicolor”,<br />

Pilát: Pilát 1939: placement in the genus Trametes<br />

Synonymous especially in France:<br />

Coriolus versicolor (L.: Fr.) Quélet (1886)<br />

Vernacular names:<br />

Germany: Schmetterlingsporling, Bunte Tramete,<br />

UK: Many-zoned polypore,<br />

France: Tramète chatoyant<br />

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2.5 Classification 49<br />

with about 120,000 species may be grouped into three divisions and a form<br />

division: Zygomycota, Ascomycota with the classes Endomycetes (yeasts) and<br />

Ascomycetes, Basidiomycota including the Basidiomycetes, and Deuteromycota<br />

(Deuteromycetes).<br />

The important fungi that inhabit or destroy wood belong to the Ascomycetes,<br />

Basidiomycetes, or Deuteromycetes. Ascomycetes and Basidiomycetes have in<br />

common a dikaryotic phase and a haploid phase as mycelium, which does not<br />

sprout yeast-like.<br />

About 30,000 Ascomycetes (additionally about 16,000 lichen fungi) are characterized<br />

by the development of the meiospores in asci, the restriction of the<br />

dikaryon to the ascogenic hyphae in the fruit body, and the predominant<br />

gametangiogamy. In the Basidiomycetes (about 30,000 species), the mature<br />

meiospores are located in the sterigmata, and after somatogamy the dikaryotic<br />

phaseisextendedtothemycelium.<br />

As the third artificial group, the Deuteromycetes (30,000 species) are added<br />

whose vegetative characteristics correspond to the Ascomycetes or Basidiomycetes,<br />

in which, however, a teleomorph is not yet known or is either<br />

temporarily or generally not present.<br />

The term “microfungi” covers the Deuteromycetes and some Ascomycetes<br />

with microscopic structures. “Macrofungi (macromycetes)” means Basidiomycetes<br />

and Ascomycetes with large fruit bodies.<br />

There are different classifications of the Ascomycetes. A traditional way<br />

considers the appearance of the fruit bodies (ascomata): Hemiascomycetes<br />

(Protoascomycetes) do not form fruit bodies, Plectomycetes have protothecia<br />

or cleistothecia, Discomycetes show apothecia, Pyrenomycetes own perithecia,<br />

and Loculoascomycetes form pseudothecia (Schwantes 1996; Fig. 2.14).<br />

Another differentiation groups the Ascomycetes according to the time of development<br />

of the fruit bodies in the two groups, euascohymenial Euascomycetes<br />

and ascolocular Loculoascomycetes. In the first, the fruit body develops after<br />

the gametangiogamy, and in the latter, the primordia develop before the<br />

gametangiogamy. With priorization of the wall structure of the ascus, the<br />

Lecanoromycetidae show ascohymenial ascomata and a primitive archaeascus,<br />

the Euascomycetidae comprise ascohymenial fungi with a prototunicate<br />

Table 2.11. General classification of fungi<br />

Protista (2,000 species): Six divisions (e.g., slime fungi and “lower fungi”)<br />

Fungi (“higher fungi”), 120,000, three divisions and one form division:<br />

1. Zygomycota<br />

2. Ascomycota: yeasts and Ascomycetes, 46,000 (lichens included)<br />

3. Basidiomycota: rust fungi, smut fungi and Basidiomycetes, 30,000<br />

Deuteromycota: Deuteromycetes (imperfect fungi), 30,000<br />

with relevance to wood: Ascomycetes, Basidiomycetes, Deuteromycetes<br />

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50 2 Biology<br />

or unitunicate ascus wall, the Loculoascomycetidae have ascolocular ascomata<br />

development and mostly a bitunicate ascus wall, and the Laboulbeniomycetidae<br />

are ascohymenial fungi with prototunicate or unitunicate ascus wall. The<br />

separate group of the Taphrinomycetidae (Taphrinales) does not form ascomata,<br />

but the asci develop between the epidermis cells of the host plant.<br />

Classifications are shown in Kreisel (1969), Breitenbach and Kränzlin (1984),<br />

Müller and Loeffler (1992), Zabel and Morrell (1992), Schwantes (1996), and<br />

Hansen et al. (2000). However, a uniform and generally accepted classification<br />

does not exist. Thus, the Ascomycetes treated in this book are only classified<br />

by their orders (Tables 8.1–8.3).<br />

The traditional differentiation of the Basidiomycetes is based on two different<br />

principles. Practically to apply is the use of the morphology of the<br />

basidium. Holobasidiomycetes have unicellular basidia, and Phragmobasidiomycetes<br />

show septate basidia. To consider natural relationships better, a differentiation<br />

that is based on the kind of spore germination seems favorable<br />

(Müller and Loeffler 1992). The basidiospores of Homobasidiomycetes germinate<br />

by germ hyphae. Heterobasidiomycetes show repetitive germination.<br />

All Homobasidiomycetes possess a holobasidium. The Heterobasidiomycetes<br />

contain orders with phragmobasidia, but initial more primitive orders have<br />

holobasidia (Schwantes 1996). Based on the principle type of the fruit body,<br />

the Homobasidiomycetes may be grouped in Hymenomycetes, which have<br />

the hymenium exposed on basidiomata surface, and Gasteromycetes with the<br />

hymenium enclosed within basidiomata.<br />

Due to overlapping among the groups, lack of clarity, and different opinions<br />

among systematists, some authors (Müller and Löeffler 1992) abstain from<br />

uniting the orders into subclasses.<br />

The former subgrouping of the Homobasidiomycetes into Aphyllophorales,<br />

Agaricales, and Gasteromycetales did only consider the fruit body type.<br />

Schwantes (1996) differentiates four order groups: Apphyllophoranae (six orders),<br />

Agaricanae (three orders), Gasteromycetanae (nine orders), and Phallanae<br />

(one order). Apphyllophoranae and Agaricanae are almost in accordance<br />

with the term Hymenomycetes, and Gasteromycetanae and Phallanae with that<br />

one of Gasteromycetes. Numerous order and family-schemes especially for the<br />

polypores either use large and comprehensive groups like in Ryvarden and<br />

Gilbertson (1993, 1994) or numerous and small groups like in Hansen et al.<br />

(1992, 1997).<br />

Some common wood-inhabiting Basidiomycetes treated in this book are<br />

grouped in Table 2.12 according to Breitenbach and Kränzlin (1986, 1991,<br />

1995), except that the Coniophoraceae were placed in the Boletales.<br />

A great number of Deuteromycetes occur on wood, like molds (Aspergillus,<br />

Penicillium and Trichoderma species), blue-stain fungi (e.g., Aureobasidium<br />

pullulans, Cladosporium species, Discula pinicola), and soft-rot fungi (e.g.,<br />

Paecilomyces variotii).<br />

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2.5 Classification 51<br />

Table 2.12. Classification of some wood-inhabiting basidiomycetous genera<br />

Class Order Family Genus<br />

Heterobasidiomycetes Auriculariales Auriculariaceae Auricularia<br />

Darcymycetales Dacrymycetaceae Dacrymyces<br />

Homobasidiomycetes Aphyllophorales Sparassidaceae Sparassis<br />

Corticiaceae s. lato<br />

Phanerochaetaceae Phanerochaete<br />

Phlebiopsis<br />

Phlebiaceae Resinicium<br />

Stereaceae Amylostereum<br />

Chondrostereum<br />

Stereum<br />

Hymenochaetaceae Asterostroma<br />

Inonotus<br />

Phellinus<br />

Fistulinaceae Fistulina<br />

Ganodermataceae Ganoderma<br />

Polyporaceae s. lato<br />

Polyporaceae s. stricto Lentinus<br />

Pleurotus<br />

Polyporus<br />

Bjerkanderaceae Bjerkandera<br />

Oligoporus<br />

Tyromyces<br />

Coriolaceae Antrodia<br />

Diplomitoporus<br />

Donkioporia<br />

Trametes<br />

Trichaptum<br />

Daedaleaceae Daedalea<br />

Daedaleopsis<br />

Fomitaceae Fomes<br />

Fomitopsidaceae Fomitopsis<br />

Gloeophyllaceae Gloeophyllum<br />

Grifolaceae Grifola<br />

Heterobasidiaceae Heterobasidion<br />

Laetiporaceae Laetiporus<br />

Meripilaceae Meripilus<br />

Phaeolaceae Phaeolus<br />

Piptoporaceae Piptoporus<br />

Rigidoporaceae Physisporinus<br />

Schizophyllaceae Schizophyllum<br />

Agaricales Tricholomataceae Armillaria<br />

Flammulina<br />

Laccaria<br />

Coprinaceae Coprinus<br />

Strophariaceae Kuehneromyces<br />

Pholiota<br />

Boletales Boletaceae Boletus<br />

Coniophoraceae Coniophora<br />

Leucogyrophana<br />

Meruliporia<br />

Serpula<br />

Paxillaceae Paxillus<br />

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52 2 Biology<br />

The Deuteromycetes are usually divided in Coelomycetes and Hyphomycetes.<br />

Coelomycetes develop conidiophores within fruit bodies (conidiomata),<br />

which are either spherical with an apical opening (pycnidium), or flat, cupshaped<br />

(acervulus). Nearly all Coelomycetes are of ascomycetous affinity. In<br />

Hyphomycetes (Moniliales), fruit bodies are absent, and conidia develop on<br />

simple or aggregated hyphae. The “black yeasts” with melanized cell walls and<br />

nearly always with true mycelium (Chap. 6.2) are anamorphs of Dothideales<br />

and are therefore also included in the Hyphomycetes.<br />

The main criterion to classify Deuteromycetes is based on their mode of<br />

conidium formation. In addition, the conidiogenous cell is used to identify<br />

and classify Deuteromycetes. The conidiogenous cells can be borne directly in<br />

or from a vegetative hypha or on differentiated supporting structures. The entire<br />

system of fertile hyphae is called the conidiophore. Conidia can be formed<br />

in acropetal chains, or by basipetal succession, viz. the youngest conidium is<br />

formedatthebase,orbysympodialsuccession,whereeachnewlyformedconidium<br />

moves into terminal position so that a geniculate, elongate or condensed<br />

rachis develops. It is differentiated whether conidia result from fragmentation<br />

and demarcation of already existing hyphae (thalloconidia, arthroconidia) or<br />

by sprouting (blastoconidia), after the origin of their cell wall from the mother<br />

cell and whether only one conidium is formed (solitary) or several one behind<br />

the other in chains (catenulate) or as clusters (botryos). Criteria for the<br />

recognition of taxa are mostly different from the fundamental characters for<br />

biological classification. Instead, species are identified with artificial key features.<br />

Descriptions and classifications are by v. Arx (1981), Barnett and Hunter<br />

(1987), Wang (1990), Müller and Loeffler (1992), Hoog and Guarro (1995),<br />

Schwantes (1996), Reiß (1997), Jennings and Lysek (1999), Kiffer and Morelet<br />

(2000) and Samson et al. (2004).<br />

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3 Physiology<br />

The wood-inhabiting fungi as well as their colonization and damaging of<br />

wood are influenced by various physical/chemical and biological influences<br />

(Table 3.1).<br />

Physical/chemical factors comprise nutrients, water, air, temperature, pH<br />

value, light, and the force of gravity. Biological influences arise because of<br />

reciprocal effects between different organisms as antagonism, synergism, and<br />

symbiosis (e.g., Rypáček 1966; Käärik 1975; Rayner and Boddy 1988). When<br />

investigating the various factors, laboratory methods do not reflect the situation<br />

under natural conditions. Often it is difficult to vary a parameter without<br />

affecting the others. The individual factors in nature do not work isolated, but<br />

strengthen or weaken themselves mutually.<br />

Table 3.1. Influences on fungal activity<br />

physical/chemical:<br />

nutrients, water, air, temperature, pH-value, light, force of gravity<br />

biological:<br />

antagonism, synergism, symbiosis<br />

3.1<br />

Nutrients<br />

Fungi consist of about 90% water and 10% dry matter (chemical composition:<br />

Bötticher 1974). This dry matter has to be synthesized in the course of each<br />

hyphal division so that nutrients must be assimilated. Regarding the source of<br />

carbon, wood fungi are heterotrophic by using carbon from organic material,<br />

which derives from the autotrophic trees. In view of the biochemical way of<br />

nutrition, wood fungi are chemo-organotrophic. These fungi use organic compounds<br />

as hydrogen suppliers to produce energy from organic substances. This<br />

energy production is created by reduction-oxidation reactions (Schlegel 1992).<br />

<strong>Wood</strong> fungi are either parasites, which affect living tree tissue, or saprobes,<br />

which grow on dead wood. Both forms can be obligatory or facultative, as<br />

a saprobe may become a weakness or wound parasite with weakening or<br />

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54 3 Physiology<br />

wounding a tree. A parasite may remain active as a saprobe for some time<br />

after tree cutting. Schmiedeknecht (1991) differentiated five main groups of<br />

the heterotrophic way of life: parasites, nekrophytes, which affect living hosts<br />

either as weakness parasites or kill them by toxic effect, sarkophytes, which<br />

prepare freshly died tissue for saprobes, saprobes, and symbionts (also Rayner<br />

and Boddy 1988).<br />

In view of the use of wood nutrients (Table 3.2), wood-inhabiting microorganisms<br />

use carbon only from enzymatically easily accessible and digestible<br />

substrates, like simply constructed sugars, peptides, or fats, or from the storage<br />

material starch in the parenchyma cells. The wood decay fungi use carbon additionally<br />

from the complex, main components of the woody cell wall, cellulose,<br />

hemicelluloses, and lignin.<br />

The cell wall components can be degraded either directly within the wood<br />

cell wall or only as a pure component after isolation from the cell wall (Table<br />

4.3). In the laboratory, sugars such as glucose, maltose (in malt extract), and<br />

saccharose are suitable C-sources for most wood fungi. The wood-inhabiting<br />

fungi [yeasts (Chap. 9.5), molds, blue-stain fungi, red-streaking fungi in the<br />

early stage (Chap. 6)] and the wood-decay fungi during initial decay nourish<br />

predominantly of sugars and other components in the wood parenchyma cells.<br />

The quantity of these primary metabolites is usually below 10% related to the<br />

wood dry weight, and these metabolites occur usually only in living or just died<br />

sapwood parenchyma cells. For example, soluble nutrients in wood increased<br />

its susceptibility to soft-rot fungi and bacteria in ground contact (Terziew and<br />

Nilsson 1999). In Pinus contorta wood samples, triglycerides were consumed<br />

and mannose was the most depleted sugar by several blue-stain fungi (Fleet<br />

et al. 2001). The wood-degrading brown, white and soft-rot fungi (Chap. 7) use<br />

carbon additionally from the macromolecular cell wall components cellulose,<br />

hemicelluloses and lignin (the latter only with the white-rot fungi) (Chap. 4).<br />

<strong>Wood</strong>-inhabiting bacteria (Chap. 5.2) consume sugars and peptides of the<br />

parenchyma cells and affect non-lignified cell tissue (parenchyma cells, epithelial<br />

cells of the resin channels, sapwood bordered pits). Under natural<br />

Table 3.2. Grouping of wood microorganisms according to nourishment and damages<br />

wood inhabitants:<br />

bacteria, slime fungi, yeasts,<br />

staining fungi (molds, blue-stain fungi, red-streaking fungi at an early stage):<br />

growth on the surface and/or in the outer wood area,<br />

nutrition from the contents of parenchyma cells and sawwood capillary liquid<br />

wood decayers:<br />

brown-rot, white-rot, soft-rot fungi:<br />

wood rot as a result of nourishment from the polymeric components<br />

(cellulose, hemicelluloses, lignin) of the lignified cell wall<br />

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3.1 Nutrients 55<br />

conditions in the soil, in lakes, and marine environments, mixed bacterial<br />

populations of the erosion, cavitation and tunneling bacteria can degrade<br />

wood (Schmidt and Liese 1994; Daniel and Nilsson 1998; Kim and Singh 2000).<br />

Even a bacterial pure culture attacked woody cell walls (Schmidt et al. 1995)<br />

(Fig. 5.3c).<br />

Whereas the fungal cell wall with openings up to 10 nm hardly limits the<br />

uptake of water and small molecules, the plasma membrane is a selectively<br />

permeable barrier for the uptake and secretion of solutes. Water, non-polar<br />

and small uncharged polar molecules, like glycerol and CO2, can diffuse freely.<br />

Larger polar molecules and ions pass the membrane by means of diffusion<br />

or active transport (Rayner and Boddy 1988; Jennings and Lysek 1999). The<br />

uptake occurs mainly at the hyphal tips (Figs. 2.3, 2.4). Three main classes<br />

of nutrient uptake and transport occur in fungi, facilitated diffusion, active<br />

transport, and ion channels (Robson 1999). A constitutive low affinity transport<br />

system of facilitated diffusion allows the energy-independent accumulation of<br />

solutes like sugars and amino acids when present at a high concentration<br />

outside of the hypha, but not against a concentration gradient. When the<br />

solute concentration is low, carrier proteins are induced that have a higher<br />

affinity for the solute and mediate the energy-dependent uptake of solutes<br />

against a concentration gradient at the expense of ATP. During this process,<br />

fungi create an electrochemical proton gradient by pumping out hydrogen ions<br />

from the hyphae at the expense of ATP via proton pumping ATPases in the<br />

plasma membrane. The proton gradient provides the electrochemical gradient<br />

that drives nutrient uptake as hydrogen ions flow back down the gradient.<br />

A number of ion channels that are highly regulated pores in the membrane<br />

and allow influx of specific ions into the cell when open have been found<br />

in fungi. Ca 2+ stimulated K + channels carry an inward flux of K + ions and<br />

are thought to be involved in regulating the turgor pressure of the hypha.<br />

A mechanosensitive or stretch-activated Ca 2+ channel is opened when the<br />

membrane is under mechanical stress like during the generation of the high<br />

calcium gradient at the hyphal tip.<br />

During early growth, nutrients surrounding the young mycelium are in excess.<br />

As the mycelium develops further, nutrients in the center are increasingly<br />

utilized, nutrient depletion and accumulation of metabolic products occur<br />

beneath the colony center. Therefore, growth becomes restricted to the periphery.<br />

Different parts of the colony are at different physiological ages, with<br />

the youngest hyphae at the edge of the colony and the oldest, non-growing<br />

mycelium at the center (Robson 1999).<br />

The movement of the nutrient over short distances from a food source on<br />

to the regions devoid of the nutrient or nutrients required for growth can<br />

occur by diffusion within the aqueous phase of the cytoplasm (Jennings and<br />

Lysek 1999). As mycelial extension proceeds, nutrients are shifted from the<br />

site of absorption to another part of the mycelium by translocation (Jennings<br />

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56 3 Physiology<br />

1987, 1991). Translocation of nutrients is predominantly by water flow. Water<br />

flow is generated by the uptake of nutrients, particularly carbohydrates, by<br />

the mycelium such that the hyphae have a lower water potential than the<br />

substrate. In consequence, water flows into the hyphae and the hydrostatic<br />

pressure so generated drives a flow of solution towards the mycelial growth<br />

front.Thevolumeflowisdissipatedatthegrowthfrontbytheincreasein<br />

volume of the hyphae and the production of droplets at the hyphal apices.<br />

The droplets have a lower osmotic potential than the hyphae or that of the<br />

substrate from which the mycelium grows. This means that the water leaves<br />

the cytoplasm ultrafiltered by the plasmalemma of many of the nutrients<br />

in the translocation stream. Pressure-driven flow of solution has been studied<br />

particularly in Serpula lacrymans(Jennings 1991). It must occur in a wide range<br />

of fungi because droplets (guttation) are common among fungi. Guttation<br />

often occurs in white-rot fungi, like during growth of Donkioporia expansa<br />

in buildings and in the edible mushrooms Lentinula edodes and Pleurotus<br />

ostreatus when the colonization phase of the substrate is completed and the<br />

fungi start fruiting. In S. lacrymans, the droplets at the hyphal tips are slightly<br />

acidic (pH 3–4), which was related to the ability of the fungus to colonize<br />

alkaline substrates (Bech-Andersen 1987a).<br />

The dry weight of fungal mycelium consists of about 5% of nitrogen (% N<br />

of the Kjeldahl method ×4.4 corresponds to the protein content of fungi. Additional<br />

nitrogen is included, e.g., in the chitin). <strong>Wood</strong> typically has a very low<br />

nitrogen content. The average nitrogen for healthy hardwoods and softwoods<br />

was 0.09% of the dry weight of wood and reached to about 0.2% N (Rayner and<br />

Boddy 1988; Fengel and Wegener 1989; Reading et al. 2003) with an average<br />

carbon to nitrogen ration of 500 to 600:1. Nitrogen content changes over the<br />

wood cross section and is lower in wounded or decayed tissue. With regard to<br />

lignocelluloses, it has to be considered, however, that the majority of carbon<br />

is present as a cell wall component and thus enzymatically difficulty accessible,<br />

while the nitrogen compounds are more easily degradable. Altogether<br />

nitrogen, however, is a limiting factor. Fungi do not fix atmospheric nitrogen,<br />

how this some bacteria are able to do. Instead, fungi use nitrogen rationally,<br />

as nitrogen compounds are translocated to the growth front at the hyphal tips<br />

due to different turgor pressure in the mycelium (Watkinson et al. 1981; Jennings<br />

1987). Protein-rich woods, e.g., Pycnanthus angolensis, are colonized by<br />

bacteria after felling and during the drying process, which leads to undesirable<br />

discolorations (Chap. 5.2) (Bauch et al. 1985). For wood fungi, ammonium is<br />

a suitable inorganic source of nitrogen in vitro, while nitrate is usually not<br />

used. Organic nitrogen from amino acid mixtures in pepton or malt extract<br />

results in good growth on agar.<br />

There are several minerals in wood. The main inorganic components found<br />

in wood ash are K, Ca, Mg, Na, Fe, silica, phosphate, chloride, and carbonate<br />

(e.g., Fengel and Wegener 1989; also Wa˙zny and Wa˙zny 1964). By SEM-EDXA,<br />

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3.1 Nutrients 57<br />

Al, S, and Zn were detected (Rodriguez et al. 2003). Particle induced X-ray<br />

emission(PIXE)quantifiedP,S,K,Ca,Ti,Mn,Fe,Ni,Cu,Zn,Pb,Sr,Rb,Ba<br />

and F (Saarela et al. 2002). Inductively coupled plasma emission (ICP) showed<br />

a content of 50–100 ppm of manganese in Scots pine sapwood (Schmidt et al.<br />

1997a). Inorganic compounds comprise 0.1–0.5%, oxide basis, of total wood<br />

componentsintemperatezonesandupto4%intropicalwoods.Mineralelementsenterthelivingtreepredominantlythroughtheroot,whichisfrequently<br />

helped by mycorrhizae fungi. The wood-inhabiting fungi use metals present<br />

in wood for their growth and to degrade it (Chap. 4). Several metals are necessary<br />

to fungi, e.g., for wood degradation. Enzymes that participate in lignin<br />

degradation contain iron (lignin- and manganese peroxidases, cellobiose dehydrogenase)<br />

or copper (laccases) (Rodriguez et al. 2003). Iron, manganese, and<br />

copper are involved in the generation of hydroxy radicals or other oxidizing<br />

agents, which, in turn, attack wood (Henry 2003).<br />

Elements present in forest and other soils can also be a nutrient source for<br />

fungi, enhancing fungal capacity to degrade wood. The wood nitrogen content<br />

can be increased by ground contact or by means of translocation through the<br />

mycelium. Nitrogen can be taken up, e.g., by Serpula lacrymans mycelium<br />

from the soil under houses and transported in the strands to the place of wood<br />

degradation within buildings (Doi and Togashi 1989).<br />

Some wood-degrading Basidiomycetes are heterotrophic for vitamin B1 (thiamine).<br />

Heterobasidion annosum is auxoheterotrophic regarding the pyrimidine<br />

half of thiamine, can however synthesize the thiazole part of the vitamin<br />

(Schwantes et al. 1976). Some wood-decay fungi additionally need vitamin H<br />

(biotin). Suitable vitamin sources in vitro are yeast and malt extract.<br />

Thiamine is decomposed in hot alkaline medium. Therefore in the USA,<br />

poles had been treated with ammonium gas under high temperature (“dethiaminization”)<br />

to destroy the vitamin and, thus, to protect the wood against<br />

decay fungi. The poles, however, were for all that attacked by fungi, as thiamine<br />

from soil bacteria (Henningsson 1967) diffused into the poles during service<br />

(treatment of cut timber: Narayanamurti and Ananthanarayanan 1969).<br />

In addition to cell wall components, primary metabolites and storage material,<br />

wood contains a broad spectrum of extractable substances (extractives,<br />

accessory compounds, secondary metabolites) like waxes, fats, fatty acids and<br />

alcohols, steroids and resins (Fengel and Wegener 1989; Obst 1998). More than<br />

10,000 compounds were reported to occur in plants (Duchesne et al. 1992).<br />

Depending on the wood species, the type, quantity, and distribution of the extractives<br />

can vary considerably. They are particularly located in the heartwood,<br />

and after wounding and microbial infection also in the sapwood as wound reaction<br />

(Chap. 8.2.1). Heartwood is a dark-colored zone in the central part of<br />

the stems of most tree species and is physiologically formed from sapwood,<br />

followed by decreased moisture content, the death of parenchyma cells, and<br />

increased extractive content. Inhibiting extractives, which cause the natural<br />

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58 3 Physiology<br />

durability of many heartwood species develop during heartwood formation<br />

from starch and soluble carbohydrates (Magel 2000) and are mainly phenols,<br />

like terpenoids, flavonoids, stilbenes, and tannins (Fengel and Wegener 1989;<br />

Obst 1998; Roffael and Schäfer 1998; Imai et al. 2005). For example, pinosylvins<br />

inhibited brown-rot fungi (Celimene et al. 1999), flavonoids inhibited Gloeophyllum<br />

trabeum and Trametes versicolor (Reyes-Chilpa et al. 1998). While the<br />

extractives during the obligatory formation of a colored heartwood penetrate<br />

in the cell walls, those that develop by exogenous influences (facultatively colored<br />

heartwood), like wound reactions, do not impregnate cell walls (Koch<br />

2004).<br />

Omnivors are the only less specialized molds (Chap. 6.1), which can grow on<br />

wood, paper, wallpaper, books and leather, and dissolve even minerals from<br />

glass by acid production (Kerner-Gang and Schneider 1969). The “polyphage”<br />

H. annosum has a broad host spectrum of over 200 wood species (Heydeck<br />

2000). As a specialized parasite, Piptoporus betulinus attacks only birch trees<br />

(host spectrum: Jahn 1990; Ryvarden and Gilbertson 1993).<br />

Nutrient media to isolate, enrich, purify, and cultivate wood-inhabiting<br />

fungi are malt extract agar and potato dextrose agar of about pH 5.5. Bacterial<br />

isolates from wood grow on nutrient media like peptone/meat extract/yeast<br />

extract of about pH 7 (Schmidt and Liese 1994). For special microorganisms,<br />

selective media are commercially available, or standard agar is enriched with<br />

selecting compounds. If bacteria have to be eliminated during fungal isolations,<br />

the substrate can be acidified by lactic or malic acid or an antibiotic is<br />

added. Orthophenylphenol selects on white-rot fungi. Benomyl inhibits molds<br />

like Penicillium and Trichoderma species.<br />

3.2<br />

Air<br />

As aerobic organisms, wood fungi produce CO2, water, and energy by respiration<br />

and need therefore air oxygen (Table 3.3).<br />

The energy production from wood, if only cellulose is consumed, is shown<br />

in Table 3.4. Aerobes, however, do not respire carbohydrates totally, but use<br />

intermediates for their metabolism.<br />

Fungal activity is affected by the composition of the gaseous phase. Usually<br />

wood decay decreases at low O2 and high CO2 content, respectively. The O2<br />

Table 3.3. Aerobic degradation of wood to CO2, water and energy<br />

cellulose, hemicellulose, lignin from wood – (ectoenzymes) →<br />

sugars, lignin derivates – (uptake, intracellular enzymes) → CO2 +2(H)<br />

2(H) + 1/2O2 – (respiratory chain) → H2O + energy (ATP)<br />

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3.2 Air 59<br />

Table 3.4. Energy production from wood cellulose<br />

Assuming that 1 kg dry wood contains 48.6% cellulose:<br />

1 mol glucose (180 g) yields 2,835 kJ,<br />

180 g glucose correspond to 162 g cellulose<br />

[162 + 18; (1 mol H2O used for hydrolysis)],<br />

3 × 162 = 486,<br />

486 g cellulose yield 8,505 kJ (2,025 kcal)<br />

content in the wood of living oak trees varied season-dependently from 1–4%<br />

and the CO2-content from 15–20% (Jensen 1969).<br />

There are various reactions occurring in wood fungi that require oxygen,<br />

such as degradation of lignin, oxidative polymerization of phenols, and<br />

melanin synthesis in blue-stain fungi and other fungi. With the onset of differentiation,<br />

there is also an increased oxygen demand. When the reproduction<br />

is initiated, there is a high requirement for protein and nucleic acid synthesis,<br />

which energetically involves a higher demand on the fungal metabolism and,<br />

thus, increased oxygen utilization (Jennings and Lysek 1999). This reason as<br />

well as access to air currents for spore dispersal explain why most fungi form<br />

their fruit bodies at or near the substrate surface.<br />

A lack of oxygen can limit wood decay. Saprobes usually react more sensitively<br />

to O2 lack than parasites living within the heartwood: The saprobes<br />

Serpula lacrymans and Coniophora puteana survived without oxygen 2 and<br />

7 days, respectively (Bavendamm 1936), the parasitic heartwood destroyer<br />

Laetiporus sulphureus more than 2 years (Scheffer 1986). In Heterobasidion<br />

annosum, mycelial growth hardly decreased at 0.1% O2 content compared to<br />

20% (Lindberg 1992). The conidia of some blue-stain fungi still germinated<br />

at 0.25% O2 content, some Mucoraceae (molds) even in a pure N-atmosphere<br />

(Reiß 1997).<br />

The yeasts, which are able to get energy also facultatively anaerobically<br />

by fermentation, form an exception of the aerobic way of life among the<br />

fungi. During the alcoholic fermentation of the hexose sugars (Saddler and<br />

Gregg 1998) in coniferous wood sulphite spent liquors which was performed<br />

in former times e.g., in Switzerland, the produced hydrogen is not transferred<br />

to atmospheric oxygen, but to the organic H-acceptor acetaldehyde:<br />

2(H) + CH3CHO → CH3CH2OH (ethanol). At low oxygen content, anaerobic<br />

metabolites like ethanol, methanol, acetic acid, lactic acid, and propionic acid<br />

have been found also in Basidiomycetes (Hintikka 1982).<br />

Inthecourseofwooddegradation,theCO2 concentration may increase.<br />

Some wood-degrading Basidiomycetes, particularly heartwood destroyer, are<br />

tolerant of a high CO2 content, since they grew well at 70% CO2 and even at<br />

100% (Hintikka 1982), while forest-litter decomposing fungi were inhibited<br />

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60 3 Physiology<br />

at more than 20% CO2. Chaetomium globosum and Schizophyllum commune<br />

can fix CO2 into organic acids of the citric acid cycle (Müller and Loeffler<br />

1992). An increasing CO2 content inhibits the growth of many Deuteromycetes,<br />

which then partly change the metabolism to fermentation and also alter their<br />

filamentous growth manner to a yeast-like appearance (Reiß 1997; Jennings<br />

and Lysek 1999).<br />

The minimum air volume in wood for degradation by fungi is between 10<br />

and 20%: 10% in H. annosum, 20% in S. commune (Rypáček 1966).<br />

Reduction of the O2 content in wood effects a protection against fungal (and<br />

insect) decay. Such protection is performed by wet storage of wind-thrown<br />

wood by dipping and floating in water or sprinkling of piled wood. From 17.6<br />

million m 3 of windfalls after the storm in north Germany in 1972, 1.4 million<br />

were protected by watering and were sold until 1976 nearly without any quality<br />

loss (Liese and Peek 1987; Groß et al. 1991; Bues 1993). In 1990, 15 million m 3<br />

of round timber were stored by sprinkling in Germany. At the density of about<br />

0.5 g/cm 3 of spruce and pine wood, the 20% critical air volume is obtained<br />

through a wood moisture content of 120% u, so that alternating sprinkling is<br />

sufficient. With new methods, logs are wrapped by plastic foil and stored in an<br />

atmosphere of CO2 and/or N2 (Mahler 1992).<br />

The soft-rot fungi are an exception among the wood decay fungi. They exhibit<br />

lower a requirement for oxygen and can also live in water-filled wood<br />

tissue like in sprinkled cooling-tower wood with about 200% u moisture content,<br />

because the cooling-tower water is enriched with the necessary O2 by the<br />

spraying effect of the dripping water (Chap. 7.3). Among the Basidiomycetes,<br />

Armillaria mellea s.l. showed a strange behavior, as it caused in sprinkled<br />

Norway spruce logs tubes in the water-saturated sapwood, through which<br />

necessary oxygen for wood decay invaded the wood (Metzler 1994).<br />

In addition, (facultatively) anaerobic bacteria degrade the non-lignified sapwood<br />

bordered pits in sprinkled and ponded wood, so that wood permeability<br />

increases and the wood shows later the unwanted, because uneven, excessive<br />

uptake of wood preservatives or pigments (Willeitner 1971).<br />

3.3<br />

<strong>Wood</strong> Moisture Content<br />

As wood degradation by fungi involves enzymes, which are active in aqueous<br />

environment, and because hyphae consist of up to 90% of water, wood fungi<br />

need water. Water is also used for the uptake of nutrients, the transport within<br />

the mycelium and as solvent for metabolism. Without water, the metabolism<br />

rests. The resting phase occurs by means of spores, in wood fungi particularly<br />

by chlamydospores. Regarding the so-called dryness resistance of wood decay<br />

fungi (Theden 1972) it was however not proven if vegetative hyphae or spores<br />

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3.3 <strong>Wood</strong> Moisture Content 61<br />

survived. Water is taken up from the substrate wood, the soil, and from masonry<br />

etc. Altogether the moisture content of wood is the most important factor<br />

for wood degradation by fungi and thus also for wood protection. Moisture<br />

in wood exists in two different forms: Bound or hygroscopic water occurs<br />

within the cell wall by means of hydrogen bounds at the hydroxyl groups<br />

mainly in the cellulose and hemicelluloses and to smaller extent in the lignin.<br />

Freeorcapillarywaterinliquidformislocatedinthecelllumenaswell<br />

as in other holes and cavities of the wood tissue (e.g., Siau 1984; Smith and<br />

Shortle 1991).<br />

There are several methods of measuring wood moisture content (Vermaas<br />

1996): oven-drying method, microwave drying Danko (1994), distillation, Karl<br />

Fischer-titration, moisture meters based on electrical and dielectrical properties,<br />

continuous moisture meters, capacity admittance moisture meters, and<br />

hygrometric methods. Determination of the moisture content without destruction<br />

is done electrically by means of resistance measurement (Skaar 1988; Du<br />

et al. 1991a, 1991b; Böhner et al. 1993; Chap. 8.2.4). With increasing moisture<br />

content of wood from the oven-dry phase to the fiber saturation range (about<br />

30% u) the electrical resistance decreases approximately by the factor 1:10 6 .<br />

Moisture can be rapidly determined in practice using an indelible pencil that<br />

is the pencil line runs if the fiber saturation point is exceeded.<br />

The proportional wood moisture (% u) is determined gravimetrically by<br />

the wood mass before and after drying a wood sample at 103 ± 2 ◦ C: u (%) =<br />

[(MW − MD) : MD] × 100 (MW = mass of wet wood, MD = mass of dry wood).<br />

If heat-implied changes in the wood samples shall be excluded to take<br />

care of wood extractives and cell wall components for subsequent microbial/enzymatic<br />

degradation experiments or chemical analyses, drying of the<br />

wood specimens can be performed in an evacuated desiccator over silicagel<br />

or P2O5. <strong>Wood</strong> samples may be also conditioned to specific relative humidity<br />

conditions prior to and after decay, e.g., at 20 ± 2 ◦ Cand65±5%relativeair<br />

humidity. With the latter method, the theoretical dry weight (MDt) of a sample<br />

results from: MDt = (100 × MC): (100 + u) (MC = mass after conditioning,<br />

u = % wood moisture after air conditioning). However, weight loss methods<br />

using moisture-conditioned wood samples instead of oven-dry blocks are<br />

influenced by changes in hygroscopicity: For brown-rot, mass loss is slightly<br />

overestimated, for white rot, no difference occurs, while for soft rot, mass loss<br />

is slightly underestimated using the moisture-condition method (Anagnost<br />

and Smith 1997).<br />

To quantify the moisture content of fungal nutrient substrates, including<br />

wood, only the proportional water content of the substrate was considered in<br />

previous investigations. At the disposal to microorganisms, however, not the<br />

whole water content of the substrate is available, but only that part of the total<br />

water, which is not bound by solved substances (salts, sugars, etc.). The relative<br />

vapor pressure of a substrate (water activity aw, 0–1) results from the quotient<br />

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62 3 Physiology<br />

of the water vapor pressure in the substrate (p) and the pressure of pure water<br />

(p0)(aw=p/p 0 ) (Siau 1984; Rayner and Boddy 1988; Reiß 1997; Table 3.5).<br />

The minimum water activity (Table 3.5) is for most bacteria with 0.98 aw<br />

higher than for many molds, which grow still at 0.80 aw. The minimum for<br />

growth of wood-decay Basidiomycetes on agar is 0.97 aw. Xerotolerant and<br />

xerophilic molds like some Aspergillus species still grow at 0.62 aw. Those<br />

fungi grow in solutions of sodium chloride around 5–6 M (Jennings and Lysek<br />

1999) and tolerate an 80% saccharose solution (Schlegel 1992; Reiß 1997),<br />

generating the appropriate osmotic pressure within their protoplasm e.g., by<br />

the synthesis of glycerol. Below 0.6 aw usually no microbial growth occurs.<br />

The situation of high salt concentrations (sodium chloride) applies also<br />

to marine fungi. Various “lower fungi”, Deuteromycetes, Ascomycetes, and<br />

a few Basidiomycetes colonize wood in the sea (Kohlmeyer 1959; Volkmann-<br />

Kohlmeyer and Kohlmeyer 1993). As in marine fungi vacuoles constitute no<br />

more than about 20% of the volume of the protoplasm, there is no preferential<br />

accumulation of sodium chloride in the vacuoles. Marine fungi synthesize glycerol<br />

and other polyols (mannitol, arabitol) which contribute to their osmotic<br />

potential (Jennings and Lysek 1999).<br />

For growth and wood degradation by fungi, particularly at low water contents,<br />

the water potential (MPa) is the most important factor for water availability.<br />

It is defined as free energy of water in a system relative to pure water,<br />

and because in the relevant range all values are negative, it can be defined<br />

as that negative pressure (“subpressure”), which is necessary to extract water<br />

from the substrate (Griffin 1977). The water potential is affected by different<br />

factors (Siau 1984; Jennings 1991). These are particularly the size and form of<br />

the boundary surfaces both between water and firm matrix and between water<br />

and air (matrix potential), and the osmotic potential due to the occurrence<br />

of solved substances. The influence of the water potential on growth of wood<br />

fungi was first examined with simple substrates, like agar plates in Petri dishes,<br />

in controlled air humidity (Bavendamm and Reichelt 1938). The observed values<br />

of mycelial growth still at −14.5 MPa (aw 0.9), however, were later classified<br />

as too low. Instead, as lower limit about −4 MPa were determined (Griffin 1977;<br />

Griffith and Boddy 1991; Table 3.5). Serpula lacrymans did not grow on agar<br />

below −0.6 MPa (Clarke et al. 1980).<br />

Due to the occurrence of pores of different size (porosity of wood: Kollmann<br />

1987), the special significance of the matrix potential becomes obvious with<br />

increasing drying of wood tissue. In water-saturated wood, all cavities are<br />

filled, and a neglectably small pressure difference is sufficient for dehydration.<br />

With progressive drying, increasingly smaller openings become free from<br />

water (Table 3.5). Large openings in wood tissue with radii over 5µm like<br />

all cell lumens are free from water, if the matrix potential amounts to less<br />

than about −0.03 MPa. Between −0.03 and −14.5 MPa, pores from 5–0.01µm<br />

radius become empty (pits, boreholes by microhyphae). Below about −14 MPa,<br />

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3.3 <strong>Wood</strong> Moisture Content 63<br />

Table 3.5. Correlations between water activity (aw, relative vapor pressure p/p0), water potential (MPa), maximum water-retaining pore radius<br />

(µm) within wood at 25 ◦C, wood emptiness class and microbial activity (compiled from Griffin 1977; Clarke et al. 1980; Siau 1984; Rayner and<br />

Boddy 1988; Viitanen and Ritschkoff 1991; Schlegel 1992; Reiß 1997)<br />

Water activity Water potential Pore radius <strong>Wood</strong> emptiness class Microbial activity<br />

(aw, p/p0) (MPa) (µm)<br />

1.0000 0 (free water) cell lumens, wood degradation and staining<br />

large openings after decay<br />

0.9999 −0.014 10.5<br />

0.9998 −0.028 5.2<br />

0.9993 −0.10 1.5 fiber saturation area, minimum for most wood fungi<br />

0.9990 −0.14 1.1 pits and small openings<br />

0.9975 −0.35 0.4<br />

0.9950 −0.69 0.2<br />

0.990 −1.4 0.1 half-maximum growth rate of<br />

wood-decay Basidiomycetes on agar<br />

0.980 −2.8 0.05 minimum for most bacteria<br />

0.970 −4.2 0.035 minimum for mycelial growth and wood decay of<br />

Serpula lacrymans<br />

0.960 −5.6 0.026 optimum for growth and sporulation of Aspergillus niger<br />

−6.0 no growth of S. lacrymans on agar<br />

0.920 −11.3 0.013 minimum for sporulation of A. niger<br />

0.900 −14.5 0.01<br />

0.880 < 0.01 temporary or intermolecular minimum for growth of A. niger<br />

0.840 openings in the cell wall minimum for germination of A. niger<br />

and growth of Paecilomyces variotii<br />

0.800 minimum for most molds<br />

0.750 minimum for halophilic bacteria<br />

0.650 minimum for A. repens<br />

0.600 lower limit for microbial growth<br />

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64 3 Physiology<br />

intermolecular cavities in the cell wall dry (liquid movement in wood: Siau<br />

1984; Skaar 1988).<br />

From the view of a hypha, a low water availability begins to become critical,<br />

if free water is no more located in the cell lumen void space, but liquid water<br />

exclusively within the cell wall and only water vapor in the lumen, or in other<br />

words, if the cell walls are fully hydrated yet with no water contained in the<br />

cellular spaces. This condition is defined as fiber saturation point or range<br />

(Babiak and Kúdela 1995) and lies at about −0.1 MPa (0.9993 aw), according to<br />

1.5µm pore radius (Table 3.5) and about 30% u wood moisture for woods of<br />

the temperate zones. The lower limit for wood degradation by Basidiomycetes<br />

is about −4 MPa (0.97 aw).<br />

Below fiber saturation, not only fungi are influenced by the moisture content,<br />

but also all technological properties of wood. With increasing moisture, e.g.,<br />

elastic, strength, and insulation properties decrease.<br />

Relative air humidity (RH), which is in equilibrium with a substrate, and<br />

water activity of a substrate stand in the relationship: RH(%) = aw × 100. For<br />

example, 99.93% RH correspond to 0.9993 aw and thus to fiber saturation, so<br />

that the critical range for Basidiomycetes of 0.97 aw (Table 3.5) is exceeded by<br />

condensation in buildings. The S-shaped sorption isotherms, which indicate<br />

the dependence of the wood moisture on the relative air humidity of the environment,<br />

are shown by Siau (1984) and Kollmann (1987). <strong>Wood</strong> is dry at the<br />

relative vapor pressure of 0, and fiber saturation is reached at 1 (100% RH).<br />

Spruce sapwood samples placed over a saturated solution of K2SO4, which<br />

results in 97% RH and 26.5% u, showed 4.5% mass loss after 3 months of<br />

incubation with S. lacrymans (Viitanen and Ritschkoff 1991a). <strong>Wood</strong> samples<br />

in 93% RH according to 23–24% wood moisture content were overgrown by<br />

S. lacrymans and Coniophora puteana (Savory 1964). For the initial colonization,<br />

21% u was necessary (Huckfeldt et al. 2005; cf. Table 8.7). Coniophora<br />

puteana colonized wood samples of 18% moisture content when a moisture<br />

source was 20–30 cm away from the wood. Timber in buildings reached however<br />

till 45% humidity in the winter during night by condensation (Dirol and<br />

Vergnaud 1992).<br />

According to Skaar (1988), the wood moisture content of living trees<br />

amounted to 83% u in hardwoods in the sapwood and to 81% in the heartwood<br />

(average of 34 species) and in conifers to 149% in the sapwood and to 55% in<br />

the heartwood (average of 27 species).<br />

The moisture content in dead wood is determined by several factors:<br />

– fungal decay: For example, the wood moistures of dry heartwood samples<br />

of different wood species increased during decay by Trametes versicolor in<br />

84 days to 78–236% and by Oligoporus placenta to 108–286% (Smith and<br />

Shortle 1991). Regarding the sorptive capacity of wood (Cowling 1961; Anagnost<br />

and Smith 1997), Rawat et al. (1998) showed that the moisture content<br />

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3.3 <strong>Wood</strong> Moisture Content 65<br />

of brown-rot decayed wood was more than that of undecayed samples at low<br />

relative humidities, but at higher humidities (about 37%) the situation was<br />

reversed. Absorptiveness also increased after pretreatment with blue-stain<br />

fungi (Fjutowski 2005).<br />

– moisture uptake, which can occur by five ways: rainfall, absorption from air,<br />

capillary penetration of water into wood in ground contact or in buildings<br />

by condensation on wood surfaces, water transport by the mycelium, and<br />

water formation by fungal metabolism,<br />

– loss of water: in wood with large pores by the force of gravity, furthermore<br />

by evaporation as a function of temperature, humidity, and matrix potential<br />

as well as by water transport via mycelium.<br />

The cardinal points of the wood moisture content for some decay fungi are<br />

shown in Table 3.6, whereby the data vary, however, depending on the fungal<br />

isolate, the wood species, and the testing method. Laboratory findings and<br />

practice observations may also yield different results (Ammer 1964; Savory<br />

1964; Cockcroft 1981; Thörnqvist et al. 1987; Viitanen and Ritschkoff 1991a;<br />

Huckfeldt et al. 2005).<br />

Generally, it applies to wood fungi: The minimum for wood decay is near<br />

the fiber saturation point of about 30% u, however, commonly slightly above<br />

this range because only then there is free water in the lumen void space. Some<br />

house-rot fungi, however, could colonize wood in laboratory culture, whose<br />

moisture was significantly below fiber saturation (minimum 18% u) before<br />

the mycelium contacts the woody substrate, because these fungi transported<br />

water from a moisture source by means of mycelium. The minimum for decay<br />

of pine wood samples by these house-rot fungi was between 22 and 37% u<br />

(Huckfeldt and Schmidt 2005; cf. Table 8.7). The optimum differs depending<br />

on the fungal species and affects the occurrence of different fungi in differently<br />

moist biotopes: For example, the optimum is at 50–100% for tree-inhabiting<br />

blue-stain fungi and below 50% for lumber blue-stain fungi (Bavendamm<br />

Table 3.6. Cardinal points of wood moisture content (% u) for some wood-decay fungi<br />

(literature data)<br />

Minimum Optimum Maximum<br />

Antrodia spp. 30 35–55 60–90<br />

Coniophora puteana 26–30 30–70 60–80<br />

Daedalea quercina 40<br />

Gloeophyllum spp. 30 40–60 80–210<br />

Heterobasidion annosum 45<br />

Lentinus lepideus 35–60<br />

Phlebiopsis gigantea 100–130<br />

Serpula lacrymans 26 30–60 55–225<br />

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66 3 Physiology<br />

1974). <strong>Wood</strong> fungi are inhibited as the cellular spaces of wood become fully<br />

saturated with water. The maximum wood moisture content allowing fungal<br />

growth is determined by the minimum air content within the wood cell.<br />

A certain water amount originates from fungal metabolism (Ammer 1964;<br />

Savory 1964). The assertion that S. lacrymans gets the total water, which is necessary<br />

to moisten dry wood, from the respiration of wood cellulose (Table 3.3),<br />

however, is wrong: It has to be considered that cellulose is not completely<br />

degraded to CO2 and 56% water. Intermediate metabolites for the synthesis<br />

of fungal biomass are necessary. According to Weigl and Ziegler (1960) about<br />

40% of the consumed cellulose is used for those metabolites. Furthermore,<br />

water production from carbohydrates is the rule for all breathing organisms.<br />

Nevertheless, some fungi, particularly S. lacrymans, show intensive guttation,<br />

that is excretion of water in drop form.<br />

In view of dry wood, in addition to spores also the mycelium of some fungi<br />

was said to be resistant to dryness (Table 3.7).<br />

The duration of this so-called dryness resistance depended on air humidity<br />

and temperature. Resistance lasted e.g., longer at 60% RH and low temperature<br />

than at 90% RH and high temperature. For S. lacrymans, the duration was<br />

8yearsat7.5 ◦ Cand1yearat20 ◦ C (Theden 1972). Dryness-resistant are also<br />

Coniophora species, indoor polypores, Gloeophyllum abietinum (on window<br />

timber), Lentinus lepideus (on sleepers), Paxillus panuoides, Schizophyllum<br />

commune, Stereum sanguinolentum, the soft-rot fungi and to smaller extent<br />

Heterobasidion annosum and Trichaptum abietinum. Towhatextentfungi,<br />

however, are qualified for dryness resistance, exclusively in the form of hyphae<br />

or as resistant spores was not examined in detail.<br />

Serpula lacrymans survived only in slowly drying wood samples. Own laboratory<br />

observations revealed that its dikaryons formed arthrospores in old,<br />

dry agar cultures, which points to monokaryotization. That is, the hyphae may<br />

have developed dryness-resistant resting stages if the substrate takes a long<br />

time to dry down, and the spores germinate again under sufficient moisture<br />

conditions. Thus, studies with wood samples that have been colonized<br />

by mycelium and subsequently slowly dried indicated that S. lacrymans, C.<br />

Table 3.7. Resistance to dryness (after Theden 1972)<br />

Years withstanding at ◦C 27 20 7.5<br />

Antrodia vaillantii ≥ 7 9 ≥ 6<br />

Coniophora puteana 0 2 4<br />

Coniophora marmorata 0 3 7<br />

Gloeophyllum abietinum 5 7 ≥ 7<br />

Gloeophyllum trabeum 11 ≥ 10 ≥ 8<br />

Lentinus lepideus 7 ≥ 9 ≥ 8<br />

Oligoporus placenta 9 ≥ 11 ≥ 5<br />

Serpula lacrymans 0.5 1 8<br />

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3.4 Temperature 67<br />

puteana, Gloeophyllum trabeum, and Donkioporia expansa may survive as<br />

arthrospores (Huckfeldt et al. 2005).<br />

3.4<br />

Temperature<br />

With respect to the temperature, Table 3.8 shows the cardinal points for some<br />

wood fungi. A comprehensive investigation was completed in 1933 grouping<br />

the species into low-temperature (optimum 24 ◦ Candbelow),intermediatetemperature<br />

(optimum between 24 and 32 ◦ C), and high-temperature group<br />

(optimum above 32 ◦ C) (Humphrey and Siggers 1933). For three species, e.g.,<br />

Gloeophyllum sepiarium, minimum, and maximum temperatures were already<br />

determined (Lindgren 1933). It has to be considered, however, that considerable<br />

differences can exist between isolates of a species (Table 3.11).<br />

Generally, it applies to wood fungi: The minimum is usually at 0 ◦ C, because<br />

below the freezing point there is no liquid water available necessary for<br />

metabolism. Exceptions of growth below 0 ◦ C are possible, if the freezing point<br />

is decreased, e.g., by trehalose and glycerol or other polyhydric alcohols as<br />

anti-freeze agents which prevent ice-crystal formation within the hypha (Jennings<br />

and Lysek 1999). In some blue-stain and mold fungi, the lower limit for<br />

mycelial growth is at −7 to −8 ◦ C (Reiß 1997). Above the lower limit, the “reaction<br />

speed-temperature rule” begins to take effect, as in a certain temperature<br />

range, enzyme activity runs two to four times faster by increasing the temperature<br />

of about 10 ◦ C(Q10 value). Frequently, the optimum lies, depending on the<br />

species (and isolate) between 20 and 40 ◦ C. Psychrophilic fungi have their optimum<br />

below 20 ◦ C, mesophilic species between 20 and 40 ◦ C and thermophilic<br />

species over 40 ◦ C. Thermotolerant fungi, e.g., Phanerochaete chrysosporium<br />

and other fungi growing in wood chip piles, prefer the mesophilic range, tolerate<br />

however still 50 ◦ C. The maximum for mycelial growth and wood damage<br />

by most wood fungi is often at 40–50 ◦ C, because then the protein (enzyme)<br />

denaturing by heat takes effect. Fungi, however, may exhibit a change in gene<br />

expression, which leads to the synthesis of “heat-shock proteins (hsp)”. The<br />

hsps appear to prevent and repair general damage, denaturation and aggregation<br />

of other cellular proteins, as they are not only induced by heat, but also by<br />

heavy metals and oxidants (Jennings and Lysek 1999).<br />

Serpula lacrymans possesses a characteristic, which can be used for identification.<br />

With the optimum of about 20 ◦ C, slight growth still at 26–27 ◦ C, and<br />

growth stop at 27–28 ◦ C, the fungus differs from the other indoor wood decay<br />

fungi, like the Cellar fungus and the white polypores, as well as from other<br />

Serpula species, because, e.g., S. himantioides still grows at 31 ◦ C. There are,<br />

however wild Himalayan isolates of S. lacrymans that showed slight growth<br />

at 32 ◦ C (Palfreyman and Low 2002). In addition, in S. lacrymans also the<br />

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68 3 Physiology<br />

Table 3.8. Cardinal points of temperature ( ◦ C) for fungal growth and survival (mainly from<br />

Humphrey and Siggers 1933; Cartwright and Findlay 1958; Ammer 1964; Cockcroft 1981;<br />

Mirič and Willeitner 1984; Thörnqvist et al. 1987; Viitanen and Ritschkoff 1991; data of<br />

house-rot fungi from Schmidt and Huckfeldt 2005)<br />

Species lethal minimum optimum maximum lethal lethal lethal<br />

on agar on agar 4 h<br />

in 2 weeks (h) in wood<br />

Armillaria mellea 25–26 33<br />

Aspergillus niger 35–37 45–47<br />

Aureobasidium pullulans 25 35<br />

Daedalea quercina 5 23–30 30–44<br />

Fomes fomentarius 27–30 34–38<br />

Heterobasidion annosum 2–4 22–25 30–34<br />

Laetiporus sulphureus 28–30 36<br />

Lentinus lepideus 3–8 25–33 37–40 60 (0.5)<br />

Paxillus panuoides 5 22–25 29<br />

Phellinus pini 20–27 30–35 55 (0.5)<br />

Piptoporus betulinus 26–30 32–36<br />

Polyporus squamosus 24–25 30–38 60 (0.5)<br />

Schizophyllum commune 28–36 44 60 (0.5)<br />

Stereum sanguinolentum < 4 20–22<br />

Trametes versicolor 24–33 34–40 55 (0.5)<br />

Trichaptum abietinum 22–28 35–40<br />

Serpula lacrymans −6 0–5 20 26–27 30 55 (3) 50–70<br />

Serpula himantioides 25–27.5 32.5 > 35 65<br />

Leucogyrophana mollusca 25–27.5 32.5 30 ≥ 35 75<br />

Leucogyrophana pinastri 20–27.5 32.5 > 35<br />

Coniophora puteana −20/−30 0–5 22.5–25 27.5 ≥ 37.5 32.5 ≥ 37.5 60 (3) 70–75<br />

Coniophora marmorata 20–27.5 25 ≥ 37.5 35 ≥ 37.5<br />

Coniophora arida 25 27.5 35<br />

Coniophora olivacea 22.5–25 32.5–35 35 ≥ 37.5<br />

White polypores (old data) 3–5 25–31 35–38 80 (0.5)<br />

Antrodia vaillantii 27.5–31 35 37–40 65 (24) > 80<br />

Antrodia sinuosa 25–30 35 37–42.5 65 (3)<br />

Antrodia xantha 5 27.5–30 35 40–42.5<br />

Antrodia serialis 22.5–25 32.5–35 37.5–42.5<br />

Oligoporus placenta 3 25 35 40–45 65 (24) > 80<br />

Gloeophyllum abietinum 0–4 25–27.5 37.5–42.5 40–42.5 > 95<br />

Gloeophyllum sepiarium 5 27.5–32.5 ≥ 45 ≥ 45 60 (3) > 95<br />

Gloeophyllum trabeum 5 30–37.5 ≥ 45 ≥ 45 80 (1) > 95<br />

Donkioporia expansa 28 34 > 40 65 (24) > 95<br />

monokaryons tolerated 28 ◦ C (Schmidt and Moreth-Kebernik 1990), so that<br />

probably some data in the literature concerning growth of the fungus above<br />

27 ◦ C (Wälchli 1977) were based on monokaryons. Last, dikaryons of S. lacrymans<br />

(and some further fungi) can be reverted to the monokaryotic stage by<br />

cultivation at relatively high temperature and thus these cultures then also<br />

grew above 27 ◦ C.<br />

From the cultivation of edible mushrooms on wood (Chap. 9.2) it is known<br />

that the optimal temperature can be lower for fruit body formation than for<br />

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3.4 Temperature 69<br />

mycelial growth. Cultivation of Lentinula edodes in Asia involves a dipping<br />

of the colonized wood in cold water to stimulate fruit body development. On<br />

the other hand, S. lacrymans is stimulated to fruit in laboratory culture, if<br />

the mycelium is incubated first 3–4 weeks at 25 ◦ C and then 2 weeks at about<br />

20 ◦ C (Fig. 3.1; Schmidt and Moreth-Kebernik 1991b). In some fungi, spore<br />

germination is activated by high temperature, in nature for example after<br />

forest fires.<br />

The temperature curve of the mycelial growth rate must not correlate with<br />

that one of fungal activity. For example, the temperature range for growth<br />

may be broader than for wood degradation (Wälchli 1977). Furthermore, the<br />

temperature optima of enzymes isolated from fungi are often higher (50–<br />

60 ◦ C) than those of mycelial growth of the respective fungus. Some wood<br />

fungi tolerate extreme values beyond minimum and maximum by resistance<br />

to cold and heat, respectively. However, there are significant differences with<br />

regard to the test method used. Results from cultures on agar revealed that<br />

S. lacrymans survived 1 h at 55 ◦ C, Coniophora puteana 1hat60 ◦ C, Antrodia<br />

vaillantii 3hat65 ◦ C (Schmidt 1995a), and Gloeophyllum trabeum 1hat80 ◦ C<br />

(Mirič and Willeitner 1984). In colonized wood samples that were slowly dried<br />

before heating, S. lacrymans survived 4 h at 65 ◦ C, C. puteana 4h at 70 ◦ C, A.<br />

vaillantii 4h at 80 ◦ C and G. trabeum 4h at 95 ◦ C, assumably by developing<br />

resistant arthrospores (Huckfeldt et al. 2005). This great resistance of the fungi<br />

to heat challenges the use of a heat treatment procedure for the eradication<br />

of fungi in houses. In Denmark, whole houses are subjected to heat treatment<br />

against S. lacrymans (Koch 1991) (Chap. 8.5.4).<br />

Vegetative cells (bacteria and fungal hyphae) are destroyed by heating at<br />

80 ◦ C (pasteurization). Exceptions with growth of up to 113 ◦ Carebacteria<br />

(Archaea) in volcanic biotopes (geysers, black smokers). Spores are frequently<br />

Fig.3.1. Fruit body formation of Serpula<br />

lacrymans in laboratory culture stimulatedbyawarmthtreatment;25mycelial<br />

growth at 25 ◦ C, 20 growth increase at<br />

20 ◦ C, F fruit body<br />

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70 3 Physiology<br />

more thermotolerant than the corresponding mycelium. The basidiospores of<br />

S. lacrymans were killed by 32 h at 60 ◦ Cor1hat100 ◦ C (Hegarty et al. 1986).<br />

However, 4 h at 65 ◦ C reduced the germination rate from 30 to 8% (Hegarty<br />

et al. 1987). The heat resistance of basidiospores has also to be considered in<br />

view of eradication of indoor wood-decay fungi by heat treatment.<br />

As spore forming bacteria may survive 100 ◦ C, nutrient media for laboratory<br />

experiments are sterilized at 121 ◦ C and 210 kPa pressure in autoclaves.<br />

Alternatively, fractionated sterilization at 100 ◦ C (tyndallization) may be used<br />

(heating at 100 ◦ C on three successive days for 30 min to destroy vegetative<br />

cells; between the three heat phases incubation at room temperature to allow<br />

germination of survived spores). Heat-sensitive nutritives can by sterilized by<br />

membrane filtration using filter membranes with a pore size of 0.1–0.45µm.<br />

Insensitive laboratory equipment like glass material becomes sterile by 1 h of<br />

dry heat at 180 ◦ C. <strong>Wood</strong> samples for decay experiments may be sterilized by<br />

ethylene oxide in special devices.<br />

In many fungi, spores and also mycelia are resistant to cold. Thus, fungal<br />

cultures in international strain collections are conserved, except by lyophilization,alsoinliquidnitrogenat−196<br />

◦ C and not like it is usually done in small<br />

laboratories in the refrigerator on agar (or also on small wood pieces: Delatour<br />

1991).<br />

3.5<br />

pH Value and Acid Production by Fungi<br />

The pH value influences germination of spores, mycelial growth, enzyme activity<br />

(wood degradation), and fruit body formation. The optimum for wood<br />

fungi is often in slightly acid environment of pH 5–6 and for wood bacteria at<br />

pH 7. Basidiomycetes have an optimum range of pH 4–6 and a total span of<br />

about 2.5–9 (Thörnqvist et al. 1987). Ascomycetes, particularly soft-rot fungi,<br />

may tolerate more alkaline substrates to about pH 11. Thus, the pH values from<br />

3.3–6.4 in the wood capillary water of living trees and in aqueous extracts of<br />

wood and bark samples from trees of the temperate zones and from trading<br />

timbers (Sandermann and Rothkamm 1959; Rayner and Boddy 1988; Fengel<br />

and Wegener 1989; Landi and Staccioli 1992; Roffael et al. 1992a, 1992b) correspond<br />

with the pH demands of wood fungi. Over the tree cross section, pH<br />

differences can occur, that is for example the heartwood of oaks and Douglas<br />

fir is more acid than the sapwood. Furthermore, an initial pH value can be<br />

changed in the context of microbial succession, because bacteria may acidify<br />

or alkalize the substrate by their metabolites (fatty acid production in acid<br />

wetwood or methane or ammonia formation in alkaline wetwood; Chap. 5.2).<br />

Outside about pH 2 and 12, respectively, microbial activity is commonly prevented.<br />

The acid pH-extreme of Aspergillus niger is 1.5 (Reiß 1997). There<br />

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3.5 pH Value and Acid Production by Fungi 71<br />

are however fungi that even grow at about pH 0 like a Cephalosporium species.<br />

Among the bacteria, the Archaea Picrophilus oshimae and P. torridus have their<br />

pH-optimum at pH 0.7 and even grow at pH −0.06 (Anonymous 1996).<br />

Various wood fungi can change pH values near the extremes by means of pH<br />

regulation through their metabolic activity (Rypáček 1966; Humar et al. 2001).<br />

Alkaline substrates are acidified by the excretion of organic acids, particularly<br />

oxalic acid/oxalate (Jennings 1991). Oxalic acid is synthesized by oxaloacetase<br />

(EC 3.7.1.1) from oxalic acetate of the citric acid cycle (Micales 1992; Akamatsu<br />

et al. 1993a, 1993b) and can also derive from the glyoxylate cycle (Hayashi et al.<br />

2000; Munir et al. 2001). Table 3.9 shows the amount of oxalic acid produced<br />

by some house-rot fungi in vitro and the resulting pH value.<br />

Figure 3.2a shows the change of the pH value by Schizophyllum commune<br />

as an example of the pH-regulation curve of fungi. If there would not have<br />

been a pH-change caused by the fungus, the diagonal in Fig. 3.2a would have<br />

resulted. Nutrient liquids with acidic initial pH values become alkalized. For<br />

example, the initial pH of 4.2 changed stepwise to the final pH of 7.5. After<br />

3–4 weeks of culture, a nearly straight plateau of pH 7.5 derived from the initial<br />

pH values 4.2, 5.1, 6.0 and 7.5. In contrast, the alkaline initial pH value of 7.5<br />

was acidified in the first 2 weeks of culture (Schmidt and Liese 1978).<br />

Aerobic bacteria alkalize their substrates by ammonia release from proteins<br />

and amino acids (Schmidt 1986) and anaerobic bacteria alkalize the wetwood<br />

in trees by methane formation (Ward and Zeikus 1980; Schink and Ward 1984).<br />

Is less intensively examined by which metabolic pathways fungi alkalize acid<br />

media. This may occur by the consumption of anions or by the formation of<br />

ammonia from nitrogen compounds (Schwantes et al. 1976).<br />

While unbuffered laboratory nutrient media approach the natural habitat<br />

of wood fungi and show the physiologically produced pH value of a fungus,<br />

buffered media of different initial pH values results in that pH-range, within<br />

which a fungus can grow without adjusting the pH. The pH-optima received<br />

Table 3.9. Content of oxalic acid (g/L) and pH-value in nutrient liquid after 2 months of<br />

incubation (from Schmidt 1995; Schmidt and Moreth 2003)<br />

Species Isolate (g/L) pH<br />

Antrodia vaillantii FPRL14 1.85 2.4<br />

R112 0.63 2.8<br />

BAM 65 0.65 2.8<br />

DFP 2375 1.20 2.4<br />

Antrodia sinuosa MAD 2538 1.10 2.6<br />

Oligoporus placenta FPRL 280 0.25 2.2<br />

Coniophora puteana Ebw. 15 0.04 4.2<br />

Serpula lacrymans BAM 133 1.85 2.4<br />

Donkioporia expansa MUCL 29391 0.16 4.6<br />

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72 3 Physiology<br />

Fig.3.2. pH value regulation by Schizophyllum commune (a) and mycelial dry matter after<br />

growth with different initial pH values (b) for 7–28 days (from Schmidt and Liese 1978)<br />

in buffered and unbuffered media can differ. For example, Schizophyllum commune<br />

grewbestonbufferedagaratpH4.7–5.1,butreachedinunbuffered<br />

nutrient liquid the highest mycelial dry matter at pH 7.5 (Fig. 3.2b). Two pHoptima<br />

may occur (Fig. 3.2b). Frequently, the optimum pH value of enzyme<br />

activity of enzymes isolated from a fungus differs in vitro considerably from<br />

the pH value for the corresponding fungal growth.<br />

Most brown-rot fungi accumulate oxalic acid (oxalate) in rather large quantities<br />

and acidify their microenvironment usually to a greater extent than do<br />

the white-rot fungi (Table 3.9: Donkioporia expansa). pH-reduction by brownrot<br />

fungi was thought to favor the activity of some non-enzymatic systems<br />

hypothesized to be active in these fungi, as well as cellulolytic enzyme activity<br />

(Goodell 2003). In brown-rot fungi, oxalate serves as an acid catalyst for the<br />

hydrolytic breakdown of wood polysaccharides (Chap. 4). The acid attacked<br />

the hemicelluloses and the amorphous cellulose, thus increasing the porosity<br />

of the wood structure for hyphae, enzymes and low-molecular degrading substances<br />

(Green et al. 1991a; Shimada et al. 1991). The enzyme system to produce<br />

oxalate was also found in the white-rot fungi like Trametes versicolor (Mu et al.<br />

1996). White-rot fungi accumulate smaller amounts of oxalate and use it in<br />

connection with the enzymatic lignin degradation by lignin peroxidase and<br />

manganese peroxidase. Under extracellular condition, the mediators, veratryl<br />

alcohol cation radicals and Mn 3+ , produced by lignin and manganese peroxidase,<br />

respectively, catalyze the decomposition of oxalate to CO2 (Shimada<br />

et al. 1994). During intercellular metabolism, oxalate is formed by oxalate<br />

decarboxylase (EC 4.1.1.2) to formate and CO2, and the formate produced<br />

is converted to CO2 by formate dehydrogenase (EC 1.2.1.2), yielding NADH<br />

(Watanabe et al. 2003). Oxalate may be also metabolized by oxalate oxidase<br />

(EC 1.2.3.4) to CO2 and H2O2. There are, however, exceptions within both fun-<br />

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3.5 pH Value and Acid Production by Fungi 73<br />

gal decay groups. Gloeophyllum trabeum, for example, degraded 14 C-labelled<br />

oxalic acid to CO2 during cellulose degradation (Espoja and Agosin 1991),<br />

and only relatively slight acidification of nutrient liquids was observed for all<br />

indoor Gloeophyllum species (Schmidt et al. 2002a).<br />

The intensive production of oxalic acid by Serpula lacrymans, which is<br />

reflected by an acidification of the growth medium to pH 2.4 (Schmidt 1995b,<br />

Table 3.9), has been discussed in connection with the preferential occurrence<br />

of the fungus within buildings. Excess oxalic acid is neutralized to Ca-oxalate<br />

by calcium from brickwork or by chelating with iron from metals, stonewool<br />

and nails (Bech-Andersen 1987b; Paajanen and Ritschkoff 1991, 1992; Paajanen<br />

1993; Palfreyman et al. 1996).<br />

The indoor polypores, especially Antrodia vaillantii, are resistant to copper<br />

mainly due to the formation of Cu-oxalate (Da Costa 1959; Sutter et al. 1983;<br />

Collett 1992a, 1992b; Schmidt 1995b; Chap. 8.5.3.2). Humar et al. (2002) showed<br />

that A. vaillantii, Gloeophyllum trabeum and Trametes versicolor transformed<br />

copper(II) sulfate in wood into non-soluble and therefore non-toxic copper<br />

oxalate. Hastrup et al. (2005) evaluated wood decay of samples impregnated<br />

with copper citrate and found 11 out of 12 isolates of Serpula lacrymans to be<br />

tolerant towards copper citrate. Table 3.10 shows the ability of some house-rot<br />

fungi to grow on copper-containing agar.<br />

Table 3.10. Copper tolerance. Growth (±) of house-rot fungi on agar containing copper<br />

sulphate (from Schmidt 1995; Schmidt and Moreth 2003)<br />

Species Isolate Molarity of copper<br />

0.001 0.005 0.01 0.03 0.05<br />

Antrodia vaillantii FPRL 14 + + + + −<br />

FPRL 14a + + + − −<br />

UK 14 + + + (+) −<br />

BAM 65 + + + + (+)<br />

BAM 486 + + + − −<br />

DFPG 6911 + + + + −<br />

DFP 2375 + + + − −<br />

Sweden R112 + + + (+) −<br />

Sweden R113 + + + − −<br />

Antrodia sinuosa MAD 2538 + − − − −<br />

Oligoporus placenta Ebw. 125 + (+) − − −<br />

FPRL 280 + + (+) − −<br />

Findlay 304A + (+) − − −<br />

Coniophora puteana Ebw. 15 + − − − −<br />

Serpula lacrymans BAM 133 + − − − −<br />

Serpula himantioides MAD 213 + − − − −<br />

Donkioporia expansa MUCL 29391 + − − − −<br />

(+) one of two duplicates<br />

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74 3 Physiology<br />

Antrodia vaillantii decreased the life-time of timber impregnated with chromated<br />

copper arsenate and borate, respectively. Chromium, which plays a role<br />

in the fixation reactions of the elements (Bull 2001; Bao et al. 2005b), and arsenate<br />

as well as borate became soluble by oxalic acid and were washed out by<br />

rain (bioleaching) (Göttsche and Borck 1990; Cooper and Ung 1992a). Copper<br />

is precipitated into the insoluble form of the oxalate, rendering the copper<br />

inert. This leaching effect was used for biological remediation (recycling) of<br />

CC-treated wood waste (Leithoff et al. 1995; Stephan et al. 1996; Samuel et al.<br />

2003; Kartal and Imamura 2003). Arsenic and chromium free copper-organic,<br />

alternative preservatives which were recently developed in view of health and<br />

environmental aspects were also attacked (Humar et al. 2004; cf. Chap. 7.4).<br />

There are further possible candidates for bioremediation of CCA-treated wood<br />

such as Laetiporus sulphureus (Kartal et al. 2004).<br />

3.6<br />

Light and Force of Gravity<br />

At first sight, light might have no significance for fungi, because fungi are<br />

carbon-heterotrophic. The vegetative mycelium including the rhizomorphs<br />

of Armillaria species and the strands of house-rot fungi grow in nature in<br />

the absence of light, namely in the soil and within trees or timber (substrate<br />

mycelium), or in buildings hidden behind wall coverings and in the subfloor<br />

area. The growth within the substrate might be rather due to hygro-, hydro-,<br />

geo- and chemotropisms than to negative phototropism (Müller and Loeffler<br />

1992). Surface and aerial mycelia also grow in the dark like during the routine<br />

fungal culturing in the laboratory or at low light intensity like in the indoor<br />

polypores and Serpula lacrymans in buildings.<br />

A requirement for light occurs particularly with respect to the initiation of<br />

reproduction and the ripening of the fruit bodies. Light is the signal that the<br />

mycelium has reached the (irradiated) surface, where there the spores can be<br />

produced in an environment suitable for spore release (Jennings and Lysek<br />

1999). For fungi, light in the short wavelengths, blue light, is effective, while<br />

light with longer wavelengths is ineffective. The light acceptor of the photons<br />

hitting the mycelium is riboflavin, which then reduces a cytochrome. The<br />

required light quantities are low, below those of the full moonlight at a clear<br />

sky (0.23µWcm −2 ).<br />

During the cultivation of Lentinula edodes on wood (Chap. 9.2), the colonized<br />

wood substrate was exposed to light for 8–15 h/day (Schmidt 1990).<br />

In the dark, the primordia did not develop further or abnormal fruit bodies<br />

occurred. Particularly suitable are wavelengths from 370–420 nm and from<br />

620–680 nm. Daedalea quercina, Gloeophyllum abietinum, Lentinus lepideus,<br />

Paxillus panuoides and some other fungi develop abnormal and frequently<br />

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3.6 Light and Force of Gravity 75<br />

sterile“darkfruitbodies”onminetimber.Serpula lacrymans fruits in buildings<br />

in twilight. In the laboratory, the daily light-dark cycles are suitable.<br />

The Deuteromycetes Aspergillus niger and Paecilomyces variotii develop<br />

conidia both with light and in the dark, likewise the ascomycete Chaetomium<br />

globosum forms fertile cleistothecia. In other Ascomycetes, conidia formation<br />

is induced by light, while in darkness ascospores develop (Reiß 1997). LightdarkcyclesleadtoarhythmicchangeofgrowthandreproductionofPenicillium<br />

species and other Deuteromycetes. When the hyphae are irradiated,<br />

their growth rate is reduced to differentiation into conidia. Concentric rings<br />

develop on agar plates from the inoculum in periodically repeated distances<br />

(Schwantes 1996; Reiß 1997; Jennings and Lysek 1999).<br />

Some fungi can grow permanently on sites exposed to light, e.g., fungi<br />

growing on plant surfaces (leaves, phylloplane). Typical phylloplane fungi<br />

are Alternaria, Aureobasidium and Cladosporium species (Jennings and Lysek<br />

1999). Some of them are potential parasites, but also effect blue stain of timber<br />

as saprobionts.<br />

UV light, particularly 254 nm, has a lethal and mutagenic effect. Nucleic<br />

acids are damaged by UV-B of 260 nm by the photochemical induction of cyclobutan<br />

dimers, which prevents the correct transcription and reduplication<br />

of DNA (Panten et al. 1996). That is mycelium and colorless spores and bacteria<br />

can be damaged by sunlight. Microbial pigmentation, particularly black<br />

(conidia of Aspergillus niger) and yellow (e.g., bacterium Micrococcus luteus),<br />

is interpreted as a protection against the irradiance. UV is thus used in microbiological<br />

and molecular laboratories to reduce the amount of bacteria and<br />

fungi in the air, on laboratory surfaces and devices.<br />

Fungi may also use the direction from which the light is coming to orientate<br />

themselves (Jennings and Lysek 1999). During the primordium growth<br />

of Basidiomycetes, the stipe grows towards the light source. In the Pilobolus<br />

species (Mucoraceae), there is a ring of yellow-orange carotenoids in the sporangiophore<br />

below the subsporangial bladder, which is shaded by the spore<br />

mass in the sporangium. If the light received by the ring is not at a minimum,<br />

the sporangial stalk bends until it is, which gives the direction in which<br />

the sporangium will be shot off, up to a distance of 40 cm (Jennings and Lysek<br />

1999). The force of gravity takes effect immediately when the developing<br />

pileus shades the tip of the stipe (Schwantes 1996). This ensures that the pores<br />

and lamellae in the growing hymenium orientate to the earth’s center (positive<br />

gravitropism, Nultsch 2001) that is, the mature basidiospores can sink<br />

tothesoil.Aknownexampleofpositivegravitropismmayoccurinthefruit<br />

body of Fomes fomentarius. The perennial, bracket fruit bodies are located<br />

at the stem of beech trees. When the white-rotten tree is wind-thrown, the<br />

fungus lives for a certain time as saprobiont in the laying stem. The new hymenia<br />

developing on the “old” fruit body orientate with a 90-degree change<br />

of direction again towards the earth’s center. If there is by chance a further<br />

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76 3 Physiology<br />

Fig.3.3. Fruit body gravitropism of Flammulina velutipes growing a on wood chips in the<br />

laboratory, 5 days old, b during 1 × g conditions on a centrifuge in the orbit, 5 days old,<br />

c under micro-gravitation influence during the D2 Spacelab mission 1993, 7 days old. (from<br />

Kern and Hock 1996). d Fruit body of Schizophyllum commune grown during turning the<br />

dish upside down<br />

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3.7 Restrictions of Physiological Data 77<br />

change of the stem direction, the next hymenia again follow this change.<br />

An exception among the hymenia of following the gravity occurs in the resupinate<br />

fruit bodies of house-rot fungi. The hymenium points upwards in<br />

fruit bodies growing on the floor, and orientates to the side in fruit bodies<br />

growing on a wall. The gravity perception in fungi was investigated by<br />

fruiting experiments with Flammulina velutipes under micro-gravitation condition<br />

during the German D-2 spacelab mission 1993 in the US space shuttle<br />

Columbia (Kern et al. 1991; Fig. 3.3). A positively gravitropic reaction can be<br />

simply demonstrated in the laboratory if a Petri dish with grown mycelium<br />

of a well-fruiting fungus like Schizophyllum commune is upside down for<br />

fruiting.<br />

According to the statolithe theory, amyloplasts and the cytoskeleton in statocyte<br />

cells are involved in gravitropic reactions of plants. Fungi however do<br />

not possess statolithes. Gravity reaction of F. velutipes was hypothesized to<br />

occur as follows: In the case of correct negative gravitropic adjustment of<br />

the fruit body, a mycohormon that is produced in the lamellae is permanently<br />

transported into the upper pileus area. The hormone effects a length<br />

increase on all sides, mediated by the synthesis of vesicles and their following<br />

insert. Incorrect adjustment effects an unequal hormone distribution that influences<br />

vesicle formation and subsequent unilateral stretching growth (Kern<br />

1994).<br />

3.7<br />

Restrictions of Physiological Data<br />

Dataintheliteraturewithrespecttothephysiologyofwoodfungilikegrowth<br />

reactions to environmental factors should be valued with proviso. First, a fungus<br />

may be misnamed due to wrong identification. Thus, DNA-analyses of<br />

closely related house-rot fungi of the genera Antrodia and Coniophora, respectively,<br />

have shown that about 15% of all investigated isolates belonging<br />

to these genera and sampled from own and various other strain collections<br />

were wrongly identified. As extreme, an isolate named A. serialis revealed to<br />

be Donkioporia expansa (Schmidt and Moreth 2003). Second, due to changes<br />

in the taxonomy, there may be considerable confusion in older references, e.g.,<br />

with respect to Antrodia vaillantii and Oligoporus placenta,becausebothhad<br />

been termed Poria vaporaria (Domański 1972). Third, generalizing statements,<br />

like a fungus is faster growing than others, have to be restricted, because there<br />

is considerable strain variation within a species. Table 3.11, based on isolates<br />

that had been verified by rDNA-ITS sequencing, shows as an example for variation<br />

that there are isolates of the so-called “fast-growing” Coniophora puteana<br />

exhibiting a lower growth rate than isolates of the “medium-growing” Antrodia<br />

vaillantii. Fourth, comparisons between different fungi/authors/publications<br />

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78 3 Physiology<br />

are only valuable if the test methods used are comparable and appropriate. It<br />

is for example senseless to compare both species in Table 3.11 with respect to<br />

the growth rate, if the experiment did not consider the different temperature<br />

optima of the species.<br />

Table 3.11. Examples for isolate variation within wood fungi (compiled from Schmidt et al.<br />

2002; Schmidt and Moreth 2003)<br />

Species Isolate with origin and year of isolation Temperature Maximum<br />

optimum daily radial<br />

growth at<br />

optimum<br />

temperature<br />

( ◦C) (mm)<br />

Antrodia FPRL 14, originally CBS 31 5.4<br />

vaillantii FPRL 14a, fruit body, UK 1936 28–31 4.3<br />

UK 14, via Denmark and BAM Berlin 28 5.5<br />

DFPG 6911, New Zealand 1953 28 5.4<br />

DFP 2375, BAM 28 5.8<br />

Sweden R112, greenhouse, Stockholm ≈ 1952 28 5.1<br />

Sweden R113 28–31 5.6<br />

Ottawa 11740, USA? 28 5.1<br />

BAM 65 25–28 4.9<br />

BAM 486 28 6.1<br />

Coniophora UK, FPRL 11e 22.5 2.5<br />

puteana BK-C-50, Uppsala 25 6.3<br />

74453-2, Uppsala 22.5 5.0<br />

FORINTEK 9 0, fruit body, Ontario 1973 25 4.8<br />

Eberswalde 15, ‘Normstamm I’ 1930 25 7.0<br />

BAM 260, building, Berlin 1940 22.5 4.5<br />

Zycha, München 1963 25 3.5<br />

outdoor fruit body, Hamburg 1997 22.5 7.0<br />

G 61, fruit body, cherry-tree, Karlsruhe 1985 22.5–25 4.8<br />

G 98, building, Karlsruhe 1990 25 7.5<br />

G 100, building, Karlsruhe 1990 22.5 9.3<br />

G 107, building, Karlsruhe 1991 22.5 9.0<br />

G 125, building, Karlsruhe 1993 22.5 7.8<br />

G 135, building, Karlsruhe 1993 22.5 11.3<br />

G 156, building, Karlsruhe 1994 25 6.8<br />

G 219, building, Karlsruhe 1996 25 9.5<br />

G 220, building, Karlsruhe 1996 22.5–25 10.0<br />

fruit body, Ludwigslust Castle 1998 22.5 10.5<br />

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3.8 Competition and Interactions Between Organisms 79<br />

3.8<br />

Competition and Interactions Between Organisms<br />

Except for axenic laboratory cultures, there are only a few cases in which<br />

a natural substrate remains occupied by only one species. A known case is<br />

Oudemansiella mucida in standing, but dead trunks of Fagus sylvatica due to<br />

the production of the antifungal compound, mucidin. Instead, nearly every<br />

substrate accessible to fungi can support more than one species (Rayner and<br />

Boddy 1988), that is, various fungi and bacteria compete for space, nutrients,<br />

water, and air. Each fungus has its own strategy to withstand competition.<br />

Competition may occur between species and between mycelia of the same<br />

species. As a result of the latter, wood colonized by Trametes versicolor shows<br />

that the individual colonies form black barrier (demarcation) lines, where the<br />

differentmyceliahaveinteractedwitheachothertoinhibitfurthermovementof<br />

each mycelium in the region of contact. Different parts of the same mycelium<br />

and even adjacent hyphae may compete. For example, reproducing hyphae<br />

might consume more nutrients and thereby affect the vegetatively growing<br />

hyphae.<br />

There are three main categories of the strategies or adaptations to ecological<br />

niches (Jennings and Lysek 1999). Through combative strategy, the fungus<br />

defends the substrate that has already been captured or attacks competitors<br />

occupying a substrate that is capable of capture (e.g., O. mucida). Through<br />

ruderal strategy, a substrate as yet unoccupied or only partly colonized is<br />

exploited. Those fungi do not attack potentially resistant substrates but degrade<br />

readily consumable or unusual compounds, like Pholiota carbonica (Europe,<br />

North America, Asia, North Africa) and P. highlandensis (USA), which both<br />

grow on former fire sites (Breitenbach and Kränzlin 1995). So these fungi<br />

occupy a substrate faster than possible competitors. Fungi concerned in the<br />

stress-tolerant strategy are adapted to environments that are too harsh for<br />

possible competitors. Examples for the latter are the soft-rot fungi growing in<br />

verywettimberoflowaircontent.<br />

3.8.1<br />

Antagonisms, Synergisms, and Succession<br />

Interactions (reciprocal effects) between wood fungi have been early investigated<br />

e.g., by Oppermann (1951) and Leslie et al. (1976), and were described<br />

in detail by Rayner and Boddy (1988).<br />

Antagonism (competitive reciprocal effect), the mutual inhibition and in<br />

abroadersensetheinhibitionofoneorganismbyothers,isbasedontheproduction<br />

of toxic metabolites, on mycoparasitism, and on nutrient competition.<br />

Antagonisms are investigated as alternative to the chemical protection against<br />

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80 3 Physiology<br />

tree fungi (“biological forest protection”) and against fungi on wood in service<br />

(“biological wood protection”) (Wälchli 1982; Bruce 1992; Holdenrieder and<br />

Greig 1998; Phillips-Laing et al. 2003).<br />

As early as 1934, Weindling showed the inhibiting effect of Trichoderma<br />

species on several fungi. Bjerkandera adusta and Ganoderma species were<br />

antagonistic against the causing agent of Plane canker stain disease (Grosclaude<br />

et al. 1990). Also, v. Aufseß (1976) examined mycelial interactions between<br />

Heterobasidion annosum and Stereum sanguinolentum and antagonistic fungi<br />

like Phlebiopsis gigantea and Trichoderma viride (also Holdenrieder 1984).<br />

Root rot by Heterobasidion annosum (Chap. 8.3.2) is the classical target for<br />

biological forest protection and the only example of a successful biological<br />

control of a fungal forest disease. Based on the work of Rishbeth, stump treatment<br />

with Phlebiopsis gigantea was developed and successfully used in several<br />

countries. Originally in England, the spread of root rot in pine sites was diminished<br />

by the immediate coating of the fresh stump surface with an aqueous<br />

spore (asexual arthrospores) suspension of P. gigantea (Meredith 1959; Rishbeth<br />

1963). The antagonist colonizes the stump, that is H. annosum cannot<br />

infect it by air-borne spores and thus an infection of neighboring trees via<br />

root grafts is prevented. The treatment of spruces yielded differently satisfactory<br />

results (Korhonen et al. 1994; Holdenrieder et al. 1997). Holdenrieder and<br />

Greig (1998) listed also several bacteria, which were antagonistic against H. annosum.<br />

Promising systems for the biological protection of growing trees have<br />

been studied against Armillaria luteobubalina, Chondrostereum purpureum,<br />

Phellinus tremulae, P. weirii, and Ophiostoma ulmi (Bruce 1998; also Palli and<br />

Retnakaran 1998).<br />

There were many attempts for biological wood protection (Bruce 1998).<br />

To date, the application of biological control to prevent wood decay and discoloration<br />

has been successful in the laboratory, but was often inconsistent<br />

in its performance in the field (Dawson-Andoh and Morrell 1997; Mikluscak<br />

and Dawson-Andoh 2004b). Much work has been done in the Forest Products<br />

Laboratory, Madison. In the laboratory, a blue stain fungus was inhibited by<br />

antibiotic substances from Coniophora puteana (Croan and Highley 1990) and<br />

Bjerkandera adusta (Croan and Highley 1993). Bacteria were examined for<br />

their suitability to prevent of blue stain (Bernier et al. 1986; Seifert et al. 1987;<br />

Benko 1989; Florence and Sharma 1990; Kreber and Morrell 1993; Bjurman<br />

et al. 1998; Payne et al. 2000; Bruce et al. 2004). A bacterial mixed culture decreased<br />

staining and molding of pine wood samples as well as decay by Trametes<br />

versicolor and Oligoporus placenta (Benko and Highley 1990). Streptomyces rimosus<br />

Sobin, Finlay & Kane (Croan and Highley 1992b) and its culture filtrate<br />

(Croan and Highley 1992c) prevented spore germination of Aspergillus niger,<br />

Penicillium sp. and Trichoderma sp.aswellasbluestainbyAureobasidium<br />

pullulans. Trichoderma species are extensively researched biological control<br />

agents for wood protection against decay fungi (Highley and Ricard 1988;<br />

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3.8 Competition and Interactions Between Organisms 81<br />

Murmanis et al. 1988; Morris et al. 1992; Doi and Yamada 1992; Bruce 1998;<br />

Phillips-Laing et al. 2003). Culture filtrates of Chaetomium globosum, Penicillium<br />

sp., Sporotrichum pulverulentum and Trichoderma viride decreased wood<br />

degradation by T. versicolor (Ananthapadmanabha et al. 1992).<br />

Current attempts for biological wood protection use a colorless mutant<br />

of the blue-stain fungus Ophiostoma piliferum. Round wood and cut timber<br />

is treated with a spore suspension of the mutant to reduce or even prevent<br />

subsequent natural colonization of the wood by blue-stain fungi (Blanchette<br />

et al. 1994; Behrendt et al. 1995; Schmidt and Müller 1996; White-McDougall<br />

et al. 1998; Ernst et al. 2004). Corresponding experiments used Gliocladium<br />

roseum to protect green lumber from molds, stain, and decay (Yang et al.<br />

2004a). Figure 3.4 demonstrates the inhibiting effect of O. piliferum against<br />

two blue-stain fungi in the laboratory.<br />

Synergism (mutualistic reciprocal effect) means the mutual promotion and<br />

inthebroadersensethepromotionofoneorganismbyothers.Topreparethe<br />

substrate, the pH value can be changed, vitamins can be excreted (Henningsson<br />

1967), and inhibiting heartwood compounds can be degraded. The nitrogen<br />

content may be increased by N-fixing soil bacteria (Baines and Millbank 1976),<br />

and nutrients can become more available (also Levy 1975a; Hulme and Shields<br />

1975). Neutralistic reciprocal effects, neither inhibition nor promotion, occur<br />

more rarely.<br />

Fig.3.4. Inhibition by a colorless mutant of Ophiostoma piliferum of blue-staining of wood<br />

samples by Phoma exigua and Aureobasidium pullulans. <strong>Wood</strong> samples A were previously<br />

dipped in a spore solution of O. piliferum and then all four samples were inoculated with<br />

the blue-stain fungi (from Müller and Schmidt 1995)<br />

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82 3 Physiology<br />

The various competition strategies and reciprocal effects influence the sequence<br />

(succession) of fungi and bacteria that are found at different stages in<br />

the degradation of a complex substrate like wood. Each species uses a different<br />

component of the substrate as it becomes available as a result of the degradation<br />

by the preceding species (Jennings and Lysek 1999). Primary colonists,<br />

bacteria and non-decay fungi (slime fungi, yeasts, molds), rely on relatively<br />

easy assimilable substrates such as simple sugars, starch and proteins and remain<br />

predominantly on the wood surface and within the outer wood parts,<br />

preparing the substrate for following organisms. There may occur a continued<br />

co-existence of non-decay organisms on the substrate. Or the primary colonists<br />

are followed by the decay fungi which are capable of degrading the relatively<br />

refractory wood cell wall components and which penetrate deeper into the<br />

wood such as staining fungi and the brown, soft and white-rot fungi (Levy<br />

1975a; Käärik 1975; Rayner and Boddy 1988).<br />

Schales (1992) found 15 wood-decay fungi on a wind-thrown beech tree<br />

and its stump. Chondrostereum purpureum and Stereum hirsutum occurred<br />

during the initial phase of 2 years. Bjerkandera adusta and Trametes versicolor<br />

were common in the following medium (optimum) phase of 5–7 years.<br />

Kuehneromyces mutabilis and Kretzschmaria deusta were observed in the final<br />

phase (also Jahn 1990; Röhrig 1991). Ten beech stumps showed within 4 years<br />

after tree felling 74 fungal species, 46 Basidiomycetes, 25 Ascomycetes and three<br />

Deuteromycetes (Andersson 1997a; also Willig and Schlechte 1995; Andersson<br />

1997b; Blaschke and Helfer 1999). Those surveys indicate that a substrate is<br />

colonized by more species than commonly described in literature and that<br />

some fungi occur earlier than expected.<br />

While most fungi colonizing wood use nutrients of the substrate, some are<br />

probably only passive occupants using the wood only as a support for fruit<br />

body formation.<br />

Interrelationships between trees and the fungi that inhabit them have been<br />

treated by Rayner (1993).<br />

3.8.2<br />

Mycorrhiza and Lichens<br />

Mycorrhiza (“fungal root”) is the association of mutual benefit (mutualistic interaction)<br />

between a fungus and the root of a higher plant (Agerer et al. to 1986;<br />

Willenborg 1990; Allen 1991; Schwantes 1996; Smith and Read 1997; Varma and<br />

Hock 1999; Egli and Brunner 2002; v.d. Heijden and Sanders 2002; Peterson<br />

et al. 2004). About 80–95% of the higher plants are capable of mycorrhization<br />

(e.g., Bothe and Hildebrandt 2003).<br />

Mycorrhizas are differently grouped. The grouping according to Hock and<br />

Bartunek (1984) in Fig. 3.5 distinguishes three major forms.<br />

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3.8 Competition and Interactions Between Organisms 83<br />

Fig.3.5. Major forms of mycorrhizas.<br />

Ek ectotrophic, En endotrophic, VA<br />

vesicular-arbuscular (modified from<br />

Hock and Bartunek 1984)<br />

The ectotrophic mycorrhiza (ectomycorrhiza) occurs predominantly on<br />

conifers and hardwoods of the boreal and temperate zone, particularly associated<br />

with Pinales, Fagales and Salicales. In many conifers and in beech<br />

and oak, the association is obligatory, and in other trees like elms it is facultative<br />

(Müller and Löffler 1992). The predominant part of the mycelium grows<br />

at the surface of side roots and forms a dense mycelial coat at the root tips.<br />

The hyphae penetrate between the cells of the outer root tissue by dissolving<br />

the middle lamellae, and coat the cells completely as “Hartig net” (Kottke<br />

and Oberwinkler 1986). The colonized roots do no longer possess root hairs;<br />

instead hyphae or rhizomorphs radiate into the soil.<br />

In the endotrophic mycorrhiza (endomycorrhiza) of the orchids, only a loose<br />

hyphal net is formed around the root, and the hyphae settle inside the cells<br />

in the root bark area. As an intermediate, the ectendotrophic mycorrhiza is<br />

particularly present on roots of 1 to 3-year-old conifers, whereby the hyphae<br />

penetrating into the bark cells degenerate with ageing.<br />

The most frequent form, the vesicular arbuscular mycorrhiza (VAM) occurs<br />

associated with over 200,000 wild and cultivated angiosperms, in addition,<br />

with Ginkgo biloba, Taxus baccata and Sequoia gigantea and S. sempervirens<br />

(Werner 1987), as well as predominant form in tropical forests. In the VAM,<br />

the unseptate hyphae extend inside the root cells bubble-shaped (vesicles)<br />

or branch out tree-shaped (arbuscules). The arbuscules develop by hyphal<br />

branching and become enclosed by the peri-arbuscular membranes from the<br />

plant (Bothe and Hildebrandt 2003).<br />

The benefit for the trees is the improved nutrient (amino acids) and mineral<br />

(N, P, K, Mg, Cu, Zn, Fe) support and the better water supply (Smith and<br />

Read 1997) due to the larger absorption area. Soils with frequently occurring<br />

ectomycorrhiza are commonly characterized by a lower nutrient content, the<br />

trees growing there would not be competitive without mycorrhizas (Schönhar<br />

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84 3 Physiology<br />

1989). The soil quality (ventilation, water permeability, stabilization of soil<br />

particles) is increased. The trees are more resistant to drying stress. In addition,<br />

mycorrhizal fungi play a role in tree defense against fungal pathogens<br />

(Strobel and Sinclair 1992). The fungi benefit from the supply of photosynthates<br />

(carbohydrates) from the trees and from supplements, e.g., thiamine.<br />

As much as 30–35% of the photosynthate by a beech forest is metabolized by<br />

the mycorrhizal fungi (Jennings and Lysek 1999).<br />

About one-third (2,000 species) of the “higher fungi” which grow in forests<br />

are mycorrhizal fungi (Egli and Brunner 2002). Among them there are many<br />

edible mushrooms (e.g., Boletus edulis, Cantharellus cibarius), but also poisonous<br />

species (e.g., Amanita species). Endotrophic mycorrhizal fungi are<br />

usually Ascomycetes. Ectotrophic fungi are usually Basidiomycetes such as<br />

Amanita species, B. edulis or the truffles (Ascomycetes). The about 150 VAM<br />

symbionts belong to the Zygomycetes, often to the genus Glomus.<br />

Many trees, like beech, oak, spruce, chestnut, pine, larch and willow, become<br />

stunted in sterile culture and previous mycorrhizal inoculation of seedlings<br />

improved tree growth (Ortega et al. 2004). Several obligatory mycorrhizal fungi,<br />

like B. edulis, only fruit in association with roots, partly host-specifically or<br />

with a narrow host spectrum, like Amanita caesarea predominantly associated<br />

with oaks, usually however hardly host-specifically, like A. muscaria at birch,<br />

eucalypts, spruce and Douglas fir (Werner 1987). The trees are usually less<br />

specific: Pinus sylvestris forms mycorrhizas with at least 155 fungal species and<br />

Picea abies with 118 fungi (Korotaev 1991).<br />

Artificial mycorrhization may de done in the tree nursery or during planting<br />

or by injection in the root area of old trees (Egli 2004; Evers and Pampe<br />

2005). About 500,000 l mycorrhizal inoculum was produced worldwide in 2003<br />

(Grotkass et al. 2004).<br />

With regard to the significance of the mycorrhizas in view of the forest<br />

dieback by pollution (Flick and Lelley 1985), there is a trend that young trees<br />

already show a fungal community, which is typical for old trees. The changed<br />

mycorrhiza was rated as signal for tree damage: “The fungi disappear before the<br />

trees” (Cherfas 1991). A negative correlation was found between the frequency<br />

of fungal occurrence and the content of nitrogen and sulfur compounds as<br />

well as ozone in the atmosphere: 71 species of fungi were observed in a certain<br />

area of the Netherlands from 1912–1954 and only 38 species between 1973 and<br />

1982. Also, the size of the fruit bodies decreased (Cherfas 1991). According<br />

to Schönhar (1989), the change of the mycorrhiza is particularly based on<br />

nitrogen imissions by fertilization. The possible role of mycorrhiza in forest<br />

ecosystems under CO2-enriched atmosphere in view of the global atmospheric<br />

change was discussed (Quoreshi et al. 2003). Experimental drought investigated<br />

in view of the expected reduction in water in Mediterranean regions showed<br />

that drought treatment did not delay mushroom appearance, but reduced<br />

mushroom production by 62% (Ogoya and Peñuelas 2005).<br />

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3.8 Competition and Interactions Between Organisms 85<br />

Investigations have been performed to regenerate the decreased mycorrhizal<br />

occurrence and the species change in forest damage sites by artificial<br />

inoculation and thus to improve the health of these trees and also of trees on<br />

other problematic sites (Römmelt et al. 1987; Marx 1991; Schmitz 1991; Lelley<br />

1992; Hilber and Wüstenhöfer 1992; Schmitz and Willenborg 1992; Göbl 1993;<br />

Kutscheidt and Dergham 1997). However, it has to be considered that thereby<br />

one intervenes only at the symptoms of the damage and not at its causes, that<br />

is, new inoculations without reduction of the emissions might be unsuccessful<br />

in the long run. To improve the isolate characteristics of mycorrhizal species,<br />

interstock matings have been done e.g., with Paxillus involutus (Strohmeyer<br />

1992).<br />

A further association of mutual benefit is lichens, a close and stable partnership<br />

between Ascomycetes (and rarely Basidiomycetes) with green algae<br />

or cyanobacteria (Kappen 1993). In the mutualistic form of lichens, the fungi<br />

receive organic nutrients and vitamins from the algae/bacteria and these get<br />

water and inorganic salts from the fungi. The association allows the pioneer<br />

settlement of inhospitable biotopes such as rocks with only traces of nutrients.<br />

In the antagonistic form, the fungi are parasitic to the algae, and the algae<br />

survive by increasing faster than they are destroyed by the fungi (Schubert<br />

1991). With respect to classification, the lichens are placed in the fungal system<br />

as lichenized fungi.<br />

Fungal associations with animals are the endosymbioses in the mycetomes<br />

of insects. Ectosymbioses occur in the “fungal gardens” of termites and in the<br />

cultivation of the ambrosia fungi in the drill ducts of bark beetles (Francke-<br />

Grosman 1958; Werner 1987). For example, Ips typographus is associated<br />

with ophiostomatoid fungi (Solheim 1999; Sallé et al. 2005). The fungi are<br />

transferred to the tree during the beetle attack and are considered important<br />

partners in beetle population establishment. In addition, fungi invade the<br />

host’s phloem and sapwood, where the hyphae can cause blue stain. Recently,<br />

a symbiosis between three partners was found: leaf cutter ants in Panama and<br />

Ecuador are associated with a basidiomycete fungus, but additionally with<br />

abacterium(Streptomyces sp.) which was shown to be antagonistic against<br />

a parasitic ascomycete that has a negative effect on the ant/basidiomycete interaction<br />

(Anonymous 1999). Aspects of the association of fungi and insects<br />

with the infected trees are described by Raffa and Klepzig (1992).<br />

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4<br />

<strong>Wood</strong> Cell Wall Degradation<br />

4.1<br />

Enzymes and Low Molecular Agents<br />

In view of the historical development of the research on wood degradation<br />

by fungi, this chapter starts with the enzymes involved in the decay of the<br />

woody cell wall, although it is now commonly accepted that non-enzymatic,<br />

low molecular weight metabolites are involved as precursors and/or co-agents<br />

with enzymatic cell wall degradation.<br />

Under the conditions within microbial cells, namely an aqueous environment<br />

with pH values around 6 and temperatures of 1–50 ◦ C, most reactions<br />

would run off only very slowly. Enzymes reduce the amount of the necessary<br />

activation energy as biocatalysts and control the reaction by substrate and<br />

effect specificity. More than 3,000 enzymes are described.<br />

Comparable with the lock/key principle, enzymes possess an active center,<br />

into which the substrate must fit, and which thus controls the conversion of<br />

the correct substrate (substrate specificity). The protein portion of the enzyme<br />

decides on the way of the reaction (effect specificity). Enzymes may consist<br />

only of protein or contain additional cofactors (e.g., Mg 2+ ,Mn 2+ ) or coenzymes<br />

(e.g., vitamin B1). Before the conversion of the substrate into a product, the<br />

enzyme substrate complex is formed: enzyme E + substrate S → enzyme<br />

substrate complex ES → enzyme E + product P.<br />

Studies on fungal polysaccharide hydrolyzing enzymes have shown a structural<br />

design composed of two functional domains, a catalytic core responsible<br />

for the actual hydrolysis and a conserved cellulose-binding terminus, with an<br />

intervening, glycosylated hinge region. A large number of genes encoding cellulases,<br />

hemicellulases, glucanases, amylolytic enzymes, and those hydrolyzing<br />

various oligosaccharides have been cloned from fungi. The best-studied organisms<br />

are Trichoderma reesei, Phanerochaete chrysosporium, andAgaricus<br />

bisporus in respect of cellulases and hemicellulases, and several Aspergillus<br />

species in respect of amylolytic enzymes, pectinases and hemicellulases (reviews<br />

by Penttilä and Saloheimo 1999; Kenealy and Jeffries 2003). For example,<br />

papain cleavage of cellobiohydrolase (CHB) from P. chrysosporium separated<br />

the catalytic domain from the hinge and binding domains. Restriction mapping<br />

and sequence analysis of cosmid clones showed a cluster of three structural<br />

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88 4 <strong>Wood</strong> Cell Wall Degradation<br />

related CHB genes. Within a conserved region, the deduced amino acid sequences<br />

of P. chrysosporium cbh1-1 and cbh1-2 were, respectively, 80 and 69%<br />

homologous to that of the Trichoderma reesei CBH I gene. Transcript levels of<br />

the three P. chrysosporium CHB genes varied, depending on culture conditions<br />

(review by Highley and Dashek 1998). Binding domains specific for xylan have<br />

also been identified (review by Kenealy and Jeffries 2003).<br />

Because of their valuable protein character, constitutive enzymes always<br />

present in the cell are the exception. Usually, the biosynthesis of the inducible<br />

enzymes is induced, if its presence is necessary, by the substrate or other<br />

molecules. Some work was done with regard to the regulation of extracellularly<br />

acting enzymes in fungi. For example with white-rot fungi, cellulase<br />

synthesis is induced in vitro by cellulose and repressed by glucose. As the wood<br />

cell-wall macromolecules are degraded outside the hypha, the most generally<br />

accepted view of the induction process is that the fungi produce a basic level<br />

of constitutive amount of enzyme that produces soluble degradation products<br />

that function as inducers. In Phanerochaete chrysosporium, which has served<br />

as a model organism for white-rot degradation studies, cellobiose concentration,<br />

a product of cellulase action, is controlled in at least four ways, by<br />

β-glucosidase, transglucosylation reactions, and two oxidative enzymes. As<br />

with cellulases, simple sugars repressed the production of most hemicellulosedegrading<br />

enzymes by white-rot fungi (review by Highley and Dashek 1998).<br />

For the naming of enzymes, particularly in former times “ase” was added<br />

to the name of the substrate (e.g., lignin, ligninase). Nowadays, the enzyme<br />

nomenclature indicates the enzymatic reaction. In accordance with the Nomenclature<br />

Committee of the International Union of Biochemistry and Molecular<br />

Biology (www.chem.qmul.ac.uk/iubmb/enzyme), enzymes are grouped<br />

according to their function into six classes and there into sub-groups: Oxidoreductases<br />

catalyze oxidation and reduction reactions by transferring hydrogen<br />

and/or electrons, transferases the transmission of different groups.<br />

Hydrolases hydrolyze glucosides, peptides etc., lyases catalyze non-hydrolytic<br />

cleavage, isomerases cause among other things reversible transformations of<br />

isomeric compounds, and ligases catalyze the covalent linkage of two molecules<br />

with simultaneous ATP cleavage. Each enzyme receives an EC number, which<br />

points out to its reaction. For daily use, the common, trivial names (ligninase,<br />

cellulase, xylanase), however, are still used.<br />

Some general characteristics of enzymes and of those enzymes involved in<br />

wood degradation are summarized in Table 4.1.<br />

The dry matter of wood consists of about 45% cellulose and, depending on<br />

wood species, of 20–30% hemicelluloses and 20–40% lignin. With exception<br />

of pectins in the middle lamella, which has significance to wood-inhabiting<br />

bacteria, further components such as the contents of parenchyma cells, resins,<br />

accessory compounds etc. are less considered in the following. Thus, relatively<br />

few enzymes are involved in the primary, extracellular enzymatic wood decay.<br />

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4.1 Enzymes and Low Molecular Agents 89<br />

Table 4.1. Some characteristics of enzymes for wood degradation<br />

altogether six classes of enzymes with subgroups:<br />

1. oxidoreductases, 2. transferases, 3. hydrolases,<br />

4. lyases, 5. isomerases, 6. ligases<br />

lignin degradation by oxidoreductases:<br />

lignin peroxidase EC 1.11.1.14<br />

manganese-peroxidase EC 1.11.1.13<br />

laccase EC 1.10.3.2<br />

hemicellulose degradation by hydrolases:<br />

endo-1,4-β-xylanase EC 3.2.1.8, xylan 1,4-β-xylosidase EC 3.2.1.37<br />

mannan endo-1,4-β-mannosidase EC 3.2.1.78, β-mannosidase EC 3.2.1.25 etc.<br />

cellulose degradation by hydrolases:<br />

cellulase EC 3.2.1.4<br />

β-glucosidase EC 3.2.1.21<br />

cellulose 1,4-β-cellobiosidase EC 3.2.1.91 etc.<br />

ectoenzymes:<br />

extracellular degradation of macromolecules pectin, hemicellulose, cellulose, lignin<br />

outside the hypha<br />

[uptake of degradation products (carbohydrate oligomers, dimers, monomers,<br />

lignin degradation products)]<br />

intracellular enzymes:<br />

metabolic transformation within the hypha to hyphal biomass, metabolites, energy<br />

endoenzyme:<br />

attack within the substrate, often randomly<br />

exoenzyme:<br />

attack at the non-reducing substrate end<br />

enzyme activity:<br />

in former times (but still used):<br />

international unit: 1 U = 1 µmol/min, (1 U = 16.67nkat)<br />

currently:<br />

kat (katal, catalytic activity): 1 kat = 1 mol/s<br />

The enzymes for the degradation of the cellulose and hemicelluloses within<br />

thewoodycellwallbelongpredominantlytothehydrolases,whichcleaveglucosidic<br />

bonds. Briefly (and thus not totally correctly), cellulose is hydrolyzed<br />

by cellulase, cellulose 1,4-β-cellobiosidase and β-glucosidase. The hemicelluloses<br />

xylan and mannan are degraded by endo-1,4-β-xylanase and mannan<br />

endo-1,4-β-mannosidase, respectively, followed by xylan 1,4-β-xylosidase and<br />

β-mannosidase and further enzymes for the side chains. Lignin is oxidatively<br />

degraded by the oxidoreductases lignin peroxidase and manganese peroxidase.<br />

Enzymatic wood degradation was summarized e.g., by Eriksson et al. 1990,<br />

Shimada 1993, Jennings and Lysek 1999, Goodell et al. 2003.<br />

Cellulose, hemicellulose, and lignin are as macromolecules too large to be<br />

taken up into the hypha. Therefore, the molecules are first degraded by extra-<br />

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90 4 <strong>Wood</strong> Cell Wall Degradation<br />

cellular enzymes (ectoenzymes) into smaller fragments, which are taken up<br />

and then metabolized by intracellular enzymes to energy and fungal biomass.<br />

Independent of this place of action, an exoenzyme attacks at the end of a macromolecular<br />

substrate, while an endoenzyme splits within the molecule. These<br />

four terms are sometimes mixed up.<br />

Occurrence and distribution of enzymes and metabolites inside hyphae, in<br />

the hyphal slime layer, and within the attacked woody tissue were investigated<br />

by means of immunological methods and electron microscopy (Sprey 1988;<br />

Goodell et al. 1988; Srebotnik et al. 1988a; Blanchette et al. 1989, 1990; Daniel<br />

et al. 1989, 1990; Srebotnik and Messner 1990; Kim 1991; Green et al. 1991b;<br />

Kim et al. 1991a, 1991b, 1992, 1993; Lackner et al. 1991; Blanchette and Abad<br />

1992). TEM of immunogold-labeled hyphae of Trametes versicolor grown on<br />

carboxymethylcellulose localized β-glucosidase on the plasmalemma, in the<br />

hyphal cell wall, and in the hyphal sheath (review by Highley and Dashek 1998).<br />

Simple methods are used in screening tests to detect enzymes and to determine<br />

their activity. For example, a cellulose is added to a fungal culture, whose<br />

cellulolytic enzymes produce glucose. The glucose of the sampled culture filtrate<br />

reduces a test compound, which is added in oxidized form and changes<br />

its color by reduction. At a specific wavelength, the quantity of the converted<br />

test substance and thus of the developed glucose is measured and the activity<br />

of “cellulolytic enzymes” is calculated. Remazol brilliant blue, which binds<br />

to cellulose and hemicellulose by a microbially relatively inert linkage, may<br />

be mixed in agar. If cellulolytic or hemicellulolytic microorganisms or their<br />

enzymes are present, the still colored degradation products are released and<br />

clearing zones occur around the active colony, which can be also quantified<br />

(Schmidt and Kebernik 1988; Takahashi et al. 1992). For detailed investigations,<br />

various purification and enrichment steps may be used (chromatography, electrophoresis,<br />

etc.).<br />

The current unit of enzyme activity is katal (catalytic activity, kat), although<br />

in practice the old definition U is still used (Table 4.1).<br />

Microbial wood degradation is influenced by several major characteristics<br />

of the substrate wood (Table 4.2).<br />

Accessory compounds in the heartwood as well as resin excretion and wound<br />

reactions after wounding inhibit the colonization and spread of microorganisms<br />

within the tree (Chap. 3.1).<br />

The polymeric structure of the nutrients cellulose, hemicelluloses, and<br />

lignin requires that the degrading agents act outside the hypha. Cowling (1961)<br />

first stated that the known enzymes of the time were too large to penetrate<br />

intotheinteriorofthewoodcellwallandhypothesizedapossibleexistence<br />

of a small mass enzyme. The molecular weights of cellulases range from 13–<br />

61 kDa (Fengel and Wegener 1989). A cellulase of 40 kDa can exhibit a thickness<br />

of about 4 nm and a length of 18 nm (Messner and Srebotnik 1989). Frequently,<br />

about an 8 nm size was measured (Reese 1977; Messner and Stachelberger<br />

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4.1 Enzymes and Low Molecular Agents 91<br />

Table 4.2. Characteristics that make wood recalcitrant to fungi and bacteria<br />

– accessory compounds in the heartwood<br />

– resin excretion of softwoods, wound reactions of parenchyma cells in hardwoods<br />

– polymeric structure of the cell wall components<br />

– extracellular degradation of the nutrients<br />

– small pore sizes within the cell wall<br />

– complex structure of the woody cell wall<br />

– partially crystalline nature of cellulose<br />

– incrustation of the more easily degradable carbohydrates by lignin<br />

– structure and non-water-solubility of lignin<br />

1984; Murmanis et al. 1987). Thus, cellulases are too large for diffusing into<br />

the capillary areas of the cell wall from 0.5–4 nm pore size (average in spruce:<br />

1 nm: Reese 1977; Kollmann 1987) (Keilisch et al. 1970; Flournoy et al. 1991).<br />

This pore size excludes compounds with kDa mass greater than 6. Bailey et al.<br />

(1968) postulated a “pre-cellulolytic phase”. Meanwhile, so-called low molecular<br />

weight agents are known to be involved in the decay of the woody cell<br />

wall. As the different groups of wood decay fungi differ with regard to the<br />

participating low molecular agents, these aspects are treated separately in the<br />

chapters on cellulose and lignin degradation.<br />

The complex ultrastructure of the woody cell wall (e.g., Booker and Sell<br />

1998) affects its degradation (Liese 1970; Daniel 2003). A great part of the cellulose<br />

is bundled up by hydrogen bonds to larger, crystalline units (“crystalline<br />

cellulose”, Fig. 4.3), the elementary fibrils. The crystalline nature of the cellulose<br />

prevents an attack of many microorganisms. Several elementary fibrils<br />

result by linkage with hemicelluloses in the next larger unit, the microfibril. At<br />

the surface of the microfibrils, hemicelluloses form a bridge to the incrusting<br />

lignin, as chemical bonds exist between lignin and hemicelluloses (lignin carbohydrate<br />

complex, Koshijima and Watanabe 2003; Fig. 4.1). Several models<br />

depicting this molecular arrangement have developed (e.g., Kerr and Goring<br />

1975; Fengel and Wegener 1989) although there is no accepted model (Daniel<br />

2003).<br />

Principally, the carbohydrates cellulose and hemicelluloses are rather easily<br />

degradable, however, the lignin is resistant to most microorganisms due<br />

to its structure of phenylpropane units and the recalcitrant linkages between<br />

them. Thus, lignin incrustation of the carbohydrates inhibits the access to<br />

the consumable holocellulose. The hydrophobic nature of lignin further prevents<br />

a diffusion of the degrading enzymes inside the three-dimensional giant<br />

molecule.<br />

The composition of the microbial enzyme apparatus and its regulation affect<br />

the type of rot. Lignin (Fig. 4.4) is effectively degraded only by white-rot fungi<br />

and acts for other microorganisms as a barrier against wood decay. Table 4.3<br />

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92 4 <strong>Wood</strong> Cell Wall Degradation<br />

Fig.4.1. Scheme of the association of cellulose (C), hemicelluloses (H) and lignin (L) within<br />

the woody cell wall<br />

Table 4.3. Lignified cell wall as carbon source for microorganisms<br />

Organism group Degradation of Degradation<br />

hemicellulose cellulose lignin of isolated within the<br />

components cell wall<br />

bacteria + + − + −a yeasts − − −<br />

molds + + − + −<br />

blue-stain fungi + − − + −<br />

soft-rot fungi + + − + +<br />

brown-rot fungi + + − −(+) +<br />

white-rot fungi + + + + +<br />

a cf. Chap. 5.2<br />

summarizes the behavior of the different groups of organisms against the<br />

nutritive “lignified cell wall”. It is differentiated if the cell wall component<br />

is degraded within the native woody substrate or only as sole nutritive after<br />

isolation from the wood. Within the bacteria, yeasts, and molds, only a few<br />

species are able to degrade isolated cell wall components.<br />

4.2<br />

Pectin Degradation<br />

Pectins comprise galacturans, galactans and arabinans as complex, branched<br />

polysaccharides of molecular weights of about 10 3 kDa. Galacturans are predominantly<br />

deposited in the middle lamella/primary wall (compound middle<br />

lamella) and in the tori of bordered pit membranes (Fengel and Wegener 1989).<br />

The content of galacturans in the wood is below 1%. They consist predominantly<br />

of α-1,4-linked galacturonic acid units and are split by hydrolases to<br />

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4.3 Degradation of Hemicelluloses 93<br />

galacturonic acid. Further enzymes are needed for the other pectins and for<br />

side chains.<br />

Various plant pathogenic fungi and bacteria and several soil (Bacillus spp.)<br />

and water bacteria (Clostridium spp.)arecapableofdegradingpectin(Schlegel<br />

1992). <strong>Wood</strong>-inhabiting bacteria lead to the “overuptake” of wood preservatives<br />

and paints (Willeitner 1971) after the degradation of the bordered sapwood<br />

pits (Chap. 5.2) during wet storage of wood.<br />

4.3<br />

Degradation of Hemicelluloses<br />

Hemicelluloses of wood are a complex combination of relatively short polymers<br />

made of xylose, arabinose, galactose, mannose, and glucose with acetyl and<br />

uronic side-groups. The major hemicellulose (polyose) of hardwoods is the O-<br />

Acetyl-(4-O-methylglucurono)-xylan, also named glucuronoxylan or briefly<br />

xylan. The xylan content in hardwoods ranges from 15 to 35%. For example,<br />

birch wood contains 22–30% xylan and 1–4% glucomannan, while pine<br />

wood contains 5–11% xylan and 14–20% glucomannan (Viikari et al. 1998).<br />

In monocotyledons, hemicelluloses may amount to 40% and exceed the cellulose<br />

portion. Beech wood xylan consists of about 200 β-1-4-linked xylose<br />

units (xylopyranose). About five to seven acetyl groups (linked to C-2 or<br />

C-3) and one 4-O-methylglucuronic acid residue (α-1-2) occur per ten xylose<br />

units (Timell 1967; Fengel and Wegener 1989; Eriksson et al. 1990; Puls 1992;<br />

Fig.4.2. Diagram of enzymatic xylan degradation. x xylose residue, Ac acetic acid residue,<br />

4-O-Me-GA 4-O-methylglucuronic acid residue<br />

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94 4 <strong>Wood</strong> Cell Wall Degradation<br />

Saake et al. 2001). The enzymatic xylan degradation is shown as a diagram in<br />

Fig. 4.2.<br />

The xylan backbone is degraded (⇑) by the ectoenzyme endo-1,4-β-xylanase<br />

(“xylanase”, systematic name: 1,4-β-D-xylan xylanohydrolase, EC 3.2.1.8)<br />

within the xylose chain (endohydrolysis) to xylo-oligomers, xylobiose and<br />

xylose (Eriksson 1990; Eriksson et al. 1990). Intracellular and/or membranebound<br />

xylan 1,4-β-xylosidase (1,4-β-D-xylan xylohydrolase, EC 3.2.1.37) removes<br />

successively D-xylose residues from the non-reducing termini (exoenzyme)<br />

of small oligosaccharides. The side-groups are split by accessory enzymes:<br />

Acetylesterase (acetic-ester acetylhydrolase, EC 3.1.1.6) removes the<br />

acetyl groups. Xylan α-1,2-glucuronidase (xylan α-D-1,2-(4-O-methyl)glucuronohydrolase,<br />

EC 3.2.1.131) hydrolyzes the α-D-1,2-(4-O-methyl)glucuronosyl<br />

links (Puls 1992). Arabinose side-groups in arabinoxylans are removed<br />

by α-arabinosidase. The structure of different xylans and their enzymatic<br />

degradation is described by Bastawde (1992).<br />

The mannans (glucomannans, galactomannans, galactoglucomannans) of<br />

the conifers, consisting mainly of the hexose mannose, are similarly hydrolyzed<br />

by mannan endo-1,4-β-mannosidase (“mannanase”, 1,4-β-D-mannan mannanohydrolase,<br />

EC 3.2.1.78), β-mannosidase (β-D-mannoside mannohydrolase,<br />

EC 3.2.1.25) and accessory enzymes like β-galactosidase, α-glucosidase,<br />

and esterase (Eriksson et al. 1990; Takahashi et al. 1992; Viikari et al. 1998).<br />

Therearehemicellulosehydrogenbondstocellulosefibrilsandalsocovalent<br />

links with lignin.<br />

Oxalic acid of brown-rot fungi might be involved first in the degradation of<br />

the side chains of the hemicellulose, thus providing entrance to arabinose and<br />

galactose, and then depolymerize the main hemicellulose chain (and amorphous<br />

cellulose) (Green et al. 1991a; Bech-Andersen 1987b).<br />

Hemicellulose degradation is common in wood fungi, but rarer in bacteria.<br />

The soft-rot fungus Paecilomyces variotii produced plenty of xylanase (Schmidt<br />

et al. 1979), and glucuronidase was excreted, e.g., by Agaricus bisporus (Puls<br />

et al. 1987; Bastawde 1992). In Oligoporus placenta, xylanases were located in<br />

the hyphal sheath (Green et al. 1991b).<br />

Basidiomycetes, which prefer conifers in nature, degraded a spruce wood<br />

mannan more intensively than a birch xylan, and in reverse hardwood fungi<br />

showed greater activity against xylan (Lewis 1976). During incipient brownrot<br />

decay, the hemicellulose components are degraded first. In southern pine,<br />

earlystrengthlossupto40%wasassociatedwithlossofarabinanandgalactan<br />

components, and subsequent strength loss greater than 40% was associated<br />

with the loss of the mannan and xylan components. Since the cellulose microfibril<br />

is surrounded by a hemicellulose envelope, significant loss of cellulose<br />

was only detected at greater than 75% modulus of rupture loss (Curling<br />

et al. 2002).<br />

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4.4 Cellulose Degradation 95<br />

4.4<br />

Cellulose Degradation<br />

In the biosphere about 2.7 × 10 11 tofcarbonareboundinlivingorganisms.<br />

According to Schwarz (2003) about 4 × 10 10 t cellulose are produced per year.<br />

Cellulose occurs in all land plants, is always fibrillarly constructed and consists<br />

of β-1,4-linked glucose anhydride units (glucopyranose). The substrate for cellulose<br />

biosynthesis is UDP-glucose which is polymerized by cellulose synthase<br />

(UDP-glucose: 1,4-β-D-glucan 4-β-D-glucosyltransferase, EC 2.4.1.12) to β-1,4<br />

glucan chains. Depending on the wood species, the degree of polymerization<br />

(DP) of native cellulose ranges from 10,000 to 15,000 glucose anhydride units.<br />

In “native cellulose”, hydrogen bridges exist between the OH groups of neighboring<br />

glucose units and neighboring cellulose molecules. Tidy (crystalline cellulose)<br />

regions and areas of lower order (amorphous, paracrystalline cellulose)<br />

alternate (Fengel and Wegener 1989; Fig. 4.3). In Boehmeria nivea, cellulose<br />

crystals of about 300 glucose residues are interrupted vertically to the longitudinal<br />

axis by an amorphous region of 4–5 glucose residues (Schwarz 2004). There<br />

are different models for the arrangement of the cellulose molecules in the fibrils.<br />

Bacterial cellulose degradation including the cellulosome was treated by<br />

Schwarz (2003). There is still some uncertainty as how cellulose is degraded<br />

by fungi. Differences occur between the various groups of fungi, brown, white,<br />

and soft-rot fungi.<br />

Fig.4.3. Diagram of enzymatic cellulose degradation<br />

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96 4 <strong>Wood</strong> Cell Wall Degradation<br />

Early workers investigating brown-rot fungi assumed that only cellulolytic<br />

enzymes were responsible for cellulose degradation. Cellulolytic activity was<br />

initially described using terminology of C1-Cx (Reese et al. 1950): native (crystalline)<br />

cellulose is prepared by C1 cellulase for the degradation by Cx cellulase,<br />

as C1 cellulase loosens the crystalline areas by cleaving the hydrogen bridges<br />

for the following attack by Cx cellulase.<br />

The C1-Cx model was later refined to refer to the action of general classes<br />

of exoglucanases and endoglucanases, respectively. As methods were further<br />

refined more specific functionalities were defined and newly isolated enzymes<br />

were found in brown-rot fungi. Brown-rot fungi produce several endo-1,4β-glucanases<br />

and β-glucosidases, but typically lack exo-1,4-β-glucanase activity.<br />

However, cellobiohydrolase and cellobiose dehydrogenase [cellobiose:<br />

(acceptor) 1-oxidoreductase, EC 1.1.99.18] have been isolated from Coniophora<br />

puteana. Brown-rot fungal wood degradation was recently reviewed by Goodell<br />

(2003). White-rot and soft-rot fungi produce the full cellulolytic enzyme<br />

system of endo- and-exoglucanases, and β-glucosidase.<br />

The enzymes produced are thought to act in concert with each other as<br />

well as with non-enzymatic systems. Attack occurs at the amorphous cellulose<br />

regions (Cx action) by cellulase (“endoclucanase”, systematic name:<br />

1,4-β-D-glucan 4-glucanohydrolase, EC 3.2.1.4), which endohydrolyzes 1,4-β-<br />

D-glucosidic linkages in cellulose and other β-D-glucans. A combined action<br />

takes place by cellulose 1,4-β-cellobiosidase (1,4-β-D-glucan cellobiohydrolase,<br />

EC 3.2.1.91), which hydrolyzes 1,4-β-D-glucosidic linkages in cellulose<br />

and cellotetraose, releasing cellobiose from the non-reducing ends (exoenzyme),<br />

and by glucan 1,4-β-glucosidase (1,4-β-D-glucan glucohydrolase, EC<br />

3.2.1.74), which acts on 1,4-β-D-glucans and related oligosaccharides and exohydrolyzes<br />

successive glucose units from the ends. The final hydrolysis of<br />

oligosaccharides is mediated by β-glucosidase (“cellobiase”,β-D-glucoside glucohydrolase,<br />

EC 3.2.1.21), which acts on terminal, non-reducing β-D-glucose<br />

residues with release of β-D-glucose. Cellobiose may be also attacked by cellobiose<br />

dehydrogenase [cellobiose:(acceptor) 1-oxidoreductase, EC 1.1.99.18]<br />

oxidizing cellobiose to cellobionolactone under reduction of O2 to H2O2,and<br />

Fe 3+ to Fe 2+ (Kruså et al. 2005).<br />

In the mold Trichoderma viride (T. reesei), three endoglucanases, two exoglucanases,<br />

and several β-glucosidases were found (Eriksson et al. 1990). In<br />

Sporotrichum pulverulentum Novobr. (anamorph of Phanerochaete chrysosporium),<br />

five endoglucanases, one exoglucanase and two β-gucosidases, which<br />

together with oxidizing enzymes (laccase and cellobiose: chinon oxidoreductase)<br />

caused a combined degradation of cellulose and lignin. Uemura et al.<br />

(1992) isolated six exoglucanases. In P. chrysosporium, cellulases have been<br />

classified into eight different families among the glycoside hydrolases (Samejima<br />

and Igarashi 2004). In addition, the importance of the cellobiose dehydrogenase<br />

(CDH) was shown, as this enzyme could participate in the extracellular<br />

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4.4 Cellulose Degradation 97<br />

metabolism of cellobiose instead of β-glucosidase.TheroleofCDHforcellulose<br />

degradation was discussed (Hyde and <strong>Wood</strong> 1997; Kruså et al. 2005). It<br />

was hypothesized that CDH act as link between cellulolytic and ligninolytic<br />

pathways (Temp and Eggert 1999).<br />

Insoluble, native cellulose is attacked comparatively slowly by a system of<br />

cellulolytic enzymes. A limited introduction of substituents into the cellulose<br />

molecule reduces the number of hydrogen bonds of cellulose chains in proportion<br />

to the degree of substitution (DS) and the pattern of occurrence along<br />

the cellulose chain. Depending on these features and the nature of the substituent,<br />

water solubility of cellulose derivatives may be obtained at DS values<br />

between 0.4 and 0.7, and cellulose loses its ordered structure and becomes<br />

enzymatically accessible. Cellulose acetates up to a DS of 1.4 were deacetylated<br />

by various enzyme preparations (Altaner et al. 2001).<br />

For in vitro-degradation tests, carboxymethylcelluloses (CMC) are often<br />

used as soluble cellulose substrate (e.g., Schmidt and Liese 1980). The molecular<br />

structure of CMCs was characterized e.g., by Saake et al. (2000).<br />

Pure crystalline cellulose substrates, like cotton or Avicel, are degraded by<br />

white and soft-rot fungi. Most brown-rot fungi hardly show enzyme activity<br />

against crystalline celluloses and attack only pre-treated cellulose derivatives<br />

(Highley 1988; Enoki et al. 1988), because brown-rot fungi do not possess the<br />

synergistic endo/exo glucanase system, but have only endoglucanases. Within<br />

the woody cell wall, brown-rot fungi, however, depolymerize cellulose rapidly.<br />

Thus, the presence of lignin, lignin breakdown products, hemicelluloses, or<br />

simple sugars was postulated.<br />

Due to the limitation of enzyme accessibility to the woody cell wall by its<br />

pore sizes, the conceptions on cellulose degradation within wood by brownrot<br />

fungi focused both on non-enzymatic procedures and enzymatic mechanisms<br />

(e.g., Eriksson et al. 1990; Highley and Illman 1991; Micales 1992;<br />

Ritschkoff et al. 1992; Goodell 2003). Bailey et al. (1968) postulated as preceeding<br />

non-enzymatic agent a “precellulolytic phase”. Koenigs (1974) and<br />

others showed that cellulose was oxidatively degraded by Fenton reagents<br />

[Fe(II) + H2O2 → Fe(III) + OH − +OH 0 ]. Since ferrous iron is required in Fenton<br />

reactions, which is, however, absent in oxygenated wood decay processes,<br />

asearchforamechanismtoreduceironwasmade.H2O2 can also react with<br />

copper ions and some chromium, vanadium and nickel species to generate<br />

OH 0 (Halliwell 2003).<br />

Numerous investigations stress the participation of oxalic acid (e.g., Green<br />

et al. 1991a, 1993; Micales 1992), as the acid reduces Fe 3+ to Fe 2+ , which forms<br />

from H2O2 the reactive hydoxylradical, which then depolymerizes the cellulose.<br />

In several brown-rot fungi, like Coniophora puteana, Serpula lacrymans<br />

and Oligoporus placenta, extracellular H2O2 was proven (Ritschkoff et al. 1990,<br />

1992; Ritschkoff and Viikari 1991; Backa et al. 1992; Tanaka et al. 1992). Serpula<br />

lacrymans dissolved by means of oxalic acid iron from stonewool, which<br />

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98 4 <strong>Wood</strong> Cell Wall Degradation<br />

promoted fungal growth and wood decay together with H2O2 (Paajanen and<br />

Ritschkoff 1992). In wood samples impregnated with chrome copper arsenic, in<br />

contact with rusting iron, probably iron ions diffusing into the wood increased<br />

wood decay (Morris 1992). Iron-sulfate reducing soil bacteria increased the<br />

iron content in wood samples as well as the mycelial growth rate of Gloeophyllum<br />

trabeum and Oligoporus placenta (Ruddick and Kundzewicz 1991). In<br />

contrast, inorganic chelating agents and iron-binding siderophores decreased<br />

growth and wood decay by brown-rot fungi (Viikari and Ritschkoff 1992). The<br />

potential function of oxalate as reducing agent of Fe 3+ is, however, limited to<br />

theinsideofwoodysubstratesbecausethistypeofreactionshalloccuronly<br />

in the absence of light (Goodell 2003). The role of oxalate in brown-rot mechanisms<br />

may rather lie in a slow action on the hemicellulose matrix to help to<br />

open up the wood structure.<br />

Since the early work on Fenton systems for hydroxyl radical production, several<br />

hypotheses have been developed explaining the function of low molecular<br />

weight metabolites, metals, and radicals, which initiate cell wall degradation<br />

by brown-rot fungi.<br />

A compound, termed “glycopeptide”, isolated from Fomitopsis palustris,<br />

with a molecular weight of 7.2 to 12 kDa reduced O2 to OH 0 and catalyzed<br />

redox reaction between NADH as electron donor and O2 to produce H2O2<br />

andtoreduceH2O2 to OH 0 . The glycosylated peptide reduced Fe(III) to Fe(II)<br />

(Enoki et al. 2003). The glycopeptide may either diffuse as a deglycosylated<br />

“effector” form of lower molecular weight in the wood matrix or the shape of<br />

the glycopeptide is elongated allowing cell wall penetration or the glycopeptide<br />

generates longer-lived radicals such as superoxide which penetrate the wall<br />

microvoid spaces (Goodell 2003).<br />

A cellobiose dehydrogenase enzyme system was proposed to occur in Coniophora<br />

puteana and to bind and reduce iron in the presence of oxalate, which<br />

the fungus employs to generate and maintain the low pH environment at least<br />

in the vicinity of the hypha, which is required to avoid autoxidation of the<br />

reduced valence state of iron (Hyde and <strong>Wood</strong> 1997; Goodell 2003).<br />

“Low molecular weight fungal chelators” from Gloeophyllum trabeum (“Gt<br />

chelator”) mediated the production of hydroxyl radicals within the wood cell<br />

wall, immunolocalized in the S2 layer, and were termed as “chelator-mediated<br />

Fenton system” (CMFS). In CMFS, iron is reduced and then repeatedly “rereduced”,<br />

exceeding a 1:1 ratio for reduction of iron by catechol. Gt chelator<br />

in CMFS reactions reduced the cellulose crystallinity of wood and the molecular<br />

weight of Avicel crystalline cellulose (Goodell and Jellison 1998; Goodell<br />

2003).<br />

Shimokawa et al. (2004) provided evidence that Serpula lacrymans employs<br />

a Fenton reaction mediated by a quinone-type chelator, and preferentially degrades<br />

amorphous regions of cellulose in the non-enzymatic cellulose degradation.<br />

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4.5 Lignin Degradation 99<br />

The accessibility of the cellulose for cellulases can be improved by several<br />

pretreatments of wood (Chap. 9): for example, soaking increases the pore areas,<br />

and chemical pretreatments decrease the lignin content.<br />

4.5<br />

Lignin Degradation<br />

Next to cellulose lignin is the most abundant polymeric organic substance<br />

in plants. Of about 10 11 t of annual production of terrestrial biomass, about<br />

2×10 10 t are lignin (Jennings and Lysek 1999). Lignin is contrary to linear<br />

polysaccharides, like cellulose, a complex, stereoirregular, three-dimensional<br />

macromolecule (see Fig. 4.4, Nimz 1974; Higuchi 2002) in the range of 100 kDa<br />

(Abreu et al. 1999) and is highly hydrophobic reducing the hygroscopicity of<br />

wood. Lignin functions as a binding and encrusting material in the cell wall<br />

distributed with hemicelluloses in the spaces of inter-cellulose microfibrils in<br />

the cell wall. It acts as a cementing component to connect cells and harden<br />

Fig.4.4. Structural scheme of beech lignin (modified from Nimz 1974)<br />

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100 4 <strong>Wood</strong> Cell Wall Degradation<br />

the cell walls of xylem tissues, which helps a smooth transportation of water<br />

through vessels and tracheids from roots to branches (Higuchi 2002). The incorporation<br />

of lignin into the cell wall gives trees with heights of 100 m the<br />

chance to remain upright. Lignin gives resistance against disease and wood<br />

decay by microorganisms. Lignin content amounts in softwoods to 26–39%<br />

(average 28%) (compression wood: 35–40%), in hardwoods of the temperatezoneto18–32%(average22%)(tensionwood:15–20%)andintropical<br />

hardwoods to 23–39% (Fengel and Wegener 1989).<br />

The monolignols (p-hydroxycinnamyl alcohols), p-coumaryl, coniferyl, and<br />

sinapyl alcohol, are the primary precursors and building units of all lignins<br />

(Fengel and Wegener 1989; Fig. 4.5). The biosynthetic pathway of monolignols<br />

starts from glucose via shikimic acid over phenylalanine and tyrosine, respectively,<br />

to p-coumaric acid which yields via intermediates p-coumaryl alcohol.<br />

p-coumaric acid is converted via caffeic acid and ferulic acid to coniferyl alcohol.<br />

Ferulic acid is transformed via 5-hydroxyferulic acid and sinapic acid to<br />

sinapyl alcohol (Higuchi 2002).<br />

For lignin polymerization (Li and Eriksson 2005), the monolignols are initially<br />

dehydrogenated by peroxidases and/or laccases to phenoxy radicals. The<br />

radicals then couple non-enzymatically to quinone methides as reactive intermediates.<br />

According to one proposal, dimeric quinone methides are converted<br />

into dilignols by water addition, or by intra-molecular nucleophilic attack by<br />

primary alcohol groups or quinone groups. Dilignols can also undergo enzymatic<br />

dehydrogenation to form the corresponding radicals, which in turn<br />

couple with phenoxy radicals to produce trilignols, etc. In a second mechanism,<br />

enzymatic dehydrogenation is restricted to monolignols. The polymerization<br />

evolves by successive non-radical addition of phenols to the quinone methides.<br />

In a third mechanism, the lignin polymer evolves from the polymerization of<br />

quinone methides.<br />

Most softwood lignins are as guaiacyl lignins (G-lignins) polymers which<br />

are predominantly made of coniferyl alcohol (spruce: C : S : p-C = 94 : 1 : 5).<br />

Hardwood lignins are guaiacyl-syringyl lignins (GS lignins) and consist predominantlyofCandS(beech:C:S:p-C<br />

= 56 : 40 : 4). Guaiacyl-syringylp-hydroxyphenyl<br />

lignins occur in grasses. Lignin quantity and composition<br />

Fig.4.5. Lignin building units. A pcoumaryl<br />

alcohol. B Coniferyl alcohol.<br />

C Sinapyl alcohol<br />

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4.5 Lignin Degradation 101<br />

vary also as with the tree age (Wadenbäck et al. 2004), between root and stem<br />

wood, heartwood and sapwood, xylem and bark, earlywood and latewood, and<br />

in different wood cells and cell wall layers. In the lignin molecule, the basic<br />

modules are linked with a variety of chemical bonds, ether and carbon-carbon<br />

linkages. Most bonds are covalent, of considerable variety and are equally in<br />

all three dimensions. The β-O-4 linkage (fat in Fig. 4.4) is the most frequent<br />

interunit linkage with about 50% (spruce) to 65% (beech) (Fengel and Wegener<br />

1989; Abreu et al. 1999; Higuchi 2002).<br />

Lignin forms an amorphic complex with hemicelluloses to encapsulate cellulose.<br />

As lignin represents a substance, which is hardly open to attack for most<br />

microorganisms, it protects within the woody cell wall the enzymatically more<br />

easily accessible carbohydrates against microbial degradation (Chap. 9, Table<br />

4.3). There are different model conceptions with regard to the arrangement<br />

of the three components (see Fig. 4.1).<br />

Causes for the resistance of lignin against microbial enzymes are: Aromatic<br />

rings are generally more difficulty degradable. The variety of the linkages<br />

between the building units and the hydrophobic nature require a breakdown<br />

system that is non-specific and, for the most part, nonhydrolytic as well as<br />

extracellular (Jennings and Lysek 1999; Reading et al. 2003).<br />

Overviews on lignin degradation are e.g., by Umezawa (1988), Higuchi<br />

(1990), Schoemaker et al. (1991), Jeffries (1994), Cullen and Kersten (1996),<br />

Yoshida (1997) and Koshijima and Watanabe (2003).<br />

An effective degradation of natural lignin (lignin within the woody cell wall)<br />

with respiration of the C-atoms from that aromatic ring exclusively occurs in<br />

white-rot fungi (Chap. 7.2). The residual lignin in wood degraded by brown-rot<br />

fungi is dealkylated, demethoxylated and demethylated, with some oxidation<br />

of the alkyl side chain. The aromatic ring is not attacked (Goodell 2003). Softrot<br />

fungi mainly cleave the methoxyl groups from the aromatic rings. Some<br />

bacteria demethylate or cleave within the alcoholic side chain, particularly<br />

in synthetic lignins with small molecular weights (dehydrogenation polymer,<br />

DHP) and in lignin model compounds (Fengel and Wegener 1989). For the<br />

“tunneling bacteria”, lignin degradation was postulated within the woody cell<br />

wall (Chap. 5.2).<br />

Many white-rot fungi produce extracellular phenol oxidases, which results<br />

in positive oxidase tests on nutrient agar with tannic and gallic acid. Only<br />

40% of the white-rot fungi studied produced the combination of lignin peroxidase<br />

and manganese peroxidase, whereas the combination of manganese<br />

peroxidase and laccase was more common. In an extreme case, Pycnoporus<br />

cinnabarinus produced only laccase, lacking both lignin and manganese peroxidase<br />

(Eggert et al. 1996; Li 2003). The test by Bavendamm (1928) is used<br />

since that time for the rapid differentiation of white and brown-rot fungi in the<br />

laboratory and is in identification keys for wood fungi among the first distinguishing<br />

characters (Stalpers 1978). Malt agar is supplemented with a lignin<br />

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102 4 <strong>Wood</strong> Cell Wall Degradation<br />

model compound (Davidson et al. 1938; Lyr 1958; Käärik 1965; Rösch and<br />

Liese 1970; Tamai and Miura 1991) and inoculated with the unknown fungus.<br />

If the fungus excretes the phenol oxidase laccase (benzenediol:oxygen oxidoreductase,<br />

EC 1.10.3.2), tannic acid, etc. are oxidized (brownish discoloration),<br />

and it usually concerns a white-rot fungus. By definition, laccases catalyze the<br />

oxidation of p-diphenols and the concurrent reduction of dioxygen to water,<br />

although the actual substrate specifities of laccases are often broad (Eggert et al.<br />

1998). Most brown-rot fungi do not oxidize tannic acid, as they usually possess<br />

only intracellular tyrosinase (1,2-benzenediol:oxygen oxidoreductase EC<br />

1.10.3.1). However, misinterpretation may occur because tyrosinase can be set<br />

free through injuring the mycelium, e.g., by the inoculation procedure, which<br />

feigns then a white-rot fungus (Rösch 1972). Furthermore, also some intensive<br />

lignin decomposer, e.g., Phanerochaete chrysosporium,maycausenegativeor<br />

only weak Bavendamm reaction (Eriksson et al. 1990). Laccase is also present<br />

in several Deuteromycetes and Ascomycetes (Butin and Kowalski 1992; also<br />

Luterek et al. 1998). Phenol oxidase (laccase) and one-electron oxidation activity<br />

was shown for the soft-rot Deuteromycetes Cladorrhinum sp., Graphium sp.,<br />

Scopulariopsis sp., and Sphaeropsis sp. (Tanaka et al. 2000). Niku-Paavola et al.<br />

(1990) used 2, 2 ′ -azino-di(3-ethylbenzothiazoline)-6-sulfonic acid as enzyme<br />

substrate, which is oxidized by laccase, while tyrosinase does not.<br />

Due to the effect of the laccase in vitro, in former times, lignin degradation<br />

was assumed to occur exclusively by phenol oxidases. The main significance<br />

of the laccase is, however, seen in the polymerization of phenols. Lignin polymerization<br />

by laccase occurs through the formation of phenoxy radicals by<br />

abstraction of hydrogen followed by a series of radical polymerization reactions.<br />

Thus, laccase has also been used to obtain wood composites like particle<br />

and MDF boards that were bound mainly or even solely by lignin when polymerized<br />

in situ by this enzyme (Kharazipour and Hüttermann 1998). On the<br />

other hand, laccases are involved in lignin degradation by fungi, which was<br />

confirmed by “synergistic cellulose lignin degradation models” (Ander and<br />

Eriksson 1976). In connection with the cell wall degradation, the significance<br />

of the phenol oxidases might be rather an adjusting function for the carbohydrate<br />

degrading enzymes (Eriksson et al. 1990). In fungi, laccases are also<br />

involved in pigmentation, fruit body formation, sporulation, and pathogenesis<br />

(Rättö et al. 2004).<br />

The isolation of the first ligninolytic enzyme was simultaneously obtained in<br />

two groups (Glenn et al. 1983; Tien and Kirk 1983) from culture filtrates of the<br />

white-rot fungus Phanerochaete chrysosporium. This fungus was well known<br />

as an intensive lignin decomposer, since it degraded 14 ClabeledligninstoCO2<br />

as well as dehydropolymers and model compounds (Kirk 1988). The enzyme,<br />

diarylpropane peroxidase (lignin peroxidase, LiP, “ligninase I”, diarylpropane:<br />

oxygen, hydrogen-peroxide oxidoreductase, EC 1.11.1.14) is a glucoprotein<br />

with a molecular weight of 42 kDa (also Srebotnik et al. 1988b), contains hem<br />

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4.5 Lignin Degradation 103<br />

(porphyrin with iron as central atom), needs extracellular H2O2, cleavesC-C<br />

bonds in a number of model compounds, and oxidizes benzyl alcohols to<br />

aldehydes or ketones.<br />

The key reaction of the LiP is a one-electron-oxidation of various nonphenolic<br />

compounds to generate instable aryl radical cations, as the enzyme<br />

delivers two electrons to hydrogen peroxide, which the enzyme then takes back<br />

from each one-phenyl propenoid unit (Kirk 1985; Higuchi 1990). Phenolic<br />

and non-phenolic lignin substructures are attacked, but not the intact lignin<br />

molecule.<br />

The radicals undergo subsequent non-enzymatic reactions to yield a variety<br />

of final products. The radical cations themselves act as oxidants. Thus, LiP<br />

initiates by means of different non-enzymatic reactions the cleavage of Cα-Cβ<br />

bond in the side chain, β-O-4 bond between side chain and next ring, as well<br />

the aromatic ring (Eriksson et al. 1990; Schoemaker et al. 1991; Fig. 4.6). Also,<br />

veratryl alcohol, which is produced independently of lignin degradation, can<br />

be oxidized by LiP to the radical cation, which itself can oxidize lignin (Jennings<br />

and Lysek 1999).<br />

The ligninolytic system of Phanerochaete chrysosporium is not induced by<br />

lignin but appears constitutively as cultures enter the secondary metabolism,<br />

that is, when primary growth ceases because of depletion of nutrients. Secondary<br />

metabolism was triggered by nitrogen, carbon, or sulphur limitation<br />

(review by Highley and Dashek 1998). Lignin cannot be used as only C source,<br />

but in cometabolism with cellulose or hemicellulose. A high O2 concentration<br />

(100% more suitable than 21%) was favorable (Kirk 1988). The enzyme was<br />

excreted by old, autolytic hyphae, but not by arthrospores and chlamydospores<br />

(Lackner et al. 1991).<br />

LiP has been found in several white-rot fungi, e.g., Trametes versicolor,<br />

Phlebia radiata (Dodson et al. 1987) and Bjerkandera adusta (Muheim et al.<br />

1990). There are numerous isomers of LiP with molecular weights of 40 to<br />

47 kDa, which differ in the carbohydrate portion of the protein (Evans 1991).<br />

The enzyme activity of LiP preparations is determined via Cα oxidation of<br />

Fig.4.6. Scheme of reactions initiated<br />

by lignin peroxidase. Cleavage of Cα-Cβ<br />

bond in the side chain (1), β-O-4 bond<br />

between side chain and next ring (2),<br />

and aromatic ring (3)<br />

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104 4 <strong>Wood</strong> Cell Wall Degradation<br />

veratryl alcohol (with presence of H2O2) to the aldehyde, whose amount is<br />

measured at 310 nm (Faison and Kirk 1985; Schoemaker et al. 1991).<br />

The second enzyme involved in lignin degradation is manganese peroxidase<br />

(MnP) [Mn(II):hydrogen-peroxide oxidoreductase, EC 1.11.1.13], which needs<br />

free phenolic groups at the aromatic ring and does not oxidize veratryl alcohol.<br />

The hemoprotein enzyme was first detected in P. chrysosporium (Glenn and<br />

Gold 1985) and occurs e.g., in Armillaria species, Lentinula edodes, Pleurotus<br />

ostreatus and T. versicolor. It oxidizes in the presence of hydrogen peroxide<br />

Mn(II) to Mn(III), a strong oxidant, which oxidizes phenolic structures by<br />

single-electron-oxidation (Perez and Jeffries 1992; Kofugita et al. 1992; Robene<br />

Soustrade et al. 1992; Chatani et al. 1998; Kamitsuji et al. 1999). MnP polymerizes<br />

more extensively and depolymerizes less than lignin peroxidase (Tanaka<br />

et al. 1999). Treatment of water-insoluble 14 C-labeled milled wheat straw and<br />

milled straw lignin with MnP preparations from the white-rot fungus Nematoloma<br />

frowardii resulted in the direct release of 14 CO2 and in the formation<br />

of soluble 14 C-lignin fragments (Hofrichter et al. 1999). MnP also degraded<br />

polyethylene (Iiyoshi et al. 1998).<br />

For the degradation of native lignin, a fungus must have enzymes, which attack<br />

both phenolic and non-phenolic lignin components (Martinez-Inigo and<br />

Kurek 1997). The lignin peroxidase is most likely responsible for the degradation<br />

of the non-phenolic components and the laccase as well manganese<br />

peroxidases for the oxidation of the phenolic parts (Evans 1991). All together,<br />

there is a variety of oxidative enzymes that may be utilized by white-rot fungi for<br />

lignin degradation (Highley and Dashek 1998). Various enzymes, low molecular<br />

weight agents, free-radical reactions, and metals have been proposed to<br />

participate in lignin degradation (Messner et al. 2003; Reading et al. 2003):<br />

Lignin peroxidase (LiP), manganese peroxidase (MnP), cellobiose dehydrogenase<br />

(CDH), laccases, oxalate, hydrogen peroxide, small molecule mediators,<br />

methyl transferases, and the plasma membrane redox potential are involved<br />

in the degradation systems. There is, however, still some uncertainty on their<br />

accurate participation in lignin degradation.<br />

Progress has been made concerning the molecular genetics of lignin and<br />

cellulose biodegradation by white-rot fungi, primarily with Phanerochaete<br />

chrysosporium, but also with Bjerkandera adusta, Phlebia radiata, and Trametes<br />

versicolor (reviews by Highley and Dashek 1998 and Li 2003). Genes encoding<br />

Lip and MnP have been cloned and sequenced (e.g., Irie et al. 2000). The<br />

total genome sequence of P. chrysosporium has been disclosed by the DoE Joint<br />

Genome Institute in the USA, which has facilitated cDNA cloning of various cellulase<br />

genes from P. chrysosporium and successive production of recombinant<br />

proteins from them (Samejima and Igarashi 2004). The X-ray crystal structures<br />

of both LiP and MnP have also been elucidated. By means of recombinant<br />

DNA techniques, laccase catalysis has been studied, and the crystal structure<br />

of a T2-copper deleted laccase has been reported. In Pycnoporus cinnabarinus,<br />

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4.5 Lignin Degradation 105<br />

genes encoding two laccase isozymes have been cloned and sequenced (also<br />

Eggert et al. 1998). Glyoxal oxidase as a source of extracellular H2O2 was found<br />

to be encoded by a single gene.<br />

Occurrence and distribution of lignin peroxidase inside hyphae and whiterotten<br />

wood were examined by immuno gold labeling (Srebotnik et al. 1988a;<br />

Blanchette et al. 1989; Daniel et al. 1989, 1990; Blanchette and Abad 1992; Kim<br />

et al. 1993). The enzyme is particularly found in the hypha and the extracellular<br />

sheath, and less so in the wood cell wall and then near the hypha. In the cell<br />

wall, it is only considerably present in late degradation stages. It was concluded<br />

from this distribution that the lignin peroxidase attacks rather lignin fragments<br />

that had been set free from the cell wall, than that it binds at the polymeric<br />

lignin inside the intact wall. The primary degradation would have then taken<br />

place by low-molecular compounds like the cation radical of veratrylalcohol,<br />

which diffuses into the wall, produces there lignin fragments, which are then<br />

degraded by ligninase (Evans 1991). It may also assumed that the limited cell<br />

wall degradation starting from the cell lumen in close neighborhood of a hypha<br />

occurs directly by the enzyme towards closely neighboring lignin. This would<br />

agreewiththeearlyresultsoftheerosion-likecellwalldegradationbywhite-rot<br />

fungi (Schmid and Liese 1964; Liese 1970; Fig. 7.2b).<br />

There are many ways that a white-rot fungus could generate hydrogen peroxide<br />

required for LiP and MnP. Extracellular H2O2-producing enzymes are arylalcohol<br />

oxidase (EC 1.1.37), glyoxal oxidase, pyranose 2-oxidase (EC 1.1.3.10),<br />

and cellobiose dehydrogenase. Intracellular enzymes include glucose 1-oxidase<br />

(EC 1.1.3.4) (Leonowicz et al. 1999), pyranose 2-oxidase, and methanol oxidase<br />

(e.g., Daniel et al. 1994; Hyde and <strong>Wood</strong> 1997; Urzúa et al. 1998). OH 0<br />

may be also formed via hydroquinone redox cycling involving semiquinones<br />

produced by peroxidase or laccase which reduce both Fe(III) and O2 to provide<br />

the components for Fenton-type hydroxyl radical formation. It is not exactly<br />

known which enzyme plays the primary role in supplying H2O2 (Li 2003).<br />

From the only slow microbial decomposition of lignin results its significance<br />

for the formation of humic substances (e.g., Haider 1988; Schlegel 1992) and<br />

also for the lastingness of archaeological woods (Chap. 5.2). The suitability of<br />

lignins as fertilizer and for soil improvement was described by Faix (1992).<br />

Mikulášová and Košíkowá (2002) indicated a potential application of lignin<br />

biopolymers as antimutagenic agents in chemoprevention.<br />

There are some general prerequisites for the action of the degradative systems.<br />

As lignin is a highly oxidized polymer, reductive as well as oxidative<br />

reactions are required to effectively degrade it, both of which must occur aerobically.<br />

These reactions must be balanced or controlled to prevent redox cycling<br />

and free-radical-based polymerization of the degradation products. The oxidizing<br />

and reducing equivalents must be unique and continuously produced<br />

since extracellular regeneration would be improbable. Common biological<br />

compounds for reducing or oxidizing equivalents, such as NADH, which would<br />

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106 4 <strong>Wood</strong> Cell Wall Degradation<br />

be difficult to regenerate once released extracellularly are precluded. In vitro,<br />

reduction of manganese dioxide was demonstrated for a ferrireductase system<br />

that includes NADPH-dependent ferrireductase and the iron-binding compound<br />

from Phanerochaete sordida (Hirai et al. 2003). Extracellularly formed<br />

free-radical species are able to diffuse away from their origin and mediate reactions<br />

with the insoluble lignin. The small, diffusible radicals and low-molecular<br />

agents achieve a greater area of reactivity than could be obtained by reactions<br />

catalyzed by enzymes or the fungi directly. The distance of the action from the<br />

hyphae also prevents self-inflicted damage to the fungus (Reading et al. 2003).<br />

The following description of systems to generate low molecular agents is<br />

according to Messner et al. (2003).<br />

In the “manganese peroxidase/Mn(II)/oxalate system”, there are two oneelectron<br />

reducing steps by Mn(II). The Mn(III) formed is chelated and released<br />

from the enzyme by the fungal metabolite oxalate. The relatively stable Mn(III)<br />

oxalate oxidizes phenolic lignin compounds and has been proposed to diffuse<br />

in the wood cell wall.<br />

In the “manganese peroxidase/Mn(II)/oxalate/cellobiose dehydrogenase<br />

system”, CDH is oxidized by O2 and metal ions such as Fe(III) and Cu(II)<br />

yielding H2O2, and Fe(II) or Cu(I) which react with H2O2 to generate hydroxy<br />

radicals which in turn demethoxylate and hydroxylate non-phenolic lignin.<br />

The phenolic lignin formed is then attacked by MnP-generated Mn(III).<br />

In the “manganese peroxidase/Mn(II)/oxalate/lipids system”, lipids extend<br />

the oxidative potential of MnP. Mn(III) promotes peroxidation of unsaturated<br />

fatty acids resulting in the formation of peroxyl radicals which are diffusible,<br />

potentially ligninolytic agents. Mn(III) also abstracts hydrogen from fatty<br />

acids to form acyl radicals. The system depolymerized both phenolic and<br />

non-phenolic lignin (Katayama et al. 2000).<br />

In the “lignin peroxidase/veratryl alcohol system”, the veratryl alcohol radical,<br />

generated during turnover of LiP, was proposed to act as a charge transfer<br />

system in wood. However, its short lifetime may prevent a diffusion into deeper<br />

cell wall areas.<br />

In the “laccase/mediator system”, laccases are combined with low molecular<br />

weight charge transfer agents, so-called mediators. The system is used to bleach<br />

pulp and depolymerized non-phenolic guaiacyl lignin.<br />

In the “glycopeptide system” (Enoki et al. 2003), low-molecular weight<br />

glycosylated peptides produce hydroxy radicals which modify lignin, resulting<br />

in new phenolic, benzyl radical, and cation radical substructures which are<br />

then attacked by LiP, MnP or laccase. The system also depolymerizes the wood<br />

carbohydrates (see Chap. 4.4).<br />

In the “coordinated Cu/peroxide system” (Messner et al. 2003), either hydrogen<br />

peroxide or organic peroxides, is the agent involved at least in the<br />

initial lignin degradation. Cu(II) is reduced to Cu(I) by either H2O2 or reducinggroupsinwood.Cu(I)formswithH2O2<br />

a reactive one-electron oxidant<br />

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4.5 Lignin Degradation 107<br />

that oxidizes phenolic and non-phenolic lignin. Cu(I) is reoxidized by lipid<br />

hydroperoxide.<br />

For the preferential white-rot type without the intense damage of cellulose,<br />

Teranishi et al. (2003) showed that Ceriporiopsis subvermispora produced<br />

ceriporic acid, which strongly inhibited the Fenton reaction to suppress the<br />

formation of OH 0 .<br />

In summary, meanwhile many details on the degradation of the various<br />

components of the woody cell wall are known. It may be considered, however,<br />

that in view of lignin and cellulose degradation, many results derive from only<br />

one fungal species, Phanerochaete chrysosporium (anamorph: Sporotrichum<br />

pulverulentum), and that this fungus has nearly no relevance for wood, neither<br />

for trees nor for construction timber, only for chip piles.<br />

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5<br />

5.1<br />

Viruses<br />

Damages by Viruses and Bacteria<br />

Viruses are small particles (10–2,000 nm in size) that infect Eukaryotes as obligate<br />

intracellular parasites. They reproduce by invading and taking over other<br />

cells as they lack own metabolism and the machinery for self-reproduction<br />

(Nienhaus 1985a). Typically, they carry either DNA or RNA surrounded by<br />

a coat of protein or protein and lipid. Plant viruses penetrate the shoot, leaf<br />

tissue and root via wounds or they are transferred by vectors [aphids, cicadas,<br />

nematodes, among fungi: Sphaerotheca lanestris (Erysiphales) on oak].<br />

Partial bleaching of chlorophyll results in angular, circular (mosaic) or diffuse<br />

chloroses. Leaf damage, dwarfing or growth inhibition, distorted growth,<br />

and necrotic areas or lesions can occur, that is, virus infection can reduce<br />

the tree growth. Over 1,000 virus diseases of plants are described for Europe.<br />

Virus diseases in forest trees have been summarized e.g., by Nienhaus and<br />

Castello (1989) and Cooper and Edwards (1996). Viruses occur in several gymnosperms<br />

(Chamaecyparis, Cupressus, Larix, Picea and Pinus), angiosperms<br />

(Acer, Aesculus, Betula, Carpinus, Cormus, Corylus, Fagus, Fraxinus, Juglans,<br />

Populus, Prunus, Quercus, Rhamnus, Robinia, Salix, Sambucus, Sorbus and<br />

Ulmus) (Nienhaus 1989; Brandte et al. 2002), in bamboos and palms. Twig<br />

increase in horse chestnut (Butin 1995), and witches’-broom on beech and<br />

robinia are probably likewise due to the participation of viruses. Viruses have<br />

been detected several times in forest dieback sites (Parameswaran and Liese<br />

1988; Winter and Nienhaus 1989; Gasch et al. 1991).<br />

Viroids are infectious agents that consist of a single-stranded RNA. Viroids<br />

are smaller than viruses, lack a protein cover and are the smallest causal<br />

agents of plant diseases, like discolorations, chloroses and distorted growth,<br />

e.g., in coconut, cucumber, hop, potato and tomato (Schlegel 1992; Butin 1995;<br />

Nienhaus and Kiewnick 1998). About 33 species of viroids have been identified.<br />

5.2<br />

Bacteria<br />

“The Prokaryotes” (Dworkin et al. 2005) is a comprehensive reference on<br />

bacterial biology.<br />

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110 5 Damages by Viruses and Bacteria<br />

The term bacteria had been used for all Prokaryotes or for a major group<br />

of them. Based on the 16S rDNA sequence the Prokaryotes were divided into<br />

the kingdoms Eubacteria and Archaebacteria (Woese and Fox 1977). Later<br />

three domains, Bacteria, Archaea and Eucarya were renamed (Fig. 5.1) and<br />

confirmed by sequencing (Gray 1996).<br />

Archaea differ from other Prokaryotes in their membrane composition,<br />

flagella development and the similarity of their transcription and translation<br />

to that one of Eukarya. Many Archaea are extremophiles and live in geysers<br />

and black smokers at 80–110 ◦ C(Pyrodictium spp.), or in acid (about pH 0),<br />

alkaline, or saline (till 30% salt content) water like Halobacterium species.<br />

Methanogenic Archaea inhabit the digestive tracts of ruminants, humans, and<br />

termites, or soil, marshland and sewage etc. In trees, methanogenic Archaea<br />

are involved in the development of the alkaline wetwood (see below).<br />

Bacteria cover a major group of Prokaryotes and are ubiquitous in soil,<br />

water, as symbionts, or pathogens. They lack cell nucleus, cytoskeleton, mitochondria,<br />

and chloroplasts. The genetic information is located on a circular<br />

DNA strand, which is not covered by a nuclear membrane. Many bacteria contain<br />

plasmids with extrachromosomal DNA. Ribosomes are made of the 70S<br />

type (Eukaryotes: 80S). Reproduction is asexual by cell division. Exchange of<br />

genetic material can occur by transformation, transduction, and conjugation.<br />

About 10,000 species are identified, characterized, and deposited in culture<br />

collections, which might, however, represent only 10% of the actually existing<br />

species. Many bacteria are rod-shaped, sphere-shaped (cocci), helix-shaped<br />

(spirillum), or comma-shaped (vibrios). Common bacteria are minute, measuring<br />

0.4–5µm in size. They occur single, or double, or in chains or clusters.<br />

Fig.5.1. Phylogenetic tree of life based on rDNA data (from www:en.wikipedia.org)<br />

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5.2 Bacteria 111<br />

Gram staining divides Gram-positive and negative species according to their<br />

wall structure and the occurrence of pepitoglycan or lipids. With regard to<br />

oxygen, aerobes grow only in the presence of oxygen and anaerobes in its<br />

absence. The latter behavior may be either facultative or obligate. Many bacteria<br />

are motile, using either flagella, axial filaments, gliding, or changes in<br />

buoyancy. In some genera (Bacillus, Clostridium), the mother cell develops<br />

an endospore, which is rather resistant against heat, radiation and chemicals<br />

(Schlegel 1992).<br />

Actinobacteria are bacteria, which often live in the soil. They play important<br />

roles in plant decomposition, humus formation, and degradation (Filip<br />

et al. 1998) and are found on timber in soil contact. Some form branching filaments,<br />

which resemble the fungal mycelium (in former times: Actinomycetes),<br />

whereby the cell diameter of about 1µm is however smaller than that of most<br />

fungal hyphae. Some actinobacteria (e.g., Streptomyces) developaplentyof<br />

air-borne spores.<br />

There are various interactions between bacteria and plants, like increase of<br />

soil fertility by nutrient release, nitrogen fixation (Azotobacter), root symbioses<br />

(Rhizobium), decomposition and humification, and parasitism as causal agents<br />

of diseases.<br />

The pathogenic bacteria of woody plants belong to the genera Agrobacterium,<br />

Erwinia, Pseudomonas, andXanthomonas (Nienhaus and Kiewnick<br />

1998). Bacteria cause the fire blight [Erwinia amylovora (Burrill) Winslow<br />

et al.] of many species of the rose family (Tattar 1978), canker of poplar [Xanthomonas<br />

populi ssp. populi (Ridé) Ridé & Ridé], willow (X. populi ssp. salicis<br />

de Kam) and ash (Pseudomonas syringae ssp. savastanoi pv. fraxini Janse)<br />

(Butin 1995). Agrobacterium species infect the roots of a wide range of dicotyledonous<br />

plants and some gymnosperms causing crown gall and hairy<br />

root diseases.<br />

Since the late 1970s, Agrobacterium-mediated gene transfer is an important<br />

tool in genetic transformation of forest trees. During the disease process,<br />

a DNA segment of the bacterium (T-DNA) is integrated into the host plant<br />

genome. The T-DNA originates from a 200-kb plasmid (Ti plasmid) and foreign<br />

genes can be inserted into this DNA for transfer into the plant (Palli<br />

and Retnakaran 1998; Häggman and Aronen 1996), e.g., for gene-manipulated<br />

poplars and white spruce (Séguin et al. 1998). Kajita et al. (2004) transferred the<br />

gene for the enzyme feruloyl-CoA hydratase/lyase, which is involved in lignin<br />

(hydroxycinnamates) metabolism, from a bacterium into aspen by Agrobacterium<br />

tumefaciens (E.F. Smith & Townsend) Conn in view of producing trees<br />

with novel characteristics.<br />

Rickettsia and Rickettsia-like organisms (RLOs) (Proteobacteria) (100–<br />

800 nm) are obligate intracellular, Gram-negative bacteria with reduced metabolic<br />

activity. They cannot be cultured in nutrient medium. RLOs in plants are<br />

transferred by arthropodes, particularly cicadas, and multiply in the vector<br />

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112 5 Damages by Viruses and Bacteria<br />

and in the phloem or xylem. They cause e.g., leaf necrosis in oak and planes<br />

and distorted growth of larch (Nienhaus 1985b; Linn 1990; Butin 1995).<br />

Mycoplasmas (genus Spiroplasma) and phytoplasmas (in former times:<br />

MLOs; genus Phytoplasma) are the smallest (100–750 nm) independently<br />

growing bacteria. They are pleomorphic, sporeless, immovable, and filterable.<br />

Spiroplasma grows on nutrient medium, Phytoplasma does not. Plant<br />

pathogens are transferred by grafting, root grafts, vegetative propagation of<br />

infected material, Cuscuta species, and sucking insects, in which they multiply,<br />

into the phloem (Nienhaus and Kiewnick 1998). They cause a great<br />

number of yellow-type diseases, necroses, growth disturbances, or dying of<br />

rice, maize and sesame, vegetables, sugar cane, fruit trees, coconut palm,<br />

whitethorn, alder and ash, witches’-brooms on poplar, and sandal spike (Tattar<br />

1978; Nienhaus 1985a, 1985b; Linn 1990; Sinclair et al. 1990; Lindner 1991;<br />

Lederer and Seemüller 1991; Raychaudhuri and Mitra 1993; Raychaudhuri and<br />

Maramorosch 1996).<br />

Bacteria appear in trees and wood as both primary and secondary colonizers<br />

often in the context of succession together with fungi. They live on easily<br />

accessible nutrients and may prepare the substrate for fungi (Shigo 1967;<br />

Cosenza et al. 1970; Shigo and Hillis 1973; Shortle and Cowling 1978; Rayner<br />

and Boddy 1988). Soil bacteria may increase vitamin content (thiamine) of<br />

wood in ground contact, which promotes subsequent decay Basidiomycetes<br />

(Cartwright and Findlay 1958; Henningsson 1967).<br />

Bacteria penetrate into the sapwood of a tree via wounds. In hardwood<br />

vessels that are not closed by tyloses or other wound reactions, they might<br />

spread with the capillary water over larger distances. In softwood samples,<br />

however, only a few tracheids were passed due to the small free spaces within<br />

the pit membrane (Liese and Schmidt 1986).<br />

The wet heartwood (wetwood) of several tree species, particularly fir, hemlock,<br />

poplar, elm, also beech and oak, means any water-saturated and dead<br />

wood in living trees. Characteristics are the unpleasant smell of butyric acid<br />

and other acids, dark discolorations and gas escape from the heartwood if an<br />

increment borer has been used. The exact cause of wetwood formation, whether<br />

being due to bacteria or necrotic changes in the parenchyma cells, is not clarified.<br />

Wetwood develops in connection with mechanical wounds, branch breaking,<br />

decay, stem cracks, and insect attack. So-called acid wetwood, predominantly<br />

in conifers, contains several organic acids (butyric, acetic, propionic<br />

acid) produced by (facultative) anaerobe bacteria. Alkaline wetwood, mostly<br />

in hardwoods, develops with participation of obligate anaerobe methanogenic<br />

Archaea. These Prokaryotes attack the pits or cause their incrustation, give rise<br />

to discolorations, their metabolites may stress the tree, and the unpermeable<br />

wetwood tends to crack during drying (Carter 1945; Hartley et al. 1961; Wilcox<br />

and Oldham 1972; Bauch 1973; Knutson 1973; Bauch et al. 1975; Tiedemann<br />

et al. 1977; Ward and Pong 1980; Ward and Zeikus 1980; Schink et al. 1981; Mur-<br />

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5.2 Bacteria 113<br />

doch and Campana 1983; Zimmermann 1983; Schink and Ward 1984; Kučera<br />

1990; Klein 1991; Walter 1993; Xu et al. 2001).<br />

Bacteria may be also associated with the development of false frost cracks in<br />

oak, ash, elm, poplar, and Silver fir. These radial shakes develop progressively<br />

from the stem interior, being initiated either from old cambial injuries or from<br />

pockets of fungal heart rot (Shigo 1972; Butin and Volger 1982). Occurrence,<br />

distribution, and enzyme activities of the bacteria isolated from pedunculate<br />

oak trees supported the assumption that bacteria may be involved in the<br />

weakening of the woody tissue in the area of the ray parenchyma cells so that<br />

mechanical factors like frost subsequently push the shake in the predamaged<br />

tissue (Schmidt et al. 2001).<br />

Several bacteria isolated from wet-stored stem wood were able to degrade<br />

pectin, hemicelluloses, and cellulose when these cell wall components had been<br />

supplied as isolated compounds (Schmidt and Dietrichs 1976). With regard to<br />

lignin, lignin derivatives or DHPs up to 1 kDa were attacked (Vicuña 1988).<br />

In view of bacterial wood degradation, bacteria attacked within partially<br />

lignified plant organs, like a shoot or a needle, only non-lignified tissue. The<br />

cell walls of the phloem cells of the vascular bundles were degraded, but those<br />

of the xylem part resisted. Inside woody tissue, bacteria preferentially feed<br />

soluble sugars, the content of parenchyma cells and attack non-lignified pit<br />

membranes (Liese 1970). In tension wood fibers, bacteria only consumed the<br />

cellulosic G-layer (Schmidt 1980). After a mild delignifying pretreatment of<br />

wood samples with sodium chlorite, however, bacteria caused mass loss up<br />

to 70% (Schmidt 1978), as the carbohydrates were now accessible. Figure 5.2<br />

Fig.5.2. Beech wood microtome sections with slightly reduced lignin content without (a)<br />

and after culture with Cellulomonas flavigena (b)<br />

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114 5 Damages by Viruses and Bacteria<br />

shows beech wood microtome sections whose lignin content have been reduced<br />

from naturally (21%) to about 19% and which subsequently had been used as<br />

the only carbon source for bacteria in liquid cultures. The microtome section in<br />

Fig. 5.2a represents the non-inoculated control. The section in Fig. 5.2b shows<br />

that only the highly lignified middle lamella primary wall region resisted to<br />

the bacterium Cellulomonas flavigena Kellerman and McBeth. However, the<br />

bacteria only consumed the carbohydrates of the pretreated wood. The lignin,<br />

which was dissociated from the pretreated woody cell wall by the bacteria, was<br />

not respired but was refound in the nutrient liquid, suggesting that lignin is<br />

a “ballast” to these bacteria that inhibits the dissimilation of the wood carbohydrates.<br />

The action of the chlorite pretreatment was assumed to result from<br />

the “opening” of the close association between carbohydrates and lignin in the<br />

woody cell wall so that the carbohydrates became accessible to the bacteria.<br />

Decay may have not been due to the reduction of the lignin content, because<br />

bacteria did not attack natural beech wood with 21% lignin content, but degraded<br />

pretreated Scots pine samples with a higher lignin content of about<br />

23% (Schmidt and Bauch 1980).<br />

Several bacteria were isolated from sawn Liriodendron tulipifera lumber already<br />

after 2 months of stacking (Mikluscak and Dawson-Andoh 2004a). After<br />

longer wood exposition under natural conditions, like in soil, or lakes and<br />

marine environment, the lignified cell wall was degraded by mixed populations<br />

and obviously the hurdle of the lignin barrier was cleared (Liese 1950;<br />

Liese and Karnop 1968; Schmidt et al. 1987; Fig. 5.3a). Dependent on the decay<br />

type within the wood cell wall, cavity, erosion, and tunneling bacteria<br />

were distinguished (Singh and Butcher 1991; Nilsson et al. 1992; Singh et al.<br />

1992; Daniel 2003). The two first types resemble the soft-rot types 1 and 2<br />

(Chap. 7.3). The tunneling bacteria are qualified by means of slime sheats to<br />

a gliding movement inside cell wall concavities created by themselves. The<br />

aggregates of the tunneling bacteria subcultured from the woody samples consisted<br />

of different bacterial species (Nilsson and Daniel 1992; Nilsson et al.<br />

1992).<br />

Aureobacterium luteolum Yokota et al. isolated from pond water caused erosions<br />

in the secondary wall in microtome sections of pine sapwood as substrate<br />

in 1 month of incubation, that is, bacterial wood degradation occurred obviously<br />

also by a pure culture under laboratory conditions (Schmidt et al. 1995;<br />

Fig. 5.3c). The result was however not reproducible using another strain of A.<br />

luteolum (Nilsson pers. comm.).<br />

In contrast to the xylem of healthy trees, which was rather “sterile”, wood<br />

samples from forest dieback sites contained several bacteria (Schmidt 1985;<br />

Schmidt et al. 1986). In view of the forest damage by pollution, bacteria (including<br />

RLOs and MLOs) were however assumed to be no causal agents, but<br />

rather, apart from other influences (emissions, climate, location), predisposing<br />

factors, or secondary parasites of the weakened trees.<br />

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5.2 Bacteria 115<br />

Fig.5.3. Bacterial wood decay. a First photo (1944 by J. Liese) of wood cell walls degraded by<br />

bacteria showing destroyed pine wood tracheids within a foundation pile (from Liese 1950).<br />

b Degradation of a pine sapwood tracheid cell wall during 3 months of ponding in a lake<br />

(TEM, from Schmidt et al. 1987). c Degradation of a tracheid cell wall in the laboratory<br />

by Aureobacterium luteolum (TEM, from Schmidt et al. 1995). B bacterium, E erosion,<br />

S secondary wall, MP middle lamella/primary walls, R cell wall residues<br />

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116 5 Damages by Viruses and Bacteria<br />

In logs, which were stored for protection from decay fungi, staining and<br />

insect attack in the open (v. Aufseß 1986; Schmidt et al. 1986) or were sprinkled<br />

(sprayed) or water-stored (ponded) (Karnop 1972a, 1972b; Berndt and Liese<br />

1973; Schmidt and Wahl 1987), bacteria degraded in situ within a few weeks<br />

the non-lignified margo fibrils of the sapwood bordered pits (Fig. 5.4). Several<br />

bacterial isolates were obtained (Schmidt and Dietrichs 1976). The increased<br />

wood porosity may cause wood cracks during artificial drying and an irregular<br />

over-uptake of preservative solutions, varnishes, stains, or paints resulting in<br />

uneven finishes (Willeitner 1971). <strong>Wood</strong> spots due to increased permeability<br />

and bad smell of bacterial metabolites are current problems when wet-stored<br />

wood is used for indoor wood paneling.<br />

Timber in service is colonized by bacteria, if the wood is very wet and thus<br />

less suitable for fungi due to reduced oxygen content. Early reports (Liese<br />

1950; see Fig. 5.3a) on bacterial degradation refer as to wood in long-lasting<br />

ground contact (Levy 1975b), as in foundation piles, sleepers, or to wood<br />

in water, like in cooling towers, harbor constructions and boats (Liese 1955).<br />

Cell wall degradation even occurred in chromium-copper-arsenic-treated piles<br />

and poles (Willoughby and Leightley 1984; Singh and Wakeling 1993). The<br />

bacteria dissolved the toxic components and thus favored wood degradation<br />

by soft-rot fungi (Daniel and Nilsson 1985). <strong>Wood</strong> samples impregnated with<br />

chromium-copper-arsenate and incubated with bacterial pure cultures showed<br />

increased wood mass loss during subsequent incubation with Coniophora<br />

puteana (Willeitner et al. 1977).<br />

Bacteria are often found in archaeological woods from buried and waterlogged<br />

environments (Blanchette 1995; Björdal et al. 1999; Kim and Singh 1999,<br />

2000; Singh et al. 2003; Björdal et al. 2005; Schmitt et al. 2005). In those wet<br />

conditions, bacterial wood degradation is often associated with soft-rot fungi<br />

(Willoughby and Leightley 1984; Singh et al. 1991; Singh and Wakeling 1993).<br />

Fig.5.4. Destruction of a pine sapwood<br />

bordered pit showing the detachment of<br />

the torus(T) by bacterial (B)degradation<br />

of the margo fibrils. (REM, from Peek<br />

and Liese 1979)<br />

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5.2 Bacteria 117<br />

<strong>Wood</strong>s from Tertiary fossil forests after 20–60 million years of burial showed<br />

indications that nonbiological degradation was responsible for the changes in<br />

the cell walls (Blanchette et al. 1991).<br />

Bacteria are also involved in wood discoloration. The wood of the light<br />

African Ilomba, Pycnanthus angolensis, is colonized after felling during storage<br />

and shipment of the round timber. The bacteria spread in the stem interior<br />

and cause reddish-brown discoloration. Further discoloration develops during<br />

air-drying of the boards in the area of the stacked wood (sticker stain). As<br />

causal bacteria e.g., Pseudomonas fragi (Eichholz) Gruber was isolated, which<br />

remained active in the damp wood parts (contact with stacked woods) and<br />

increased there the pH value from about 5.5 to 7.5–8.5 by producing ammonia<br />

from the protein of the protein-rich wood species. This alkalinity results in<br />

chemical reactions (phenol oxidation and polymerization) of accessory components<br />

in the parenchyma cells, which cause the brown discoloration (Bauch<br />

et al. 1985). The bacterium also discolored wood samples in vitro (Fig. 5.5).<br />

Bacterial discoloration of Ilomba wood during air-drying could be almost<br />

completely prevented by previous dipping the fresh boards in a solution of<br />

each 5% formic acid and propionic acid.<br />

Several bacteria were isolated from beech trees that possessed an irregular<br />

stellar-shaped red heart (splash-heart). The bacteria caused also in vitro<br />

brown discoloration of light beech wood samples and wood capillary liquids<br />

by raising the pH value to over 7.3 (Schmidt and Mehringer 1989; also Mahler<br />

et al. 1986; Walter 1993).<br />

Pseudomonas aeruginosa (Schroeter) Migula discolored Obeche, Triplochiton<br />

scleroxylon (Hansen 1988). In water-stored pine stems, bacteria produced<br />

flavonoids from flavone glycosides, which diffused to the wood surface during<br />

drying the sawn timber and caused there brown discolorations (Hedley and<br />

Meder 1992).<br />

Bacteria were inhibited by chromium-copper wood preservatives and further<br />

preservation salts used against fungi. Concentrations used for fungi were<br />

mostly sufficient to prevent bacterial activity (Schmidt and Liese 1974, 1976;<br />

Liese and Schmidt 1975; Schmidt et al. 1975). Archaeological woods, like<br />

the Bremen Cog of 1380, are stabilized against further deterioration using<br />

polyethylene glycol (Hoffmann et al. 2004).<br />

Fig.5.5.Bacterial discoloration of Ilomba<br />

wood within 1 day by a pure culture of<br />

Pseudomonas fragi inoculated as a line<br />

on the light wood sample<br />

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118 5 Damages by Viruses and Bacteria<br />

Reviews on “bacteria and wood” are by Liese (1992), Schmidt and Liese<br />

(1994), Daniel and Nilsson (1998) and Kim and Singh (2000).<br />

Several bacteria, like Bacillus spp., Pseudomonas spp. and Streptomyces spp.,<br />

were investigated in view of antagonism (Chap. 3.8.1) against fungal parasites<br />

(Armillaria spp.: Dumas 1992), wood staining fungi (Bernier et al. 1986; Seifert<br />

et al. 1987; Benko 1989; Florence and Sharma 1990) and decay fungi (Benko<br />

and Highley 1990).<br />

Bacteria are currently discussed in connection with the hygiene status of<br />

wood used for packing, transport, and preparation of foodstuffs. A study, which<br />

compared wooden and plastic boards used in kitchens, revealed that especially<br />

pine boards possess hygienic advantages due to its extractives compared to<br />

other woods and plastic (Milling et al. 2005).<br />

Pretreatment of spruce wood chips with the actinobacterium Streptomyces<br />

cyaneus (Krasil’nikov) Waksman for mechanical pulping decreased the energy<br />

consumption during fiberizing of 24% and increased some strength properties<br />

of handsheets (Hernández et al. 2005).<br />

To identify bacteria, predominantly on the basis of morphological and biochemical<br />

characteristics, “Bergey’s Manual of Determinative Bacteriology”<br />

(Buchanan and Gibbons 1974) is suitable. “Bergey’s Manual of Systematic Bacteriology”<br />

(Garrity 2001 et seq.) is the classic reference on bacterial taxonomy<br />

considering numerous rearrangements and changes in nomenclature, which<br />

are mainly due to molecular techniques notably sequencing of 16S rDNA and<br />

analysis of fatty acids.<br />

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6<br />

<strong>Wood</strong> <strong>Discoloration</strong><br />

The damage of wood by fungi is essentially caused by the degradation of<br />

the cell wall by fungi, which decreases the mechanical wood properties and<br />

substantially reduces wood use. However, wood quality is also influenced by<br />

bacterial, algal and fungal discolorations (e.g., Grosser 1985; Zabel and Morrell<br />

1992; Eaton and Hale 1993).<br />

<strong>Discoloration</strong>s in the wood of living trees, in round wood, timber and wood<br />

in service are long-known problems and are based on different biotic and<br />

abiotic causes (Bauch 1984, 1986; Kreber and Byrne 1994; Koch et al. 2002;<br />

Koch 2004; Table 6.1).<br />

<strong>Discoloration</strong>s in standing trees occur after wounding by wound reactions<br />

ofthetree(Chap.8.2)andbythecolonizationofthestemwoodwithbacteria<br />

and fungi as a result of microorganism-own pigments (e.g., melanin of bluestain<br />

fungi, Zink and Fengel 1989) or of their metabolism (brown, white, and<br />

soft rot in trees, chemical reactions of accessory compounds after pH-change<br />

by wetwood bacteria and in the splash-heart of beech trees).<br />

Algae like Chlorococcum sp. and Hormidium sp. soiled and discolored timber<br />

surfaces (Ohba and Tsujimoto 1996; also Krajewski and Wa˙zny 1992a), whereby<br />

the green algae Chlorhormidium flaccidum (Kützing) Fot. and Chlorococcum<br />

lobatum (Kortschikoff) Fritsch & John caused even slight cell wall erosion<br />

(Krajewski and Wa˙zny 1992b).<br />

Table 6.1. Biotic and abiotic wood discolorations (completed after Bauch 1984; Butin 1995)<br />

tree reactions on wounding<br />

microbial discolorations<br />

– staining by algae, molds, blue stain and red-streaking fungi<br />

– grey stain of poplar wood by Phialophora fastigiata<br />

– pink stain by Arthrographis cuboidea<br />

– black streaking of beech wood by Bispora monilioides<br />

– red spotting of beech wood by Melanomma sanguinarum<br />

– “green rot” by Chlorociboria spp.<br />

– wood rots<br />

physiological reaction of living parenchyma cells (“Ersticken” of beech and oak)<br />

biochemical reaction by wood-own enzymes (“Einlauf” of alder)<br />

chemical reactions (iron-tannic acid reaction of oak, discoloration of hemlock by zinc)<br />

combined reaction (brown discoloration of Ilomba by bacterial pH-increase and<br />

subsequent chemical reaction of phenols)<br />

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120 6 <strong>Wood</strong> <strong>Discoloration</strong><br />

The wood-discoloring molds and staining fungi live on nutrients in the<br />

parenchyma cells of the sapwood. Conifers and hardwoods, round wood, lumber,<br />

finished wood and wood products can be colonized. Discoloring fungi<br />

do not cause any or only very little cell wall attack. Prioritization of the color<br />

damage depends on subsequent wood use.<br />

Several Deuteromycetes and Ascomycetes stain woody substrates. Phialophora<br />

fastigiata (Hyphomycetes) causes a grey stain of poplar wood. Arthrographis<br />

cuboides (Hyphomycetes) produces a pink stain in several hardwoods<br />

and softwoods, and a naphthalenedione has been isolated from such wood<br />

(Golinski et al. 1995). Red alder wood used in the USA for furniture is stained<br />

reddish purple by Ophiostoma piceae if not rapidly processed after harvesting<br />

(Morrell 1987). Black streaking of beech logs occurs by Bispora monilioides.<br />

Red spotting of beech wood is effected by Melanomma sanguinarum (Dothideales).<br />

Paecilomyces variotii produces a yellow discoloration of oak wood<br />

during drying through its pH-change, which causes chemical reactions of the<br />

hydrolyzable gallotannins (Bauch et al. 1991).<br />

So-called green rot is caused by species of the ascomycete Chlorociboria<br />

(Helotiales). Chlorociboria aeruginascens and C. aeruginosa discolor rotten<br />

and moist hardwood (and conifer) branches and other woody debris in the<br />

forest (Jahn 1990). The green wood has often been employed in marquetry<br />

and veneering and is a feature of the famous Tunbridge ware (Ellis 1976).<br />

The naphthoquinone pigment, xylindein, produced by the fungus is mainly<br />

deposited in the ray parenchyma cells as well as in vessels and fibers adjacent<br />

to the rays. The pigment is now since more than 500 years durable<br />

(Blanchette et al. 1992a; Michaelsen et al. 1992). In a recent reproduction of<br />

a violin from the 17th century, green stained wood was used for the ornaments<br />

(Fig. 6.1).<br />

Fig.6.1. “Green rot” caused by Chlorociboria species. a Green-rotten poplar wood. The<br />

missing section was used for the green intarsia b of the replica c, d by T. Schmitt in 1998 of<br />

a violin by J. Meyer from 1670 (photos b–d:T.Schmitt)<br />

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6.1 Molding 121<br />

6.1<br />

Molding<br />

Thetermmoldoriginatesfromdailylifeandisnotataxonomicnameofasingle<br />

systematic group (Reiß 1997; Kiffer and Morelet 2000). The Deuteromycetes<br />

(fungi imperfecti) constitute an artificial group and comprise a great variety<br />

of 20,000–30,000 species of 1,700 genera of Hyphomycetes and 700 genera of<br />

Coelomycetes. The different molds have a broad spectrum of physiological<br />

response with regard to temperature, water activity, pH value etc. and thus can<br />

colonize and damage very diverse materials (molding). Molds are significant<br />

in view of damages to foodstuffs, deterioration of natural materials (leather,<br />

books, textiles, wallpapers), with regard to human and animal health, and for<br />

biochemists and the manufacturers of antibiotics [772 of about 3,200 admitted<br />

antibiotics originate from fungi: Müller and Loeffler (1992)], organic acids<br />

[e.g., citronic acid, malic acid: Rehm (1980)], enzymes (e.g., amylase, protease,<br />

lipase, cellulase, pectinase), cheese (Penicillium camemberti, P. roqueforti),<br />

salami sausages (P. nalgiovense), and “country cured ham” (Aspergillus spp.,<br />

Penicillium spp.) (Schwantes 1996; Reiß 1997). Botrytis cinerea causes the<br />

“noble rot” of sweet wines. Fusarium oxysporum ssp. cannabis is used as an<br />

herbicide for suppressing marijuana plants (Kiffer and Morelet 2000). Even<br />

synthetic floor coverings, airplane fuels, oils, glues, paints, optical glasses, and<br />

textiles can be overgrown with and damaged by molds.<br />

With regard to lignocelluloses, seeds, seedlings, young tree roots (Schönhar<br />

1989), standing trees (Schmidt 1985), stored and blocked wood (Wolf and<br />

Liese 1977; Bues 1993), piled wood chips (Feicht et al. 2002) of the pulp industry<br />

(Hajny 1966), stored annual plants, like sugarcane bagasse (Schmidt and Walter<br />

1978), and books (Kerner-Gang and Nirenberg 1980) can be colonized by<br />

molds. Paecilomyces variotii (mold and soft-rot activity) is involved in the<br />

yellow discoloration of oak wood during storage and drying (Bauch et al.<br />

1991). There are German and European standards and test methods to measure<br />

growth of molds on and resistance of substrates like electrotechnical products,<br />

plastics, textiles, optic apparatus, and timber (Kruse et al. 2004).<br />

Frequently, molds are recognizable by their fast growth on the surface of<br />

substrates, on which conidia develop rapidly (Fig. 6.2a). Due to the speciesspecific<br />

color of the conidia, wood colonized by several mold species can make<br />

a multicolored impression, or it outweighs e.g., black due to Aspergillus niger<br />

or green after Penicillium spp. or Trichoderma spp. colonization.<br />

Trichoderma species were the most frequent fungi on spruce roots from forest<br />

dieback sites (Schönhar 1992). Stored beech stems are frequently colonized<br />

by Bispora monilioides, which causes black, radially arranged, elliptical strips<br />

on the fresh trunk cross surface.<br />

Molds develop on fresh cuts after tree felling, particularly on the moist<br />

sapwood, on inappropriately stored lumber, insufficiently dried and airtight<br />

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122 6 <strong>Wood</strong> <strong>Discoloration</strong><br />

Fig.6.2. Molding. a Substrate surface with various molds (REM, photo W. Kerner). b Molding<br />

of insufficiently dried and then plastic-covered paneling<br />

sealed wood, like plastic-coated paneling (Fig. 6.2b), during sea transport of<br />

round timber and wood products under deck and in chip piles of pulp industry.<br />

Among 427 isolates from stacked yellow-poplar lumber, Penicillium<br />

implicatum and Aspergillus versicolor accounted for 29.7 and 14.5%, respectively<br />

(Mikluscak and Dawson-Andoh 2004b).<br />

Thehyphaepenetratethewoodonlyafewmillimetersandliveonparenchyma<br />

cells (sugar, starch, protein). In the laboratory, some species degraded<br />

isolated pectin, hemicelluloses, and cellulose, but not lignified cell walls. Thus,<br />

wood strength properties remain unchanged.<br />

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6.1 Molding 123<br />

Molded wood is, however, unmarketable. For decorative purpose, e.g., wall<br />

paneling (Fig. 6.2b), molded wood is unsuitable, as the color spots are not mechanically<br />

removable, but can be only masked by colored paints. Infected wood<br />

is not suitable for various hygienic requirements, e.g., packaging material. In<br />

addition, technological characteristics, for example the gluing of plywood, can<br />

be affected by molds (Wolf and Liese 1977).<br />

Mold growth in buildings is increasingly becoming a problem. Molding<br />

in indoor environments (Thörnqvist et al. 1987) is favored by high substrate<br />

moisture (water activity 0.9–1.0), high air humidity around 95%, warmth and<br />

insufficient ventilation (Viitanen and Ritschkoff 1991b), like in cellars and<br />

bathrooms. According to the German standard DIN 4108 part 2, the relative air<br />

humidity on the indoor surfaces shall not amount to over 80% (Borsch-Laaks<br />

2005). Moisture with following mold contamination can arise from condensation,<br />

flood, and various types of leaks. Excessive insulation after the petroleum<br />

crisis has markedly favored condensation areas (cold bridges), from cellars<br />

to attics, which rapidly become sites of mold growth. Accompanying lifestyle<br />

changes (frequent showers, new cooking methods, inadequate airing of bedrooms)<br />

have led increasingly to the production and accumulation of moisture<br />

in the home. A study in Belgium of isolated molds in homes of patients with<br />

allergic problems showed that more than 90% of those houses were contaminated<br />

by molds of the genera Cladosporium, Penicillium and Aspergillus (Nolard<br />

2004). Cladosporium sphaerospermum infiltrated 60% of the homes and<br />

was responsible for high contaminations, particularly in bedrooms and bathrooms.<br />

Aspergillus versicolor, Penicillium chrysogenum, P. aurantiogriseum,<br />

P. spinulosum, P. brevicompactum, Chaetomium globosum, Stachybotrys chartarum,<br />

andAlternaria alternata are often found on the walls of bedrooms,<br />

living rooms, and kitchens. While Cladosporium herbarum, a phytopathogen,<br />

does not grow in houses, large numbers of spores enter through windows and<br />

doors mainly during the summer months.<br />

Molds may cause health problems. About 200 fungal species produce various<br />

mycotoxins (about 100), of which some are highly toxic to humans and<br />

animals (mycotoxicoses) (Müller and Loeffler 1992; Schwantes 1996; Reiß 1997;<br />

Kiffer and Morelet 2000; Samson et al. 2004). The cancerogenic aflatoxins from<br />

Aspergillus fumigatus and A. flavus in food (agricultural crops, cereals etc,<br />

Meister and Springer 2004) are well known. Human health damage can further<br />

develop by mycoallergies through direct contact with a fungus or inhaled<br />

spores (molds in the living space). Five to 15% of the population suffering<br />

from respiratory allergy has been sensitized to one or several molds. Exposure<br />

of young children to molds and their metabolites may have a “stimulating”<br />

effect on the onset of later allergies (Nolard 2004). Mold allergies also occur<br />

in work environments. <strong>Wood</strong>workers inhale spores of Cryptostroma corticale<br />

and Alternaria species (woodworker’s lung). “Bagassosis” may develop during<br />

bagasse processing. “Suberosis” is due to Penicillium glabrum growing on cork<br />

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124 6 <strong>Wood</strong> <strong>Discoloration</strong><br />

bark. Pulpwood handler’s disease is caused by Alternaria species growing on<br />

paper pulp. Farmers inhale spores of Aspergillus fumigatus when damp hay<br />

is worked. Dustmen and compost makers may be exposed to molds when<br />

kitchen waste is stocked in closed containers for too long. Mushroom growers<br />

may be exposed to huge quantities of spores released by the basidiomycete<br />

they cultivate, and the culture substrate is sometimes contaminated by molds<br />

(mushroom grower’s disease) (Nolard 2004).<br />

Superficial mycoses occur on mucous membranes (fingernail bed, lips) and<br />

profound mycoses after wounding the skin or inner body (ear, eye, lung, blood<br />

vessels). Deuteromycetes are also significant in view of immunodepression in<br />

cases of transplants and of diminished defense mechanisms of AIDS sufferers.<br />

With regard to indoor environments (Frössel 2003; Hankammer and Lorenz<br />

2003) only a few molds are considered as producers of important toxic compounds<br />

which can be released in the environment and which may cause severe<br />

health problems (Samson and Hoekstra 2004). These are Alternaria alternata,<br />

Aspergillus flavus, A. fumigatus, A. versicolor, Chaetomium globosum, Emericella<br />

nidulans, Memnoniella echinata, andStachybotrys chartarum, whereby<br />

the latter is considered the most important toxic fungus in buildings producing<br />

the cytotoxic satratoxins. A questionnaire study among U.S. homebuilders,<br />

new homeowners, and real estate agents indicated that overall, respondents<br />

did not have a strong understanding of how mold forms in new constructions.<br />

Ten percent of homeowners believed that mold was an issue in their neighborhoods<br />

while 35% of home builders and 19% of real estate agents believed<br />

that this was an issue in the homes they built (Vlosky and Shupe 2004). The<br />

aspect of molds on indoor piled chips was treated by Feicht et al. (2002). Air<br />

sampling is performed to quantify and identify contamination. Measurement<br />

of microbial volatile organic compounds (MVOCs) in houses serves as note<br />

for contamination, especially for hidden contaminations (Keller 2002). Stachybotrys<br />

chartarum and Chaetomium globosum emitted ketones and alcohols<br />

(Korpi et al. 1999). There are also dogs trained to detect molds by sniffing.<br />

For remediation, first of all the cause of the damage (dampness) has to be<br />

removed continuingly (Neubrand 2004). In view of allergies, the spores may<br />

be taken away. There are primers and paints with prophylactic anti-molding<br />

substances, like organic sulfur-nitrogen compounds (thiocarbamate) and organic<br />

tin compounds (tributyltin oxide). Yang et al. (2004b) proposed that<br />

incorporating tree bark (white spruce), which inhibited mold growth in vitro,<br />

into the production of composite boards may increase the resistance of panels<br />

to fungi.<br />

Particularly several Trichoderma species are antagonistic against other organisms<br />

and also destroy (mycoparasitisms) fungal parasites and saprobionts<br />

(v. Aufseß 1976; Highley and Ricard 1988; Murmanis et al. 1988; Giron and Morrell<br />

1989; Doi and Yamada 1991; Dumas and Boyonoski 1992; Phillips-Laing<br />

et al. 2003).<br />

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6.2 Blue Stain 125<br />

There are various textbooks and keys to identify molds (e.g., Wang 1990;<br />

Kiffer and Morelet 2000; Samson and Hoekstra 2004; Samson et al. 2004).<br />

The attachment of a species to the molds is not always strict. There are overlappings<br />

with blue-stain and soft-rot fungi since fungi traditionally implicated<br />

in wood discoloration can cause soft rot if the conditions are suitable (e.g., Alternaria<br />

alternata, Cladosporium herbarum, Aspergillus fumigatus) and many<br />

soft-rot fungi are highly melanized (e.g., Phialophora spp.). That is, a fungus<br />

all may show the typical superficial mold growth and is treated in textbooks<br />

on molds, but also effected blue stain, or produced weight loss in soft-rot tests<br />

(Seehann et al. 1975; Daniel 2003).<br />

6.2<br />

Blue Stain<br />

Blue stain (synonymous sap stain) is a blue, grey or black, radially striped<br />

wood discoloration of sapwood, which can be caused by about 100 to 250<br />

(Käärik 1980) fungi belonging to the Ascomycetes and Deuteromycetes. Seifert<br />

(1999) and others differentiated three groups of blue-stain fungi: – Ceratocystis,<br />

Ophiostoma and Ceratocystiopsis species (Upadhyay 1981; Perry 1991;<br />

Gibbs 1999), – black yeasts such as Hormonema dematioides, Aureobasidium<br />

pullulans, Rhinocladiella atrovirens, andPhialophora species, – dark molds<br />

such as Alternaria alternata, Cladosporium sphaerospermum,andC. cladosporioides.<br />

Yang (1999) differentiated dark staining fungi, such as Ophiostoma<br />

piliferum on jack pine, Ceratocystis minor on white pine, and C. coerulescens<br />

on white spruce, and light staining fungi, such as O. piceae, C. adiposa and<br />

Leptographium sp. Frequently, like in the Ophiostoma species, the teleomorph<br />

is a perithecium (Figs. 2.14, 6.3E). Blue stain occurs in conifers, particularly<br />

in pine, but also in spruce, fir, and larch, in hardwoods, like beech and birch,<br />

and in tropical woods. The stain may be superficial or penetrate deeply into<br />

the wood. In heartwood species, only the sapwood discolors, since blue-stain<br />

fungi live mainly on the content of the parenchyma cells. Figure 6.3 shows<br />

some details of blue stain.<br />

The hyphae are brown colored due to melanin (Zink and Fengel 1989) and<br />

relatively thick (Fig. 6.3C). Some species like A. pullulans develop dark-brown,<br />

thick-walled chlamydospores (Fig. 6.3D). The blue-black color of the wood<br />

develops as optical effect due to refraction of light. Hyphae penetrate into stem<br />

wood from cross sections or radially through bark fissures and move via the<br />

medullary rays. Easily accessible nutrients (sugars, carbohydrates, starch, proteins,<br />

fats, extractives) are taken up from the ray parenchyma cells. Xylanase,<br />

mannanase, pectinase and amylase have been detected in several blue-stain<br />

fungi (Schirp et al. 2003a). From the rays, the hyphae penetrate into the longitudinal<br />

tracheids with mechanical pressure through the torus of the bordered<br />

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126 6 <strong>Wood</strong> <strong>Discoloration</strong><br />

Fig.6.3. Blue stain in wood. A Artificial bluing of pine boards by Phoma exigua. B Detail.<br />

C Thick, brown hyphae of P. exigua. D Chlamydospores (photo G. Koch). E Perithecia (A,<br />

B, C, E from Schmidt and Huckfeldt 2005), — 5 cm, --- 5 mm<br />

pits (thin hyphae through the margo) and grow there from cell to cell through<br />

the pits. Because fungi colonize the sapwood tracheids and fibers, components<br />

of the capillary liquid also might be used as nutrients. Although there are<br />

special microhyphae, transpressoria (Fig. 2.5), which can break through the<br />

wood cell wall, probably by physical pressure and/or enzymatic action (Schmid<br />

and Liese 1966; Liese 1970), in most cases the strength properties of wood are<br />

hardly affected. Thus, the occasionally used term “blue rot” is wrong. Some<br />

species however caused some strength loss. Toughness was the property most<br />

seriously affected (Seifert 1999; Schirp et al. 2003b). In most cases, however,<br />

the damage to wood is mainly cosmetic. The damage however affects domestic<br />

and export earnings for the forest industries. For example, Pinus radiata in<br />

New Zealand is highly susceptible to blue stain with an estimated annual loss<br />

in revenue of NZ$ 100 million per year (Thwaites et al. 2004).<br />

Temperature minimum depends on the species, and is between 0 and −3 ◦ C;<br />

the optimum is between 18 and 29 ◦ C and the maximum is between 28 and<br />

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6.2 Blue Stain 127<br />

40 ◦ C. The moisture span reaches from fiber saturation close to umax.Inmany<br />

species, the optimum is between 30 and 120% (Käärik 1980; Schumacher and<br />

Schulz 1992). For log colonization, moisture loss in the felled tree of 10–15%<br />

is sufficient. Blue stain occurs during seasoning or transportation of green<br />

lumber before the wood is dried and is enhanced at relative humidities above<br />

90% (Seifert 1999).<br />

Blue-stain fungi were arranged into different ecological groups (Butin 1995):<br />

In blue stain of stems (primary blue stain), spores of Ophiostoma species (moisture<br />

optimum 50–130%), particularly Ophiostoma piceae (Harrington et al.<br />

2001) and also Discula pinicola are transferred by wind in bark wounds (forest<br />

work or wood transport) as well as by bark beetles particularly in un-debarked<br />

pine stems which are allowed to dry out slowly over weeks or months while lying<br />

in the forest (Neumüller and Brandstätter 1995). Hormonema dematioides,<br />

A. pullulans, and a Leptographium species were the most frequently isolated<br />

stain-fungi from bark and sapwood of living Pinus banksiana trees. There were<br />

indications that none of the well-known log-staining fungi was associated with<br />

healthy living jack pine trees, and it was deduced that prompt transportation<br />

of logs from forests to sawmills and sanitary treatment of log storage yards<br />

helps to reduce the severity of log staining before sawing (Yang 2004). The<br />

most aggressive sapstain species on fresh Pinus contorta logs was Ceratocystis<br />

coerulescens, followed consecutively by Leptographium spp., C. minor, O. piliferum,<br />

O. piceae, O. setosum, C. pluriannulata, andA. pullulans (Fleet et al.<br />

2001). Discula pinicola is the main cause of the so-called internal blue stain,<br />

which is characterized by a central wood discoloration without any external<br />

staining. A comparison of the growth of several blue-stain fungi in freshly cut<br />

pine billets has been performed by Uzunović and Webber (1998). The bluestain<br />

fungal composition on Pinus radiata logs harvested in New Zealand and<br />

shipped to Japan showed differences between summer and winter transport<br />

(Thwaites et al. 2004).<br />

Blue stain of sawn timber (secondary blue stain) is caused e.g., by Cladosporium<br />

species (moisture optimum 50–100%) and Strasseria geniculata (Butin<br />

1995) in sawn timber that is not completely dry or badly stacked in timber<br />

yards (Schumacher et al. 2003).<br />

The classical distinction in primary and secondary blue-stain fungi was not<br />

confirmed however by the frequent occurrence of D. pinicola both in stored<br />

pine stems and in boards (Schumacher and Schulz 1992). Battens of Sitka<br />

spruce were stained by O. piceae when the surface moisture content in a stack<br />

was 22% or more (Payne et al. 1999).<br />

Tertiary blue stain (moisture optimum 30–80%) results frequently from A.<br />

pullulans and Sclerophoma pithyophila on timber that has been converted into<br />

products, was painted and re-imbibe moisture while in service, like wooden<br />

façades, window frames, garage doors and garden furniture. Through damages<br />

of the coating in window wood e.g., by nails or due to inappropriate<br />

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128 6 <strong>Wood</strong> <strong>Discoloration</strong><br />

window construction, water is taken up, distributes in the wood and cannot<br />

evaporate through the coat layer. Fungi start growing and their mycelia, spore<br />

masses or perithecia (Fig. 6.3E) cause the paint layer to flake off with further<br />

moisture increase (Sell 1968). Hyphae of A. pullulans were able to grow<br />

through alkyd paints (Sharpe and Dickinson 1992). Colonization of painted<br />

wood by blue-stain fungi was treated by Bardage (1997). Tertiary blue-stain<br />

fungi do not originate from infected stems or lumber, but are new infections.<br />

Colonized wood shows excessive uptake of solutions, so that spot-shaped<br />

color differences develop after painting, similarly like at the excessive uptake<br />

caused by bacteria. The isolate A. pullulans P 268 is test fungus in the standard<br />

EN 152.<br />

Air-borne blue stain means the spread of blue-stain fungi by wind or rain,<br />

insect blue stain is due to fungi, which are associated with bark beetles (Solheim<br />

1992).<br />

There are different results in view of blue staining of wood that derives from<br />

forest dieback sites. Practical observations and fungal isolations (Schmidt<br />

1985) showed that wood from polluted forest sites was more stained than<br />

that from healthy forests. Laboratory experiments however did not show these<br />

differences (Liese 1986; Saur et al. 1986). Klepzig et al. (1996) found different<br />

interactions of ecologically similar saprogenic fungi with healthy and<br />

abiotically stressed trees. Regarding the storage of spruce, pine and beech<br />

stems (v. Aufseß 1986; Göttsche-Kühn and Frühwald 1986; Schmidt et al. 1986;<br />

Schmidt and Wahl 1987; Nimmann and Knigge 1989) the wood from diseased<br />

trees first tended to faster discolorations due to fungal attack. However, after<br />

longer storage no relation was found between the state of health of the<br />

tree and the damage extent during storage. On the contrary, the stems of<br />

healthytreeswereevenmorestronglydiscolored,sincetheirlongerlasting<br />

drying period provided for the fungi a longer time favorable growth<br />

conditions. Stored planks from damaged pine trees were also slightly less<br />

stained than wood from healthy trees (Schumacher and Schulz 1992). Altogether,<br />

there are no results justifying the occasionally used term “damage<br />

wood”.<br />

Incubation of fresh Scots pine sapwood samples with blue-stain fungi increased<br />

wood absorptiveness and the wood may show a greater ability to<br />

impregnation with water-based preservatives (Fojutowski 2005).<br />

Stained wood is used due its color effects by Swedish woodworkers and<br />

was also used to produce attractive violins (Seifert 1999). Corresponding attempts<br />

to stain timber artificially did however not yield regular discoloration<br />

of the samples (Fig. 6.3A). It is possible to remove the stain from the wood<br />

using oxidizing agents such as sodium chlorite or hydrogen peroxide (Seifert<br />

1999).<br />

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6.3 Red Streaking 129<br />

6.3<br />

Red Streaking<br />

Red-streaking discoloration (known as “Rotstreifigkeit” in Germany) is one of<br />

the most common and important damage in seasoning logs and sawn lumber,<br />

occurring only in conifers (spruce, pine, fir) and recognized as a distinct condition<br />

in continental Europe. The stripe-shaped to spotted yellow to reddishbrowndiscolorationextendsinlogsfromboththeirbark-coveredfacesand<br />

from their cut ends (Butin 1995; Baum and Bariska 2002) (Fig. 6.4). Stems that<br />

are not debarked show a rather flat discoloration and debarked stems exhibit<br />

a streakier staining (v. Pechmann et al. 1967).<br />

Causal agents are several white-rot Basidiomycetes, in spruce particularly<br />

Stereum sanguinolentum (Kleist and Seehann 1997) and Amylostereum areolatum.InsouthGermany,Amylostereum<br />

chailettii is common (Zycha and Knopf<br />

1963; v. Pechmann et al. 1967). In pine, red streaking is mainly due to Trichaptum<br />

abietinum (Butin 1995). According to Kreisel (1961), S. sanguinolentum<br />

and T. abietinum occur often together in stored logs.<br />

Red streaking develops if the wood remains in a semi-moist state over<br />

a long period, especially in the warmer season (v. Pechmann et al. 1967). The<br />

fungi gain access to the wood through the exposed cut ends and bark fissures.<br />

The mycelium reaches its greatest density in the medullary rays, where the<br />

fungus uses the primary storage compounds in the ray parenchyma cells.<br />

From there, the discoloration spreads axially deeply in the wood, penetrating<br />

the bordered pits and also by thin bore hyphae that perforate the tracheids<br />

cell wall (Kleist and Seehann 1997; Kleist 2001). Logs may be stained during<br />

overseas shipment, and red streaks producing fungi become again active in<br />

rewetted boards due to their ability to dryness resistance. The staining is mainly<br />

an oxidative process (Butin 1995). Kleist (2001) stated that the fungi involved<br />

excrete the pigments.<br />

The moisture optimum of most species lies between 50 and 120% u. Redstreaking<br />

fungi are slowly growing white-rot fungi, so that initially no serious<br />

strength loss is connected with turning red. During longer colonization however<br />

an intensive white rot develops with substantial mass and strength loss, so<br />

that red streaking damage represents a transition from discoloration to decay<br />

(v. Pechmann et al. 1967; Peredo and Inzunza 1990).<br />

Secondary infections by brown-rot fungi may occur. Red-streaked wood<br />

samples were degraded in the lab test more strongly by brown-rot fungi than<br />

controls without pre-infection. From reddish discolored fir wood, 26 Basidiomycetes<br />

(white and brown rot) and numerous blue-stain and mold fungi<br />

were isolated (v. Pechmann et al. 1967). From Pinus radiata wood, different<br />

molds, blue-stain fungi, Stereum sp. and the white-rot fungi Ganoderma sp.,<br />

Schizophyllum commune and Trametes versicolor were isolated (Peredo and<br />

Inzunza 1990). Spruce wood samples from forest dieback sites contained more<br />

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130 6 <strong>Wood</strong> <strong>Discoloration</strong><br />

Fig.6.4. Red-streaking discoloration of spruce wood by Stereum sanguinolentum. a Fruit<br />

bodies of S. sanguinolentum on the crosscut stem surface. b <strong>Wood</strong> discoloration some<br />

centimeters beneath the surface (photos G. Kleist)<br />

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6.4 Protection 131<br />

often A. areolatum and S. sanguinolentum compared to samples from healthy<br />

forests (Schmidt et al. 1986).<br />

Stereum sanguinolentum Bleeding Stereum<br />

small, thin, resupinate to semipileate fruit body, soft-leathery-crusty, bowlshaped,<br />

upper surface: felty, concentrically zonate, yellow-brown, whitish-wavy<br />

margin (Fig. 6.4a); bright to grey-brown hymenium blood-red after injury;<br />

dimitic (Breitenbach and Kränzlin 1986); amphithallic (Calderoni et al. 2003);<br />

apart from the saprobic way of life also parasitic after penetration through<br />

wounds and thus the most important species of “wound rot of spruce” (Butin<br />

1995); stacked wood not attacked; genus Stereum with multiple clamps (Kreisel<br />

1969).<br />

Trichaptum abietinum Fir Polystictus<br />

fruit body: annual, resupinate to semipileate and pileate, singly and roofing<br />

tile-like; upper surface: white-grey-brown, thin, felty, hirsute, zonate, leathery;<br />

pore surface: young net-shaped to porous, old: labyrinthine; young hymenium<br />

reddish with angular violet pores, later brown-violet; dimitic (Breitenbach and<br />

Kränzlin 1986); tetrapolar heterothallic (Nobles 1965); saprobic on stumps,<br />

stored logs and finished wood; severe white rot at high wood moisture; rarely<br />

on living trees (Kreisel 1961).<br />

6.4<br />

Protection<br />

To avoid microbial wood discoloration, the generally suitable measures against<br />

fungi (e.g., Liese et al. 1973; Liese and Peek 1987; Groß et al. 1991; Yang and<br />

Beauregard 2001) are listed in Table 6.2.<br />

Felling in the cold season and fast processing of the stems through well<br />

coordination between forestry and wood industry reduces microbial activity<br />

during storage of the stems in the forest. Cool, shady, and ventilated storage<br />

without ground contact and with unhurt bark to maintain high wood moisture<br />

content and to prevent lateral infections are favorable. Lumber discoloration<br />

can be prevented by prompt air-drying in well-ventilated stacks protected<br />

against rain by a roof, or by kiln-drying. Wet storage of stemwood by sprinkling<br />

or ponding protects against fungi and insects. Currently, stem storage<br />

Table 6.2. Preventive measures to avoid microbial wood discolorations and decay<br />

– felling in the cold season<br />

– appropriate storage of fresh wood<br />

– coordination between forestry and wood industry<br />

– drying<br />

– wet storage<br />

– storage in N2/CO2 atmosphere<br />

– chemical preservation<br />

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132 6 <strong>Wood</strong> <strong>Discoloration</strong><br />

is performed in a N2/CO2 atmosphere (Mahler 1992; Bues and Weber 1998;<br />

Maier et al. 1999).<br />

During wet storage, however, wood quality may become reduced by degradation<br />

of the pits by anaerobic bacteria (Willeitner 1971; Karnop 1972a, 1972b;<br />

Adolf et al. 1972; Fig. 5.4), by oxidative discolorations of phenolic compounds<br />

diffusing outward (Höster 1974), and by brown discoloration of the outer<br />

log parts through phenolics from the bark (Peek and Liese 1987; Bues 1993).<br />

Sprinkled stems were even colonized by Armillaria mellea, which “drilled”<br />

a borehole from the bark into the xylem to provide itself with air and subsequently<br />

decayed the wet wood (Metzler 1994).<br />

Discoloring fungi and molds may be rather tolerant towards several fungicides,<br />

which inhibit decay fungi. Numerous protective agents were investigated<br />

for their effectiveness against mold and blue-stain fungi: e.g., Karstedt<br />

et al. (1971), Wolf and Liese (1977), Nunes et al. (1991), Laks et al. (1993),<br />

Wakeling et al. (1993), and Suzuki et al. (1996). Sodium pentachlorophenate<br />

(PCP-Na) had been used for dipping and spraying procedures against discoloration<br />

and decay (Willeitner et al. 1986). In view of the negative impact on<br />

humans, animals, plants, and the environment, utilization of PCP and import<br />

of PCP-treated woods are however restricted in Germany due to contaminations<br />

of PCP with polychlorinated dibenzodioxines and dibenzofuranes as well<br />

as due to the development and release of these compounds during burning of<br />

PCP containing woods. Dependent of material and intended purpose, e.g.,<br />

boron compounds, quaternary ammonium compounds or dithiocarbamates<br />

may be used (Chap. 7.4). Solid wood, wood composites (Gardner et al. 2003),<br />

and gypsum wallboard treated with borate were tested for mold performance<br />

(Fogel and Lloyd 2002). Boron compounds were used against blue-stain in<br />

Norway spruce (Babuder et al. 2004) and rubber wood (Akhter 2005). Against<br />

discolorations of drying oakwood by Paecilomyces variotii, treatment of the<br />

fresh wood with 5–10% propionic acid was recommended (Bauch et al. 1991).<br />

Growth of molds and bacteria during the outdoor storage of sugarcane bagasse<br />

on Trinidad that is used there for the production of fiberboards was reduced<br />

by organic sulfur compounds and propionic acid (Liese and Walter 1980).<br />

Although blue-stain fungi do not reduce wood quality significantly, discoloration<br />

is considered as substantial damage and is a perpetual problem of<br />

round wood and timber. Despite felling during the cold season as well as using<br />

ventilated stacking of the lumber, damage nevertheless occurs by blue-stain<br />

fungi. A two-year experiment with pine wood using different felling times and<br />

storage variations showed that damage of the round timber might be reduced<br />

and that rapid timber seasoning has the greatest influence (Schumacher and<br />

Schulz 1992).<br />

Un unsolved problem is the discoloration of bright tropical woods, like<br />

Pycnanthus, Virola, Aningeria and Pterygota (Bauch et al. 1985), after felling<br />

and during shipment and drying of the sawn timber (Karstedt et al. 1971;<br />

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6.4 Protection 133<br />

Fougerousse 1985). <strong>Discoloration</strong>s result from oxidative reactions of accessory<br />

compounds with atmospheric oxygen and phenol oxidases (e.g., Neger 1911;<br />

Oldham and Wilcox 1981), from chemical reactions of wood contents with<br />

metals [iron, zinc: e.g., Bauch (1984)], or from microorganisms, particularly<br />

blue-stain fungi, and in some woods, like Ilomba, from “combined influences”<br />

[bacterial pH-change and subsequent chemical reactions (Bauch 1986; see<br />

Fig. 5.5, Table 6.1)]. The practical processing of wood preservation in the<br />

tropics against discolorations and decay is summarized by Willeitner and<br />

Liese (1992) (also Findlay 1985).<br />

Comprehensive investigations on red streaks producing fungi, their reduction<br />

of wood quality and on suitable storage are described by v. Pechmann<br />

et al. (1967). Since fungal damage is usually only superficial in the first months,<br />

deeper discolorations can be limited to a practically insignificant extent, if<br />

the log does not remain in the forest in the warm season longer than some<br />

months. The wet to moist condition of the wood should rapidly run through either<br />

by suitable forest storage (no ground contact, ventilated, shady), or a high<br />

moisture content should be maintained in the sapwood by an unhurt bark.<br />

Attempts of a “biological wood protection” by antagonism are described in<br />

Chap. 3.8.1.<br />

To prevent enzyme-mediated, non-microbial sapwood discolorations such<br />

as sticker stain in ash or grey stain in oak, logs were treated with fumigants to<br />

kill living parenchyma cells (Amburgey et al. 1996; also Schmidt et al. 1997b;<br />

cf. Chap. 8.1.2.2).<br />

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7<br />

<strong>Wood</strong> Rot<br />

There are three types of fungal wood rot: brown, white, and soft rot (see<br />

Figs. 7.1–7.4). Further terms are either older names (e.g., destruction rot =<br />

brown rot), specifications (red rot = white rot by Heterobasidion annosum)or<br />

terms used in practice (marble rot = white rot with black demarcation lines) or<br />

false names (blue rot = blue stain). According to the classical school of thought<br />

a fungal species causes only one type of decay, and species causing different<br />

rots shall not be grouped in the same genus [e.g.: Lentinus lepideus: brown rot;<br />

Lentinula (in former times Lentinus) edodes:whiterot].<br />

Regarding the delineation between the three decay types, there are, however,<br />

exceptions: The brown-rot fungus Coniophora puteana produced cavities to be<br />

typical of soft-rot fungi and erosion and thinning of the cell wall to be characteristic<br />

of white-rot fungi (Kleist and Schmitt 2001; Lee et al. 2004). Fistulina<br />

hepatica revealed the soft-rot mode in cell walls rich in syringyl lignin, whereas<br />

brown rot was associated with cells rich in guaiacyl lignin (Schwarze et al. 2000).<br />

Several white-rot Basidiomycetes like Phellinus pini (Liese and Schmid 1966)<br />

as well as Inonotus hispidus and Meripilus giganteus caused cavities (Schwarze<br />

and Fink 1998; Schwarze et al. 1995a), which differed between the host trees,<br />

cell type, and location in the annual ring. Cavities in the secondary wall of<br />

fibers and tracheids were also found to be caused by two Armillaria species as<br />

well as by Stereum sanguinolentum, Ganoderma applanatum, and Grifola frondosa<br />

(Schwarze and Engels 1998). It was hypothesized that soft-rotting activity<br />

of white-rot Basidiomycetes may commonly precede white rotting when the<br />

fungus invades previously uninfected zones in the xylem, in which moisture<br />

content is high. Delignification of Norway spruce tracheids by Stereum sanguinolentum<br />

was associated with the presence of radial and concentric clefts<br />

containing cell wall entities in the secondary wall (Schwarze and Fink 1999)<br />

supporting observations of a radial and concentric arrangement of cell wall<br />

constituents within the S2 (Sell and Zimmermann 1993).<br />

7.1<br />

Brown Rot<br />

Brown rot is caused by Basidiomycetes, which metabolize the carbohydrates<br />

cellulose and hemicelluloses of the woody cell wall by non-enzymatic and<br />

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136 7 <strong>Wood</strong> Rot<br />

enzymatic action and leave the lignin almost unaltered (Fig. 7.1A; Chap. 4),<br />

whereby the brown color develops.<br />

Brown-rot fungi do not produce lignin-degrading enzymes. There are however<br />

reports of lignin peroxidase and manganese peroxidase in some brown-rot<br />

fungi, and lignin loss or metabolization by brown-rot fungi have been reported.<br />

Particularly in later stages of decay, the highly lignified middle lamella/primary<br />

walls were observed to undergo attack. Also, the penetration of the wood cell<br />

wall by bore holes removes lignin in the process, all suggesting that low molecular<br />

weight lignin degrading agents and potentially even lignin degrading<br />

enzymes max occur in some brown-rot fungi, at least with localized activity<br />

(Goodell 2003). Laccase activity was also found in Coniophora puteana (Lee<br />

Fig.7.1. Brown rot. A Cubic crack. B <strong>Wood</strong> cell wall showing remaining lignin after carbohydrate<br />

degradation (TEM, photo W. Liese). C Brown cubical rot by Oligoporus amarus. MP<br />

middle lamella/primary walls, S secondary wall, L lumen<br />

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7.1 Brown Rot 137<br />

et al. 2004), and in Gloeophyllum trabeum and Oligoporus placenta (Goodell<br />

2003). Non-enzymatic, low molecular agents produced by the brown-rot fungi<br />

are responsible for initial stages of cell wall attack (Goodell 2003; Chap. 4).<br />

Of about 1,700 wood-degrading Basidiomycetes in North America, only 120<br />

species (7%) caused brown rot, and of these 79 (65%) were polypores (Eriksson<br />

et al. 1990; Ryvarden and Gilbertson 1993). White-rot fungi distribute broader<br />

over the different basidiomycetous groups and some belong to the Ascomycetes<br />

(Rayner and Boddy 1988). Most brown-rot fungi affect conifers (Ryvarden and<br />

Gilbertson 1993), while white-rot fungi occur more frequently on hardwoods.<br />

Brown rot occurs in standing trees, felled and processed wood as well as in<br />

sapwood and heartwood. In the northern hemisphere, the majority of timber<br />

used in construction is from conifers. Thus, a large part of wood in outdoor and<br />

indoor service is destructed due to the action of brown-rot fungi. Brown rot is<br />

usually uniformly distributed over the substrate. A brown cubical pocket rot is<br />

caused by Laurelia taxodii in cypress and by Oligoporus amarus (Fig. 7.1C) in<br />

incense cedar. Decay pockets are localized and surrounded by firm wood (Zabel<br />

and Morrell 1992). A woody substrate both may show brown rot and white rot;<br />

a standing tree of Picea engelmannii exhibited “white pocket rot” by Phellinus<br />

pini in the heartwood (Chap. 8.3.8), and after wind throw the healthy areas<br />

became brown-rotten (Blanchette 1983). Brown-rot wood debris is extremely<br />

stable due to its content of slightly modified lignin and has remained unaltered<br />

in the soil for centuries. In conifers forests, this humic material may comprise<br />

up to 30 vol% in the upper layers (Swift 1982; Ryvarden and Gilbertson 1993).<br />

Table 7.1 lists some important brown rot.<br />

Table 7.1. Some common brown-rot fungi<br />

Fungus Predominant occurrence<br />

standing timber timber softwood hardwood<br />

tree outdoors indoors<br />

Laetiporus sulphureus × ×<br />

Phaeolus schweinitzii × ×<br />

Piptoporus betulinus × ×<br />

Sparassis crispa × ×<br />

Gloeophyllum spp. × ×<br />

Daedalea quercina × ×<br />

Lentinus lepideus × ×<br />

Paxillus panuoides × ×<br />

Antrodia spp. × ×<br />

Coniophora spp. × ×<br />

Serpula lacrymans × ×<br />

Meruliporia incrassata × × ×<br />

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138 7 <strong>Wood</strong> Rot<br />

Brown-rot fungi colonize the wood via the rays and spread in the longitudinal<br />

tissue through pits and by means of microhyphae. They grow inside<br />

the cell lumina (Fig. 7.1B) and there in close contact with the tertiary wall.<br />

The low-molecular agents and/or the cellulolytic enzymes penetrate through<br />

the relatively resistant tertiary wall (high lignin content) and diffuse into the<br />

secondary wall, where they degrade the carbohydrates completely (Fig. 7.1).<br />

Typically, brown-rot fungi do not cause lysis zones around their hyphae, while<br />

this is characteristic of many white-rot fungi. The hyphae are surrounded by<br />

slimelayers(Table2.1).<br />

In the early stages of decay, the carbohydrates are rapidly depolymerized.<br />

In Serpula lacrymans, the compression strength is decreased by 45% at only<br />

10% mass loss (Liese and Stamer 1934). Hemicellulose degradation runs up<br />

to about 20% mass loss faster than the respiration of the cleaving products.<br />

The relative lignin content increases parallel to carbohydrate degradation, the<br />

absolute lignin content slightly decreases. Due to the rapid cellulose depolymerization,<br />

the dimensional stability particularly decreases. The wood breaks<br />

up into rectangular blocks if it shrinks by drying (Fig. 7.1A), which led to the<br />

former term “destruction rot”. In some older literature, brown rot is falsely<br />

named as “red rot”, which however means the typical white-rot caused by Heterobasidion<br />

annosum.Inadvanceddecay,brown-rottenwoodcanbecrushed<br />

with one’s fingers to a brown powder (“lignin”). “House rot” means decay inside<br />

buildings, mostly by brown-rot fungi, particularly by Serpula lacrymans,<br />

Meruliporia incrassata, Coniophora species, Antrodia species, Donkioporia expansa<br />

(white rot) and Gloeophyllum species. There are further about 60 more<br />

rarely indoor occurring fungi (Table 8.6).<br />

7.2<br />

White Rot<br />

White-rot research has been reviewed by Ericksson et al. (1990) and Messner<br />

et al. (2003). White rot means the degradation of cellulose, hemicelluloses,<br />

and lignin usually by Basidiomycetes and rarely by Ascomycetes, e.g.,<br />

Kretzschmaria deusta and Xylaria hypoxylon. White rot has been classified<br />

by macroscopic characteristics into white-pocket, white-mottled, and whitestringy,<br />

the different types being affected by the fungal species, wood species,<br />

and ecological conditions. From microscopic and ultrastructural investigations,<br />

two main types of white rot have been distinguished (Liese 1970).<br />

In the simultaneous white rot (“corrosion rot”), carbohydrates and lignin<br />

are almost uniformly degraded at the same time and at a similar rate during all<br />

decay stages. Typical fungi with simultaneous white rot are Fomes fomentarius,<br />

Phellinus igniarius, Phellinus robustus,andTrametes versicolor in standing<br />

trees and stored hardwoods (Blanchette 1984a). <strong>Wood</strong> decayed by F. fomen-<br />

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7.2 White Rot 139<br />

tarius, T. versicolor and some other fungi shows black demarcation lines (zone<br />

lines) (Fig. 7.2a), by which different species, or incompatible mycelia of the<br />

same species separate themselves from each other, or mycelia dissociate themselves<br />

from not yet colonized wood (“marble rot”, in German: “Marmorfäule”).<br />

The lines result from fungal phenol oxidases, whereby fungal compounds or<br />

also host-own substances are transformed to melanin (Li 1981; Butin 1995).<br />

As a function of the moisture distribution in wood, or between different fungal<br />

species or incompatible genotypes, a compartmentalization of individual<br />

decay centers can result from black pseudosclerotic layers of firmly structured<br />

mycelium (Rayner and Boddy 1988; Eriksson et al. 1990).<br />

Cell wall decay can start by microhyphae producing holes in the secondary<br />

wall (Schmid and Liese 1966), which flow together to larger wall openings with<br />

advancingdecay.Usually,however,thehyphaegrowinsidethelumenwithclose<br />

contact to the tertiary wall. The hypha surrounded by a slime layer (Table 2.1)<br />

excretes the degrading agents, which are active only in direct proximity of the<br />

hypha. Thus, a lysis zone develops under the hypha, and the hypha produces<br />

groovesinthewallwhichisgraduallyreducedinthickness,likearivererodes<br />

the ground (Schmid and Liese 1964; Liese 1970; Fig. 7.2b).<br />

Fig.7.2. White rot. a Simultaneous white rot by Trametes versicolor in beech wood with black<br />

demarcation lines. b Clamped hypha of T. versicolor digging into the cell wall (TEM, from<br />

Schmid and Liese 1964). c Successive white rot by Ganoderma adspersum in the Chilean<br />

“palo podrido” (photo J. Grinbergs). d White pocket rot (photo W. Liese)<br />

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140 7 <strong>Wood</strong> Rot<br />

In the successive (sequential) white rot, e.g., by Heterobasidion annosum<br />

(root rot in spruce), Xylobolus frustulatus (“Rebhuhnfäule” in standing and<br />

felled oaks: Otjen and Blanchette 1984, 1985), or in the Chilean “palo podrido”<br />

(Fig. 7.2c), lignin and hemicelluloses degradation run faster at least in<br />

early stages of attack, so that first cellulose relatively enriches. Further fungi<br />

showing successive white rot are e.g., Ceriporiopsis subvermispora, Dichomitus<br />

squalens, Inonotus dryophilus, andMerulius tremellosus. Frequently, e.g.,<br />

by Phellinus pini (Liese 1970) in the heartwood of living conifers as well as<br />

by Bjerkandera adusta and some other fungi (Blanchette 1984a; Otjen et al.<br />

1987), there are small, elongated cavities within a wood tissue, where the<br />

lignin and also the hemicelluloses are “selectively” (preferentially) degraded<br />

(“selective white rot”, “selective delignification”, preferential white rot). The<br />

greatest part of the cellulose remains. These decayed regions are surrounded<br />

by tissue that appears sound (white pocket rot, honeycomb rot; Fig. 7.2d).<br />

With advancing decay, the wood becomes fibrous in texture by the decay of<br />

the more lignified middle lamella/primary wall area. Some Ganoderma species<br />

caused within a wood tissue as well white pocket rot as simultaneous rot, or,<br />

depending on the wood species, white pocket rot in birch and oak and simultaneous<br />

rot in poplar (Blanchette 1984a; Dill and Kraepelin 1986; Otjen and<br />

Blanchette 1986).<br />

The terms “selective white rot” and “selective delignification” have been<br />

propagated in the period of biopulping research (Chap. 9.3) as these terms<br />

promise more experimental success than would do names like successive white<br />

rot. As in most cases of “selective white rot” and particularly in late stages<br />

of attack, cellulose is also degraded to some extent, the term “preferential<br />

delignification” should be used.<br />

Many white-rot fungi, e.g., Heterobasidion annosum (Hartig 1874), Fomes<br />

fomentarius, Ganoderma species, and Trametes versicolor cause black spots of<br />

manganese dioxide deposits in the attacked wood (Blanchette 1984b; Erickson<br />

et al. 1990; Daniel and Bergman 1997). Manganese deposits may occur in<br />

connection with lignin degradation by manganese peroxidase. Physisporinus<br />

vitreus, isolated from cooling-tower wood (Schmidt et al. 1996) exhibited these<br />

manganese deposits predominantly in the slime layer and in the inner S2<br />

beneath a hypha shown by TEM/EDX spectra (Fig. 7.3B).<br />

White-rot fungi attack predominantly hardwoods, either as pioneer organisms<br />

or later in the context of a succession. As conifers are the main timbers<br />

used in the northern hemisphere for constructions, white-rot fungi occur there<br />

rarely in buildings. In Table 7.2, some important white-rot fungi are specified.<br />

In all white rot types, the wood strength properties are reduced to a lesser<br />

extent than in brown-rotten wood, since at the same mass loss, lesser cellulose<br />

is consumed, and it does not come to cracking or cubical rot. In a very late<br />

stage of attack, a wood mass loss of 97% has been measured.<br />

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7.2 White Rot 141<br />

Fig.7.3. Manganese deposits occurring during decay of a Scots pine sapwood block by<br />

Physisporinus vitreus. A <strong>Wood</strong> sample with black manganese deposits after culture (from<br />

Schmidt et al. 1996). B TEM-micrograph showing electron-dense material in the hyphal<br />

slime layer (c) and the secondary wall (b). C TEM/EDX spectra of manganese and other<br />

elements in different areas of the attacked wood (see B). a control from a healthy area within<br />

the S2, b spectrum from the S2 beneath a hypha, c spectrum from dense deposit material<br />

within the hyphal slime layer. The copper peaks result from the metal grids. (from Schmidt<br />

et al. 1997a)<br />

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142 7 <strong>Wood</strong> Rot<br />

Table 7.2. Some common white-rot fungi<br />

Fungus Predominant occurrence<br />

standing tree timber outdoors softwood hardwood<br />

Armillaria mellea × × ×<br />

Donkioporia expansa indoor × ×<br />

Fomes fomentarius × ×<br />

Heterobasidion annosum × ×<br />

Meripilus giganteus × ×<br />

Phellinus pini × ×<br />

Polyporus squamosus × ×<br />

Schizophyllum commune × ×<br />

Stereum sanguinolentum × × ×<br />

Trametes versicolor × ×<br />

7.3<br />

Soft Rot<br />

The term “soft rot” was originally used by Findlay and Savory (1954) to describe<br />

a specific type of wood decay caused by Ascomycetes and Deuteromycetes<br />

which typically produce chains of cavities within the S2 layer of soft- and<br />

hardwoods in terrestrial and aquatic environments (Liese 1955), for example<br />

when the wood-fill (Fig. 7.4a) in cooling towers became destroyed despite<br />

water saturation, and when poles broke, although they were protected against<br />

Basidiomycetes. About 300 species (Seehann et al. 1975) to some 1,600 examples<br />

of ascomycete and deuteromycete fungi (Eaton and Hale 1993) cause soft rot,<br />

e.g., Chaetomium globosum (Takahashi 1978), Humicola spp., Lecythophora<br />

hoffmannii, Monodictys putredinis, Paecilomyces spp., and Thielavia terrestris.<br />

Soft-rot fungi differ from brown-rot and white-rot Basidiomycetes by growing<br />

mainly inside the woody cell wall (Fig. 7.4b). The wood is colonized via<br />

the wood rays. In conifers, the fungi penetrate, starting from the tracheidal<br />

lumina, by means of thin perforation hyphae of less than 0.5µm thickness into<br />

the tertiary wall and re-orientate then as thin hyphae after L-bending in one<br />

direction or after T-branching in both directions along the microfibrils in the<br />

secondary wall (soft rot type 1, Nilsson 1976).<br />

In longitudinal wood sections, hyphal activity is recognizable in the polarized<br />

light by rhombus-shaped cavities in the secondary wall of different size and<br />

arrangement (Levy 1966; Butcher 1975), which may be lined up like a string<br />

of pearls (Fig. 7.4c): The thin hypha stops its growth and the cavity is then<br />

developed around the hypha by the release of enzymes (putatively endoglucanases)<br />

along what is described as the proboscis hypha. Within the cavity,<br />

hyphal thickness increases to about 5µm. From the tip of the cavity, the next<br />

fine hypha starts its growth, which results in the next cavity, and continuous<br />

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7.3 Soft Rot 143<br />

Fig.7.4. Soft rot. a <strong>Wood</strong>fill from a cooling tower. b Hole-shaped decay of the secondary<br />

walls in latewood tracheids of pine sapwood (LM, photo M. Rütze). c Cavities inside a fiber<br />

(LM, photo by W. Liese)<br />

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144 7 <strong>Wood</strong> Rot<br />

enlargement of existing cavities and the formation of new cavities lead to total<br />

destruction of the S2 layer (Eriksson et al. 1990; Daniel 2003). SEM and TEM<br />

showed that the hyphae are normally associated with a variety of granular and<br />

fibrillar materials including extracellular slime (Table 2.1), melanin and lignin<br />

breakdown products. In Lecythophora mutabilis, CCA was concentrated in the<br />

granular material (Daniel 2003). Several causes are discussed for oscillating<br />

hyphal growth and cavity formation (Table 7.3).<br />

In cross sections, the cavities appear hole-shaped (“initial stage”) and increase<br />

with advancing decay to larger wall openings (Fig. 7.4b). Finally, it<br />

comes to circular detaching of the tertiary wall (“advanced stage”). Because of<br />

their high lignin content, the tertiary and primary walls are attacked in the end<br />

(“late stage”). It remains an incomplete skeleton of middle lamella/primary<br />

walls (“destruction stage”).<br />

In the soft rot type 2, which particularly occurs in hardwood (Zabel et al.<br />

1991), the hyphae erode particularly from the lumen the tertiary wall and<br />

penetrate till the middle lamella/primary wall. As rare variant, diffuse and<br />

irregular cavities in the secondary wall were described (Anagnost et al. 1994).<br />

Soft rot develops also in monocotyledons (bamboos: Liese 1959; Sulaiman<br />

and Murphy 1992). In a broader definition for soft rot, each significant fungal<br />

decay of the woody cell wall by non-basidiomycete fungi was suggested, which<br />

however contrasts to the white-rot causing Ascomycetes.<br />

Since the tertiary and middle lamella/primary wall are resistant over longer<br />

time against fungal attack due to stronger lignification (Fig. 7.4b), wood with<br />

soft rot frequently first will not be recognized with the naked eye. Also with<br />

the “hammer test” it does not result in the hollow sound of decayed wood<br />

(Liese 1959), so that in former times during repair work of poles accidents<br />

arose several times by pole breaks due to the unawareness of the officials. Soft<br />

rot penetrates slowly from the outside to the wood center. Moist wood is dark<br />

colored and the surface is soft. Although softening of wet wood is typical,<br />

attacked CCA treated timber has shown degraded wood to be hard. The dry<br />

wood shows cubical rot with a fine-cracked, charcoal-like surface (Fig. 7.4a).<br />

Table 7.3. Possible factors involved in cavity formation by soft-rot fungi<br />

– chemical and morphological structure of the wood cell wall (Liese 1964)<br />

– accumulation of toxic phenolic substances from lignin degradation (Liese 1970)<br />

– oscillating cellulase activity as reaction to the produced sugars (Nilsson 1974)<br />

– unequally distributed chemical factor of the carbohydrates in the cell wall<br />

(Nilsson 1982)<br />

– composition and distribution of lignin in the cell wall<br />

– nutrients obtained by cavity formation allowing only limited growth of a hypha<br />

– small channel between two cavities due to intense enzyme production at the<br />

hyphal apex and less enzyme production at the hyphal basis (Eriksson et al. 1990)<br />

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7.3 Soft Rot 145<br />

Further infection symptoms are the blunt fracture and short-fibrous breaking<br />

out of splinters when puncturing.<br />

Within the cell wall, soft-rot fungi degrade cellulose and hemicelluloses.<br />

Compared to the brown-rot fungi the cellulolytic agents diffuse, however, not<br />

sodeepintothecellwall,butremainindirectproximityofthehyphae(Liese<br />

1964). Lignin is not (or little) attacked at least in the initial stage, mainly<br />

by demethylation, so that soft rot with regard to the decay type resembles<br />

brownrot.IsolatedligninsandDHP’sarenotdemethylated.Inligninmodel<br />

compounds, the β-O4 linkage and the aromatic ring were cleaved (Eriksson<br />

et al. 1990; also Bauch et al. 1976).<br />

The inhibiting effect of lignin was demonstrated by the result that a delignifying<br />

pretreatment promoted the carbohydrate degradation (Zainal 1976).<br />

<strong>Wood</strong> decay by soft-rot fungi is further affected by the quantity and type of the<br />

lignin: Lignin-rich softwood with lignin predominantly made of coniferyl units<br />

is more resistant than the lignin-poorer hardwood made of sinapyl-coniferyl<br />

units (Nilsson et al. 1988; Eriksson et al. 1990). In conifers, wood decay occurs<br />

preferentially in the late wood (Fig. 7.4b) with its relative low lignin and high<br />

cellulose content.<br />

Due to the intensive carbohydrate degradation, soft-rot fungi, just like<br />

brown-rot fungi, already cause about 50% decrease of impact bending at only<br />

5% mass loss, and cracks occur by the reduction of the dimensional stability.<br />

Soft rot develops in trees, stored wood, and in outside used wood. Soft-rot<br />

fungi can decay wood under extreme ecological conditions, which are unsuitable<br />

for Basidiomycetes: constantly wet wood till almost water saturation, like<br />

in harbor constructions and ships, but not permanently submerged, as well<br />

as wood in soil contact, like poles, piles, sleepers (Liese 1959). Several soft-rot<br />

fungi were found on rotting branches (Butin and Kowalski 1992). Soft-rot fungi<br />

(and Basidiomycetes) under marine conditions were described by Kohlmeyer<br />

(1977), Leightley and Eaton (1980) and Troya et al. (1991). The wood moisture<br />

tolerance of the fungi reaches from dryness resistance to decay at almost water<br />

saturation. For example, Chaetomium globosum and Paecilomyces spp. did not<br />

show any inhibition of their decay ability in beech wood samples of 200%<br />

wood moisture content (Liese and Ammer 1964). With altogether relatively<br />

low oxygen demand, soft-rot fungi receive the necessary oxygen for the decay<br />

of water-saturated wood in cooling towers by the sprinkling effect of the water,<br />

which brings oxygen in solution. Thermophilic species and those with the ability<br />

of heat resistance destroy wood in the inner of wood chip piles (Hajny 1966;<br />

Smith 1975). Chaetomium globosum canstartgrowinginnutrientsolutions<br />

with initial pH values from 3 to 11. Some soft-rot fungi decay woods with high<br />

natural durability, like Bongossi or Teak. After 21 years of outdoor exposure<br />

in soil, the heartwood of several hardwoods exhibited soft rot in about threequarters<br />

of all the samples, about one-quarter white rot and only 3% brown<br />

rot (Johnson and Thornton 1991). Soft-rot fungi are tolerant to chrome fluo-<br />

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146 7 <strong>Wood</strong> Rot<br />

rine salts, which inhibit brown and white-rot fungi, but are sensitive to copper<br />

(Chap. 7.4). <strong>Wood</strong> in soil contact must therefore be treated with a preservative<br />

that contains copper if coal tar oil is not applied. Large economic losses developed<br />

nevertheless in Australia when hundreds of thousands of eucalyptus<br />

poles, which were treated with chrome copper arsenic, prematurely failed by<br />

soft rot due to unequal preservative distribution in the wood (Dickinson et al.<br />

1976; Liese and Peters 1977; Greaves and Nilsson 1982). Several soft-rot fungi<br />

were isolated from CCA treated (Zabel et al. 1991; Wong et al. 1992) and coal<br />

tar oil-impregnated poles (Lopez et al. 1990; Dickinson et al. 1992).<br />

7.4<br />

Protection<br />

This chapter focuses on fundamentals upon prevention of wood damage by<br />

fungi, and protection and preservation of wood (e.g., Willeitner and Liese 1992;<br />

Eaton and Hale 1993; Palfreyman et al. 1996; Murphy and Dickinson 1997;<br />

Zujest 2003; Goodell et al. 2003; Müller 2005). Protection in the broader sense<br />

comprises non-chemical methods like organizational measures and measures<br />

by design, use of naturally durable woods, application of antagonisms, or wood<br />

modifications that do not affect the environment. Preservation predominantly<br />

stands for chemical measures.<br />

Table 7.4 shows the conditions for the development of wood fungi and<br />

protection principles that can be deduced from them.<br />

The principle of the wood protection consists of changing at least one of the<br />

three life prerequisites of fungi in wood in such a way that the development<br />

of fungi is impossible or at least inhibited. Fungal attack can be prevented<br />

Table 7.4. Prerequisites for the development of wood fungi and principles of protection<br />

deduced from them (supplemented from Willeitner and Schwab 1981)<br />

Prerequisite Preventive measure Protection principle<br />

Suitable moisture Reduce, keep away Timber drying,<br />

constructional wood protection,<br />

wood modification<br />

Suitable food Make inedible Use of durable wood,<br />

chemical wood preservation,<br />

wood modification,<br />

(use of antagonisms)<br />

Sufficient oxygen Keep away Drying, wet storage,<br />

storage in CO2/N2 atmosphere,<br />

use below the water level<br />

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7.4 Protection 147<br />

(Willeitner and Schwab 1981; Erler 2002; Willeitner 2000, 2003; Goodell et al.<br />

2003; Böttcher 2005; Borsch-Laaks 2005; Schmidt 2005) by:<br />

– organizational protection (e.g., short and appropriate wood storage),<br />

– use of durable wood species (natural methods),<br />

– keeping away water by structural wood protection measures by design:<br />

appropriate surface and weather protection, use of vapor barriers, avoidance<br />

of condensation due to thermal insulations, salient roof to protect timber<br />

from rain, drawing off of rain, barrier to avoid direct contact between wood<br />

and adjacent material, or inside the wall against raise of moisture from the<br />

ground,<br />

– chemical wood preservation,<br />

– wood modifications that increase dimensional stability of wood, reduce<br />

uptake of moisture, or make it hard to digest,<br />

– use of antagonisms.<br />

The moisture conditions in wood are of decisive importance for the development<br />

of wood fungi (Chap. 3.3). Table 7.5 shows the hazard classes of wood<br />

[to be replaced by “use classes” according to prEN 335-1 (2004) respectively<br />

ISO] that depend on wood use and timber moisture according to the German<br />

standard DIN 68800, parts 2 and 3 (1990, 1996), the corresponding potential<br />

application of durable timber, and the minimum requirements of chemical<br />

preservation measures.<br />

Natural durability means the wood-own resistance against bacteria, wooddecay<br />

fungi, beetles, termites and marine borers, which will differ for a timber<br />

species against the various organisms. <strong>Wood</strong> durability is based on the presence<br />

of accessory compounds, whereby it concerns numerous compounds from<br />

different chemical classes (Fengel and Wegener 1989; Obst 1998). They are produced<br />

in the living tree during transition from the sapwood to the heartwood<br />

and are deposited in the heartwood (Taylor et al. 2002). Thus only the heartwood<br />

exhibits natural durability, while the sapwood of all wood species is only<br />

little or not durable. The European standard EN 350-2 (1994) uses a five-class<br />

system to group 128 timbers according to their durability against fungi. <strong>Wood</strong><br />

with high durability against fungi (durability class 1, very durable) is e.g.,<br />

greenheart (durable also against termites and marine organisms). European<br />

oak is durable (class 2), walnut is moderately durable (class 3), Norway spruce<br />

is slightly durable (class 4), and European beech not durable (class 5) (also Augusta<br />

and Rapp 2003, 2005; Willeitner 2005a). Natural durability of some bamboo<br />

species against four decay fungi was investigated by Remadevi et al. (2005).<br />

The influence of the felling time on resistance is controversially discussed.<br />

It has to be considered that fresh winter-felled wood is less susceptible to<br />

damage due to other moisture, drying, and climatic conditions than wood<br />

felled in the summer. There are however no differences if the wood is carefully<br />

dried (Willeitner 2005a).<br />

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148 7 <strong>Wood</strong> Rot<br />

Table 7.5. Hazard classes of timber, conditions for wood use, resistant wood species, and<br />

chemical preservation measure<br />

Hazard condition for wood use durable wood minimum<br />

class preservative measure<br />

0 indoors, if<br />

wood moisture ≤ 12%,<br />

timber open at 3 sides or<br />

coating against insects<br />

none<br />

1 indoors colored heartwoods prevention of insects<br />

air humidity ≤ 70%, sapwood proportion < 10%<br />

wood moisture < 20%<br />

2 indoors: colored heartwoods prevention of<br />

air humidity > 70% of durability class fungi and insects<br />

in wet areas: 1, 2 or 3<br />

water-repellent coating<br />

outdoors: without<br />

weathering<br />

3 outdoors: weathered colored heartwoods prevention of<br />

without permanent of durability class fungi and insects,<br />

ground or water contact 1 and 2 weatherproof<br />

indoors: wet rooms<br />

4 permanent ground colored heartwoods prevention of<br />

or fresh water contact, of durability class 1 fungi and insects,<br />

special prerequisites weatherproof,<br />

for cooling towers and prevention of<br />

marine timber soft-rot fungi<br />

There is still a worldwide spread superstition that wood properties like<br />

resistance against fungi depend on the moon. The wood of trees felled at<br />

a certain date related to the moon phase is thought not to swell nor shrink,<br />

to be incombustible, resistant to fungi and insects, and to become very hard.<br />

Those oscillating changes of the properties of the woody tissue, which mainly<br />

consists of dead fiber or tracheid cell walls, are biologically impossible. Thus,<br />

all specifications are in contradiction to scientifically based results (Wa˙zny and<br />

Krajewski 1984; Seeling 2000; bamboo: Yamamoto et al. 2005). The positive<br />

effects of a certain felling date observed in the practice may be due to other<br />

influences: People which believe in lunar influences select in the forest wellgrown<br />

trees, use appropriate drying, storage methods and wood design, that<br />

is, the wood, its processing and use are of high quality and thus the wood is<br />

more resistant to deterioration.<br />

There are several standards to determine the resistance of untreated wood<br />

and wood-based composites against fungi and also to test the efficacy of<br />

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7.4 Protection 149<br />

preservatives. In Europe, the standards are ruled by the European Committee<br />

for Standardization (Table 7.6; Willeitner 2005b).<br />

Figure 7.5 shows a Kolle flask that is used according to the European standard<br />

EN 113 to determine the toxic values of wood preservatives against wooddestroying<br />

Basidiomycetes cultured on agar medium. The method can be also<br />

used to test the natural durability of timber species etc.<br />

Chemical wood preservation is used, if structural-constructive measures, or<br />

natural durability, or wood modifications alone are insufficient for an increased<br />

wood endangering to meet the requirement of long-term use of wood. Not<br />

durable wood species or those of insufficient durability and the sapwood<br />

of all wood species can be made resistant for a long time against damage<br />

by treatment with appropriate wood preservatives, provided that the wood<br />

shows permeability. Prerequisite is, corresponding to the wood use, to bring<br />

effective formulations in sufficient amount deeply into the wood (Schoknecht<br />

and Bergmann 2000) using appropriate methods (Willeitner and Schwab 1981;<br />

Table 7.6. European standards that deal with resistance and preservation of wood against<br />

fungi<br />

EN 335 (1992/95) Durability of wood and wood-based products; Definition of<br />

hazard classes of biological attack (3 parts)<br />

EN 350 (1994, 2 parts), EN 460 (1994) Durability of wood and wood-based products –<br />

Naturaldurabilityofsolidwood<br />

ENV 12038 (1996) Durability of wood and wood-based products – <strong>Wood</strong>-based panels<br />

ENV 12404 (1997) Durability of wood and wood-based products – Assessment of the<br />

effectiveness of a masonry fungicide to prevent growth into wood of Dry rot Serpula<br />

lacrymans (Schumacher ex Fries) F.S. Grey<br />

EN 113 (1996) Determination of toxic values of wood preservatives against wood<br />

destroying Basidiomycetes cultured on agar medium<br />

EN 152 (1989) Test methods for wood preservatives; Laboratory method for<br />

determining the protective effectiveness of a preservative treatment against blue<br />

stain in service (2 parts)<br />

EN 252 (1990) Field test method for determining the relative protective effectiveness of<br />

a wood preservative in ground contact<br />

EN 330 (1993) <strong>Wood</strong> preservatives; Field test for determining the relative protective<br />

effectiveness of a wood preservative for use under a coating and exposed out of<br />

ground contact: L-joint method<br />

ENV (prestandard) 807 (2001) <strong>Wood</strong> preservatives – Determination of the effectiveness<br />

against soft rotting micro-fungi and other soil-inhabiting micro-organisms<br />

ENV 839 (2002) <strong>Wood</strong> preservatives – Determination of the effectiveness against wood<br />

destroying Basidiomycetes – Application by surface treatment<br />

ENV 12037 (1996) <strong>Wood</strong> preservatives – Field test method for determining the relative<br />

protective effectiveness of a wood preservative exposed out of ground contact<br />

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150 7 <strong>Wood</strong> Rot<br />

Fig.7.5. Kolle flask according to EN<br />

113 to determine the toxic values of<br />

wood preservatives against wooddestroying<br />

Basidiomycetes cultured<br />

on agar medium. a Non-impregnated<br />

control. b Impregnated sample<br />

Tables 7.9, 7.10). It is distinguished between “preventive wood preservation”<br />

(Kleist 2005) and “controlling wood preservation” after a damage (Sallmann<br />

2005).<br />

There are different national regulations with regard to testing, approval,<br />

application and toxicological aspects of chemical wood preservatives. Thus,<br />

the following only describes the German situation (Fischer 2005; Reifenstein<br />

2005).<br />

The official approval of wood preservatives used for load-bearing construction<br />

takes place by the “Deutsches Institut für Bautechnik (DIBt)”, which evaluates<br />

the results of tests that had been performed in view of minimum requirements<br />

(efficacy, no unfavorable side effects). The Federal Institute for Risk Assessment<br />

(BfR) evaluates hygienic-toxicologic aspects of the preservative and<br />

the Federal Environmental Office (UBA) its ecotoxicologic behavior. Preservatives<br />

with approval obtain a general national approval by the DIBt. Important<br />

characteristics of a wood preservative are described by test ratings (Table 7.7).<br />

About 95% of the mainly professionally used preservation salts possess the<br />

DIBt approval (23% share of the market), while only 10% of the predominantly<br />

solvent-based preservatives that are used by do-it-yourselfers have been previously<br />

proven by neutral boards.<br />

<strong>Wood</strong> preservatives for non-load-bearing constructions can receive a quality<br />

mark by the RAL Quality Community of <strong>Wood</strong> Preservatives, including an<br />

evaluation by BfR and UBA.<br />

For blue stain-preventing preservatives for timber outdoors without ground<br />

contact including windows and outside joinery, a registration process concern-<br />

Table 7.7. Test ratings of wood preservatives in view of efficacy<br />

P prevention of fungi<br />

Iv prevention of insects<br />

Ib control of insects<br />

W for weathered wood without permanent soil or water contact<br />

E for wood in permanent soil or water contact or with dirt deposits in joints<br />

M preventionofSerpula lacrymans to grow through brickwork<br />

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7.4 Protection 151<br />

ing efficacy and toxicology is possible by the German Association of Varnish<br />

Industry (VdL) on a voluntary basis.<br />

All wood preservatives with DIBt approval, RAL quality mark, and the<br />

VdL-blue stain preventing preservatives are listed and specified by the active<br />

components in the annual wood preservative register (Deutsches Institut für<br />

Bautechnik 2005; Table 7.8). There is also a consumer guide on wood preservatives<br />

by the German Federal Ministry of Consumer Protection, Food and<br />

Agriculture (2003).<br />

Water-based boron salts without chromate are only suitable for inside use<br />

due to their leachability (Peylo and Willeitner 1995, 2001). <strong>Wood</strong> preservatives<br />

based on protein borates greatly retarded the leaching of boron from<br />

treated timber (Thevenon et al. 1998). In chromate-containing salt mixtures,<br />

the biocides are fixed to the wood tissue (Bull 2001). By the fixation process,<br />

the hexavalent chromium (Cr VI ) is reduced by wood components to the trivalent<br />

less toxic Cr III . This helps to stabilize the other preservative components<br />

in the wood (Bao et al. 2005b), in different degrees, e.g., copper is almost<br />

completely fixed. Therefore, those mixtures are also suitable for outside use.<br />

Chrome fluorine boron salts (CFB) are suitable for inside and outdoor use<br />

without ground or permanent water contact. Chrome copper salts (CC) are<br />

Table 7.8. Major groups of wood preservatives for prevention and control of decay fungi and<br />

insects (based on Deutsches Institut für Bautechnik 2005)<br />

DIBt approval-preservatives:<br />

for prevention:<br />

water-based preservatives<br />

boron, CFB, CC, CCA, CCB, CCF salts<br />

quaternary ammonium compounds<br />

quaternary ammonium-boron compounds<br />

chromium-free copper compounds (Cu-HDO, Cu-quaternary ammonium,<br />

Cu-triazol)<br />

various other compounds<br />

solvent-based preservatives (e.g., Al-HDO, pyrethroides)<br />

solvent-based and water-soluble preservatives (only insects, carbamates)<br />

coal tar oil distillates (creosotes)<br />

special compounds for wood-based composites (only fungi, anorganic boron<br />

compounds, K-fluorides, K-HDO)<br />

for control:<br />

water-based and solvent-based preservatives to control insects<br />

boron compounds, quaternary ammonium compounds, carbamates<br />

to prevent growth of Serpula lacrymans through masonry<br />

RAL quality mark-preservatives to prevent blue stain, decay fungi, insects, and termites,<br />

to control insects, and to protect masonry against S. lacrymans<br />

Blue stain preventing primers according to VdL instructions<br />

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152 7 <strong>Wood</strong> Rot<br />

allowed for indoor and outdoor wood, especially if it is exposed to leaching,<br />

and also for wood in ground contact, e.g., poles, exterior structures, such as<br />

decks and fences, mine timber (Narayanappa 2005), and wood in permanent<br />

water contact, such as cooling towers and marine works. Chrome copper salts<br />

with the addition of either boron (CCB) or fluorine (CCF) may be used indoors<br />

and outdoors.<br />

Chrome copper arsenic salts (CCA) are restricted to outdoor use and certain<br />

application such as noise barriers (Commission Directive 2003/2/EC 2003).<br />

In the USA and Canada, industry registrants voluntary agreed to withdraw<br />

CCA treatment for use in such residential applications as decks, fences, and<br />

playground components effective as of 2004, although it is still registered for<br />

commercial/industrial products (Bao et al. 2005b). Component leaching from<br />

CCA-treated wood during above-ground exposure was affected by climatic<br />

variables like precipitation and temperature (Taylor and Cooper 2005). Bao<br />

et al. (2005b) showed for CCA, CCB and acid copper chromate (retention about<br />

7kg/m 3 ) fixation times of 8–32 days at 21 ◦ C and between 12 and 48 h at 50 ◦ C.<br />

Treatment of freshly impregnated wood with hot steam of 110 ◦ C for 1 h was<br />

also suitable for sufficient fixation (Peek and Willeitner 1981, 1984; also Cooper<br />

and Ung 1992). Timber treated with water-based fixing salts should thus be<br />

protected from rain, depending on the type of preservative, to avoid leaching of<br />

the not yet fixed components, which would decrease the protection and pollute<br />

the environment. Cookson et al. (1998) evaluated the fungicidal effectiveness<br />

of water-repellent CCAs.<br />

Molybdenum and tungsten have been studied as substitutes for arsenic in<br />

CC-salts (Cowan and Banerjee 2005). Schultz et al. (2005a) used a mixture of<br />

copper(II) and oxine copper for an outdoor ground-contact exposure.<br />

Toxicological aspects have lead to an increased use of chromium-free preservatives<br />

that are just as fixing. These preservatives are based e.g., on ACQ (alkaline<br />

copper quaternary ammonium salts), copper HDO [bis-(N-cyclohexyldiazeniumdioxy)-copper]<br />

and Cu-triazoles. Some of these products also include<br />

boron. Quaternary ammonium compounds are used as N-dimethylalkylbenzylammoniumchloride,<br />

didecylpoly(ethox)ethylammoniumborate (polymeric<br />

Betain), and N,N-didecyl-N-methyl-poly-(oxethyl)-ammoniumpropionate.<br />

Zabielska-Matejuk et al. (2004) showed antifungal activity of bis-quaternary<br />

ammonium and bis-imidazolium chlorides (also Pernak et al. 1998).<br />

Didecyldimethylammoniumtetrafluoroborate inhibited mold and stain (Kartal<br />

et al. 2005a) and decay fungi (Kartal et al. 2005b). Copper(II) octanoate/<br />

ethanolamines were investigated by Humar et al. (2003). Mazela et al. (2005)<br />

used copper monoethanolamine complexes with quaternary ammonium compounds.<br />

The group of triazoles as wood preservatives was treated by Wüstenhöfer<br />

et al. (1993).<br />

Solvent-based preservatives contain e.g., Al-HDO [tris (N-cyclohexyl-diazeniumdioxy)-aluminum]<br />

or triazoles (e.g., tebuconazole, propiconazole) as<br />

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7.4 Protection 153<br />

fungicides and pyrethroides as insecticide. Pentachlorophenol is totally banned<br />

and γ-hexachlorocyclohexane (lindane) is not used any more. The addition<br />

of emulsifiers enables the use of various organic substances as emulsions in<br />

water-based systems.<br />

Distillates of coal tar oil (creosote) are a complex mixture of some hundred<br />

compounds, mainly polycyclic aromatic hydrocarbons (Majcherczyk and<br />

Hüttermann 1998), and are allowed for outdoor use of timber in permanent<br />

ground and water contact that is not in contact with human beings. Preferably,<br />

creosotes are applied to wood that is exposed to leaching, e.g., railroad sleepers<br />

and telegraph poles. According to legislation, the content of benzo(a)pyren<br />

is limited to 50 ppm, classified by the Western-European Institute for <strong>Wood</strong><br />

Preservation as type WEI B and C.<br />

Boron compounds, quaternary ammonium compounds, and carbamates are<br />

suitable to prevent growth of Serpula lacrymans through masonry.<br />

For the protective effect, the moisture content, the type of preservative (Table<br />

7.8), the treatment process (Tables 7.9, 7.10), and the duration of treatment<br />

have to be considered. In addition, the timber species and part of the timber<br />

determine the permeability for preservatives. The treatability (EN 350-2)<br />

varies between completely permeable (class 1: easy to treat like the sapwood of<br />

Quercus robur and Pinus sylvestris) to extremely refractory (class 4: extremely<br />

Table 7.9. Applicability of wood preservatives and treating processes depending upon the<br />

wood moisture content (modified from Willeitner and Liese 1992)<br />

Moisture <strong>Wood</strong> Treating process<br />

content preservative<br />

water- creosote organic<br />

based solventbased<br />

green<br />

much above<br />

yes no no sap-displacement (diffusion)<br />

fiber saturation<br />

markedly above<br />

yes no no diffusion, long-term soaking<br />

fiber saturation<br />

slightly above<br />

yes no no diffusion, long-term soaking,<br />

simple methods, OPM<br />

fiber saturation<br />

below<br />

yes no (yes) soaking, simple methods,<br />

(diffusion), (pressure processes)<br />

fiber saturation yes yes yes pressure processes (except OPM),<br />

soaking, simple methods<br />

underlined preferably recommended, in brackets possible but not recommended,<br />

OPM oscillating pressure method<br />

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154 7 <strong>Wood</strong> Rot<br />

Table 7.10. Major groups of application procedures of wood preservatives (after Willeitner<br />

and Schwab 1981; Willeitner and Liese 1992)<br />

Pressure processes, which use intervals of any difference of pressure until 0.8 N/mm 2<br />

(including or excluding vacuum) and which follow different treatment schedules,<br />

dependent on preservative and timber, yield deep penetration and high retention.<br />

In long-term procedures, the timber or the part of it to be treated is kept completely<br />

immersed (soaking) in the preservative, which slowly (some days) penetrates into<br />

the wood.<br />

Short-term procedures (dipping, spraying, deluging, brushing) yield only little<br />

penetration (surface treatment) and low retention.<br />

Special procedures preserve timber in use, like bored-holes in constructional timber,<br />

pilings or poles, and pastes or bandages used as a ground-line treatment for poles<br />

difficult to treat like the heartwood of Q. robur). The role of bordered pits to<br />

the refractory nature of softwoods has been reviewed by Usta (2005).<br />

The penetrability of refractory timbers like Picea abies (class 3–4) can<br />

be improved by using oscillating pressure methods (Breyne et al. 2000), by<br />

incising methods or by ponding. During the latter, bacteria attack the pits,<br />

but only irregularly and only in the sapwood. There were attempts to pretreat<br />

wood with chemicals (Militz and Homan 1992) and with enzymes to improve<br />

the permeability of conifers (Adolf 1975; Militz 1993) and hardwoods (Knigge<br />

1985). Jagadeesh et al. (2005) improved penetration and retention of CCA in<br />

bamboo by using shockwaves.<br />

Therearedifferentpreconditionsforchemical treatmentofwood(Willeitner<br />

and Liese 1992): All wood must be debarked and free from phloem remainings<br />

(“white-peeled”) before treatment. An exception is sap-displacement treatments<br />

(Boucherie process), where a water-based preservative is introduced<br />

under low pressure at the butt end of freshly felled trees replacing the sap of<br />

the sapwood by the preservative. Sap-displacement is out of use now for wood,<br />

but is applied to bamboo culms, whereby boron-salts are most commonly and<br />

successfully used (Liese and Kumar 2003). When the water content of wood is<br />

much above fiber saturation, a water-based preservative either of a high concentration<br />

or by long-term soaking in its solution can be used to distribute the<br />

chemicals into the timber by diffusion. Chemical treatment of seasoned wood<br />

with moisture content below fiber saturation requires penetration of a liquid<br />

into the capillary structure of the wood and subsequent distribution into the<br />

wooden tissue. Movement is effected either by externally applied pressure or<br />

by internal capillary forces.<br />

Before treatment, working the timber like final cross cuttings, sawing, borings<br />

and shapings should be completed. Otherwise, the newly exposed part of<br />

the timber has to be treated once more, e.g., by brushing it several times. This<br />

applies also to later developing drying shakes if the wood was insufficiently<br />

dried before treatment.<br />

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7.4 Protection 155<br />

Table 7.9 shows the applicability of wood preservatives and treating processes<br />

depending upon the wood moisture content.<br />

For pressure treatments [full-cell process, empty-cell process (Lowryprocess,<br />

Rüping-process), vacuum-process] and principally for creosote, the<br />

moisture content should be below fiber saturation. For short-term procedures<br />

(superficial treatments) and also for water-based preservatives, at least the<br />

wood surface must begin to dry. To bring the active substances into the wood,<br />

the procedures may be arranged into four major groups (Table 7.10).<br />

In Germany, there are 234 pressure plants and 2,115 plants that use soaking<br />

(Quitt 2005). The necessary retention of a preservative depends on the endangerment<br />

of the wood, on the efficacy of the active ingredient, and the treatment<br />

procedure. The minimum quantities are shown in the respective DIBt approval.<br />

The preventing chemical preservation of wood-based composites is regulated<br />

in DIN 68800 part 5 (1978).<br />

<strong>Wood</strong> plastic composites (WPCs) are a new material with plastic as a matrix<br />

and embedded wood particles and fibers as well as distinctive additives<br />

(Teischinger et al. 2005). The material is produced. e.g., by an extrusion process<br />

or injection molding process. <strong>Wood</strong> is added for better technical properties<br />

and for cost reduction. WPCs are increasingly used as a substitute for wooden<br />

decks especially in North America. Marketing of WPC products as “maintenance<br />

free” has been a key factor contributing to their success with the<br />

consumer. WPCs are nevertheless susceptible to fungal degradation despite<br />

the close association of wood with the plastic. <strong>Wood</strong> particles close to the surface<br />

of WPC products can attain moisture levels high enough to facilitate the<br />

onset of decay. Borates markedly reduced mass loss of WPC by Gloeophyllum<br />

trabeum in a soil block test (Simonsen et al. 2004). Mankowski et al. (2005)<br />

showed almost no mass loss by G. trabeum and Trametes versicolor in samples<br />

that had been treated with zinc borate.<br />

The non-chemical protection and chemical preservation of bamboo are<br />

described by Liese (2002) and Liese and Kumar (2003).<br />

Methods to determine the amount of active substances in the wood and<br />

to measure penetration depth are described by Petrowitz and Kottlors (1992),<br />

Schoknecht et al. (1998) and Schoknecht and Bergmann (2000). An overview<br />

is in the Internet (www.holzfragen.de/seiten/hsm reagenzien.html). N-cyclohexyl-diazeniumdioxide<br />

in impregnated pine wood was measured by direct<br />

thermal desorption-gas chromatography-mass spectrometry (Jüngel et al.<br />

2002).<br />

Since about 1975 critical reports increase with regard of possible environmental<br />

impacts by chemical wood preservation, like by pentachlorophenol and<br />

chromate-containing preparations, the pollution of the soil by leached chemicals<br />

(Willeitner 1973; Willeitner et al. 1991; Leiße 1992; Hartford 1993) and<br />

due to problems arising from the disposal of treated timber (Marutzky 1990;<br />

Voß and Willeitner 1992). Pentachlorophenol (PCP) has protected wood since<br />

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156 7 <strong>Wood</strong> Rot<br />

1935 from staining and from decay by fungi and insects (Prewitt et al. 2003).<br />

The life expectancy of utility poles increased from approximately 7 years in<br />

an untreated pole to about 35 years in a treated pole, thereby saving utility<br />

companies millions of dollars in replacement costs. In the USA, 36 million<br />

PCP-treated poles have been estimated to be in service in 1990. In view of the<br />

negative impact on humans, animals, plants, and the environment, utilization<br />

of PCP and import of PCP treated woods are however restricted in Germany.<br />

Disposal of spent treated wood has increasingly become a major concern.<br />

Popular methods, such as burning (incineration, combustion) and land filling,<br />

are costly or even impractical because of increasingly strict regulatory requirements.<br />

Recycling of the preserved wood and removal of the toxic preservatives<br />

from the treated wood is of great importance. Research in this area (Lin and<br />

Hse 2005) focus on direct recycling of preserved wood into composite manufacturing,<br />

CCA removal from spent CCA-treated wood performed by lowtemperature<br />

pyrolysis, solvent extraction, hydrogen peroxide extraction (Kim<br />

et al. 2004), electrodialytic remediation (Christensen et al. 2005), biological<br />

remediation, and dual treatment processes involving biological remediation<br />

and chemical extraction. Li and Hse (2005) liquefied CCA-treated wood in<br />

polyethylene glycol and removed more than 90% of the metals by precipitation<br />

from aqueous solvents. Kartal and Imamura (2005) used chitin and chitosan<br />

for remediation of CCA-treated wood. Studies on bioremediation, particularly<br />

creosote, DDT, lindane and PCP, used several bacteria and fungi (review by<br />

Majcherczyk and Hüttermann 1998). Fungi which excrete high amounts of oxalic<br />

acid and are copper tolerant like Antrodia vaillantii (Collett 1992a, 1992b;<br />

Schmidt 1995b) have been used to bio-recycle CCA and CCB treated wood<br />

(Leithoff et al. 1995; Stephan et al. 1996; Kartal and Imamura 2003; Samuel<br />

et al. 2003; Humar et al. 2004; Kartal et al. 2004). Clausen (1997b) enhanced<br />

CCA removal from treated wood by Bacillus licheniformis (Weigmann) Chester.<br />

There is a great bulk of investigations on new, alternative wood protection<br />

procedures that deal with the chemical and/or physical modification of wood<br />

(e.g., Militz and Krause 2003). Rapp and Müller (2005) grouped the recent wood<br />

protection procedures that are already used or are expected to be used into<br />

wood modification, wood hydrophobization, and supercritical fluid treatment.<br />

<strong>Wood</strong> modification comprises various treatments that decrease the swelling<br />

of the woody cell wall and thus its accessibility for the fungal degradation<br />

agents.<br />

Reactive organic compounds like acetic anhydride (“acetylation”) are introduced<br />

in the wood (Hill et al. 1998), which react with the hydroxyl groups of<br />

the cell wall polymers and thus increase the dimensional stability of the wood<br />

as well as its resistance against decay and discoloring fungi. Acetylation with<br />

acetic anhydride results in covalently bonded acetyl groups (“plugging of hydroxyl<br />

groups”) in the wood and acetic acid as a by-product. Acetylated wood<br />

is non-toxic and has no harmful impact on the environment, but may have an<br />

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7.4 Protection 157<br />

unpleasant smell. Stake tests according to EN 252 with acetylated pine wood<br />

samples showed that the resistance of samples with an acetyl content of about<br />

20% equals that of CCA treated wood with 10 kg/m 3 retention (Larsson Brelid<br />

et al. 2000). Brown-rot decay became zero at a weight percent gain (WPG) of<br />

about 20% due to acetylation, and white-rot was prevented at a WPG of about<br />

12% (Ohkoshi et al. 1999). As other anhydrides, propionic, butyric and hexanoic<br />

anhydrides were tested against brown, white and soft-rot fungi (Suttie<br />

et al. 1999; Papadopoulus 2004). Several carboxylic acid anhydrides were used<br />

for pine sapwood (Dawson et al. 1999).<br />

Impregnation with melamine resins leads to a deposition of the resin in the<br />

cell wall (Rapp et al. 1999) and there to the “blockade of hydroxyl groups”<br />

without chemical linkage, which also improves the mechanical properties and<br />

durability of wood (Rapp and Peek 1996; Lukowsky et al. 1999).<br />

Impregnation with 1,3-dimethylol-4,5-dihydroxyethylen urea (DMDHEU)<br />

effects the “linking-up of neighbored hydroxyl groups” by etherification with<br />

the N-methylol groups (Rapp and Müller 2005). There was no significant<br />

weight loss by Trametes versicolor of beech wood samples with 25% WPG of<br />

DMDHEU (Verma et al. 2005).<br />

There are various methods to produce thermally modified timber (“thermal<br />

modification of wood”) which leads to improved dimensional stability<br />

(Tjeerdsma et al. 1998) and biological resistance, but also partial wood degradation<br />

and discoloration. The processes have in common that the wood is<br />

subjected to temperatures between 160 and 260 ◦ Cinanatmospherewithlow<br />

oxygen content (Leithoff and Peek 1998; Rapp 2001; Ewert and Scheiding 2005).<br />

Potentially toxic byproducts have been considered by Kamdem et al. (2000). In<br />

Europe, about 45,000 m 3 of thermally modified timber were produced in 2004.<br />

Four basic technologies have been established: the Finnish “Thermo wood”,<br />

the Dutch “Plato wood”, the French “Retification”. Heat is transferred to the<br />

wood in the gas phase of air, exhaust fumes of combustion gases or nitrogen.<br />

The German “oil heat treatment” uses a vegetable oil (rape) for heat transfer,<br />

which additionally affects hydrophobization (Sailer et al. 2000; Bächle et al.<br />

2004). The wood is used outdoors, e.g., for façade covering, noise barriers,<br />

and in gardens for decks, and indoors, e.g., for floorings. Four years lasting<br />

field tests of wood samples from the four European industrial heat treatment<br />

processes indicated that heat treated wood appears to be not suitable for in<br />

ground application, since only durability classes in the range from 2 (durable)<br />

to 4 (slightly durable) were achieved (Welzbacher and Rapp 2005). Thermalhygro-mechanically<br />

densified wood showed reduced hygroscopy and improved<br />

mechanical performance, and resistance to fungal degradation (Schwarze and<br />

Spycher 2005).<br />

<strong>Wood</strong> hydrophobization occurs by oils, waxes, paraffins, and silicons. Sailer<br />

(2001) and Rapp et al. (2005) used vegetable oils. The oil, which is deposited in<br />

the cell lumina, reduces water uptake without inhibiting vapor release. A wax-<br />

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158 7 <strong>Wood</strong> Rot<br />

type end coating of logs considerably reduced stain and checking (Linars-<br />

Hernandez and Wengert 1997). Hill et al. (2004) impregnated the wood cell<br />

wall with silane monomers, which polymerize in situ. Furuno and Imamura<br />

(1998) used sodium silicate-boron. The use of organic silicon compounds<br />

was reviewed by Mai and Militz (2004). Both hydrophobization and increased<br />

wood density were obtained in doubly modified wood samples when the wood<br />

was treated with reagents bearing isocyanate, carboxylic anhydride or oxirane<br />

functionstoinducereactionswiththeOHgroupsandwhenthereagentsalso<br />

carried a polymerisable function by incorporating a monomer (styrene or<br />

methyl methacrylate) into the wood (Bach et al. 2005).<br />

Supercritical fluid treatments use the principle that the preservative carrier<br />

e.g., CO2 possesses at a certain pressure and temperature at the same time the<br />

properties of a gas and a liquid. The effective substance is similarly well soluble<br />

as in an organic solvent, but the penetration into the wood is deeper due to the<br />

minimal surface tension. At the end of the treatment, the carrier regains the<br />

gas phase by falling below the supercritical point that is the carrier loses the<br />

dissolving ability for the preservative, which remains deposited in the wood,<br />

and leaves the wood. Due to the minimal swelling of the wood, supercritical<br />

fluid treatment is particularly suitable for size-constant components like windows<br />

and doors (Rapp and Müller 2005). Morrell et al. (2005) impregnated<br />

wood-based composites with tebuconazole using supercritical carbon dioxide.<br />

Chitosan, a linear copolymer of β(1-4)-linked 2-amino-2-deoxy-D-glucopyranose<br />

and 2-acetoamido-2-deoxy-D-glucopyranose residues, is produced<br />

commercially by alkaline deacetylation of chitin. Most chitosan is produced in<br />

India, Japan, Poland, Norway, and Australia, mainly based on crab and shrimps<br />

shells discarded by the canning industries in the USA and Japan. In contrast to<br />

chitin, which is highly crystalline and thus insoluble in water and most organic<br />

solvents, chitosan is soluble in diluted acids (Eikenes et al. 2005). It was tested<br />

against a brown-rot fungus (Lee et al. 1993), and blue-stain and mold fungi<br />

(Chittenden et al. 2003, Torr et al. 2005). <strong>Wood</strong> decay tests according to EN 113<br />

showed that Coniophora puteana and Gloeophyllum trabeum were inhibited by<br />

about 6 kg chitosan/m 3 , but Oligoporus placenta may be stimulated (Schmidt<br />

et al. 1995). Militz et al. (2005) showed a protecting effect against all three<br />

fungi. On the other hand, chitin and chitosan act as chelators for metal ions<br />

and enhanced removal of CCA components from treated sawdust in view of<br />

remediation of CCA-treated wood (Kartal and Imamura 2005).<br />

Vanillin polymerized by laccase reduced the weight loss by C. puteana from<br />

25 to 5% (Rättö et al. 2004). Proteinase inhibitors like hen egg white inhibited<br />

growth of Ophiostoma piceae in pine sapwood samples (Abraham et al. 1997).<br />

Antioxidants enhanced efficacy of organic biocides in decay tests (Schultz et al.<br />

2005b). Chelators create metal limited conditions (Viikari and Ritschkoff 1992)<br />

or interact with enzymatic systems, like 2-hydroxypyridine-N-oxide (Mabicka<br />

et al. 2004). Cashew (Anacardium occidentale) nut shell liquid (CNSL), which<br />

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7.4 Protection 159<br />

is a mixture of phenolics extracted from the shells of the cashew nut, reduced<br />

growth of some decay fungi (Pelayo et al. 2000). Venmalar and Nagaveni (2005)<br />

tested copperised CNSL and neem (Azadirachta indica) seed oil, containing<br />

azadirachtin, as preservatives. Alcoholic neem leaves extracts decreased wood<br />

mass loss by Oligoporus placenta and Trametes versicolor (Dhyani et al. 2005).<br />

Recent research on the various aspects of modified wood was compiled at<br />

the Second European Conference on <strong>Wood</strong> Modification (2005).<br />

There were (and are) many attempts at biological wood protection. To<br />

date, the application of microbiological control to prevent wood decay and<br />

discoloration has been successful in the laboratory, but inconsistent in its performance<br />

in the field (reviews by Bruce 1998; Bjurman et al. 1998; Chap. 3.8.1).<br />

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8<br />

Habitat of <strong>Wood</strong> Fungi<br />

Microbial damages to trees and wood can be differentiated into damage to the<br />

living tree, to felled and stored wood and in outside use, and to wood in indoor<br />

use.<br />

Such grouping is however rather for didactical reasons. There are many<br />

overlappings: For example Daedalea quercina is occasionally found as wound<br />

parasite on living oaks, frequently on stumps, more rarely on timber in outdoor<br />

use, like sleepers or bridge timber, and sometimes also on buildings (halftimbering<br />

and windows). Stereum sanguinolentum causes as well the “wound<br />

rot” of spruce trees (Butin 1995) as the red streaking of stored coniferous wood<br />

(v. Pechmann et al. 1967).<br />

8.1<br />

Fungal Damage to Living Trees<br />

This chapter belongs to the field of “forest pathology” and only gives an<br />

overview. For further reading see Tattar (1978), Schwerdtfeger (1981), Sinclair<br />

et al. (1987), Hartmann et al. (1988), Schönhar (1989), Butin (1995), Schwarze<br />

et al. (1997), and Nienhaus and Kiewnik (1998). Defense mechanisms of the<br />

trees are described by Blanchette and Biggs (1992) (also Chap. 8.2.1).<br />

The tree can be already damaged on its flowers, seeds, and seedlings by<br />

fungi that belong to the Oomycetes, Deuteromycetes, or Ascomycetes. Among<br />

the more frequently occurring fungi on flowers or inflorescences are host<br />

specific Taphrina species that affect alder catkins, or female flowers of poplar,<br />

and Thekopsora areolata damaging spruce inflorescence (Butin 1995).<br />

Seeds can be damaged by non-specific molds of the genera Alternaria,<br />

Fusarium, Penicillium,andTrichothecium. Among the specialists that can cause<br />

internal rotting of seeds are Rhizoctonia solani on beechnuts and Ciboria<br />

batschiana on acorns. Conedera et al. (2004) list several parasitic fungi that<br />

colonize chestnuts.<br />

Heat damage in seedlings is often followed by secondary infections by Alternaria,<br />

Fusarium, and Pestalotia species. Thelephora terrestris, Helicobasidium<br />

brebissonii, Rosellinia minor and R. aquila can smother seedlings or<br />

young plants. Seedling rots are among the most common diseases in the forest<br />

nursery. Important fungi on conifer seedlings are Phytium debaryanum, Phy-<br />

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162 8 Habitat of <strong>Wood</strong> Fungi<br />

tophthora species, Fusarium species, Rhizoctonia solani, andMacrophomina<br />

phaseolina. The Shoot tip disease of conifer seedlings is caused by Strasseria<br />

geniculata, Botrytis cinerea, and Sphaeropsis sapinea. Sirococcus shoot dieback<br />

of spruce is caused by Sirococcus strobilinus, particularly on Picea pungens and<br />

Pinus contorta. Meria laricis causes the Meria needle-cast of young larch. The<br />

Table 8.1. Some leaf diseases caused by fungi (compiled from Butin 1995)<br />

Disease Causal fungus Classification<br />

Needle-cast of Douglas fir Rhabdocline pseudotsugae Sydow Rhytismatales (A)<br />

Phaeocryptopus gauemannii (Rohde) Petrak Dothideales (A)<br />

Lophodermium needle blight Lirula macrospora (R. Hartig) Darker Rhytismatales (A)<br />

of spruce<br />

Spruce needle reddening Lophodermium piceae (Fuckel) Höhn. Rhytismatales (A)<br />

Spruce needle rust Chrysomyxa species Uredinales (B)<br />

Rhizosphaera needle browning Rhizosphaera kalkhoffii Bubák Coelomycetes (D)<br />

of spruce<br />

Lophodermium needle-cast Lophodermium seditiosum Minter, Rhytismatales (A)<br />

of pine Staley & Millar<br />

Lophodermella pine needle-cast Lophodermella sulcigena (E. Rostrup) Höhn. Rhytismatales (A)<br />

Naemacyclus needle-cast of pine Cyclaneusma minus (Butin) DiCosmo, Rhytismatales (A)<br />

Peredo & Minter<br />

Dothistroma needle blight of pine Mycosphaerella pini E. Rostrup ap. Munk Dothideales (A)<br />

Pine needle rust Coleosporium species Uredinales (B)<br />

Larch needle-cast Mycosphaerella laricina (R. Hartig) Neger Dothideales (A)<br />

Herpotrichia needle browning Herpotrichia parasitica (R. Hartig) Dothideales (A)<br />

of Silver fir E. Rostrup<br />

Silver fir needle blight Hypodermella nervisequia (DC.) Lagerb. Rhytismatales (A)<br />

Silver fir needle rust Pucciniastrum epilobii (Pers.) Otth Uredinales (B)<br />

Black snow mold Herpotrichia juniperi (Duby) Petrak Dothideales (A)<br />

White snow mold Phacidium infestans P. Karsten s.l. Helotiales (A)<br />

Keithia disease of Thuja Didymascella thujina Rhytismatales (A)<br />

(E. Durand) Maire<br />

Giant leaf-blotch of sycamore Pleuroceras pseudoplatani (Tubeuf) Monod Diaporthales (A)<br />

Powdery mildew of maple Uncinula tulasnei Fuckel, Erysiphales (A)<br />

Uncinula bicornis (Wallr.) Lév.<br />

Tarspotofmaple Rhytisma acerinum (Pers. ) Fr. Rhytismatales (A)<br />

Cristulariella leaf spot of maple Cristulariella depraedans (Cooke) Höhn. Hyphomycetes (D)<br />

Birch leaf rust Melampsoridium betulinum (Pers.) Kleb. Uredinales (B)<br />

Beech leaf anthracnose Apiognomonia errabunda (Roberge) Höhn. Diaporthales (A)<br />

Oak leaf browning Apiognomonia quercina (Kleb.) Höhn. Diaporthales (A)<br />

Oak mildew Microsphaera alphitoides Grif. & Maubl. Erysiphales (A)<br />

Taphrina gall of alder Taphrina tosquinetii (Westend.) Magnus Taphrinales (A)<br />

Leaf browning of hornbeam Gnomoniella carpinea (Fr.) Monod Diaporthales (A)<br />

Asteroma carpini (Lib.) Sutton Coelomycetes (D)<br />

Apiognomonia leaf browning Apiognomonia tiliae (Rehm) Höhn. Diaporthales (A)<br />

of lime<br />

Poplar leaf blister Taphrina populina Fr. Taphrinales (A)<br />

Marssonia leaf-spot of poplar Drepanopeziza punctiformis Gremmen Helotiales (A)<br />

Septotinia leaf blotch of poplar Septotinia populiperda Helotiales (A)<br />

Waterman & Cash ex Sutton<br />

Poplar and willow leaf rust Melampsora species Uredinales (B)<br />

Anthracnose of plane Apiognomonia veneta (Sacc. & Speg.) Höhn. Diaporthales (A)<br />

Leaf blotch of Horse chestnut Guignardia aesculi (Peck) Stew. Dothideales (A)<br />

A ascomycete, B basidiomycete, D deuteromycete<br />

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8.1 Fungal Damage to Living Trees 163<br />

Table 8.2. Some fungal damages to buds, shoots, and branches (compiled from Butin 1995)<br />

Disease Causal fungus Classification<br />

Cucurbitaria bud blight of spruce Gemmamyces piceae (Borthw.) Cassagrande Dothideales (A)<br />

Grey mold Botryotinia fuckeliana (de Bary) Whetzel Helotiales (A)<br />

Sphaeropsis shoot-killing of pine Sphaeropsis sapinea (Fr.) Dyko & Sutton Coelomycetes (D)<br />

Pine twisting rust Melampsora pinitorqua E. Rostrup Uredinales (B)<br />

Brunchorstia dieback of conifers Gremmeniella abietina (Lagerb.) Morelet Coelomycetes (D)<br />

Shoot shedding of pine Cenangium ferruginosum Fr. Helotiales (A)<br />

Juniper rust Gymnosporangium sabinae (Dickson) Winter Uredinales (B)<br />

Kabatina shoot killing Kabatina thujae Schneider & Arx Coelomycetes (D)<br />

of Cupressaceae<br />

Pollaccia shoot blight of poplar Venturia macularis (Fr.) E. Müller & Arx Dothideales (A)<br />

Myxosporium twig blight of birch Myxosporium devastans E. Rostrup Coelomycetes (D)<br />

Marssonina leaf and shoot blight Drepanopeziza sphaerioides (Pers.) Höhn. Helotiales (A)<br />

of willow<br />

A ascomycete, B basidiomycete, D deuteromycete<br />

Beech seedling disease is due to Phytophthora cactorum. OtherPhytophthora<br />

species attack chestnuts. Rosellinia quercina, Cylindrocarpon destructans and<br />

Fusarium oxysporum lead to root damage in young oaks.<br />

Forest canopy fungi were investigated by Stone et al. (1996). A total of 344<br />

different morphotaxa of endophytic fungi were isolated from leaves of Theobromae<br />

cacao. Most common were Colletotrichum sp., Xylaria sp. and Nectria<br />

sp. Inoculation of sterile leaves of young cocoa trees with these endophytes<br />

reduced subsequent damage by a parasitic Phytophthora sp. (Kull 2004).<br />

Many species of fungi are capable of causing leaf diseases. Hardwood leaf<br />

diseases showing superficial fungal growth, or swollen, raised, or dead leaf areas,<br />

may be grouped simplistically into leaf spot, blotch, anthracnose, powdery<br />

mildew, leaf-blister, and shot-hole. Conifers may show needle spot, cast, blight,<br />

and rust (Tattar 1978; Stephan 1981; Butin and Kowalski 1989; Stephan et al.<br />

1991). Table 8.1 only lists some fungi causing leaf diseases. Details on a specific<br />

disease may be read in Butin (1995).<br />

Some fungal damages to buds, shoots, and branches are listed in Table 8.2.<br />

8.1.1<br />

Bark Diseases<br />

Some bark diseases caused by fungi are listed in Table 8.3.<br />

Three bark diseases are described in detail.<br />

8.1.1.1<br />

Beech Bark Disease<br />

Beech bark disease (Fig. 8.1) has been known in Europe since about 1849<br />

and was imported to North America (Shigo 1964; Parker 1974; Schütt and<br />

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164 8 Habitat of <strong>Wood</strong> Fungi<br />

Table 8.3. Some bark diseases (compiled from Butin 1995, supplemented from Jung and<br />

Blaschke 2005)<br />

Disease Causal fungus Classification<br />

Phacidium disease of conifers Phacidium coniferarum (Hahn) DiCosmo Helotiales (A)<br />

Spruce bark disease Nectria fuckeliana Booth Hypocreales (A)<br />

Crumenulopsis stem canker Crumenulopsis soraria (P. Karsten) Groves Helotiales (A)<br />

of pine<br />

Pine stem rust Cronartium flaccidum (Alb. & Schwein.) Uredinales (B)<br />

(Resin-top disease) Winter<br />

Endocronartium pini (Pers.) Hiratsuka Uredinales (B)<br />

White pine blister rust Cronartium ribicola J.C. Fischer Uredinales (B)<br />

Larch canker Lachnellula willkommii (R. Hartig) Dennis Helotiales (A)<br />

Beech canker Nectria ditissima Tul. Hypocreales (A)<br />

Beech bark disease Nectria species Hypocreales (A)<br />

Black bark scab of beech Ascodichaena rugosa Butin Rhytismatales (A)<br />

Fusicoccum bark canker of oak Fusicoccum quercus Oudem. Coelomycetes (D)<br />

Chestnut blight Cryphonectria parasitica (Murrill) Barr Diaporthales (A)<br />

Dothichiza bark necrosis and Cryptodiaporthe populea (Sacc.) Butin Diaporthales (A)<br />

dieback of poplar<br />

Canker stain of plane Ceratocystis fimbriata (Ellis & Halstead)<br />

Davidson f. platani Walter Ophiostomatales (A)<br />

Stereum canker rot of Red oak Stereum rugosum (Pers.) Fr. Aphyllophorales (B)<br />

Pezicula canker of Red oak Pezicula cinnamomea (DC.) Sacc. Helotiales (A)<br />

Coral spot Nectria cinnabarina (Tode) Fr. Hypocreales (A)<br />

Sooty bark disease of sycamore Cryptostroma corticale (Ell. & Ev.) Hyphomycetes (D)<br />

Gregory & Waller<br />

Sudden oak death Phytophthora ramarum (Werres, Pythiales (O)<br />

De Cock & Man in’t Veld)<br />

A ascomycete, B basidiomycete, D deuteromycete, O oomycete<br />

Lang 1980; Eisenbarth et al. 2001). It develops particularly on trees older<br />

than 60 years of European Fagus sylvatica and American beech F. grandifolia<br />

by a disturbance of the water regime due to a abiotic/biotic factor complex:<br />

moist site, dry summer, participation of the Beech scale, Cryptococcus fagisuga<br />

(Lunderstädt 2002) and either one of two bark-killing Ascomycetes, in Europe<br />

Nectria galligena and in North America N. coccinea var. faginata (Mahoney<br />

et al. 1999), and possibly of mycoplasmas. Classical pathogenesis is an often<br />

short-lived mass reproduction of the Beech scale, which causes subcortical<br />

changes and subsequent infestation with Nectria. Xylem breeding Trypodendron<br />

domesticum and Hylecoetus dermestoides may follow. The larval galleries<br />

may be subsequently colonized by white-rot fungi. The susceptibility to the<br />

disease is biotically effected, whereby the physiological condition of the tree<br />

and its genetic potential determine the efficacy of the damaging agents (Beech<br />

scale, Nectria spp., beetles, white-rot fungi). The outbreak and/or healing can<br />

be controlled by the site conditions (Braun 1977; Lunderstädt 1992).<br />

The fungus invades the bark that was previously altered by the feeding<br />

activity of the Beech scale. A red-brown to blackish (bark tannic substances)<br />

slimy liquid may ooze from the bark tissue (Wudtke 1991). Under the bark<br />

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8.1 Fungal Damage to Living Trees 165<br />

Fig.8.1. Beech bark disease. a tarry spots on the bark, b occluded bark lesions, c determination<br />

of extent of necrosis by scoring the bark with a timber scribe, d early stage of necrosis,<br />

e late stage with incipient white rot (from Butin 1995, by permission of Oxford University<br />

Press)<br />

develop dark regions with dead cambium to over 1 m in extension. Small<br />

necroses with exposed wood may be closed by callus formation, which leads<br />

to a T-shaped fault in the xylem. Tylosis formation causes wilting. Massive<br />

invasions can result in tree dieback. Larger necroses form infestation gates for<br />

white-rot fungi (Bjerkandera adusta, Fomes fomentarius, Fomitopsis pinicola,<br />

Hypoxylon species, Stereum hirsutum) (Eisenbarth et al. 2001).<br />

8.1.1.2<br />

Chestnut Blight<br />

The Chestnut blight (chestnut bark canker) (Fig. 8.2) is caused by the ascomycete<br />

Cryphonectria parasitica (Halmschlager 1966; Heiniger 1999). The<br />

pathogen was imported on Asian rootstock to New York in 1904 and caused<br />

lethal cankers on more than 3.5 billion susceptible American chestnut trees,<br />

Castanea dentata, across 9 million acres of the eastern US, being there at that<br />

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166 8 Habitat of <strong>Wood</strong> Fungi<br />

Fig.8.2. Pathogenesis of Chestnut blight by Cryphonectria parasitica (translated from<br />

Heiniger 1999, with permission of Swiss Federal Institute for Forest, Snow and Landscape<br />

Research)<br />

time the most important hardwood species. The disease appeared in Europe<br />

first in 1938 in Genoa in the European chestnut sites (Castanea sativa)ofItaly,<br />

then in southern France, Spain, Switzerland (1948), Germany (1992), and Eastern<br />

Europe. The fungus penetrates as a spore by means of wind, rain, insects,<br />

or birds through wounds into the bark until the cambium. Then reddish-brown<br />

bark spots that break to longitudinal fissures, branch-surrounding necroses,<br />

wilt, and death of the affected branch or crown region occur. One- to 2mm-large,<br />

orange-yellow-ochre pustules (conidiomata, ascomata) develop on<br />

the bark.<br />

The disease in Europe does not run however as intensively as in the USA<br />

probably due to lesser aggressive fungal strains. The reduced pathogenicity is<br />

caused by Cryphonectria-hypovirus 1 that infests the fungus, that is, it becomes<br />

lesser virulent and only produces superficial cankers, which soon heal up. The<br />

virusisalsofoundinthenaturalC. parasitica populations in Japan and China,<br />

but not in the North American populations. To limit the distribution of the<br />

fungus in non-infested countries, there are official regulations (European and<br />

Mediterranean Plant Protection Organization) (Heiniger 2003).<br />

Breeding experiments are performed between C. dentata and resistant Asian<br />

species. There are also attempts on a biological control based on vegetative<br />

pairing of hypo-virulent fungal isolates with virulent strains. Infested sites<br />

are inoculated with hypo-virulent isolates that can transfer the virus in the<br />

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8.1 Fungal Damage to Living Trees 167<br />

pathogen if both belong to the same vegetative compatibility group (Haller-<br />

Brem 2001). There are biotechnological attempts for transgenic chestnut trees<br />

(Gartland and Gartland 2004).<br />

8.1.1.3<br />

Plane Canker Stain Disease<br />

The Plane canker stain disease (plane tree canker) (Fig. 8.3) is caused by the<br />

ascomycete Ceratocystis fimbriata f. sp. platani (Wulf 1995). The disease was<br />

for the first time observed on Platanus species in 1926 in the eastern USA<br />

and occurred in the 1940s in Europe [France, Italy, Spain, Switzerland, Turkey;<br />

Clerivet and El Modafar (1994)]. About 80% of the city-trees along motorways<br />

became destroyed until 1950 in the USA. Marseille lost over 1,500 100-year-old<br />

plane trees in 12 years. The fungus penetrates through wounds predominantly<br />

after pruning, more rarely by insects, into the bark of the stem and the branches<br />

and leads to cambium dying and elliptical bark necroses. Later, it colonizes<br />

the outer sapwood with bluish-brown discoloration. Excretion of toxins by<br />

the fungus and tyloses effect wilting of individual crown portions. Thus, the<br />

fungus both produces a bark and a wilt disease (Butin 1995). The trees die<br />

usually within 3–6 years. Reproduction organs are predominantly found on<br />

Fig.8.3. Plane canker stain disease. a Symptoms on plane, b stem cross section showing<br />

stained wood, c tangential stem section showing the stain as streaks, d phialide with conidia<br />

of the Chalara anamorph, e conidiophore with chlamydospores, f perithecium, g ascospores<br />

(from Butin 1995, by permission of Oxford University Press)<br />

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168 8 Habitat of <strong>Wood</strong> Fungi<br />

cut sections of debranched or felled trees: perithecia with ascospores and three<br />

different anamorphs, e.g., Chalara. Necroses can by secondarily colonized by<br />

other fungi (Chondrostereum purpureum, Schizophyllum commune).<br />

Transfer may be reduced by hygienic measures like removal of infested trees.<br />

National and EC regulations have to be considered.<br />

8.1.2<br />

Wilt Diseases<br />

Diseases that affect the vascular system of a plant are called wilt diseases.<br />

A fungus causes moisture stress that leads to wilting, killing of large branches<br />

and even entire trees (Tattar 1978). Two important wilt diseases caused by<br />

fungi are Dutch elm disease and Oak wilt.<br />

8.1.2.1<br />

Dutch Elm Disease<br />

Dutch elm disease (“elm dying”) (Fig. 8.4) is caused by the ascomycetous<br />

fungus Ophiostoma ulmi s.l. (Gibbs 1974; Rütze and Heybroek 1987; Sinclair<br />

et al. 1987; Ouellette and Rioux 1992; Butin 1995; Harrington et al. 2001;<br />

Kirisits et al. 2001; Nierhaus-Wunderwald and Engesser 2003). The pathogen<br />

is composed of two separate species or three subgroups: the non-aggressive<br />

(NAG) subgroup, referred to as O. ulmi, and the two races, Eurasian (EAN) and<br />

North American (NAN), of the aggressive subgroup, referred to as O. novoulmi<br />

(Brasier 1999). The disease was probably imported from East Asia around<br />

1917 over France into the Netherlands in 1919 (NAG), where 1920/21 the first<br />

comprehensive investigations took place, so that the disease was called Dutch<br />

elm disease. In 1923, it had arisen for the first time in England, 1930 via veneer<br />

wood in the USA, 1934 in almost all European countries and 1939 in the former<br />

Soviet Union (Heybroek 1982). Between 1940 and 1960 it receded, but again<br />

a new aggressive eastern race (EAN), probably from Romania/Ukraine, spread<br />

westward over the whole of Europe and eastward to middle Asia. Assumably<br />

after the import to North America, there the aggressive western race (NAN)<br />

shall have developed and imported to Great Britain (Röhrig 1996).<br />

The wood loss in an economical view is very great. Altogether, hundreds of<br />

millions of decade- to centuries-old elm trees in Europe, North America, and<br />

in parts of Asia were destroyed. About 25 million elms died since the 1970s in<br />

England (Wörner 2005), and in Utrecht and Amsterdam, half of all the elms<br />

died.<br />

Scolytid bark beetles are the principal agents of the long-distance transmission<br />

introducing the pathogen into healthy trees during adult feeding. In<br />

Europe, the principal vectors are Scolytus scolytus and S. multistriatus, but also<br />

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8.1 Fungal Damage to Living Trees 169<br />

Fig.8.4. Pathogenesis of Dutch elm disease (translated from Nierhaus-Wunderwald and<br />

Engesser 2003, with permission of Swiss Federal Institute for Forest, Snow and Landscape<br />

Research)<br />

other vector species are recognized (Wingfield et al. 1999). In North America,<br />

vectors are the imported S. multistriatus and the American elm bark beetle<br />

Hylurgopinus rufipes. The females select almost exclusively diseased, dying, or<br />

already dead elms for their breeding galleries. The larvae take up the pathogen,<br />

which is passed on alive via the pupa to the young beetle. The young beetles<br />

contaminated with spores (conidia or ascospores) infect healthy trees in twig<br />

crotches of small branches during maturation feeding. Since this bark is too<br />

thin for oviposition, the beetles leave the healthy tree and use the thick-barked<br />

parts of diseased elms for their breeding galleries. The change between the stem<br />

of infected elms and the branches of healthy trees makes the Scolytus beetles<br />

effective vectors (v. Keyserlingk 1982). Root graft transmission via connections<br />

from adjacent trees is the major cause of elm death in urban areas.<br />

The principal reaction compounds developing in elms following invasion<br />

by the fungus are cadinane sesquiterpenoids [mansonones, elm phytoalex-<br />

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170 8 Habitat of <strong>Wood</strong> Fungi<br />

ins; e.g., Meier and Remphrey (1997)]. Barrier zones containing starch-filled<br />

parenchyma and swollen ray parenchyma have also been observed. During<br />

pathogenesis, the fungus develops within the xylem vessels with associated<br />

tyloses and vessel plugging, ultimately resulting in the wilt syndrome<br />

(Smalley et al. 1999), promoted by fungal toxins (cerato-ulmin) (Brasier et al.<br />

1990). A branch cross section shows dark spots in the earlywood, which form<br />

brownish longitudinal strips in the tangential plane. An infection with a nonaggressive<br />

strain can be buried by new annual rings (chronic form); an aggressive<br />

strain grows through the annual ring borders (acute form), and the tree<br />

can die within 2 years.<br />

The use of pheromones as an attractant does not cover all beetles. Fungal<br />

inhibitors such as benomyl only result in a dilatory effect. There were attempts<br />

of a biological control with the bacterium Pseudomonas syringae van Hall and<br />

with Trichoderma species (Aziz et al. 1993). Mansonones inhibited the growth<br />

of O. ulmi in vitro. Control measures are felling of infected or weakened trees as<br />

well as debarking and burning the bark and thicker branches in order to reduce<br />

the beetle population. In view of resistance to the pathogen, the major sources<br />

of genes for resistance are possessed by Asiatic elms. The responses of the European<br />

and North American elms vary depending on the individual subgroups<br />

of the pathogen. Classical breeding for resistance by selection of individuals<br />

from native populations have been made since the 20s, and hybrid elms have<br />

been bred, incorporating natural resistance from Asian elms. There are indications,<br />

which are based on DNA techniques, that most of the English elms,<br />

Ulmus minor var. vulgaris, are clones deriving from an Italian tree exported<br />

by the Roman agronomist Columella from Latium via Spain to England. That<br />

would explain the observed small genetic diversity within the English elms<br />

and thus their high susceptibility to the pathogen (Wörner 2005). Currently,<br />

two biotechnological approaches are pursued: Double-stranded RNA viruses,<br />

known as d-factors, may have the potential to reduce aggressivity if introduced<br />

into a fungal population at large in sufficient quantities to become established<br />

and spread through fungal populations. Transgenic Ulmus procera trees have<br />

been produced using Agrobacterium rhizogenes (Riker et al.) Conn and A.<br />

tumefaciens as mediator, demonstrating that a variety of exogenous genes can<br />

be expressed in regenerant elms (Gartland and Gartland 2004).<br />

8.1.2.2<br />

Oak Wilt Disease<br />

The North American oak wilt (Fig. 8.5; Rütze and Liese 1980, 1985a; Sinclair<br />

et al. 1987) is a vascular disease that is endemic among oaks in the USA and<br />

caused by the ascomycete Ceratocystis fagacearum. It was recorded for the first<br />

time in Minnesota in 1928, Wisconsin in 1942, already in 1979 in 21 US states<br />

east of the Great Plains and is now also found in Texas and Tennessee. The<br />

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8.1 Fungal Damage to Living Trees 171<br />

fungus can both infect red oaks (Quercus falcata var. pagodaefolia, Q. rubra,<br />

Q. shumardii)andwhiteoaks(Q. alba, Q. bicolor, Q. macrocarpa, Q. michauxii,<br />

Q. muehlenbergii). Red oaks become systematically infected and die quickly,<br />

mostly within the year of first wilting symptoms and sometimes within a few<br />

weeks after infection. The economically more important white oaks are more<br />

resistant and show the damage often being restricted to just a few branches.<br />

The lower susceptibility of the white oak is attributed to smaller earlywood<br />

vessel diameter, more intensive tylosis formation resulting in a slower spread<br />

of the fungus in the tree and the ability to “bury” infected tissue by a new<br />

annual ring.<br />

The infection usually occurs via root graft transmissions between the diseased<br />

and healthy trees (Fig. 8.5a), so that the distribution is low with 1 to 2 m<br />

(maximum 8 m) per year. Local spreading via root grafts can be inhibited by<br />

ditches. The fungus invades the vessels of the youngest two annual rings and<br />

stimulates the adjacent parenchyma cells to tylosis formation. Thus, wilt and<br />

defoliation occur in the undersupplied crown regions. Additionally, wilt toxins<br />

are produced. The leaves become flabby and discolor, are light green from the<br />

edge, and later bronze-brown in red oak and pale-light brown in white oak.<br />

After tree death, the hyphae grow inward in the sapwood as well as outward<br />

Fig.8.5. Transmission of the Oak wilt<br />

fungus, Ceratocystis fagacearum, via<br />

root-grafts (a), during maturation feeding<br />

of bark boring beetles (b), and from<br />

sporulating mat by sap feeding nitidulids<br />

(c) (from Rütze and Parameswaran 1984)<br />

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172 8 Habitat of <strong>Wood</strong> Fungi<br />

through the cambium under the bark. In the cambial layer particularly in red<br />

oak, 5 to 8-cm-large sporulation mats (usually conidia) develop from May<br />

to October, which cause bark detachment and fissure by means of pressure<br />

cushions.<br />

There are two different ways for long-distance transmission by insects (about<br />

100 m/year): First, oak bark beetles (Pseudopityophthorus spp.) breed in dying<br />

or dead oaks, and the young beetles transfer the pathogen during the maturation<br />

feeding on shoots and twigs of healthy oaks (Fig. 8.5b). Since asexual<br />

spores do not develop in the larval galleries, this transmission way has only<br />

less significance. Second, sap beetles, particularly Nitidulidae, are attracted by<br />

the smell of the sporulating mats and transmit infectious material to healthy<br />

trees into fresh wounds, attracted by their smell (Fig. 8.5c) (Appel et al. 1990).<br />

The nitidulids effect that the bipolar heterothallic fungus is dikaryotized and<br />

develops ascospores, if conidia with contrary mating factor were introduced<br />

from other sporulation mats. Since wounds are infectious only a few days in<br />

healthy oaks, this infection way has also less significance. Furthermore, the<br />

subcortical mats of C. fagacearum were observed to be rapidly overgrown by<br />

Graphium pyrinum Goid. (anamorph of Ophiostoma piceae). This colonization<br />

reduces the chance of contamination of the insect vectors with spores of the<br />

pathogen and is likely to contribute to the low efficacy of insect transmission<br />

(Rütze and Parameswaran 1984).<br />

Since 1951, the import of unpeeled oak logs from North America to Germany<br />

was allowed according to a plant protection order, if the wood derives<br />

from healthy areas (“white counties”), in accordance with the plant protection<br />

departmentoftheUSDepartmentofAgriculture.Ithadhowevertobeconsidered<br />

that also the European oaks, although usually white oaks (Quercus petraea<br />

and Q. robur), are more susceptible from nature and that the European oak<br />

bark beetle Scolytus intricatus is more aggressive in its transmission behavior<br />

than the North American species. In order to prevent the import of the fungus<br />

(Gibbs et al. 1984), oak wood became subject to specific treatment requirements<br />

under Council Directive 77/93/EC including bark removal, kiln drying,<br />

etc.Sincesuchwoodcannotbeconvertedtoveneers,thosemeasureswould<br />

have equaled practically an import stop for oak logs and the endangerment of<br />

the European veneer industry. Thus, experiments were performed in a cooperative<br />

venture between the Federal Research Center for Forestry and Forest<br />

Products Hamburg and the Universities of Minnesota and West Virginia on log<br />

fumigation with bromomethane (methyl bromide) as a means of ensuring that<br />

thelogswerefreefromC. fagacearum (Liese et al. 1981; Schmidt 1988). The<br />

European community permitted by EEC Plant protection guidelines of 1978<br />

the import of unpeeled oak logs if they were disinfected before export with<br />

240 g bromomethane per m 3 of wood for 3 days at a minimum temperature<br />

of 3 ◦ C in plastic tents (Rütze and Liese 1983). The use of bromomethane has<br />

fallen off considerably since the Montreal Conference of 1997 because of its<br />

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8.2 Tree Wounds and Tree Care 173<br />

destruction to the ozone layer. Log fumigation needs an exemption. In Europe,<br />

to monitor that sufficient bromomethane fumigation of the oaks has been carried<br />

out, the TTC test (Brunner and Ruf 2003) is suitable. The test is based on<br />

the fact that the gas kills not only the oak wilt fungus but also the living cells<br />

of oak sapwood. These cells would survive for several months in logs that are<br />

not treated with gas. Increment cores of the whole sapwood are treated with<br />

a 1% solution of 2,3,5-triphenyl-2H-tetrazolium chloride (colorless), which<br />

discolors dark red to triphenylformazan in contact with living cells by their<br />

dehydrogenase activity (Rütze and Liese 1985b).<br />

Fumigation with bromomethane has also been applied to four pathogenic<br />

fungi in larch heartwood (Rhatigan et al. 1998). Due to the pending restrictions<br />

of bromomethane for phytosanitation in general, the potential substitution by<br />

sulfuryl fluoride and iodomethane was investigated (Schmidt et al. 1997c,<br />

Unger et al. 2001).<br />

There are privileges of the import regulations for the fewer endangered white<br />

oak: no fumigation during winter months, however immediate debarking and<br />

burning of the bark as well as immediate wood processing. Since the wood of<br />

both oak groups is hardly or not at all to differentiate by appearance, a color<br />

test is suitable: When sprayed on the heartwood of any species of white oak<br />

a sodium nitrite solution produces a blue-black color within a few minutes,<br />

whereas the color is a reddish brown in red oak (Willeitner et al. 1982).<br />

The possible oak wilt transmission to Europe was discussed several times<br />

in connection with the increasing illness of European oaks (Siwecki and Liese<br />

1991). These damages develop however due to a complex effect of abiotic factors<br />

(dryness and pollutants as predisposing factors, severe winter frost as acute<br />

stressor) and biotic influences (leaf-eating insects, nematodes, phytoplasmas,<br />

and Armillaria spp. as weakness parasites, other Ceratocystis species, other<br />

fungi.) The literature on the role of pathogens in the present oak decline in<br />

Europe has been compiled by Donaubauer (1998).<br />

8.2<br />

Tree Wounds and Tree Care<br />

8.2.1<br />

Wounds and Defense Against <strong>Discoloration</strong> and Decay<br />

Initiation for discolorations and decay are predominantly wounds that are<br />

frequently caused by animals chewing, branch breaking, pruning, mechanized<br />

wood harvest, construction injury, and motor traffic (Tattar 1978).<br />

Rots in living trees might occur fast or result from processes of many years,<br />

which frequently remain hidden for a long time, until fruit bodies appear, or<br />

the tree is broken, thrown by the wind, or felled.<br />

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174 8 Habitat of <strong>Wood</strong> Fungi<br />

After wounding, tree-own discolorations (deposition of heartwood substances)<br />

develop by living cells, followed by microbial stain and finally by<br />

wood rot (Shigo and Hillis 1973; Hillis 1977; Shortle and Cowling 1978; Bauch<br />

1984; Rayner and Boddy 1988; Fig. 8.6).<br />

Depending on the fungus and tree species, brown, white, or even soft-rot<br />

decay can develop in the tree. Sapwood and/or heartwood can be colonized.<br />

Fungi may be saprobionts of parasites. Development and spread of decay are<br />

influenced by the tree species, which can be susceptible, like birch or poplar,<br />

or exhibits natural durability in its heartwood due to inhibiting accessory<br />

compounds.<br />

It has to be distinguished between passive mechanisms, which are already<br />

present before damage, and active defense mechanisms, which trees trained in<br />

the course of their phylogenetic development to limit wounds, infections, and<br />

senile damages (Blanchette 1992; Duchesne et al. 1992; Rayner 1993).<br />

After the xylem is wounded, two defense functions have to be differentiated:<br />

First, the tree must avoid an interruption of the transpiration stream by air<br />

embolism, and second, limit the spread of invaded microorganisms (Liese and<br />

Dujesiefken 1996).<br />

When a softwood tracheid is injured, its lumen is filled with air at ambient<br />

pressure. Thus, a pressure drop exists across the pit membranes of the watercontaining<br />

neighboring tracheids. Their tori are therefore pulled against their<br />

pit borders, and the air-blocked tracheid is thus sealed off from the waterconducting<br />

tracheids (Zimmermann 1983). Conifers protect themselves from<br />

Fig.8.6. Model of successive changes in<br />

the stem wood after prior injury to the<br />

bark. w wound, c callus margin, f fruit<br />

body, b barrier zone, r rot, m microbial<br />

wood discoloration, t tree-own wood<br />

discoloration (after Shigo 1979)<br />

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8.2 Tree Wounds and Tree Care 175<br />

wounds and penetrating microorganisms by phenolic compounds, terpenoids,<br />

and resin (Tippett and Shigo 1981).<br />

In hardwoods, the defense reactions depend on physiologically active parenchyma<br />

cells. The water-conducting system is protected against damage by<br />

tyloses, plugs or membranes, and phenolic substances or suberin are deposited<br />

on the cell wall or in the lumen (Schmitt and Liese 1993).<br />

For the graphic understanding of the spatial cut off within a tree, Shigo<br />

developed the CODIT model (Fig. 8.7; Shigo and Marx 1977; Shigo 1984),<br />

which stands for “compartmentalization of decay in trees”. The model means<br />

that the tree protects itself from penetrating microorganisms by four inhibiting<br />

walls and that the spatial expansion of discoloration and decay is determined<br />

by the anatomical structure of the wood. The axial “walls 1” with the weakest<br />

partitioning effect are formed by the closure of the vessels and pits above and<br />

underneath a wound by gums and tyloses. The tangential “wall 2” stem-inward<br />

occurs by the annual ring borders and by the sapwood/hardwood boundary.<br />

The radial “walls 3” are caused by the lateral wood rays. The most effective<br />

compartmentalization is by “wall 4”, also termed barrier zone, formed by the<br />

cambiumaftertheinjurywithincreasedparenchymacontent.<br />

The CODIT model interprets the tree-own reactions as compartment formation<br />

against microorganisms. It seems, however, more biological that the<br />

tree protects itself first from penetrating air, particularly since wood fungi<br />

can only settle the tissue if air is present. With changed definition, the term<br />

CODIT has been expanded by Liese and Dujesiefken (1989, 1996): the D does<br />

not only stand for decay, but also for damage and covering desiccation as well<br />

as dysfunction.<br />

The histological changes that occur in wood and bark as wound reactions<br />

in hardwoods are schematically shown in Fig. 8.8.<br />

The parenchyma cells die at the surface of the damaged wood area. The<br />

tissue beneath the wound plane also dies, without mobilizing reserve materials,<br />

Fig.8.7. CODIT model with walls 1 to 4<br />

(after Shigo 1979)<br />

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176 8 Habitat of <strong>Wood</strong> Fungi<br />

Fig.8.8. Changes in the xylem and phloem of hardwoods after wounding (after Liese and<br />

Dujesiefken 1989)<br />

since the defense reactions in the wood begin temporally retarded. In this<br />

bright zone of about 1 cm, the vessels remain open, and the lumina do not<br />

contain inclusions. With increasing distance to the wound, reserve material<br />

is mobilized, and the vessels are closed. In beech, the degeneration of the<br />

parenchyma is limited, as parenchyma cells in the wounded area are divided<br />

by transverse walls and limit the damage by suberization of the wound-near<br />

compartments (Schmitt and Liese 1993).<br />

A closure by tyloses (Schmitt and Liese 1994) only takes place in tree species,<br />

which possess pit sizes of at least 8µm. Trees without tyloses, like lime and<br />

maple, can prevent air embolism by blocking the vessels with plugs. In birch,<br />

the ladder-shaped vessel openings are closed on one side by membranes, and<br />

parenchyma cells excrete fibrillar material in neighboring vessels and fibers<br />

(Schmitt and Liese 1992a).<br />

The tissue behind the wound area, which is discolored by means of accessory<br />

compounds and which contains died parenchyma cells and vessels<br />

out of function, had been termed protection wood. As it is colonized however<br />

frequently by fungi, it obviously does not possess increased durability.<br />

The healthy wood outside this area shows microscopically in an area of a few<br />

millimeters mobilization of reserve material and vessel closure, but no fungi,<br />

so that the actual protective layer obviously lies outside of the visible discoloration.<br />

Also in the phloem the parenchyma dies at the wound surface and the<br />

tissue beneath is set out of function. A wavy-shaped wound periderm, which<br />

attaches the periderm of the young callus bark to the outer bark, develops in<br />

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8.2 Tree Wounds and Tree Care 177<br />

the transition of the discolored to the functional phloem (Trockenbrodt and<br />

Liese 1991).<br />

The cambium reacts to the damage at the wound margin with intensified<br />

cell formation (callus) to overwall the opened wood body (Stobbe et al. 2002a).<br />

The wound wood, which is later formed outside the callus, effectively limits<br />

discoloration and decay outward.<br />

8.2.2<br />

Pruning<br />

Forest tress are pruned to produce high-class timber, trees in urban areas are<br />

pruned for safety reasons and along motorways and power-lines for clearance.<br />

Each cut causes a wound, which leads in the exposed wood to discoloration<br />

and decay (Fig. 8.9).<br />

Until the 80s in Germany, the flush cut had been regarded as the correct<br />

method when removing a branch back at the stem. Studies on the pruning<br />

of hardwoods carried out by Shigo and staff (Shigo 1989) caused confusion.<br />

Comparing the effects of different cut locations of a total of 750 pruning<br />

wounds on 115 street and park trees led to the Hamburg Tree Pruning System<br />

(Dujesiefken and Stobbe 2002), which is integrated since 1992 into the<br />

German rules and regulations for tree care methods. The recommendations<br />

Fig.8.9. <strong>Discoloration</strong> reaching far into<br />

thestemofhorsechestnut9years<br />

after flush cut pruning (a); reduced<br />

discoloration after a branch collar cut<br />

(b) (from Dujesiefken and Stobbe 2002)<br />

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178 8 Habitat of <strong>Wood</strong> Fungi<br />

for branches without branch collar are also part of the European Tree Pruning<br />

Guide. According to the branch attachment (branches with or without a collar),<br />

the cut has to be done outside the stem so that the branch bark ridge is not<br />

damaged. Flush cuts have to be avoided. When pruning dead branches, the<br />

distinctive swelling at branch base must remain at the stem. Regardless of the<br />

time of year and the tree species, radical tree pruning, e.g., a drastic removal<br />

of crown parts, should not be done. If possible, branches greater than 5 cm<br />

in diameter of weak compartmentalizing trees (e.g., Aesculus, Betula, Malus,<br />

Populus, Prunus, Salix), and greater than 10 cm of strong compartmentalizing<br />

trees (e.g., Carpinus, Fagus, Quercus, Tilia) should only be reduced partially<br />

rather than completely.<br />

For organizational reasons and due to nature protection laws, pruning is<br />

usually done during the dormant season. However, wounding of maple, birch,<br />

beech, oak, ash, lime tree and spruce showed on the basis the intensity of<br />

the wood discolorations that injuries should be avoided in hardwoods during<br />

the dormant stage and in spruce from late summer to winter due to different<br />

wound reactions (Lenz and Oswald 1971; Armstrong et al. 1981; Dujesiefken<br />

et al. 1991; Schmitt and Liese 1992b).<br />

8.2.3<br />

Wound Treatment<br />

In the 50s and 60s, large stem wounds were shaped out and filled with concrete.<br />

Since concrete and wood shrink and extend differently under weather<br />

influence, shakes develop, water penetrates and leads to rot. Since the 70s, the<br />

cleaned wounds were treated with wound dressings or with wood preservatives.<br />

Disinfection of the opened wood body with ethanol or alcoholic iodine<br />

solutionbeforewoundtreatmentdidnotledtoapreventionofdiscoloration<br />

and decay in beech and ash (Dujesiefken and Seehann 1995). The use of wood<br />

preservatives was disputed for tree care measures, as they are not developed for<br />

theprotectionoftreewounds.Thetreatmentofartificialwoundswithwood<br />

preservatives resulted in beech in more intensive discolorations behind the<br />

wound area than at wounds, which were only treated with wound dressings.<br />

Wound dressings belong to the plant preservatives. In Germany, they must<br />

be tested according to efficacy and environmental compatibility to become<br />

licensed (Balder 1995).<br />

Alternatively, cavities can be foamed with polyurethane (Dujesiefken and<br />

Kowol 1991). Figure 8.10 shows reduced discoloration in a beech tree after<br />

filling the wound with polyurethane.<br />

Currently, traffic wounds on street trees are covered by black plastic wraps,<br />

which promote the development of a surface callus overgrowing the wound<br />

area (Fig. 8.11).<br />

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8.2 Tree Wounds and Tree Care 179<br />

8.2.4<br />

Detection of Tree and <strong>Wood</strong> Damages<br />

Fig.8.10. <strong>Discoloration</strong> of beech at the<br />

control wound protected with wound<br />

dressing (a) and at the cavity filled with<br />

polyurethane (b) (from Dujesiefken and<br />

Kowol 1991)<br />

To investigate trees with regard to microbial damage, particularly to detect decay,<br />

discolorations, cavities, shakes and generally pathological changes, as well<br />

as to determine wood quality in felled timber, construction wood and woodbased<br />

composites, numerous methods are available. Inspection methods were<br />

described by McCarthy (1988, 1989), Zabel and Morrell (1992), Niemz et al.<br />

(1998), Londsdale (1999), Harris et al. (1999), Unger et al. (2001). Methods<br />

can be classified as destructive, nondestructive, or near-nondestructive. They<br />

reach from technically simple procedures like using increment bore tools to<br />

expensive equipment like computer tomography (Habermehl and Ridder 1993;<br />

Habermehl 1994) as well from subjective visual inspection to objective molecular<br />

techniques. In view of tree care, noninvasive or less destructive methods are<br />

preferable (Niemz et al. 1999; Kaestner and Niemz 2004). Modern techniques<br />

for nondestructive characterization and imaging of wood were reviewed by<br />

Bucur (2003) and comprise ionizing radiation computed tomography, thermal<br />

imaging, microwave imaging, ultrasonic imaging, nuclear magnetic resonance<br />

and neutron imaging. Some methods are preferentially used for trees, others<br />

for lumber, some may be used on the spot, others are pure laboratory tech-<br />

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180 8 Habitat of <strong>Wood</strong> Fungi<br />

Fig.8.11. Use of a plastic wrap to improve<br />

the development of a surface callus.<br />

a Fresh, cleaned wound. b Wound<br />

covered with a black plastic wrap.<br />

c After9weeksnearlyhalfofthewound<br />

coveredwithabrightsurfacecallus<br />

tissue (from Stobbe et al. 2002b)<br />

niques, and some of the latter are capable to identify the causal agent. Due<br />

to some overlapping in their use, the methods are listed together in Table 8.4.<br />

Limits of ultrasonic evaluation of wood defects have been shown by v. Dyk and<br />

Rice (2005). There is a great bulk of references on the various techniques; thus,<br />

only examples are given in Table 8.4.<br />

The earliest nondestructive evaluation of trees is the visual inspection of<br />

the tree condition (growth, foliation, wilt) and occurrence of wounds, resin<br />

excretion, necrosis, canker, or fruit bodies. Visual inspection is also applied<br />

for lumber, poles, and wood in indoor use. Fruit bodies might serve to identify<br />

the causal agent. This visual inspection is by definition neither objective nor<br />

sure. Olfactory detection is done by the use of sniffer dogs that detect dry rot<br />

(Koch 1991), molds, or termites (Zabel and Morrell 1992).<br />

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8.2 Tree Wounds and Tree Care 181<br />

Table 8.4. Inspection methods for fungal activity and wood quality in trees and timber<br />

Method Procedure Advantage, disadvantage Reference<br />

Optical Visual Non-destructive, in situ, subjective<br />

Endoscopy Hidden spaces in buildings, bore holes may be required Janotta (1995)<br />

Rhizoscopy Root system Seufert et al. (1986)<br />

Light microscopy Simple, destructive Schwarze et al. (1997), Anagnost (1998)<br />

Electron microscopy Accurate, photographic record, destructive Liese (1970), Daniel (2003)<br />

IR/NIR/FTIR spectroscopy Laboratory method, printed record Körner et al. (1992), Schwanninger et al. (2004)<br />

UV microspectrophotometry Laboratory method, 3D wood topochemistry Koch and Kleist (2001)<br />

Raman spectroscopy Laboratory method, wood topochemistry Röder et al. (2004)<br />

Spectrometrical GC-MS Laboratory method, MVOC’s, mold and rot detection Keller (2002), Blei et al. (2005)<br />

MALDI-TOF MS Laboratory method, fungal identification Schmidt and Kallow (2005)<br />

Acoustic Speed of ultrasound (Impulse hammer) Non-destructive, in situ, density of sound wood must be known Rust (2001), Niemz et al. (2002)<br />

Acoustic emission Non-destructive, in situ Noguchi et al. (1992)<br />

Electrical Electrical resistance, conductivity Shigo et al. (1977), Kučera (1986)<br />

(Shigometer, Vitamat) Less destructive, in situ, handy devices Larsson et al. (2004)<br />

Nuclear magnetic resonance Non-destructive, not transportable, expensive Müller et al. (2002)<br />

Radar Ground penetrating radar for root investigation, in situ Barton and Montagu (2004)<br />

Microwaves Non-destructive Takemura and Taniguchi (2004)<br />

Mechanical Increment cores Handy instruments, low cost, destructive Niemz et al. (1998)<br />

Needle penetration (Pilodyn) Handy instruments, low cost, nearly non-destructive Niemz and Kučera (1999)<br />

Drill resistance (Resistograph) Portable instruments, printed data plots, destructive Rinn (1994), Isik and Li (2003)<br />

Thermographic Heat radiation Non-destructive, handy instruments, resolution insufficient Niemz et al. (1998)<br />

Radiographic X-ray, γ-ray computed tomography Non-destructive, in situ, expensive Habermehl (1994)<br />

Calorimetric Isothermal microcalorimetry Laboratory method, non-destructive Xie et al. (1997)<br />

Microbiological Culturing to pure culture Laboratory method, fungal identification<br />

Biochemical CO2 Laboratory method, fungal activity Kirk and Tien (1986)<br />

ATP Laboratory method, fungal activity McCarthy (1983), Bjurman (1992a)<br />

Chitin Laboratory method, fungal quantification Nilsson and Bjurman (1998)<br />

Ergosterol Laboratory method, fungal quantification Pasanen et al. (1999), Dawson-Andoh (2002)<br />

pH-value Non-destructive, fungal activity, brown/white rot differentiation Peek et al. (1980)<br />

Sniffer dogs Non-destructive, detection of dry rot, molds Koch (1991), Keller et al. (2004)<br />

Molecular Protein gel electrophoresis Laboratory method, fungal identification Schmidt and Kebernik (1989), Vigrow et al. (1989)<br />

Immunology Laboratory method, early decay, fungal identification Vigrow et al. (1991a,b), Clausen (1997a)<br />

DNA-based methods Laboratory method, fungal identification, objective White et al. (2001), Schmidt (2000)<br />

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182 8 Habitat of <strong>Wood</strong> Fungi<br />

The type and intensity of a biological attack can be recognized by different<br />

macromorphologic changes of the wood tissue. Typical discolorations occur<br />

on and inside wood that is colonized by molds, blue stain, and red-streaking<br />

fungi. Brown- and soft-rotten woods differ in color and shape of the brown<br />

and soft-rotten cubes, and white-rotten wood between simultaneous and white<br />

pocket rot.<br />

Various mechanical and physical wood changes occur when wood-inhabiting<br />

microorganisms colonize wood. <strong>Wood</strong> mass (weight) loss is a commonly<br />

used measure of decay capability. The basic calculation is: [(weight before −<br />

weight after): weight before] ×100%. The extent of decay in a specimen that<br />

was sampled from attacked wood can be determined the same way, if its dry<br />

weight is compared to that of a comparable healthy control: mass loss ML<br />

(%) = [(DW1 −DW2) :DW1] × 100 (DW1 = dry weight of control, DW2 =dry<br />

weight of decayed sample).<br />

Mass loss of wood samples exposed to fungi is likewise used to determine the<br />

efficacy of wood preservatives and to examine the natural durability of wood<br />

species. There is a permanent discussion if fungal pure cultures or artificial<br />

mixed cultures should be used in laboratory tests (Kolle flask method, soilblock<br />

test, vermiculite method) or if soil contact decay tests are preferable.<br />

Laboratory tests are reproducible as they are based on defined test fungi.<br />

Field stake tests result in a severe exposure condition as the natural microbial<br />

composition may contain microorganisms that degrade wood, biodegrade<br />

organic wood preservatives or modify inorganic preservatives making them<br />

more susceptible to leaching (Nicholas and Crawford 2003). In Europe, the<br />

Kolle flasks method with malt extract agar and defined wood blocks of 5 ×<br />

2.5 × 1.5 cm in size from Scots pine sapwood and European beech is used for<br />

Basidiomycetes according to the standard EN 113 (Fig. 7.5; Table 7.6). In this<br />

method, specified isolates of certain fungal species, e.g., Coniophora puteana<br />

Ebw. 15, have to be used. The wood decay capacity of the test organisms is,<br />

however, erroneously named “virulence”, although it concerns fungi and not<br />

viruses.Soft-rotfungi tests are performedinplasticcontainers with vermiculite<br />

(grainy substance of aluminum iron magnesium silicate) as moisture and<br />

nutrient depot. The standard soil block test AWPA E10 uses either 14-mm or<br />

19-mm wood cubes that are exposed to white- and brown-rot fungi that were<br />

previously inoculated onto wood wafers on top of a sterile moist soil bed in<br />

a bottle. Soil bed testing based on the methodology described in the European<br />

Pre-standard ENV 807 uses 100 mmlong ×10mmrad ×5mmtang specimens that<br />

are exposed to the naturally soil-inhabiting microorganisms (v. Acker et al.<br />

2003). Field stake tests use stakes or posts of the selected wood species that<br />

are half buried vertically in soil and inspected for decay at intervals. <strong>Wood</strong><br />

assembly above-ground tests (post-rail, L-joint, lap-joint), all including some<br />

type of joint that effectively traps rainwater, simulate decking, door frames or<br />

joinery (Zabel and Morrell 1992; Nicholas and Crawford 2003).<br />

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8.3 Tree Rots by Macrofungi 183<br />

The degree of wood decay can be quantified by changes in wood strength<br />

properties, modulus of rupture, work to maximal load in bending, maximal<br />

crushing strength, compression perpendicular to the grain, impact bending,<br />

tensile strength parallel to the grain, toughness, hardness, and shear strength<br />

(Wilcox 1978; Zabel and Morrell 1992; Nicholas and Crawford 2003).<br />

Isothermal microcalorimetry has been used to determine the activity of<br />

fungi after exposure to high and low temperature, oxygen depletion, and drying<br />

(Xie et al. 1997).<br />

Different stainings detect fungal hyphae and spores in woody tissue (Erb<br />

and Matheis 1983; Krahmer et al. 1986; Weiß et al. 2000). Treatment with<br />

safranine and astra blue stains lignified wood areas red and lignin-free parts<br />

blue, and thus differences between sound and decayed wood may become visible.<br />

Light-microscopic degradation patterns have been summarized (Schwarze<br />

et al. 1997). There is a key to identify wood decays based on light microscopic<br />

features (Anagnost 1998).<br />

Transmission (TEM) and raster electron microscopy (REM) result in detailed<br />

views of the cell wall decay by the various groups of fungi (Liese 1970;<br />

Daniel 1994). UV microspectrophotometry (UMSP) characterizes lignin and<br />

phenolic compounds in situ, determines their content semiquantitatively in<br />

the various layers of the wood cell wall (Koch and Kleist 2001), and has also<br />

been applied to measure lignin content after microbial wood attack (Bauch<br />

et al. 1976; Schmidt and Bauch 1980; Kleist and Seehann 1997; Kleist and<br />

Schmitt 2001). General wood quality, microbial activity in wood, and composition<br />

in fossil specimens may be quantified by chemical analyses of the wood<br />

cell wall components, by UV and IR spectroscopy, and by gas chromatography/mass<br />

spectrometry of lignin components (Faix et al. 1990, 1991; Nicholas<br />

and Crawford 2003; Schwanninger et al. 2004; Uçar et al. 2005).<br />

Biochemical methods to quantify microbial activity comprise assay of chitin<br />

as component of the fungal cell wall (Braid and Line 1981; Vignon et al.<br />

1986; Jones and Worrall 1995; Nilsson and Bjurman 1998) and ergosterol as<br />

fungal membrane component (Nilsson and Bjurman 1990; Pasanen et al. 1999;<br />

Dawson-Andoh 2002).<br />

Molecular methods to detect and identify fungi, like protein gel electrophoresis,<br />

immunology, and DNA-based techniques, are described in<br />

Chap. 2.4.2.<br />

8.3<br />

Tree Rots by Macrofungi<br />

There is a broad spectrum of macrofungi (macromycetes) affecting trees. Most<br />

fungi belong to the Homobasidiomycetes (Table 2.12). About 20 species have<br />

greater economic importance. Among them, the Agaricales are represented<br />

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184 8 Habitat of <strong>Wood</strong> Fungi<br />

by Armillaria. The other important fungi belong to the Aphyllophorales and<br />

there predominantly to the Polyporaceae sensu lato (“polypores”: Ryvarden<br />

and Gilbertson 1993, 1994). These polypores are summarized by the practical<br />

forester as “tree polypores” (Table 8.5; Seehann 1971). Fungi occurring on<br />

park and urban trees have been compiled e.g., by Seehann (1979), Wohlers et<br />

al. (2001), Wulf (2004) and Dujesiefken et al. (2005). Fungi affect predominantly<br />

older hardwoods and conifers of all climate zones. Infection occurs through<br />

wounds (wound parasites). Weakened trees may be more susceptible to fungi<br />

(weakness parasites). However, samples of dead wood from weakened spruces<br />

of different damage classes from forest dieback sites did not show differences in<br />

decayexperimentswith Heterobasidion annosum,Trametes versicolor (Schmidt<br />

et al. 1986), Coniophora puteana, Gloeophyllum abietinum and Oligoporus<br />

placenta (Liese 1986), compared to healthy trees.<br />

Fungi either penetrate via the roots (root rots) or the stem (stem rots).<br />

Root-decay Basidiomycetes are e.g., Armillaria species, Heterobasidion annosum,<br />

Meripilus giganteus, Phaeolus schweinitzii, andSparassis crispa. Among<br />

the Ascomycetes, Rhizina undulata (Pezizales) attacks the roots of spruce,<br />

pine and larch, and Kretzschmaria deusta (Xylariales) invades injured roots<br />

of beech, horse chestnut, elm, lime tree, maple, and plane causing white rot<br />

in the root and the stem (Butin 1995; Schwarze et al. 1995b; Baum 2001).<br />

Some common stem-decay Basidiomycetes in Europe (Butin 1995) and the<br />

USA (Zabel and Morrell 1992) are listed in Table 8.5. Most English names derive<br />

from Käärik (1978), Larsen and Rentmeester (1992) and Rune and Koch<br />

(1992).<br />

Fungi may attack the heartwood (heart rots) and effect thus a considerable<br />

strength and volume reduction of the tree xylem. They cause either brown or<br />

white rot in a several years of development, whereby all combinations between<br />

hardwoods and conifers as well as brown rot and white rot occur. However,<br />

also a soft-rot decay pattern may develop in the standing tree. Tree decay fungi<br />

have great economical importance, since a great part of the wood body can<br />

be devaluated, and felling of infected trees may be necessary. After felling,<br />

windthrow, or death of the tree, some fungi continue growth as saprobes in<br />

the wood for several years, then however usually die, that is, typically they<br />

do not endanger structural timber. The variously sized fruit bodies (basidiocarps,<br />

basidiomata) are either pileate, shelf-shaped, bracket-like, coral-like,<br />

or resupinate (see Fig. 2.17). Shape and size of the pores are distinguishing<br />

features (Breitenbach and Kränzlin 1986; Ryvarden and Gilbertson 1993, 1994;<br />

Krieglsteiner 2000). Beside fungi with annual fruit bodies, species with perennial<br />

basidiomes produce new hymenial layers each year and may become very<br />

large, hard and woody (see Fig. 8.15a).<br />

Daedalea quercina, Fomes fomentarius, Phellinus igniarius, Laetiporus sulphureus,<br />

Piptoporus betulinus, Polyporus squamosus, andMeripilus giganteus<br />

occur predominantly on hardwoods. Heterobasidion annosum, Phaeolus<br />

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8.3 Tree Rots by Macrofungi 185<br />

Table 8.5. Some stem-decay Basidiomycetes<br />

Amylostereum areolatum (Chaill.: Fr.) Boidin white<br />

Armillaria mellea (Vahl: Fr.) Kummer, Honey fungus, and further Armillaria white<br />

species<br />

Bjerkandera adusta (Willd:Fr.)P.Karsten,Smokeypolypore white<br />

Chondrostereum purpureum (Pers.: Fr.) Pouzar, Silver-leaf fungus white<br />

Climacocystis borealis (Fr.: Fr.) Kotl. & Pouzar white<br />

Coniophora arida (Fr.: Fr.) P. Karsten brown<br />

Coniophora olivacea (Fr. Fr. ) P. Karsten brown<br />

Daedalea quercina (L.: Fr.) Fr., Maze-gill brown<br />

Daedaleopsis confragosa (Bolton: Fr.) J. Schröter white<br />

Fistulina hepatica (Schaeffer: Fr.) Fr., Beef-steak fungus brown<br />

Fomes fomentarius (L.: Fr.) Kickx, Tinder fungus white<br />

Fomitopsis pinicola (Sw.: Fr.) P. Karsten, Red-belted polypore brown<br />

Ganoderma adspersum (S. Schulzer) Donk, white<br />

Ganoderma applanatum (Pers.) Pat. white<br />

Ganoderma lipsiense (Batsch) G.F. Atk., Artist’s conk white<br />

Ganoderma lucidum (Curtis: Fr.) P. Karsten white<br />

Grifola frondosa (Dicks.: Fr.) S.F. Gray white<br />

Heterobasidion annosum (Fr.: Fr.) Bref., Root rot fungus white<br />

Inonotus dryadeus (Pers.: Fr.) Murr. white<br />

Inonotus hispidus (Bull.: Fr.) P. Karsten white<br />

Laetiporus sulphureus (Bull.: Fr.) Murr., Sulphur polypore brown<br />

Meripilus giganteus (Pers.: Fr.) P. Karsten, Giant polypore white<br />

Oligoporus stipticus (Pers.: Fr.) Kotl. & Pouzar brown<br />

Onnia tomentosa (Fr.: Fr.) P. Karsten white<br />

Phaeolus schweinitzii (Fr.: Fr.) Pat., Dye polypore brown<br />

Phellinus chrysoloma (Fr.) Donk white<br />

Phellinus hartigii (Allesch. & Schnabl) Pat. white<br />

Phellinus igniarius (L.: Fr.) Quélet, False tinder fungus white<br />

Phellinus pini (Brot.: Fr.) A. Ames, Ochre-orange hoof polypore white<br />

Phellinus pomaceus (Pers.: Fr.) Maire white<br />

Phellinus robustus (P. Karsten) Bourdot & Galzin white<br />

Pholiota squarrosa (Pers.: Fr.) Kummer white<br />

Piptoporus betulinus (Bull.: Fr.) P. Karsten, Birch polypore brown<br />

Pleurotus ostreatus (Jacq.) Kummer, Oyster mushroom white<br />

Polyporus squamosus (Hudson: Fr.) Fr., Scaly polypore white<br />

Resinicium bicolor (Alb. & Schwein.: Fr.) Parm. white<br />

Schizophyllum commune Fr.: Fr., Split-gill white<br />

Sparassis crispa Wulfen: Fr. brown<br />

Stereum rugosum (Pers: Fr.) Fr. white<br />

Stereum sanguinolentum (Alb. & Schwein.: Fr.) Fr., Bleeding Stereum white<br />

Trametes hirsuta (Wulfen: Fr.) Pilát white<br />

Tyromyces caesius (Schrader: Fr.) Murr., Blue cheese polypore brown<br />

Tyromyces stipticus (Pers.: Fr.) Kotl. & Pouzar brown<br />

Xylobolus frustulatus (Pers.: Fr.) Boidin, Ceramic parchment white<br />

Rot<br />

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186 8 Habitat of <strong>Wood</strong> Fungi<br />

schweinitzii, Phellinus pini, and Sparassis crispa inhabit softwoods. Species of<br />

Armillaria attack both tree groups.<br />

Inthefollowing,somecommontreefungiaredescribed,mostlyinnote<br />

form. For details see Seehann (1971, 1979) and textbooks e.g., by Butin (1995),<br />

Breitenbach and Kränzlin (1986, 1991), Rayner and Boddy (1988), Jahn (1990),<br />

Ryvarden and Gilbertson (1993, 1994), Krieglsteiner (2000), and Schwarze et al.<br />

(2004).<br />

8.3.1<br />

Armillaria Species, Honey Fungi<br />

The genus Armillaria (Fr.: Fr) Staude comprises worldwide about 40 species.<br />

The rather similar fungi form rhizomorphs in the soil and beneath the tree<br />

bark, the mycelium shines in the dark, the secondary mycelium is diploid<br />

and normally clampless (Marxmüller and Holdenrieder 2000). There are exannulate<br />

and annulate species (Shaw and Kile 1991; Guillamin et al. 1993).<br />

In Europe, five intersterility groups that had been referred to as A, B, C, D,<br />

E (Korhonen 1978b) within the annulate Armillaria mellea complex were assumed<br />

until the 1980s to be polymorphic members of the species Armillaria<br />

mellea (“Armillaria mellea complex”). In the 90s, the groups were assigned<br />

to five biological species (Guillaumin et al. 1993; Nierhaus-Wunderwald 1994;<br />

Holdenrieder 1996):<br />

A=Armillaria borealis Nordic honey fungus,<br />

B = Armillaria cepistipes,<br />

C = Armillaria ostoyae Dark honey fungus,<br />

D=Armillaria mellea s.s. Honey fungus,<br />

E = Armillaria gallica Marxm. & Romagn.<br />

Based on the verification of isolates by mating tests between monospore cultures,<br />

between diplonts and haplonts (Buller phenomenon), and by somatic<br />

compatibility tests, morphological variation of the fruit bodies of the five<br />

annulate European species was recently shown in color plates with suitable<br />

characters for species identification (Marxmüller and Holdenrieder 2000). In<br />

North America, nine annulate species are known (Anderson and Ullrich 1979;<br />

Anderson et al. 1980; Bruhn et al. 2000). The six species in Australasia (Kile and<br />

Watling 1983) are incompatible with European and North American species.<br />

In Africa, a subspecies of A. mellea was found (Agustian et al. 1994).<br />

Occurrence: The Armillaria species differ in host preference, pathogenicity<br />

(primary parasite, opportunist attacking weakened plants, destructive agent of<br />

non living tissue resulting in heart wood rot), geographical distribution, type<br />

and frequency of rhizomorphs, and in cultural characteristics such as mat<br />

morphology and optimum temperature (Rishbeth 1985, 1991; Shaw and Kile<br />

1991; Guillaumin et al. 1993; Marxmüller and Holdenrieder 2000; Schwarze<br />

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8.3 Tree Rots by Macrofungi 187<br />

and Ferner 2003; Prospero et al. 2003). The damage, Armillaria root disease<br />

(Hartig 1874, 1882), occurs in conifers and hardwoods, particularly spruce,<br />

pine, maple, poplar, oak, in plantations of fruit, vine, flowers, ornamentals,<br />

and tropical cash crops (Seehann 1969; Schönhar 2002a; Schwarze and Ferner<br />

2003). The fungi occur also on stumps, piles, etc., and even in sprinkled wood<br />

(Metzler 1994).<br />

Physiology: Parasite, saprobe, white rot; slow growth in the laboratory;<br />

Characteristics: in pine and spruce, resin excretion; white, fan-like mycelial<br />

mats and brown-black, inside white rhizomorphs (0.25–4 mm; Schmid and<br />

Liese 1970; see Fig. 2.7) between bark and wood (Hartig 1874; Fig. 8.12a);<br />

wood colonized by living mycelium shining in the dark; clampless;<br />

Fig.8.12. Armillaria mellea. a Fruit<br />

bodies and rhizomorphs (translated<br />

from Hartig 1874); b White-rotten<br />

stump with rhizomorphs after removing<br />

the bark. c Fruit bodies and white<br />

mycelial sheet beneath the bark (photo<br />

W. Liese)<br />

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188 8 Habitat of <strong>Wood</strong> Fungi<br />

Fruit body (Fig. 8.12c): central stipe (to 15 cm), cap 5–15 cm in diameter;<br />

annual, in groups on stumps and at the root collar in late autumn; upper<br />

surface (A. mellea): small, yellow-brown scales on honey-yellow ground (Honey<br />

fungus); gill surface: cream-white to brownish-red gills; monomitic; clamps<br />

only at the basidium basis; pileus with white ring; young edible, danger of<br />

sickness when insufficiently cooked or overmatured;<br />

Significance: The Armillaria fungi, which are feared by the foresters, belong<br />

to the most important and cosmopolitan pathogens inside and outside<br />

the forest. They can attack almost all species of hardwoods and conifers of<br />

all ages (Hartig 1874; Schönhar 1989; Livingston 1990; Klein-Gebbinck and<br />

Blenis 1991; Gibbs et al. 2002). They live as saprobes in the soil on dead wood<br />

remainders and on stumps. The transition to the parasitic phase occurs, if the<br />

tree is weakened by stress (other parasites, wetness, dryness, pollution), so that<br />

forest damage sites showed increased occurrence of Armillaria. The infection<br />

occurs by rhizomorphs (Fig. 8.13). Solla et al. (2002) showed that A. mellea<br />

Fig.8.13. Development and transmission of Armillaria root disease (translated from<br />

Nierhaus-Wunderwald 1994, with permission of Swiss Federal Institute for Forest, Snow<br />

and Landscape Research)<br />

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8.3 Tree Rots by Macrofungi 189<br />

and A. ostoyae penetrated Picea sitchensis root bark without prior wounding,<br />

but neither species formed rhizomorphs. The rhizomorphs grow in the soil<br />

from tree to tree and serve for nutrient translocation and infection. If the tree<br />

does not succeed in defending the fungus by histological or chemical barriers<br />

(<strong>Wood</strong>ward 1992a; Wahlström and Johansson 1992), the fungus spreads between<br />

bark and xylem in the cambial region. The sap stream is interrupted, and<br />

toxic metabolites are excreted by the fungus. If the whole cambium is colonized<br />

around the stem, the tree dies rapidly (“cabium killer”). Beside the parasitic<br />

way of life, the fungus can spread via the wood rays in the heartwood of the<br />

root and stem basis (butt rot). Armillaria species and Heterobasidion annosum<br />

showed an increased occurrence in forest dieback sites (Kehr and Wulf 1993).<br />

AdirectcontrolofArmillaria spp. (e.g., Fox 1990) is practically impossible,<br />

particularly since the fungus occurs almost everywhere in the soil. In Oregon,<br />

the upper ground layer was colonized over an area of about 9 km 2 by only<br />

one mycelial clone of A. ostoyae, whose age was supposed to be 2,400 years.<br />

In England, a clone of A. gallica of about 500 years of age covered an area of<br />

9 ha. In France and Germany, clone diameter reached about 200 m in diameter<br />

(Marxmüller and Holdenrieder 2000).<br />

Armillaria is more frequent on soils with balanced microclimate and high<br />

air humidity at ground level as well as on nutrient-rich soils of about pH 5.<br />

Since young conifers are particularly susceptible on former hardwood soils,<br />

oldstumpsandrootsshouldberootedoutbeforeplantingconiferstolimit<br />

the vitality of the fungus, which, during its saprobic phase, depends on easily<br />

degradable nutrients (Butin 1995). Isolation of infected tree groups by 30 to 50cm-deep<br />

ditches is usually unsuccessful. Armillaria-infected plants in gardens<br />

and parks should be promptly removed. The resistance of the plant hosts can<br />

be increased by suitable soil preparation, good planting, and tree care. Douglas<br />

fir, Sitka spruce, fir and larch are lesser susceptible species. The application of<br />

chemicals within the root range is strenuous and therefore only suitable for<br />

valuable garden and park trees (Schönhar 1989).<br />

Pinosylvin from Pinus strobus inhibited mycelial growth of A. ostoyae<br />

(Mwangi et al. 1990). Growth rate, spread and survival of rhizomorphs decreased<br />

by several bacteria, particularly Pseudomonas fluorescens Migula (Dumas<br />

1992), Trichoderma species (Dumas and Boyonoski 1992), wood-inhabiting<br />

Basidiomycetes (Pearce 1990) and mycorrhizal fungi (Kutscheidt 1992).<br />

8.3.2<br />

Heterobasidion annosum s.l. Root Rot Fungus, Fomes Butt Rot<br />

From the Root rot fungus, several intersterility groups have been distinguished,<br />

which differ in relation to distribution, fruit body morphology and host tree<br />

(Korhonen 1978a). In Europe, three groups have been referred to as P-group<br />

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190 8 Habitat of <strong>Wood</strong> Fungi<br />

(pine), S-group (spruce), and F-group (fir) (Holdenrieder 1989; Siepmann<br />

1989; Capretti et al. 1990; Stenlid and Karlsson 1991; Korhonen et al. 1992). In<br />

North America occur the P- and S-type. The Asian forms are lesser characterized<br />

(e.g., Dai and Korhonen 1999). The three European forms show significant<br />

differences in their distribution and host preference and have been attributed<br />

to three distinct species (Niemelä and Korhonen 1998; Korhonen and Holdenrieder<br />

2005):<br />

Heterobasidion annosum s.s. corresponds to the European P-type of H.<br />

annosum s.l. and may named pine root rot fungus, as it typically occurs<br />

in pine forests. In addition, the fungus attacks Juniperus communis, Picea<br />

abies, P. sitchensis, Pseudotsuga menziesii, Larix decidua, L. x eurolepsis, and<br />

L. kaempferi. The distribution area covers the whole of Europe except for the<br />

most northern forests and possibly the great parts of Siberia.<br />

Heterobasidion parviporum (European S-type of H. annosum s.l.; Spruce<br />

root rot fungus) occurs in Europe nearly exclusively on Picea abies, but as it<br />

seems, it is not found in Western Europe. In Russia, it attacks also Abies sibirica<br />

and in East Asia further Picea and Abies species.<br />

Heterobasidion abietinum (European F-type of H. annosum s.l.; Fir root<br />

rot fungus) occurs in fir forests from the Pyrenees to South Polonia and the<br />

Caucasus, particularly on Abies alba, but also on A. borisii-regis, A. cephalonica<br />

and A. nordmanniana.<br />

The three closely related species can be differentiated by cultural studies,<br />

mating tests and DNA techniques. The hymenium of H. parviporum has small<br />

pores (up to 5 pores/mm) and the upper side shows short hairs, while H. annosum<br />

s.s. has bigger pores and a bald upper side. The features of H. abietinum<br />

often overlap with those of the two former species, but its occurrence on firs<br />

is a suitable clue (Korhonen and Holdenrieder 2005). Hybridization of the<br />

species occurs in the laboratory. A natural hybrid between S- and P-type has<br />

been found in North America, but generally, hybrids occur more easily between<br />

forms from different continents. Regarding the evolution of H. annosum<br />

s.l., the origin of H. parviporum and H. abietinum seems to be East Asia, as<br />

there occurs a form that showed high compatibility with all three species. Assumably,<br />

H. annosum s.l. spread from the eastern Himalayas and has thereby<br />

increasingly differentiated via different routes: H. abietinum arrived in Europe<br />

via the South Asian conifer forests, H. parviporum via northern Asia, and the<br />

American S-type reached North America over the Bering Strait. Not much is<br />

known on the P-types (Korhonen and Holdenrieder 2005). Molecular analyses<br />

have shown a close relation of the genus Heterobasidion to the Russulales.<br />

The following description concerns H. annosum s.l.<br />

Occurrence: common in Europe, North America; predominantly conifers; in<br />

heartwood and rootwood of spruce, larch and Douglas fir; in pine restricted to<br />

the root area due to greater resin content; broad host range of over 200 woody<br />

plants (Heydeck 2000); largest diameter of a genet smaller than 30 m, only in<br />

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8.3 Tree Rots by Macrofungi 191<br />

single cases up to 55 m; maximum age of an individual genet around 200 years<br />

(Queloz and Holdenrieder 2005);<br />

Physiology: white rot, root rot, butt rot, so-called red rot due to reddish<br />

discoloration of the wood; at initial decay preferential lignin degradation, later<br />

simultaneous white rot (Peek and Liese 1976); parasite and saprobe;<br />

Characteristics: anamorph Spiniger meineckellus (A.J. Olson) Stalp.<br />

(Fig. 8.14C) on agar and fresh wood samples at high relative humidity: clubshaped<br />

thickened conidiophore after spore dispersal like a morning star<br />

(“Brefeld conidia” as identification feature: Brefeld 1889); flask-shaped increase<br />

of the stem basis of spruce by cambial irritation; resin excretion;<br />

Fruit body (Fig. 8.14A): annual to enduring crusty brackets in autumn,<br />

often resupinate (1 cm thick, 3–20 cm wide) in rows and roofing tile-similar,<br />

usually fused, at the stem basis and on flat-running roots, frequently covered<br />

by needle litter; yearly a new pore layer; fresh: tough, old: hard and woody;<br />

upper surface: bumpy-wrinkled, brown, often zonate, leathery-crusty, whiteyellowish<br />

margin; pore surface: white-cream with circular-angular pores (4–<br />

5/mm); dimitic; bipolar.<br />

Significance: The fungus is one of the most important pathogens in coniferous<br />

forests of temperate regions (Hartig 1874, 1878; Rishbeth 1950, 1951;<br />

Zycha et al. 1976; Hallaksela 1984; Tamminen 1985; Benizry et al. 1988; Schönhar<br />

1990; <strong>Wood</strong>ward 1992a, 1992b; LaFlamme 1994; <strong>Wood</strong>ward et al. 1998;<br />

Heydeck 2000; Greig et al. 2001; Gibbs et al. 2002; Korhonen and Holdenrieder<br />

2005), which causes substantial damage particularly in older forests. The infection<br />

occurs by germinating spores or by mycelium that is already present<br />

in roots or soil. Several infection ways are possible: by basidiospores (also<br />

conidia) via stump infection (Redfern et al. 1997), by mycelial growth through<br />

root graft transmission from diseased to healthy roots (Hartig 1878; Schönhar<br />

2001), or via spores [germinable about 1 year: Brefeld (1889)], which are<br />

washed into the soil by rain and germinate on the roots. The fungus penetrates<br />

into older roots through wounds and into young uninjured roots through the<br />

thin bark (Rishbeth 1951; Peek et al. 1972a, 1972b; Lindberg and Johansson<br />

1991; Lindberg 1992; Solla et al. 2002). The hyphae penetrate into sound spruce<br />

roots via the pit channels of the thick-walled stone cork cells. The walls of the<br />

following thin-walled stone cork cells and the sponge cork cells are degraded.<br />

The fungus colonizes the tracheids from the bark rays via the wood rays. The<br />

tracheids are degraded by enzymes and perforated by microhyphae (Peek and<br />

Liese 1976). Embryos of Pinus spp. showed three days after artificial inoculation<br />

intercellular penetration of hyphae through the epidermis and into the cortex<br />

(Nsolomo and <strong>Wood</strong>ward 1997). Infection of spruce seeds of 4–7 days of age<br />

showed that infective structures on the root surfaces were evident 24 h after<br />

inoculation. Internal colonization of cortical tissues started after 24–48 h and<br />

reached the endodermis within 72 h. Severe destruction of stelar cells occurred<br />

12–15 days postinfection (Asiegbu et al. 1993). Infection of nonsuberized and<br />

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192 8 Habitat of <strong>Wood</strong> Fungi<br />

Fig.8.14. Fomes root rot by Heterobasidion annosum. A Fruit bodies at the stem basis. B<br />

Sequent sections of a stem showing the different color and decay zones (photos W. Liese);<br />

C Pathogenesis, a longitudinal section through a spruce with heart rot, with stem cross<br />

sections, b cross section through a stem at an early stage of disease, c a late stage in the<br />

wood decay, d fruit bodies, e Brefeld conidiophores with conidia, f a heart rot caused by<br />

Armillaria sp. shown for comparison (from Butin 1995, by permission of Oxford University<br />

Press)<br />

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8.3 Tree Rots by Macrofungi 193<br />

young suberized roots of spruce seedlings showed host reaction to delimit the<br />

infection by the formation of a necrotic ring barrier in the outer cortex. In cases<br />

where the inner cortex became infected, hyphae accumulated just before the<br />

endodermis, which acted as a new barrier. Only in nonsuberized roots, the stele<br />

was almost completely digested within 3 days after inoculation (Heneen et al.<br />

1994a). In woody roots 2–4 mm in diameter, fungal infection was restricted<br />

to the remnant cortex cells and the rhytidome after an incubation period of<br />

20 days; accumulation of granular materials prevailed in the infected periderm<br />

cells, which enclosed degenerated hyphae, both leading to the conclusion that<br />

the rhytidome acts as a successful barrier to infection of the inner parts of<br />

the root for at least 20 days following inoculation (Heneen et al. 1994b). Stem<br />

infections are rare and limited to wounds at the root collar (Schönhar 1990).<br />

Main infection is by airborne basidiospores that germinate on fresh stump<br />

surfaces. Infection of neighboring trees occurs by vegetative mycelia via root<br />

contacts. Once established in the root system, the fungus can remain active<br />

for about 60 years. The fungus spreads into trees of the next generation from<br />

infected stumps (Vasiliauskas and Stenlid 1998).<br />

The significance of the fungus is not only based on its parasitic capability<br />

to kill living roots, but it is at the same time causal agent of “red rot”, which<br />

ascends in the heartwood (heart rot) of the stem and is economically usually<br />

more serious. In Europe, on average, a 10% stem wood devaluation is counted<br />

for spruce by “red rot”. In Scotland, the fungus is responsible for 90% of<br />

losses due to rot (Blanchette and Biggs 1992). The yearly damage in Germany<br />

amounts to e56 million (Dimitri and Tomiczek 1998) and in the EU countries<br />

to about e500 million (<strong>Wood</strong>ward et al. 1998). “Red rot” increased in forest<br />

dieback sites.<br />

The parasitic phase of the fungus develops first as root rot. In pine, the<br />

fungus predominantly grows stemwards in the root cambium area, until it is<br />

stopped by resin formation and a bark wound periderm. Large root parts die<br />

off. In the less resinous spruce, fir, larch and Douglas fir, fungal activity shifts,<br />

as soon as the mycelium reaches roots of more than 2 cm in diameter, into the<br />

root interior, that is, side roots and thus also the infected tree remain alive.<br />

Only if all roots are colonized, the mycelium also grows into the cambium and<br />

kills the tree.<br />

The saprobic phase begins with penetration in the heartwood. Sapwood<br />

colonization occurs only after felling due to reduction of moisture content and<br />

particularly due to inhibition by the living sapwood (Shain and Hillis 1971).<br />

The effects of heartwood colonization depend on the tree species. In pine, the<br />

fungus spreads usually only insignificantly in the stem, but the tree dies due to<br />

the root damage. In larch, the mycelium grows in the heartwood/sapwood area<br />

and reaches likewise only low stem height. In spruce, the fungus climbs up in<br />

the stem 25–40 cm/year (Stenlid and Redfern 1998). Likewise, the Douglas fir<br />

stem can be colonized. The infected wood shows first a “1. color zone” (grey-<br />

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194 8 Habitat of <strong>Wood</strong> Fungi<br />

violet striping), then a “bright hard rot” (light brownish, wood still firm), later<br />

a “dark hard rot” (brownish-red, only wood structure remaining) and finally<br />

a “soft rot” (Fig. 8.14B; Zycha 1964), where the wood is fibrously dissolved<br />

and interspersed with small, white spindle-like nests with a black center of<br />

manganese deposits (Fig. 8.14C) (Hartig 1978; see Chap. 7.2).<br />

Imperiled for H. annosum are first plantings on formerly agriculturally<br />

used pasture soils and arable lands (“field-dying”, German: “Ackersterbe”).<br />

Conifers on base-rich and compacted ground, and on sites with very variable<br />

moisture content suffer more from the disease than those on acidic, more open<br />

soils with a more uniform water supply (Butin 1995; Schönhar 1997; Heinsdorf<br />

and Heydeck 1998). The inhibition of acidophilic, antagonistic mycorrhizas<br />

may play a role. A direct control is difficult, and only preventing measures are<br />

used (Schönhar 1990, 2002b). Rooting out and removing the infected stumps<br />

as well as isolating the infected sites by ditches are difficult and not always<br />

successful (Schönhar 1989). The most effective measure is to perform thinnings<br />

during the wintertime, as spore infection decreases during frost (Korhonen<br />

and Holdenrieder 2005). In not-yet-infected first plantings, the stumps which<br />

are the starting point for a propagation of the fungus via root grafts, have<br />

been coated on the fresh surface with carbolineum, which however delays the<br />

stumpdecomposition.Immediatetreatmentofthefreshsurfacewithasodium<br />

nitrite solution prevented spore germination of H. annosum.Aschemical,also<br />

urea (Schönhar 2002b) and boron compounds are used (Pratt 1996). Originally<br />

in the U.K and later in Scandinavia and further European countries, a spore<br />

solution of the antagonistic fungus Phlebiopsis gigantea is immediately applied<br />

to the fresh stump surface of pines (Meredith 1959; Rishbeth 1963; Schwantes<br />

et al. 1976; Lipponen 1991; Gibbs et al. 2002) and spruce (Korhonen et al. 1994;<br />

Holdenrieder et al. 1997). There are spore preparations, which are specifically<br />

suited for spruce, but generally, P. gigantea is more suitable for pines. The<br />

wood can be automatically inoculated with spores through holes in the saw<br />

blade of the harvester (Metzler et al. 2005). The antagonist overgrows the<br />

stump cross surface, so that H. annosum cannot colonize it by spores. Thus, an<br />

infection of neighboring trees over root grafts is prevented. Further antagonists<br />

to H. annosum are treated by Holdenrieder and Greig (1998) and compiled by<br />

<strong>Wood</strong>ward et al. (1998).<br />

Root graft transmission can be reduced by far planting faces and admixture<br />

of hardwoods. Lesser sensitive hardwoods as well as fir or larch should be<br />

selected for particularly endangered sites instead of spruce and pine. In vitro,<br />

mycelial growth was inhibited by stilbenes, flavonoids and lignans (Zycha et al.<br />

1976; Shain and Hillis 1971; Yamada 1992). Breeding attempts with the aim of<br />

red-rot resistant tree clones were performed, but did yet not reach a practical<br />

use. Recent resistance research mainly deals with the genetic mechanisms of resistance<br />

and the physiology of defense reactions (Korhonen and Holdenrieder<br />

2005). Viruses in the root rot fungus, which are morphologically similar to the<br />

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8.3 Tree Rots by Macrofungi 195<br />

Cryphonectria-hypovirus (Chap. 8.1.1.2), only reduced spore germination of<br />

the fungus.<br />

8.3.3<br />

Stereum sanguinolentum, Bleeding Stereum,<br />

Bleeding Conifer Parchment<br />

Occurrence: conifers, particularly spruce; as saprobe causing red streaking<br />

discoloration (see Fig. 6.4a);<br />

Significance: white rot, most important fungus involved in “Wound rot of<br />

spruce” (Butin 1995); 2/3 of about 20% of annual harvest of fir wood with fungal<br />

damage affected by wound rots, particularly by S. sanguinolentum (Schönhar<br />

1989); wounds often due to mechanized wood harvest or bark damage by game;<br />

infection of the opened wood body by spores; also transmission of mycelial<br />

fragments by woodwasps (Sirex spp.); small and superficial wounds often<br />

closed by resin excretion; extension of white rot in the outer stem wood with<br />

reddish discoloration; fast rot extension (20 cm/year) in the first years after<br />

infection; rot spreads more rapidly after injuries at the root collar than after<br />

wounding the stem or small roots; injured roots of less than 2 cm in diameter<br />

and wounds in more than 1-m distance of the stem foot hardly lead to stem rot.<br />

To prevent wound rot by S. sanguinolentum, tree harvest should be done<br />

carefully and injuries treated with a wound dressing. Amylostereum species<br />

maybealsoinvolvedinwounddecayofspruceandotherconifers,A. areolatum<br />

and A. chailletii, both also being associated with woodwasps (Vasiliauskas<br />

1999).<br />

8.3.4<br />

Fomes fomentarius, Tinder Fungus, Hoof Fungus<br />

Occurrence: common, circumboreal, south to North Africa, through Asia to<br />

eastern North America; mostly hardwoods, common on birches in the north<br />

and on beeches in the south, also on oak, lime tree, maple, poplar, and willow,<br />

rarely on alder and hornbeam, exceptionally on softwoods (Schwarze 1994,<br />

2001);<br />

Fruit body (Fig. 8.15a): perennial (over 30 years, increase in early summer<br />

to autumn), thick, large (to 50 cm in diameter), hard brackets, mostly solitary;<br />

often high at the stem; firmly attached to the bark; upper surface: light brown to<br />

blackish-grey, bulging-zonate; pore surface: flat, cream-brownish hymenium<br />

with white margin; circular pores (4–5/mm); trimitic; soft-tough trama beneath<br />

a 1 to 2-mm-thick hard crust; 1–3 new hymenial layers per year; up to<br />

240 million spores per cm 2 hymenium and hour; tetrapolar. In former times<br />

(e.g., in Haitabu), the trama was soaked with salpetre for tinder production.<br />

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196 8 Habitat of <strong>Wood</strong> Fungi<br />

Fig.8.15. Fruit bodies of tree decay fungi. a Fomes fomentarius. b Laetiporus sulphureus.<br />

c Meripilus giganteus. d Phaeolus schweinitzii. e Phellinus pini. f Piptoporus betulinus.<br />

g Polyporus squamosus. h Sparassis crispa (photos T. Huckfeldt)<br />

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8.3 Tree Rots by Macrofungi 197<br />

A part of a fruit body was found at the “Ötzi” mummy. Still, around 1890, about<br />

50 t of trama per year were sampled in the Bavarian, Bohemian and Thuringian<br />

forests for fire igniting, as styptic, and for the production of hoods, gloves and<br />

trousers (Hübsch 1991; Scholian 1996).<br />

Significance: one of the most remarkable “large polypores”; infection of<br />

weakened and old trees via bark wounds or branch breakings; natural member<br />

in the biocoenosis of birch and beech forests; simultaneous white rot with<br />

black demarcation lines; at final stage, danger of windthrow; involved in the<br />

final decay of beech bark-diseased trees; saprobe on thrown or felled trees for<br />

several years (“Verstocken”).<br />

8.3.5<br />

Laetiporus sulphureus, Sulphur Polypore, Giant Sulphur Clump<br />

Occurrence: cosmopolitan, Europe, western North America, northeast Asia;<br />

preferentially on hardwoods with colored heartwood, like oak and robinia,<br />

also apple, beech, cherry, elm, lime tree, maple, pear, plum, poplar, willow,<br />

rarely on conifers; common on park and urban trees (Schwarze 2002);<br />

Fruit body (Fig. 8.15b): annual (summer to autumn), conspicuous (upper<br />

surface: sulfur-yellow to reddish) wavy-velvety brackets (15–40 cm); pore surface:<br />

sulfur-yellow with angular pores (3–4/mm); single or in clusters; fresh:<br />

succulent-soft, later: inflexible, chalk-like, straw-colored to grey; dimitic; eaten<br />

in North America;<br />

Significance: infection of the stemwood usually via wounds; brown rot in<br />

the heartwood; yellowish mycelium in broad, bind-like strips along the tears<br />

and shakes that develop in the wood; sapwood usually not attacked; infected<br />

trees alive for many years till broken or thrown by storm; rarely saprobic, e.g.,<br />

on wooden boats.<br />

8.3.6<br />

Meripilus giganteus, Giant Polypore<br />

Occurrence: circumboreal in the northern hemisphere, but nowhere common;<br />

usually hardwoods, particularly horse chestnut, beech, lime and oak; often on<br />

park and urban trees (Seehann 1979; Schwarze 2003);<br />

Fruit body (Fig. 8.15c): annual (summer to autumn) on stumps of freshly<br />

felled trees and at the basis of standing trees; often apparently growing from<br />

the ground, but always in contact to wood; large and pileate with fan-shaped<br />

to spatulate pilei from a common base; aggregates to 1 m in diameter and 70 kg<br />

fresh weight; upper surface: cream-white to yellow-brown zonate; pore surface:<br />

cream to yellow-orange-brown pores (3–5/mm), rapidly blackish when<br />

bruised or cut; monomitic; eaten in Japan;<br />

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198 8 Habitat of <strong>Wood</strong> Fungi<br />

Significance: white rot in damaged roots of usually older trees, weakened<br />

due to compressed soil, asphalting, salting, and by wounds due to building<br />

operations or road traffic; fruit bodies indicate a heavily destroyed root system<br />

leaving only little time to the trees for surviving; stem hardly infected. Tree<br />

care in the urban area reduces the damage.<br />

8.3.7<br />

Phaeolus schweinitzii, Dye Polypore, Velvet Top Fungus<br />

Occurrence: circumglobal, in European conifer forests north to 70 °N in Finnmark,<br />

Norway, particularly pine, Douglas fir, also spruce and larch, rarely on<br />

hardwoods (Ryvarden and Gilbertson 1993);<br />

Fruit body (Fig. 8.15d): annual (late summer), easy-passing; at the stem<br />

basis or on the soil on hidden roots; stipitate, short, central, upward more<br />

thick, cylindrical to knotty stipe, first with spinning-top-like, later with several<br />

tile-like caps (to 40 cm); on the cross cuts of felled trees with lateral stipe;<br />

frequently including plant residues or small branches during ripening; upper<br />

surface: when young orange, later yellowish-brown, old often black; yellowbrown<br />

margin; woolly; pore surface: angular pore (1–2/mm) layer at first<br />

orange,latergreenishtorustybrown,discolorswithpressurered-brownish;<br />

monomitic;<br />

Significance: brown rot, major cause of butt rot in the heartwood of old<br />

pine and Douglas fir; frequently in conifers forests on former hardwood soils<br />

(Schönhar1989);firstonroots andinstemwounds,laterinthe stemheartwood,<br />

less ascending the stem (butt rot); decayed wood and laboratory cultures with<br />

turpentine smell; saprobe on dead trees, stumps and logs for several years.<br />

8.3.8<br />

Phellinus pini, Ochre-Orange Hoof Polypore<br />

Occurrence: circumglobal, widespread in northeast Europe on pine, in North<br />

America and Asia on other conifers as well (Heydeck 1997; Frommhold and<br />

Heydeck 1988);<br />

Fruit body (Fig. 8.15e): perennial (to 50 years), brackets only 5–20 years<br />

after infection near branch holes and stubs; often high at the stem of old<br />

trees (Naumann 1995), 5–12 cm; upper surface: zonate, rough, cracked, at<br />

first rust-brown, hirsute, later dark-brown-blackish, glabrous and encrusted;<br />

pore surface: yellow to grey-brown with round to angular/daedaleoid pores<br />

(1–3/mm); dimitic, bipolar;<br />

Significance: infection of old (30–50 years) pine and larch at exposed heartwood<br />

(branch stubs, wounds); living sapwood usually not penetrated; often<br />

high at the stem (Hartig 1874; Liese and Schmid 1966); from deep-reaching<br />

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8.3 Tree Rots by Macrofungi 199<br />

dead branches decay upwards and downwards in the stem; white-pocket rot,<br />

preference for latewood of Pinus and Larix (Liese and Schmid 1966; Blanchette<br />

1980), pockets in some hosts concentrated in the earlywood bands (“laminated<br />

rot”, ring shake); occurrence of transpressoria and formation of cavity-shaped<br />

decay pattern (Liese and Schmid 1966); local bark deepenings, outer sapwood<br />

resin-infiltrated (in former times wood used as resinous wood); in spruce,<br />

infection also via sapwood; wood still relatively firm at early decay; dying after<br />

tree felling.<br />

8.3.9<br />

Piptoporus betulinus, Birch Polypore, Birch Conk Fungus<br />

Occurrence: circumboreal, north to Norwegian North Cape at 71 °N (Ryvarden<br />

and Gilbertson 1994); only birch; also in gardens and parks;<br />

Fruit body (Fig. 8.15f): annual (summer to late autumn), but enduring;<br />

solitary and in groups; shell-shaped, fan-like brackets (8–30cm); pilei pendent,<br />

dimidiate, or reniform; often several meters high on the stem; upper surface:<br />

dull-smooth, unzonate, young cream-white, later ochre-brown to grey-brown,<br />

old usually cracked; pore surface: white to cream-brownish circular to angular<br />

pores (3–5/mm); dimitic; some isolates bipolar (Stalpers 1978); fruit body<br />

previously used in Fennoscandia as a cushion for knives, which do not rust<br />

while standing in the fruit body;<br />

Significance: weakness-parasite, host-specific on older and weakened (e.g.,<br />

lack of light) birch; infection via wounds (branch breakage); brown rot; danger<br />

of windthrow.<br />

8.3.10<br />

Polyporus squamosus, Scaly Polypore<br />

Occurrence: circumpolar in Europe (north to Finnmark at 70 °N), Australia,<br />

Asia, and America; hardwoods such as ash, beech, elm, horse chestnut, lime,<br />

maple, planetree, poplar, and willow (Schwarze 2005); frequently on urban and<br />

park trees;<br />

Fruit body (Fig. 8.15g): annual (early summer); solitary or in groups from<br />

a branched base; usually laterally stipitate, with circle to fan-like cap (to 80 cm<br />

wide and 2 kg fresh weight); upper surface: yellow-ochre with concentrically<br />

arranged light to dark-brown, scale-like patches, smooth and sticky; pore<br />

surface: cream-yellowish with angular-oval pores (1–2/mm); whitish stipe (up<br />

to 10 cm) at the basis dark-brown to black-felty; dimitic; tetrapolar (Stalpers<br />

1978); young edible;<br />

Significance: white rot in the heartwood of living and dead hardwoods with<br />

black demarcation lines after penetration through wounds.<br />

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200 8 Habitat of <strong>Wood</strong> Fungi<br />

8.3.11<br />

Sparassis crispa<br />

Occurrence: rare in Europe; particularly pine, also Douglas fir, spruce and fir;<br />

Fruit body (Fig. 8.15h): annual (summer to late autumn); solitary at the root<br />

area of living pines, lateral and at cross surface of stumps and fallen stems;<br />

hemispherical to cushion-shaped; resembling a large (up to 70 cm and 6 kg<br />

fresh weight) sponge, cauliflower, or coral (German: “Krause Glucke”); consisting<br />

of numerous, wavy, narrow upright-standing branches deriving from<br />

a fleshy stalk; frizzy, leaf-like branch-ends partly growing together, similar to<br />

Icelandic moss; surface: smooth, cream, later ochre, when old with brown margin,<br />

finally completely brown; hymenium on the outside, downward arranged<br />

side of the branches; monomitic; when young well edible mushroom (in Germany<br />

certified as market fungus) with whitish meat, spicy morel-similar smell<br />

and nut-like taste; fruit bodies also on agar cultures; some isolates tetrapolar<br />

(Stalpers 1978);<br />

Significance: parasitically in roots of older pines, ascending to 3 m high<br />

with brown rot in the stem heartwood; decayed wood with turpentine smell;<br />

economically important wood losses in pine and Douglas fir (Heydeck 1994).<br />

8.4<br />

Damage to Stored <strong>Wood</strong> and Structural Timber Outdoors<br />

After felling or falling of a tree, the living cells die some time later. The active<br />

defensesystemsdonotfunctionanylonger.Somefungithatarealreadypresent<br />

in the stem can continue degradation by their now saprobic way of life, e.g.,<br />

Fomes fomentarius. The exposed wood surfaces however rapidly dry, and new<br />

ecological conditions develop. Thus, the stem usually provides a new energyrich<br />

substrate for rapid colonization by several saprobic organisms (Zabel and<br />

Morrell 1992).<br />

Colonization and discolorations of the stem in the forest occur frequently<br />

within short time by bacteria, algae, slime fungi, molds, and blue-stain and<br />

red-streaking fungi. After longer exposure wood decays by brown, white<br />

and soft-rot fungi develop, which may be summarized as “decay of stored<br />

wood”, or “colonization of fallen and cut wood” (Rayner and Boddy 1988).<br />

Among the Basidiomycetes are e.g., Armillaria gallica, Bjerkandera adusta,<br />

Chondrostereum purpureum, Fomes fomentarius, Stereum spp., Schizophyllum<br />

commune and Trametes versicolor. Several fungi are involved in the decomposition<br />

of the stumps remaining in the soil e.g., Armillaria spp., B. adusta,<br />

C. purpureum, Daedalea quercina, Fistulina hepatica, Ganoderma spp., Gloeophyllum<br />

spp., Grifola frondosa, Heterobasidion annosum, Meripilus giganteus,<br />

Phaeolus schweinitzii, Phlebiopsis gigantea, Pleurotus ostreatus, Stereum spp.,<br />

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8.4 Damage to Stored <strong>Wood</strong> and Structural Timber Outdoors 201<br />

S. commune and T. versicolor. On tree residues remaining in the forest (top,<br />

branches) grow e.g., B. adusta, C. purpureum, Coniophora puteana, Gloeophyllum<br />

sepiarium, Stereum sanguinolentum and T. versicolor. Forest-litter<br />

degrading Basidiomycetes were described by Frankland et al. (1982).<br />

Damages on roundwood (logs, poles) and boards may occur during transport<br />

and inappropriate storage e.g., by C. puteana, Fomitopsis pinicola, Gloeophyllum<br />

trabeum, Paxillus panuoides, Phlebiopsis gigantea, S. sanguinolentum<br />

and Trichaptum abietinum. <strong>Wood</strong> chips are damaged by B. adusta, Gloeophyllum<br />

spp., Phanerochaete chrysosporium, T. versicolor, and by several Deuteroand<br />

Ascomycetes (molds, blue-stain and soft rot fungi). Several bacteria, yeasts,<br />

Deuteromycetes and Ascomycetes were found in stored annual plant residues,<br />

like sugarcane bagasse (Schmidt and Walter 1978).<br />

Yeasts commonly colonize twigs, leaves, litter, and humus, are however also<br />

found on freshly sawn lumber (Mikluscak et al. 2005).<br />

Structural timber that is used outdoors in ground contact, like sleepers,<br />

poles, posts, fences, bridges and garden furniture, is attacked by soft-rot fungi if<br />

it is insufficiently treated with wood preservatives. Among the Basidiomycetes<br />

occur e.g., Antrodia vaillantii, H. annosum, Lentinus lepideus, Leucogyrophana<br />

pinastri, Oligoporus placenta, Phanerochaete sordaria, Phlebiopsis gigantea,<br />

Serpula himantioides, Sistotrema brinkmanni, Trametes versicolor and Trichaptum<br />

abietinum (e.g., Lombard and Chamuris 1990; Morrell et al. 1996).<br />

Mine timber was decayed by A. vaillantii and C. puteana as well as by<br />

Armillaria spp., G. sepiarium, H. annosum, L. lepideus, L. pinastri, O. placenta,<br />

Paxillus panuoides, Schizophyllum commune, Serpula lacrymans, Stereum spp.<br />

and T. versicolor (Eslyn and Lombard 1983). Earliella scrabosa, Loweporus<br />

lividus, Rigidoporus lineatus, and R. vinctus were isolated from gold mine<br />

poles in India (Narayanappa 2005).<br />

<strong>Wood</strong> in fresh water, like in cooling towers, is often destroyed by soft-rot<br />

fungi. Among the Basidiomycetes, e.g., Donkioporia expansa and Physisporinus<br />

vitreus have been isolated from cooling-tower woods (v. Acker and Stevens<br />

1996). The latter fungus degraded pine sapwood samples that showed a final<br />

moisture content of up to 320% u (Schmidt et al. 1996). Schwarze and<br />

Landmesser (2000) hypothesized that the preferential degradation of tracheidal<br />

pit membranes is associated with the adaptation of this fungus to very wet<br />

substrates. <strong>Wood</strong> in salt water below (not permanent) the sea level, as in harbor<br />

constructions, is predominantly attacked by Deuteromycetes and Ascomycetes<br />

and rarely by Basidiomycetes (Jones et al. 1976; Kohlmeyer 1977; Leightley<br />

and Eaton 1980). Basidiomycetes, like Antrodia xantha, Daedalea quercina,<br />

Gloeophyllum sepiarium, Laetiporus sulphureus, Lentinus lepideus, Phlebiopsis<br />

gigantea, Schizophyllum commune and Xylobolus frustulatus dominate in wood<br />

above the water level, like in docks, stakes or boats (Rayner and Boddy 1988).<br />

Damages on stored and structural timber in outside use can be reduced or<br />

even avoided by means of protection measures against fungal activity described<br />

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202 8 Habitat of <strong>Wood</strong> Fungi<br />

inChap.6.4:winterfelling,shortandadequatestorageofthefreshroundwood,<br />

wet storage, rapid drying, storage in a gas atmosphere (N2/CO2), and storage<br />

of cut timber in well-ventilated piles with protection against rain as well as<br />

chemical protection.<br />

In the following, some common Basidiomycetes on wood in outside use are<br />

described, mostly in note form. For details see also Grosser (1985), Breitenbach<br />

and Kränzlin (1986, 1991), Zabel and Morrell (1992), Eaton and Hale (1993),<br />

Ryvarden and Gilbertson (1993, 1994), Bech-Andersen (1995), Butin (1995),<br />

Kempe (2003), Krieglsteiner (2000), and Weiß et al. (2000).<br />

8.4.1<br />

Daedalea quercina, Maze-Gill, Thick-Maze Oak Polypore<br />

Occurrence: circumglobal and throughout Europe, North America, North and<br />

Central Asia, North Africa; in northern Europe only on oaks, in central and<br />

southern Europe also on Acer, Carpinus, Castanea, Chamaecyparis, Corylus,<br />

Eucalyptus, Fagus, Fraxinus, Juglans, Juniperus, Populus, Picea, Prunus,<br />

Robinia, Sorbus, Tilia, and Ulmus (Wa˙zny and Brodziak 1981);<br />

Fruit body (Fig. 8.16h): perennial, single or fused, broadly sessile, dimidiate,<br />

flat or ungulate, sometimes imbricate, sometimes nodular or deformed, large<br />

brackets (up to 30 cm wide and 8 cm thick) often high at the stem; hard and<br />

corky to woody; upper surface: grooved, uneven, covered with nodes, glabrous<br />

or somewhat pubescent, cream, ochraceous grey to brown; pore surface: sinuous,<br />

or daedaleoid to labyrinthine, or almost lamellate, pores 1–4 mm wide<br />

measured tangentially, walls up to 3 mm thick; monstrous fructification in the<br />

dark; trimitic; bipolar;<br />

Significance: brown rot in the durable heartwood of oaks and other hardwoods;<br />

on wounded standing trees via exposed heartwood, dead branches,<br />

on stumps, fallen stems, on sleepers, poles, stakes, wooden bridges, mine<br />

timber; occasionally in buildings on weathered timber, like window sills and<br />

half-timbering.<br />

8.4.2<br />

Gloeophyllum Species, Gill Polypores<br />

Three Gloeophyllum species are relevant to wood. The fungi have similar fruit<br />

bodies and life conditions (Hof 1981a, 1981b, 1981c; Grosser 1985; also Bavendamm<br />

1952a), and are thus usually united as “wood gill polypores”. They<br />

are widespread in Europe, North America, North Africa, and Asia on conifers<br />

and hardwoods. Gloeophyllum abietinum is a somewhat southern species, G.<br />

trabeum a southern species.<br />

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8.4 Damage to Stored <strong>Wood</strong> and Structural Timber Outdoors 203<br />

Fig.8.16. Fruit bodies of decay fungi on stored wood and on timber in outdoor use. Gloeophyllum<br />

abietinum. a Upper side. b Lower side. c Darkness fruit bodies; Gloeophyllum<br />

sepiarium d Upper side. e Lower side; Gloeophyllum trabeum f Upper side. g Lower side.<br />

h Daedalea quercina; i Lentinus lepideus; j Paxillus panuoides; Schizophyllum commune<br />

k Upper side. l Lower side. m Trametes versicolor (photos T. Huckfeldt)<br />

Gloeophyllum abietinum, Fir Gill Polypore<br />

Fruit body (Fig. 8.16a,b): perennial, pileate (2–8 cm wide), broadly attached,<br />

ofteninrowsortile-like,ontimberlowersideresupinate;uppersurfacehirsute<br />

to velutinate, in age zonate, scrupose to warted or smooth, rusty yellow,<br />

reddish-brown to dark grey and black when old, when young whitish-yellowbrown,<br />

wavy, sharp margin; hymenophore ochre-grey brown, wavy lamellae<br />

(8–13/cm, behind the margin) with anastomosing, serrate, mixed with poroid<br />

areas; monstrous fruit bodies in the dark (Fig. 8.16c); trimitic; bipolar;<br />

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204 8 Habitat of <strong>Wood</strong> Fungi<br />

Strands: only rarely on timber in laboratory culture, cream-ochre-dark<br />

brown; fibers to dark brown; no vessels.<br />

Gloeophyllum sepiarium, Yellow-Red Gill Polypore<br />

Fruit body: (Fig. 8.16d, e) annual to perennial, pileate, broadly sessile, dimidiate,<br />

rosette shaped, often imbricate in clusters from a common base or fused<br />

laterally, to 7 cm wide, 12 cm long and 6–8 mm thick, margin slightly wavy;<br />

upper surface when young yellowish brown, then reddish brown and grey to<br />

black when old; scrupose, warted to hispid, finally zonate often differently<br />

colored; hymenophore with straight lamellae (15–20/cm, behind the margin),<br />

edges of lamellae golden brown in active growth, later umber brown, side surface<br />

of lamellae ochre-brown; usually mixed with daedaleoid to sinuous pore<br />

areas (1–2/mm); monstrous fruit bodies in the dark; trimitic; bipolar;<br />

Strands: only rarely on timber in laboratory culture, white-cream; fibers<br />

yellow to brown, no vessels.<br />

Gloeophyllum trabeum, Timber Gill Polypore<br />

Fruit body (Fig. 8.16f, g): annual to perennial, pileate, sessile, imbricate with<br />

several basidiomes from a common base or elongated and fused along wood<br />

cracks, to 3 cm wide, 8 cm long, 8 mm thick; upper surface soft and smooth,<br />

hazelnut to umber brown to grayish when old, weakly zonate to almost azonate,<br />

lighter margin; hymenophore semi-lamellate or labyrinthine to partly poroid<br />

(2–4/mm), rarely lamellate specimens with up to four lamellae/mm along the<br />

margin, ochre to umber brown; monstrous fruit bodies in the dark; dimitic;<br />

bipolar;<br />

Strands: only on timber in laboratory culture, white-beige to yellow-orangegrey<br />

brown, below 1 mm thick; fibers yellow to brown; no vessels.<br />

Significance: predominantly saprobic, G. sepiarium and G. trabeum exceptionally<br />

on living trees; belonging to the strongest brown-rot fungi of coniferous<br />

structural timber; often on stumps; broad moisture optimum (about 40 to<br />

200% u; Table 8.7), on stored timber and on finished timber that is again<br />

moistened, like poles, posts, fences, sleepers and mining timber. The fungi are<br />

the most important destroyers of conifers windows (cf. Fig. 8.17) that had accumulated<br />

moisture due to inappropriate window construction and handling<br />

faults by the user (e.g., injuring of the lacquer layer by nails). For example,<br />

3.5 million (7%) of wooden windows were partly or completely destroyed by<br />

fungi, predominantly by G. abietinum, in Germany between 1955 and 1965<br />

(Seifert 1974). Fungi survive in the sun-warmed and dry window timber due<br />

to their heat and dryness resistance [G. abietinum: 5–7yearssurvivalindry<br />

timber: Theden (1972)]. Fungi cause (by means of substrate mycelium) decay<br />

first only in the wood interior (“interior rot”). The serious brown rot under<br />

the varnish layer is often only recognized if fruit bodies develop. Except on<br />

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8.4 Damage to Stored <strong>Wood</strong> and Structural Timber Outdoors 205<br />

window timber, the gill polypores occur in buildings after moisture damages<br />

or incorrect structure on roofing timbers, on façades, outside doors, balconies,<br />

andontimberinsaunasandmines.<br />

8.4.3<br />

Lentinus lepideus, Scaly Lentinus<br />

Occurrence: temperate zones, common in Europe, North America, former<br />

Soviet Union, India; conifers, particularly Pinus, alsoAbies, Cedrus, Larix,<br />

Picea, Pseudotsuga, Tsuga;<br />

Fruit body (Fig. 8.16i): mainly eccentric, stipe (up to 7 cm long), pileus 5–<br />

15 cm wide; fleshy-tough to hard in age, initially convex, later applanate; upper<br />

surface: pale to cream or purplish brown, with brownish scales (name!) in radial<br />

orientation; lower surface: whitish to yellow-ocher, serrate gills; monstrose,<br />

sterile fruit bodies in the dark (Seehann and Liese 1981); dimitic (Kreisel<br />

1969);<br />

Significance: brown rot of heartwood, via wounds and dead branches in<br />

standing trees, on stumps, felled logs, serious damage on structural timbers<br />

outdoors in ground contact (poles, sleepers, fence posts, stakes, wooden<br />

bridges, harbor timbers) (Bavendamm 1952b), on mine timber; particularly<br />

dangerous due to resistance to heat, desiccation and coal tar oil (test fungus<br />

in EN 113 for tar oil and comparable compounds); degradation of pine heartwood<br />

(interior rot) in improperly impregnated (drying shakes developed after<br />

treatment) poles and sleepers; rarely in buildings, particularly in the cellar<br />

and on damp timber on the ground floor, on joist heads in contact with wet<br />

masonry, door posts, roof timber; pleasant smell of the fresh mycelium of Peru<br />

balsam.<br />

8.4.4<br />

Paxillus panuoides, Stalkless Paxillus<br />

Occurrence: mostly conifers;<br />

Fruit body (Fig. 8.16j): annual, thin, small (2–12 cm), shell-shaped, bellshaped,<br />

small eccentric stipe or attached, solitary or in groups, also tile-like;<br />

upper surface: pale-yellow to olive brown; lower surface: saffron-orange gills;<br />

monomitic; normal fructification in the dark (Kreisel 1961);<br />

Significance: slowly growing, but serious brown rot; rarely at the basis of<br />

living pines, on stumps, stored wood, structural timber outdoors (sleepers,<br />

bridges, balconies), garden furniture, mine timber, rarely in buildings, associated<br />

with the Coniophora spp., on very moist places in cellars, cow-sheds,<br />

greenhouses.<br />

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206 8 Habitat of <strong>Wood</strong> Fungi<br />

8.4.5<br />

Schizophyllum commune, (Common) Split-Gill<br />

Occurrence: circumglobal, temperate to tropical, very common, predominantly<br />

hardwoods like Fagus, Quercus, Tilia, fruit woods, bamboos, straw, tea-leaves,<br />

coconut fibers;<br />

Fruit body (Fig. 8.16k, l): annual, but durable, thin, small, shell-shaped<br />

(1–5 cm), dimidiate; usually in groups, leathery-tough; upper surface: greybrown<br />

to flesh-colored becoming white with dryness, downy-woolly; lower<br />

surface: appearing as if gilled, hymenium covering fan-like arranged, at the<br />

beginning grey, later violet-brown pseudolamellae, which are lengthwise split<br />

and outwardly bent (Fig. 3.3d); hygroscopic movements of the split lamellae<br />

by being hard and rolled up in dry weather and being again flexible and<br />

sporulating after years of dryness when again moist; monomitic, tetrapolar<br />

(Raper and Miles 1958); formerly eaten in Assam, Congo, Peru and Thailand,<br />

and used as chewing gum in Hong Kong, Indonesia and Malaysia (Dirol and<br />

Fougerousse 1981); fructification also in culture;<br />

Significance: white rot; as wound parasite on living trees after bark fire<br />

damage, on stumps, stored stems, frequently on beech as first colonizer; on<br />

stored and structural timber outdoors surviving dryness and exposition to<br />

sun by dryness resistance; in the tropics serious wood destroyer, fruit bodies<br />

often on imported timber; in vitro only little wood decay (Schmidt and Liese<br />

1980).<br />

8.4.6<br />

Trametes versicolor, Many-Zoned Polypore<br />

Occurrence: circumglobal, very common throughout Europe, dead wood of<br />

almost all hardwoods, particularly Fagus, alsoBetula, no attack of Quercus,<br />

Castanea, and Robinia (Jacquiot 1981), rarely conifers, also fruit woods after<br />

pruning;<br />

Fruit body (Fig. 8.16m): annual, often reviviscent, hard-leathery, sessile<br />

or effused-reflexed, pilei dimidiate-substipitate, convex or imbricate, rarely<br />

resupinate, to 10 cm wide, often in large imbricate clusters, rarely solitary;<br />

upper surface: hirsute to tomentose, highly variable in color, with sharply<br />

contracted concentric zones of brown, buff, reddish or bluish colors (name!),<br />

often green by algae; lower surface: cream-white to ochraceus-yellow, angular<br />

to circular pores (4–5/mm); in the dark self-colored fruit bodies with totally<br />

white hirsute upper surface; trimitic; tetrapolar;<br />

Significance: white-rot, often with black demarcation lines (“marble rot”);<br />

on wounded or dead standing trees, on stored stems, common on 4–6 years<br />

old hardwood stumps; rarely on sleepers, fence posts, garden timber; on mine<br />

timber; dryness resistance; used after World War II in the former East Germany<br />

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8.5 Damage to Structural Timber Indoors 207<br />

for the production of “myco-wood” for pencils, rulers, etc. (Luthardt 1963);<br />

test fungus in EN 113 for hardwood samples.<br />

8.5<br />

Damage to Structural Timber Indoors<br />

8.5.1<br />

General and Identification<br />

The indoor wood decay fungi (“house-rot fungi”) cause considerable economical<br />

damage in buildings. They may be considered to be the most important<br />

“wood fungi” as they deteriorate wood at the end of the economical series<br />

“forestry” – “timber harvest” – “storage” – “structural timber” – “indoor use”.<br />

For Britain, it has been estimated that the cost of repairing fungal damage of<br />

timber in construction in 1977 amounted to £ 3 million per week (Rayner and<br />

Boddy 1988). An estimate for the former East Germany amounts to an avoidable<br />

damage in old houses of e1.5 billion (Huckfeldt 2003). In the northern<br />

hemisphere, mainly coniferous wood is used as interior structural timber, in<br />

Germany particularly Picea abies. The most important wood-degrading fungi<br />

within buildings in Europe and North America are therefore fungi that cause<br />

brown rot in conifers. White-rot fungi, which preferentially attack hardwoods,<br />

are less common in buildings. Depending on the state of knowledge, formerly<br />

often only three more well-known species (groups) were called house-rot<br />

fungiinEurope:theTruedryrotfungus,Serpula lacrymans, the cellar fungi<br />

Coniophora spp. (formerly only C. puteana) and the indoor polypores, formerly<br />

called “Poria group” (probably mainly Antrodia vaillantii). These three<br />

groups cause about 80% of the fungal wood damages in buildings. Recently,<br />

the Oak polypore, Donkioporia expansa, has also been accepted as important<br />

indoor rot fungus (Kleist and Seehann 1999). The Gill polypores (Falck<br />

1909) may be included to the indoor species as they are common destroyer of<br />

painted coniferous window timber (Fig. 8.17) and also occur on damp roofing<br />

timber.<br />

There are some evaluations on the frequencies of the various species involved<br />

in indoor wood decay. A survey of 1,500 buildings in New York State<br />

from 1947 to 1951 showed several fungi and Hyphodontia spathulata, G. sepiarium,<br />

A. xantha, andG. trabeum as most frequent isolations from decayed<br />

wood (Silverborg 1953). An investigation of 3,050 buildings in Poland showed<br />

53.8% S. lacrymans, 22.4% C. puteana and 11.3% A. vaillantii (Wa˙zny and<br />

Czajnik 1963). A survey of 1,200 biotic damages in buildings of the former<br />

East Germany over 21 years resulted in 34.8% S. lacrymans, 14.6% Coniophora<br />

spp., 13% soft rot and 8.7% “Poria” (Schultze-Dewitz 1985). An evaluation of<br />

749 damages in Belgium between 1985 and 1991 revealed 59.4% S. lacrymans,<br />

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208 8 Habitat of <strong>Wood</strong> Fungi<br />

Fig.8.17. Gloeophyllum sp. on window joinery. Fruit body and brown-rotten softwood<br />

10.1% C. puteana, C. marmorata, 9.5%Donkioporia expansa, 2.3%Antrodia<br />

vaillantii, A. sinuosa, A. xantha and some further species (Guillitte 1992).<br />

An evaluation of a total number of 3,434 decay fungi in Norwegian buildings<br />

from 2001 to 2003 found as the most frequent fungi 18.4% Antrodia<br />

species, 16.3% C. puteana, 16.0% S. lacrymans and 2.9% G. sepiarium (Alfredsen<br />

et al. 2005). A recent survey over 4 years in 63 buildings in North<br />

Germany yielded 36 basidiomycetous species (Table 8.6). Supplemented by<br />

literature research, altogether about 70 different house-rot fungi have been<br />

reported (Huckfeldt and Schmidt 2005). However, those literature compilations<br />

might be uncertain due to the use of synonyms and the change in fungal<br />

nomenclature.<br />

A survey of 5,000 cases of damage in multistorey houses revealed that all<br />

timbers without sufficient basic protection are endangered, but that there are<br />

different damage centers in a home: “Poria” and soft rot in the attic and upper<br />

floor, and S. lacrymans and Coniophora spp. on the ground and in the cellar<br />

(Schultze-Dewitz 1990).<br />

Some of the less common indoor Basidiomycetes are listed in Table 8.6.<br />

Among them, Lentinus lepideus is particularly found in damp cellars, on the<br />

ground floor and in beam-ends in contact with wet masonry (Bavendamm<br />

1952b). Paxillus panuoides occurs in cellars (Bavendamm 1953). Daedalea<br />

quercina affects structural oak-wood (windows, half-timbering). Falck (1927)<br />

mentioned for cellars Polyporus squamosus and Coggins (1980) also Laetiporus<br />

sulphureus, Phlebiopsis gigantea and Trametes versicolor. A description<br />

of the Dry rot fungus and other fungi in houses and on timber in exterior use<br />

has been compiled by Bech-Andersen (1995). Some of the more rare indoor<br />

species normally occur on trees or timber in outdoor use and are described<br />

in Chaps. 8.3 and 8.4. Further indoor damages are discolorations of window<br />

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8.5 Damage to Structural Timber Indoors 209<br />

Table 8.6. Species and frequency of house-rot fungi and accompanying fungi in buildings<br />

in northern Germany (from Huckfeldt and Schmidt 2005)<br />

Species Frequency<br />

Serpula lacrymans 53<br />

Coniophora puteana 7<br />

Antrodia sp. 6<br />

Antrodia xantha 5<br />

Coprinus spp., three species 5<br />

Donkioporia expansa 5<br />

Asterostroma cervicolor 4<br />

Antrodia sinuosa 3<br />

Antrodia vaillantii 2<br />

Coniophora marmorata 2<br />

Dacrymyces stillatus 2<br />

Diplomitoporus lindbladii a 2<br />

Gloeophyllum trabeum 2<br />

Lentinus lepideus 2<br />

Leucogyrophana pinastri 2<br />

Leucogyrophana pulverulenta 2<br />

Paxillus panuoides 2<br />

Trechispora farinacea 2<br />

Asterostroma laxum a 1<br />

Cerocorticium confluens a 1<br />

Cerinomyces pallidus a,b 1<br />

Gloeophyllum abietinum 1<br />

Gloeophyllum sepiarium 1<br />

Gloeophyllum sp. 1<br />

Grifola frondosa a 1<br />

Heterobasidion annosum 1<br />

Hyphoderma praetermissum 1<br />

Leucogyrophana mollusca 1<br />

Oligoporus placenta 1<br />

Oligoporus sp. 1<br />

Phellinus contiguus 1<br />

Phellinus pini 1<br />

Pluteus cervinus a 1<br />

Stereum rugosum 1<br />

Trametes multicolor 1<br />

Trichaptum abietinum 1<br />

Volvariella bombycina 1<br />

non-decay fungi:<br />

Peziza repanda 5<br />

Reticularia lycoperdon 3<br />

Cladosporium sp. 2<br />

Fuligo septica 1<br />

Ramariopsis kunzei 1<br />

Scutellinia scutellata a 1<br />

a For the first time proven to occur in houses<br />

b First proof in Germany (Huckfeldt and Hechler 2005)<br />

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210 8 Habitat of <strong>Wood</strong> Fungi<br />

timber and outside doors by blue-stain fungi and molding in damp rooms<br />

(Chap. 6) (Frössel 2003; Hankammer and Lorenz 2003).<br />

The common house-rot fungi are serious wood decayers. Among them, S.<br />

lacrymans is considered in Europe as most dangerous and most hardly controllable<br />

fungus due to its ability to transport nutrients and water. Traditionally, it<br />

is also supposed to possess some further specific features, which, however, do<br />

not all stand up to laboratory results. Nevertheless, in Germany, S. lacrymans<br />

has to be clearly differentiated from the other house-rot fungi in view of refurbishment.Morefar-reachingmeasureshavetobeperformedinthecaseofits<br />

presence. Thus species identity should be known.<br />

For identification, fruit bodies are preferentially used (Grosser 1985; Breitenbach<br />

and Kränzlin 1986; Jahn 1990; Ryvarden and Gilbertson 1993, 1994;<br />

Krieglsteiner 2000; Weiß et al. 2000; Kempe 2003; Bravery et al. 2003). A diagnostic<br />

key for fungi on structural timbers based on their fruit bodies is<br />

available in the internet and is to be completed in time (Huckfeldt 2002).<br />

Some species only rarely fructify in buildings, or after isolation in laboratory<br />

culture, or do it never. However, some house-rot fungi form mycelial strands<br />

(cords). The classical strand diagnosis from Falck (1912) is old and includes<br />

only a few species. A diagnostic key including color photographs based on<br />

measurements in infected buildings and on wood samples in laboratory culture<br />

comprises several species (Huckfeldt and Schmidt 2004, 2006). An updated<br />

version is shown in Appendix 1. A recent textbook comprises photographs and<br />

identification keys for fruit bodies and strands of fungi occurring on wood in<br />

indoor and exterior use (Huckfeldt and Schmidt 2005).<br />

If neither fruit bodies nor strands, but only vegetative mycelia are present,<br />

e.g., if only mycelium is found in buildings, or as it is the case for fungi cultured<br />

in the laboratory on agar, there are keys and books for mycelia (Nobles<br />

1965; Stalpers 1978; Lombard and Chamuris 1990). However, some genera<br />

among the house-rot fungi are hardly or not at all distinguishable into species,<br />

like Antrodia, Coniophora and Leucogyrophana. Thus, molecular methods<br />

may be used (Chap. 2.4.2). Among the DNA-based techniques, species-specific<br />

ITS-PCR differentiated seven indoor wood-decay Basidiomycetes (Fig. 2.23,<br />

Table 2.9; Moreth and Schmidt 2000). The technique is meanwhile used in<br />

Germany for commercial identification of house-rot fungi. Sequencing of the<br />

internal transcribed spacer (ITS) of the ribosomal DNA (rDNA) and subsequent<br />

sequence comparison by BLAST with ITS sequences from correctly<br />

identified fungi deposited in the nucleotide databases is to date the best<br />

molecular tool for diagnosis (Table 2.8 and Fig. 2.22; Schmidt and Moreth<br />

2002, 2003).<br />

There is a great number of investigations on the physiology of house-rot<br />

fungi in text books (e.g., Jennings and Bravery 1991), monographs (e.g., Cockcroft<br />

1981), and publications that may used in support of identification. Among<br />

the physiological parameters, growth rate and reaction to wood moisture con-<br />

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8.5 Damage to Structural Timber Indoors 211<br />

Table 8.7. Cardinal points of wood moisture content (% u) of some house-rot fungi for<br />

colonization and decay of wood (after Huckfeldt and Schmidt 2005)<br />

Species Minimum for Minimum Optimum Maximum<br />

colonization for decay for decay for decay<br />

(moisture source (mass loss (mass loss (mass loss<br />

20–30 cm away) above 2%) above 10%) above 2%)<br />

Serpula lacrymans 21 26 45–140 240<br />

Leucogyrophana pinastri 30 37 44–151 184<br />

Coniophora puteana 18 22 36–210 262<br />

Antrodia vaillantii 22 29 52–150 209<br />

Donkioporia expansa 21 26 34–126 256<br />

Gloeophyllum abietinum 20 22 40–208 256<br />

Gloeophyllum sepiarium 28 30 46–207 225<br />

Gloeophyllum trabeum 25 31 46–179 191<br />

tent and temperature are important features. However, some of the older data<br />

suffer in so far as they derive from only vague or incorrectly identified fungi.<br />

Data that are based on genetically verified fungi are shown in Tables 2.2, 3.8–<br />

3.11, and 8.7.<br />

Regarding the most important influence on wood decay, wood moisture,<br />

opinion has it that the indoor polypores need moisture above the fiber saturation<br />

range, which often occurs only after wetting with water, whereas the<br />

Coniophora spp. mostly attack wood, which was moisturized by vaporous water<br />

or by contact with damp material. The Dry rot fungus is halfway as it<br />

germinates on contact-wetted timber, but takes water from wet substrates by<br />

capillary mechanism and translocates water in its mycelium to timber for<br />

further growth (Schultze-Dewitz 1985).<br />

In piled Scots pine sapwood samples placed on agar in 2-L Erlenmeyer<br />

flasks, a continuous wood moisture gradient developed within 6 weeks by diffusion<br />

from the agar via the lowest sample, which was water-saturated to the<br />

uppermost air-dried sample (Huckfeldt 2003). Table 8.7 shows that all fungi<br />

subsequently inoculated on the agar near the bottom wood sample degraded<br />

very wet wood. For example, S. lacrymans showed more than 2% wood mass<br />

loss in a sample of 240% final moisture content. The optimum moisture for<br />

decay (mass loss above 10%) varied among the species from 36 to 210% u. The<br />

minimum moisture for decay (mass loss above 2%) was slightly below fiber<br />

saturation and for C. puteana and G. abietinum significantly low at 22% u.<br />

Minimum moisture for wood colonization was for some fungi around 20% u,<br />

whereby the wood sample was 20–30 cm away from the agar as the water source<br />

(Huckfeldt and Schmidt 2005).<br />

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212 8 Habitat of <strong>Wood</strong> Fungi<br />

8.5.2<br />

Lesser Common Basidiomycetes in Buildings<br />

The following species description starts with some lesser common fungi and<br />

ends with the most serious European fungus, the True dry rot fungus Serpula<br />

lacrymans,inorderofatransitiontotheremedialtreatments.Daedalea<br />

quercina, Gloeophyllum species, Lentinus lepideus and Paxillus panuoides,<br />

which also occur in buildings, have been already described in Chap. 8.4. The following<br />

data are based on observations and measurements in attacked buildings<br />

and on genetically verified pure cultures on wood samples in the laboratory<br />

(Huckfeldt 2003; Huckfeldt and Schmidt 2005; Huckfeldt et al. 2005; Schmidt<br />

and Huckfeldt 2005), and were supplemented mainly from Grosser (1985),<br />

Breitenbach and Kränzlin (1986), Ryvarden and Gilbertson (1993, 1994), and<br />

Bravery et al. (2003).<br />

8.5.2.1<br />

Diplomitoporus lindbladii<br />

Occurrence: circumpolar in the conifers zone, in Europe throughout the conifer<br />

forest regions, but rare in the Mediterranean region, North America, also on<br />

hardwoods;<br />

Fruit body (Fig. 8.18a): annual to biannual, resupinate, becoming widely<br />

effused (a few decimeters), up to 6 mm thick, biannual basidiomes thicker,<br />

frayed margin, easily separable; upper surface white-cream, grey when old;<br />

pore surface with 2–4 circular-angular pores/mm, to 3 mm deep; trimitic;<br />

allantoid to cylindrical, hyaline spores (5–7 × 1.5–2µm); bipolar;<br />

Strands (Fig. 8.18b): on timber in laboratory culture, white, yellowing when<br />

dry, root-like, iceflower-like, similar to A. vaillantii; fiberssimilartoA. vaillantii,butsolublein5%KOH;<br />

Significance: white rot, indoors.<br />

8.5.2.2<br />

Asterostroma cervicolor and A. laxum<br />

Fruit body (Fig. 8.18c): resupinate, sheet-like, thin, whitish to ochre or cinnamon,<br />

hardly distinguishable from mycelium; no pores; may be found on<br />

masonry; spores warty (A. cervicolor), without warts (A. laxum); monomitic;<br />

Strands and mycelium (Fig. 8.18d): cream-brown, up to 1-mm-wide strands<br />

with a rough appearance, flexible when dry, sometimes across and inside masonry<br />

over a long distance, brown strands often present next to fruit body,<br />

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8.5 Damage to Structural Timber Indoors 213<br />

Fig.8.18. Diplomitoporus lindbladii a Fruit body and detail. b Mycelium and strands on<br />

white-rotten wood; Asterostroma cervicolor c Fruit body on a ground ceiling. d Knotty<br />

mycelium and strands on a floorboard. e Stellar setae; Dacrymyces stillatus f Young fruit<br />

bodies. g Old fruit bodies on window joinery (photos T. Huckfeldt) — 5 cm, - - - 5 mm<br />

embedded in white mycelium or in fruit bodies (A. laxum); surface mycelium<br />

of A. cervicolor first white, then brown, partly only small mycelial plugs;<br />

Stellar setae (Fig. 8.18e): within basidiome, mycelium and strand (German:<br />

“Sternsetenpilz”); setae dichotomically branched, to 90 µm in diameter and<br />

partly rare in A. laxum, setae rarely branched and to 190µm indiameterin<br />

A. cervicolor;<br />

Significance: white-rot, softwoods, often on joinery, e.g., skirting boards,<br />

floor and ceiling boards, windows, fiber and gypsum boards, decay often<br />

limited in extent.<br />

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214 8 Habitat of <strong>Wood</strong> Fungi<br />

8.5.2.3<br />

Dacrymyces stillatus, Orange Jelly<br />

Fruit body (Fig. 8.18f, g): yellow-orange-red, also whitish, dark orange when<br />

dry, button-shaped, lenticular to mug- or plate-like, 1–15 mm wide, gelatinouselastic,slimy<br />

meltingwhenold,solitary andingroups,oftentwodifferentforms<br />

on the same place, a brighter form with basidiospores and a darker form with<br />

arthrospores, often appearing through paint;<br />

Significance: white rot, softwoods and hardwoods, wood darkens, decay<br />

commonly patchy with small pockets of rot, often restricted to interior of<br />

timber, on window and doorframes, common outdoors on windows, claddings<br />

and along the gable board of the roof (Alfredsen et al. 2005).<br />

8.5.3<br />

Common House-Rot Fungi<br />

There is a bulk of knowledge on the common indoor wood decay fungi due<br />

to their economic importance. Thus, these species and species groups are<br />

described in more detail in the following (also Findlay 1967; Bavendamm<br />

1969; Coggins 1980; Cockcroft 1981; Grosser 1985; Jennings and Bravery 1991;<br />

Ryvarden and Gilbertson 1993, 1994; Krieglsteiner 2000; Weiß et al. 2000;<br />

Kempe 2003; Sutter 2003; Huckfeldt and Schmidt 2005).<br />

8.5.3.1<br />

Donkioporia expansa, Oak Polypore<br />

This fungus is only recognized since the 1920s as relevant for practice and<br />

since about 1985 as important decay fungus in buildings (Kleist and Seehann<br />

1999; Erler 2005). Assumably, the species was often overlooked despite the less<br />

common decay type of a white rot in buildings and the large size of its fruit<br />

bodies. A reason it was overlooked may be that damage is often restricted to<br />

wood interior and not noticed until fruit bodies appear and furthermore that<br />

the fruit bodies are inconspicuously embedded in plentiful surface mycelium.<br />

Occurrence: fairly rare, Central Europe, North America, in Germany preferentially<br />

in the south, at least in Europe almost exclusively restricted to structural<br />

timber, preferably Quercus, but also Castanea, Fraxinus, Populus and<br />

Prunus,frequentlyalsoonindoortimberofPicea and Pinus;<br />

Fruit body (Fig. 8.19a, b): perennial, resupinate, first white, then ochre to<br />

reddish-tobacco-brown to grey with ageing, to 10 cm thick, becoming widely<br />

effused to a few square meters, firmly attached, an walls wavy to stairs-like,<br />

often multi-layered, tough-elastic with silvery surface when fresh, hard and<br />

brittle when dry, easily separable when old, mainly made up of long tubes, 4–5<br />

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8.5 Damage to Structural Timber Indoors 215<br />

Fig.8.19. Donkioporia expansa a Fruit body and mycelium. b Detail showing the long pores.<br />

c Old mycelium. d Strand-like structures grown on wood in laboratory culture; Antrodia<br />

vaillantii e Mycelium and strands. f Fruit body and detail. g Antrodia sinuosa fruit body<br />

and detail. h Antrodia xantha fruit body and detail. i Antrodia serialis fruit body and detail.<br />

j Oligoporus placenta fruit body and detail (photos b–j: T. Huckfeldt) — 5 cm, --- 5 mm<br />

circular to angular pores/mm, often amber guttation drops, which leave behind<br />

small black pits when dry; trimitic; ellipsoid spores 4.5−7 × 3.2−3.7µm;<br />

Mycelium (Fig. 8.19a,c): inside wood shakes and cavities, at high air humidity<br />

also on free wood surfaces with thin, skin-like mycelial flaps with bizarre<br />

seeds, later thick, brownish surface mycelium, guttation as on fruit bodies,<br />

black demarcation lines between mycelium and woody substrate;<br />

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216 8 Habitat of <strong>Wood</strong> Fungi<br />

Strands (Fig. 8.19d): not yet observed in buildings, strand-like structures<br />

on wood samples in laboratory culture, rare, cream, yellowish to grey-brown,<br />

root-like, hidden under mycelium;<br />

Significance: The Oak polypore inhabits damp areas in kitchens, bathrooms,<br />

WC, cellars, cow-sheds, occurs on beams, under floors, in mines, on<br />

bridge timber, and cooling tower wood [Azobé, Bangkirai; v. Acker et al.<br />

(1995); v. Acker and Stevens (1996)]. It produces a white-rot. Continuous high<br />

wood moisture promotes growth (defective sanitary facilities, cooling tower<br />

wood). The fungus is often found at beam-ends that are enclosed in damp<br />

walls. At initial attack of softwoods, the timber surface remains often nearly<br />

intact (“interior rot”). In laboratory culture, minimum wood moisture for<br />

wood colonization was 21% u and for wood decay 26%. Greatest wood mass<br />

losses occurred between 34 and 126% (Table 8.7). Moisture maximum was<br />

256%. Temperature optimum was 28 ◦ C, and maximum was 34 ◦ C(Table3.8).<br />

The fungus survived for 4 h in dry wood of 95 ◦ C (Huckfeldt 2003). <strong>Wood</strong><br />

mass losses according to EN 113 were: oak sapwood 45%, oak heartwood<br />

23%, beech 50%, birch 60%, pine sapwood 40% (Kleist and Seehann 1999).<br />

Assumably,thereisnospreadbystrandsfrommoisttodrywoodandno<br />

growth through the masonry because strands were only found in vitro to date.<br />

Thus, refurbishment only needs drying and exchange of destroyed timber. In<br />

oaks, the fungus is often associated with the death-watch beetle, Xestobium<br />

rufovillosum.<br />

8.5.3.2<br />

Indoor Polypores: Antrodia Species and Oligoporus placenta<br />

Four Antrodia species and O. placenta may be assigned to the indoor polypore<br />

fungi.<br />

Occurrence: circumglobal in the coniferous forest zone, mostly on softwoods<br />

(Findlay 1967; Domański 1972; Coggins 1980; Lombard and Chamuris<br />

1990; Grosser 1985; Lombard 1990; Ryvarden and Gilbertson 1993, 1994;<br />

Krieglsteiner 2000; Sutter 2003);<br />

Antrodia vaillantii occurs circumglobal in the coniferous forest zone and in<br />

Europe widely distributed, but rather rare in Fennoscandia. It is the most frequent<br />

fungus in British mines (Coggins 1980). Antrodia sinuosa is circumpolar<br />

in the boreal conifer zone, widespread in Europe, North America, East Asia,<br />

North Africa, and Australia (Domański 1972). The species was in Sweden with<br />

1,045 damages between 1978 and 1988 with 13% portion the most common indoor<br />

polypore (Viitanen and Ritschkoff 1991a). Antrodia serialis attacks logs<br />

and piles, causes heart rot in standing trees and occurs widespread, also in<br />

Himalaya and Africa (Seehann 1984; Breitenbach and Kränzlin 1986), rarely<br />

(1.4%) in buildings (Viitanen and Ritschkoff 1991a; Coggins 1980), within<br />

the roof area, in cellars and under corridors (Domański 1972). Antrodia xan-<br />

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8.5 Damage to Structural Timber Indoors 217<br />

tha (Domański 1972) occurs in Europe and North America on fallen stems,<br />

branches, stumps, in greenhouses (Findlay 1967), at windows (Thörnqvist et al.<br />

1987), on timber in swimming pools and in flat roofs (Coggins 1980). Oligoporus<br />

placenta is rare, but widespread in Europe except for the Mediterranean.<br />

In North America, the fungus is the most common wood decayer in ships<br />

(Findlay 1967) and was exported to Great Britain (Coggins 1980). In North<br />

America, O. placenta and A. serialis are common on mine timber and poles<br />

(Gilbertson and Ryvarden 1986).<br />

Antrodia vaillantii, Mine polypore, Broad-spored white polypore<br />

Fruit body (Fig. 8.19f): annual, resupinate, first white, then light yellow to grey,<br />

drying, as corky layer (to 1 cm thick) on the wood underside or above as pad;<br />

2–4 circular-angular pores/mm hymenium, to 12 mm long; dimitic; hyaline<br />

spores 5–7 × 3–4µm;<br />

Strands (Fig. 8.19e): pure white, felty, 0.5–7 mm in diameter, ice flower-like,<br />

flexiblealsoifdry;fibersnumerous,white,flexible,2–4µm thick, unsoluble<br />

in 5% KOH; vessels not rare, to 25µm in diameter, partly with thick walls and<br />

reduced lumen, no wall thickenings; vegetative hyphae with clamps, 2–6µm<br />

in diameter, often also thick-walled.<br />

Antrodia sinuosa, White polypore, Small-spored white polypore<br />

Fruit body (Fig. 8.19g): similar to A. vaillantii, annual,resupinate,to5mm<br />

thick; 1–3 circular-sinuous pores/mm, to 3 mm long; dimitic; hyaline spores<br />

4−6×1−2µm;<br />

Strands: similar to A. vaillantii.<br />

Antrodia xantha, Yellow polypore<br />

Fruit body (Fig. 8.19h): annual, resupinate, first yellowish, then pale, whitecream,<br />

crusty to bracket-shaped, to 10 mm thick, 1 m wide; 3–7 circularangular<br />

pores/mm, to 5 mm long; margin without pores; on vertical substrates<br />

small knots, to 8 mm large, partly grown together; dimitic; hyaline spores<br />

4−5×1−1.5µm;<br />

Strands: similar to A. vaillantii, but partly yellow discolored, later often pale<br />

and then undistinguishable from A. vaillantii.<br />

Antrodia serialis, Effused tramete, Row polypore<br />

Fruit body (Fig. 8.19i): annual to biennial, resupinate to pileate, first white to<br />

cream-ochre, then pink-spotted, to 6 mm thick, to a few decimeters wide; 2–4<br />

circular, partly slitted pores/mm, to 5 mm long; distinct, wavy margin; also in<br />

rows; dimitic; hyaline spores 4−7 × 3−5µm;<br />

Strands: not yet found.<br />

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218 8 Habitat of <strong>Wood</strong> Fungi<br />

Oligoporus placenta, (Reddish) Sap polypore<br />

Fruit body (Fig. 8.19j): annual, resupinate, either white to grey-brown (form<br />

monticola) or later pink to salmon-violet (reddish form placenta)(Domański<br />

1972), easily passing, to 1 cm thick; 2–4 circular-angular-slitted pores/mm, to<br />

15 mm long; monomitic; hyaline spores 4−6 × 2−2.5µm;<br />

Strands: on wood samples in laboratory culture, white, partly yellowing,<br />

easily refractable, to 1 mm in diameter; fibers and vessels rare or absent.<br />

Significance: The five “indoor polypores” form a group of brown-rot fungi that<br />

are associated with the decay of softwoods in buildings. In Central Europe,<br />

these fungi belong after the Dry rot fungus, Serpula lacrymans, andtogether<br />

with the Coniophora cellar fungi to the most common indoor decay fungi. They<br />

accounted for 14% of indoor decay fungi in Denmark (Koch 1985) and Finland<br />

(Viitanen and Ritschkoff 1991a). A survey in California ranked A. vaillantii,<br />

A. sinuosa, A. xantha and O. placenta with29%occurrenceasthemaingroup<br />

(Wilcox and Dietz 1997).<br />

The polypores have similar biology and distribution (Lombard and Gilbertson<br />

1965; Donk 1974; Breitenbach and Kränzlin 1986; Lombard and Chamuris<br />

1990; Bech-Andersen 1995; Schmidt and Moreth 1996, 2003). They differ in<br />

their fruit body, spore morphology (Jülich 1984; Ryvarden and Gilbertson<br />

1993, 1994) and sexuality. Some species also fruit in laboratory culture, which<br />

supports identification of mycelia and tests for sexuality. Antrodia vaillantii<br />

is tetrapolar heterothallic (Lombard 1990), A. serialis, A. sinuosa and O.<br />

placenta are bipolar (Domański 1972; Stalpers 1978). Three Antrodia species<br />

develop strands (Falck 1912; Stalpers 1978; Jülich 1984), O. placenta only in<br />

vitro. However, the vegetative mycelium that has been isolated from decayed<br />

wood is hardly distinguishable (Nobles 1965). Due to the limited differentiating<br />

features, misinterpretations occur.<br />

Furthermore, the nomenclature has a confusing history and is still not always<br />

uniform (Cockcroft 1981). Fungi have been variously classified as Polyporus,<br />

Poria, Amyloporia, Fibroporia (Domański 1972). Misleading synonyms in the<br />

older literature such as Polyporus vaporarius and Poria vaporaria have been<br />

used for different species, viz. A. vaillantii (Bavendamm 1952c), A. sinuosa,<br />

and O. placenta. According to Ryvarden and Gilbertson (1994), the Reddish<br />

sap polypore, formerly Tyromyces placenta (Fr.) Ryv., was placed in Oligoporus,<br />

since the genus Tyromyces is restricted to fungi causing a white rot. Older<br />

synonyms are Postia placenta (Fr.) M.J. Larsen & Lomb., Poria placenta (Fr.)<br />

Cooke sensu J. Eriksson, Poria monticola Murr., and the haploid standard<br />

strain Poria vaporaria (Pers.) Fr. sensu J. Liese (Domański 1972). Postia is<br />

a nomen provisorium/nudum in the sense of Fries and illegitimate in the sense<br />

of Karsten. Isolate MAD 698 of Postia placenta was thoroughly investigated in<br />

view of brown-rot decay mechanisms (e.g., Clausen et al. 1993; Highley and<br />

Dashek 1998). Difficulties may increase because O. placenta separates into the<br />

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8.5 Damage to Structural Timber Indoors 219<br />

forms placenta with salmon-pink fruit bodies (“Reddish sap polypore”) and<br />

monticola, never with reddish stain (Domański 1972). Monokaryotic isolates<br />

of O. placenta were used for testing wood preservatives in Germany (Poria<br />

vaporaria “standard strain II”) and are obligatory in the recent European<br />

standard EN 113 (see Table 3.9, 3.10, named “Poria placenta” FPRL 280). Even<br />

literature from 2005 uses the names Postia placenta and Poria placenta.<br />

For species identification in the case that only vegetative mycelium is present,<br />

rDNA-ITS sequencing separates the five species (Schmidt and Moreth 2003;<br />

Chap. 2.4.2.2).<br />

For an easier understanding during a practical valuation of a fungal damage,<br />

the different fungi are often summarized as “indoor polypores” or as “Vaillantii<br />

group”, particularly because they differ from the Cellar fungus and Dry rot<br />

fungus by their mycelia, strands, and fruit bodies. The polypores, particularly<br />

A. vaillantii, form a well-developed white and cottony surface mycelium without<br />

“inhibition colors”, which, thus, can be confused with the young mycelium<br />

of the Dry rot fungus. Polypore mycelium spreads ice flower-like over the substrate,<br />

that of the Dry rot fungus is converted with ageing into silvery-grey<br />

skins, and that of the cellar fungi is dominated by fine black strands. White<br />

(A. vaillantii), to string-thick, smooth and flexible strands develop within<br />

the mycelium and grow over non-woody substrates and also through porous<br />

masonry (Grosser 1985), the latter, however, less intensive than by the Dry<br />

rot fungus. The white to yellow (A. xantha) orred(O. placenta f. placenta)<br />

fruit bodies show pores that are visible with the naked eye (Fig. 8.19). The<br />

dry wood shows the typical brown-cubical rot. It is often said that the cubes<br />

caused by the polypores and the cellar fungi are smaller than those by the<br />

Dry rot fungus. The cube size varies however also as a function of the wood<br />

moisture content (Grosser et al. 2003). After advanced decay, the dried substrate<br />

of most brown-rot fungi can be ground with the fingers to a brown<br />

powder (“lignin”).<br />

The polypores attack predominantly coniferous woods in damp new and<br />

old buildings, particularly in the upper floor, furthermore mine timber, stored<br />

timber as well as timber in outside use, particularly in the soil/air zone, such<br />

as poles and sleepers. They also attack trees as wound parasites and live<br />

on stumps and fallen trees (Krieglsteiner 2000). Antrodia serialis was found<br />

in over-mature Sitka spruce trees (Seehann 1984). “Dry” wood should not<br />

become infected. In the laboratory, however, wood of 22% moisture content<br />

was colonized (Table 8.7). As so-called “wet-rot fungi” (Coggins 1980; Bravery<br />

et al. 2003), they need wet wood with moisture contents from 30 to 90% u for<br />

a long time. According to literature, the optimum is around 45% (Table 3.6).<br />

Laboratory experiments revealed that minimum moisture for wood decay by<br />

A. vaillantii was 29% and the optimum 52 to 150% (Table 8.7). With timber<br />

drying, Antrodia species were supposed to die (Bavendamm 1952c; Coggins<br />

1980). However, more convincing seems that they only stop growth (Grosser<br />

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220 8 Habitat of <strong>Wood</strong> Fungi<br />

1985). In the laboratory, over 11 years were survived by “dryness resistance”<br />

(Theden 1972), so that fungi may come to life again. There is also resistance to<br />

high temperature: Antrodia vaillantii, A. sinuosa and O. placenta survived on<br />

agar 3 h at 65 ◦ C. Antrodia vaillantii and O. placenta withstood heat of 80 ◦ C for<br />

4 h in slowly dried wood samples (Huckfeldt 2003), which has to be considered<br />

in view of a possible treatment of infected homes with hot air.<br />

Some species destroy timber in soil contact, like poles and palisades, even<br />

if it is properly impregnated with chrome-copper salts (Stephan et al. 1996).<br />

Especially A. vaillantii but also A. xantha and O. placenta are known for<br />

copper tolerance (Da Costa and Kerruish 1964) due to the production of oxalic<br />

acid (Rabanus 1939; Da Costa 1959; Sutter et al. 1983, 1984; Jordan et al.<br />

1996). Strain variation occurred (Da Costa and Kerruish 1964; Collett 1992a,<br />

1992b), and monokaryons were more tolerant than their parental strains (Da<br />

Costa and Kerruish 1965). In vitro, A. vaillantii was the most copper-tolerant<br />

fungus among the five species (Table 3.10) and produced most oxalic acid<br />

(Table 3.9; Schmidt and Moreth 2003). Antrodia vaillantii is also tolerant to<br />

arsenic (Göttsche and Borck 1990; Stephan and Peek 1992).<br />

8.5.3.3<br />

Cellar fungi: Coniophora species<br />

Occurrence: The genus Coniophora comprises about 20 species occurring<br />

worldwide with a broad host range primarily on conifers (Ginns 1982). Seven<br />

species occur in Europe (Jülich 1984) and five in Western Germany (Krieglsteiner<br />

1991). Coniophora puteana is frequently associated with brown-rot<br />

decay in European buildings. The fungus was estimated to be twice as common<br />

as the Dry rot fungus in the UK (Eaton and Hale 1993). It comprised over<br />

50% of the inquiries at the Danish Technological Institute (Koch 1985), 16.3%<br />

in Norway (Alfredsen et al. 2005), and 13% at the Finnish Forest Products<br />

Laboratory (Viitanen and Ritschkoff 1991a). The fungus has been used for<br />

nearly 70 years as a test fungus for wood preservatives in Europe. It also occurs<br />

in the USA, Canada, South America, Africa, India, Japan, Australia, and New<br />

Zealand. Further “cellar fungi” that attack indoor timber in Europe are especially<br />

C. marmorata,andalsoC. arida and Colivacea(Fig. 8.20). In Europe, the<br />

cellar fungi cause with about 10% frequency the two to third most common<br />

fungal indoor wood decay after S. lacrymans. In Australia and New Zealand, C.<br />

arida and C. olivacea are common. Some further Coniophora species also occur<br />

in buildings, mines and glass houses, but predominantly in warm climatic<br />

zones (Ginns 1982). The species can be differentiated by their fruit bodies<br />

(Jülich and Stalpers 1980; Breitenbach and Kränzlin 1986; Krieglsteiner 2000).<br />

However, the species concept within Coniophora is difficult because there are<br />

only a few, and unstable characteristics, which complicates species identification<br />

in infected buildings. With regard to isolates in culture, Coniophora cannot<br />

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8.5 Damage to Structural Timber Indoors 221<br />

Fig.8.20. Cellar fungi. Coniophora puteana a Fruit body. b Fruit body margin. c Fruit body<br />

detail with warts. d Strands in a false ceiling. e Strands on a steel girder. f Coniophora arida<br />

fruit body. g Coniophora olivacea fruit body (photos T. Huckfeldt) — 5 cm, --- 5 mm<br />

be differentiated at the species level by morphological and cultural characteristics<br />

(Stalpers 1978). Thus, isolations from buildings were summarized as C.<br />

puteana/ C. marmorata (Guillitte 1992). Sequencing of the rDNA-ITS separated<br />

the species (Schmidt et al. 2002b). Based on fruit-body identification, C. marmorata<br />

is rather common in southern Germany. The following description is<br />

based mainly on Huckfeldt (2003), Huckfeldt and Schmidt (2005) and Schmidt<br />

and Huckfeldt (2005).<br />

Coniophora puteana, (Brown) Cellar fungus<br />

Fruit body (Fig. 8.20a–c): annual, resupinate, light to dark brown, first whiteyellow,<br />

then brownish; indistinct, fibrous margin; to 4 mm thick, to a few<br />

decimeters wide, firmly attached, fragile when dry; warty knots up to 5 mm<br />

thick; monomitic; yellow-brown spores 9−16 × 6−9µm;<br />

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222 8 Habitat of <strong>Wood</strong> Fungi<br />

Strands (Fig. 8.20d, e): first white, soon brown-black, to 2 mm thick, rootlike,<br />

fragile, black wood beneath the strands; fibers brown, 2–5µm thick,<br />

lumina visible; vessels 10–30µm thick, often deformed, no bars; vegetative<br />

hyphae mostly clampless, rarely with multiple clamps, with brown drops (1–<br />

5µm) holding the hyphal net together.<br />

Coniophora marmorata, Marmoreus cellar fungus<br />

Fruit body: annual, resupinate, pale to olive-brown, grey margin, to 0.4 mm<br />

thick, to 15 cm wide, separable, felty; dimitic; no picture available because not<br />

yet found in buildings in northern Germany;<br />

Strands: brownish, to 1 mm thick, easily separable, no drops.<br />

Coniophora arida,Aridcellarfungus<br />

Fruit body (Fig. 8.20f): annual, resupinate, white-ochre to yellow-brown, light<br />

margin, to 0.3 mm thick, to 10 cm wide, firmly attached, smooth to felty, finefrayed<br />

margin; monomitic;<br />

Strands: rare, white to brown, 0.1 mm thick.<br />

Coniophora olivacea, Olive cellar fungus<br />

Fruit body (Fig. 8.20g): annual, resupinate, olive-brown, margin lighter, fraying<br />

with strands, to 0.6 mm thick, to 6 cm wide, firmly attached, smooth to warty,<br />

fibrous-cottony, septate cystidia, monomitic, partly merging fruit bodies;<br />

Strands: brown, thin.<br />

Significance: The older European literature on occurrence, biology and significance<br />

of the cellar fungi summarizes the several fungi to C. puteana. This<br />

fungus was said to be the most common species in new buildings. It however<br />

occurs also in damp old buildings, on stored wood, timber in soil contact like<br />

poles, piles, sleepers and on bridge timber as well as rarely on stumps and<br />

as wound or a weakness parasite on living trees (Bavendamm 1951a; Grosser<br />

1985; Breitenbach and Kränzlin 1986; Sutter 2003). Of 177 Basidiomycetes<br />

on American mine timbers, 83 isolates were C. puteana (Eslyn and Lombard<br />

1983). In buildings it does not occur, like the name misleadingly suggests,<br />

only in cellars, but it can ascend everywhere on damp timber up to the roof<br />

(Schultze-Dewitz 1985, 1990). Beside softwoods, it attacks also several hardwoods<br />

(Wälchli 1976). As a so-called wet rot fungus (Bravery et al. 2003) with<br />

relatively high requirement for moisture from 30 to about 70% u and the optimum<br />

around 50% (Table 3.6), all timber in the area of damp walls (beam<br />

ends and wall slats), damp floors and ceilings in kitchens, bathrooms and toilets<br />

as well as all timber in areas with water vapor development (swimming<br />

pools, launderettes) is endangered. In vitro, minimum moisture of C. puteana<br />

for wood colonization was 18% u and for decay 22%. The optimum moisture<br />

was broad, from 36 to 210% (Table 8.7). Damage by the cellar fungi is quite<br />

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8.5 Damage to Structural Timber Indoors 223<br />

comparable with that one of the Dry rot fungus and can even exceed it. A fresh<br />

floorboard can be completely destroyed in 1 year, so the danger exists that<br />

furniture or persons can fall through. These types of damages occurred in<br />

Germany frequently during the building boom in the postwar years, if insufficiently<br />

dried wood were used, or the homes had not sufficiently dried before<br />

they were moved into and drying was prevented by humidity-impermeable<br />

painting, linoleum, or carpet.<br />

The cellar fungi belong to the fast-growing house-rot fungi and reached on<br />

agar at 23 ◦ C up to 11 mm radial increase per day (Table 3.11). The optimum<br />

temperature (Table 3.8) was between 20 and 27.5 ◦ C, whereby C. marmorata<br />

preferred the warmer range, and the maximum was between 25 and about<br />

37.5 ◦ C. Isolate Ebw. 1 of C. puteana survived 15 min. at 60 ◦ C(Miričand<br />

Willeitner 1984) and 3 h at 55 ◦ C (Table 3.8). In slowly dried wood samples,<br />

even 4 h at about 70 ◦ C were withstood (Huckfeldt 2003). The data concerning<br />

a possible dryness resistance of the fungus vary: after observations from practice,<br />

it dies when drying; up to 7 years were however survived in dry wood in<br />

the laboratory (Theden 1972). There was isolate variation with regard to the<br />

sensitivity to wood preservatives (Gersonde 1958).<br />

Recognition characteristics (Fig. 8.20): The diagnosis is not always easy,<br />

since fruit bodies are rare and colonized wood shows frequently no or only meager<br />

surface mycelium (Käärik 1981). The few centimeters to several decimeters<br />

wide, resupinate, brownish fruit bodies resemble those of the Dry rot fungus,<br />

are however thinner. The species C. puteana is easy to recognize of the warty<br />

knots on the hymenophore (name: “carrying cones”). Characteristic on agar<br />

are double and multiple clamps. The initial stages of the rot are frequently<br />

ignored, since hardly infection signs become visible on exposed wood exterior<br />

surfaces, e.g., on baseboards, while the wood at the backside is already<br />

completely rotten and overgrown by thread-thin, radiate to root-like, brown<br />

to black strands (Fig. 8.20d,e). Early signs of rot are often dark discolorations<br />

under the paints.<br />

8.5.3.4<br />

Dry-rot fungi: Serpula species, Leucogyrophana species, Meruliporia incrassata<br />

This chapter deals with the brown-rot causing dry-rot fungi, namely Serpula<br />

lacrymans and S. himantioides,andtheLeucogyrophana species, L. mollusca,<br />

L. pinastri and L. pulverulenta (Fig. 8.21). Due to its economic relevance in<br />

Europe, emphasis is laid on S. lacrymans, however, the American pendant, the<br />

American dry rot fungus, Meruliporia incrassata,isconsidered.<br />

The way of spelling of the epithet “lacrimans”, which can be attributed to<br />

Fries (1821), is linguistically correct, however illegal, since the original spelling<br />

by Wulfen in 1781 was with “y” (Pegler 1991).<br />

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224 8 Habitat of <strong>Wood</strong> Fungi<br />

Occurrence and significance: The True dry rot fungus, S. lacrymans, isthe<br />

most dangerous house-rot fungus in central, eastern, and northern Europe,<br />

northwards to the Hebrides. It grows however also in cooler areas of Japan<br />

(Doi 1991), Korea, India, Pakistan and Siberia (Krieglsteiner 2000), in New<br />

Zealand and southern Australia (Thornton 1991), in Mexico, Canada and in the<br />

northern USA (Rayner and Boddy 1988). The data concerning its involvement<br />

in fungal indoor damage reach from 16% in Norway (Alfredsen et al. 2005)<br />

over 22% in Denmark (Koch 1991), 54% in Poland (Wa˙zny and Czajnik 1963)<br />

and North Germany (Schmidt and Huckfeldt 2005) to 59% in Sweden (Viitanen<br />

and Ritschkoff 1991a). For example, the annual repair costs of dry rot damage<br />

amount to at least 150 million £ in Great Britain (Jennings and Bravery 1991).<br />

Since the fundamental work by Hartig (1885), Mez (1908), Falck (1912:<br />

cf. Hüttermann 1991) and Wehmer (1915) S. lacrymans belongs to the bestinvestigated<br />

fungi. The older observations and results are described by Liese<br />

(1950), Bavendamm (1951b), Cartwright and Findlay (1958), Harmsen (1960),<br />

Savory (1964), Wagenführ and Steiger (1966), Findlay (1967), Bavendamm<br />

(1969), Coggins (1980) and Segmüller and Wälchli (1981). A literature search<br />

from 1988 lists 1200 publications (Seehann and Hegarty 1988). Informative<br />

photographsfordiagnosisonthebasisfruitbodies(Fig.8.21a,b)areby<br />

Grosser (1985) and on the Internet (www.hausschwamminfo.de). Younger reviews<br />

and laboratory findings to the biology and physiology are by Jennings<br />

and Bravery (1991), Viitanen and Ritschkoff (1991a), Schmidt and Moreth-<br />

Kebernik (1991a), Eaton and Hale (1993), Huckfeldt (2003), Schmidt (2003),<br />

Huckfeldt and Schmidt (2005), Huckfeldt et al. (2005), Schmidt and Huckfeldt<br />

2005). There is a German instruction leaflet with experiences from the practice<br />

on life conditions and refurbishment (Grosser et al. 2003).<br />

As cause of the special danger of the fungus the following features were<br />

specified: Its “omnipresent” spores germinate on damp wood or other cellulosic<br />

materials (paper, cardboard), and the mycelium can reach wood by<br />

growing over and through substrates that do not serve as a nutrient. For initial<br />

colonization, it only needs low wood moisture content. The conventional<br />

wisdom is that it is the only fungus that can infect so-called “dry” timber<br />

(min. 21% u) and masonry (min. 0.6% water content) and widely spread by<br />

mycelium (Fig. 8.21c) and its highly developed strands (Fig. 8.21d; name: “small<br />

serpent”), thereby growing over and through wood and several other<br />

materials, like porous or ruptured masonry or its wall joints, supplying channels<br />

for electricity, and water pipes (Coggins 1991; Jennings 1991). However,<br />

recent laboratory experiments showed that S. lacrymans is not unequalled as is<br />

also other indoor fungi colonized dry wood (Table 8.7). Coggins (1980, 1991)<br />

stressed that the initial colonization of a substrate, as for example the growth<br />

throughwalljoints,occursbytheyoungesthyphaeofthevegetativemycelium,<br />

in contrast to the infection way of Armillaria species that do this by means of<br />

rhizomorphs. In contrast, the strands develop as a secondary mycelium behind<br />

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8.5 Damage to Structural Timber Indoors 225<br />

Fig.8.21. Dry-rot fungi. Serpula lacrymans a Fruit body. b Detail. c Mycelium. d Strands.<br />

e Serpula himantioides fruit body; Leucogyrophana pinastri f Old fruit body. g Detail. h Old<br />

strands and sclerotia, iMyceliumand sclerotia.jYoungsclerotia.kLeucogyrophana mollusca<br />

fruit body. l Hair-like strands and sclerotia. m Mycelium and sclerotia; Leucogyrophana<br />

pulverulenta n Old fruit body, o Mycelium and strands (photos b–o:T.Huckfeldt)—5cm,<br />

---5mm<br />

the growth front and serve rather to transport nutrients to the hyphal margin.<br />

Alkaline materials to pH 10 can be overgrown, and alkalinity is decreased by<br />

excretion of liquid (pH 3–4) at the hyphal tip. An acute infection is often for<br />

a longer time not recognized due to the “hidden way of life”. Spores and still<br />

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226 8 Habitat of <strong>Wood</strong> Fungi<br />

alive mycelia can lead to re-infections in the case of careless or inappropriate<br />

remedial treatments (Bravery et al. 2003). Thick mats of surface mycelium may<br />

cover the attacked timber assumably preventing the wood from drying.<br />

Serpula lacrymans occurs predominantly in older buildings and in the cellar<br />

and ground floor area (Schultze-Dewitz 1985, 1990; Koch 1990). Uninhabited<br />

and poorly ventilated houses and all buildings with high relative air humidity in<br />

connection with damages to the structural fabric are particularly endangered.<br />

Importantcausesofdryrotinfectionsarebuildingdefectsthataffectincreased<br />

wood moisture content (e.g., Paajanen and Viitanen 1989). The mycelium reacts<br />

sensitively to draught and humidity removal, generally to climatic changes, so<br />

that it often develops in false ceilings and false soil areas under floors and<br />

behind wall coverings, from where it spreads. Because of this hidden way of<br />

life, often only fruit bodies on masonry, baseboards, doorframes or stairway<br />

steps show that the higher floors are already infected. In extreme cases, e.g.,<br />

during the refurbishment of listed buildings, all timbers as well as large parts<br />

of the masonry have to be removed. A survey of houses in northern Germany<br />

indicated that old buildings are particularly at risk, which had insulating<br />

windows as the only measure of heat insulation. Now, the moisture in the<br />

building condenses on other weak spots like empty spaces of the brickwork at<br />

the back of heaters (Huckfeldt et al. 2005).<br />

Except in homes, the fungus occurs on mine timber and rarely in the open<br />

(poles, sleepers), but in the boreal climate not in the forest. However, according<br />

to Pegler (1991), the species occurs outdoors in Central Europe and North<br />

America, and according to Bech-Andersen (1995), in the Himalayas in conifers<br />

forests. Phylogenetic trees based on the rDNA-ITS sequence showed that the<br />

outdoor isolates from the Himalaya and from California belong to the species<br />

S. lacrymans (Chap. 2.4.2.2). Phylogenetic analyses indicate that the indoor<br />

isolates of S. lacrymans may have originated from an ancient lineage closely<br />

related to the Californian outdoor isolates (Kauserud et al. 2004b).<br />

In the open, the Wild merulius S. himantioides (Fig. 8.21e) is common, in<br />

Europe frequently on spruce wood, stumps, structural timber in outdoor use,<br />

and rarely on living trees. Occasionally, it is also found in buildings (Falck<br />

1927; Harmsen 1978; Grosser 1985; Seehann 1986; Pegler 1991).<br />

As further dry-rot fungi occur three Leucogyrophana species (Fig. 8.21f–o)<br />

in the forest on fallen stems and branches, and on wood in indoor use: L. mollusca,<br />

L. pinastri (Schulze and Theden 1948; Siepmann 1970) and L. pulverulenta<br />

(Harmsen 1953). They differ from Serpula by smaller spores (Ginns 1978;<br />

Pegler 1991; Breitenbach and Kränzlin 1986). Leucogyrophana pulverulenta is<br />

rather common in Denmark. The three fungi need a higher wood moisture<br />

content than S. lacrymans (cf. Table 8.7).<br />

Whereas S. lacrymans is restricted in North America to the northern parts<br />

of the USA and Canada, the American dry rot fungus Meruliporia incrassata<br />

(first reported in the USA in 1913) occurs particularly in the southern states<br />

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8.5 Damage to Structural Timber Indoors 227<br />

and the Pacific northwest of the USA (Verrall 1968; Palmer and Eslyn 1980;<br />

Gilbertson and Ryvarden 1987; Burdsall 1991; Zabel and Morrell 1992; Eaton<br />

and Hale 1993; Jellison et al. 2004). Being a warm-temperature fungus, two<br />

isolates from the USA and Canada grew best between 22.5 and 25 ◦ Canddied<br />

after3weeksofculturingatabout35 ◦ C (Schmidt 2003). Burdsall (1991) named<br />

24–30 ◦ C as the optimal temperature range for growth and above 36 ◦ Casthe<br />

lethal temperature. Jellison et al. (2004) quoted 28–30 ◦ C as the optimal range<br />

for growth, and 3–30 h at 40 ◦ C for lethal. Sapwood and heartwood of many<br />

gymnosperms and angiosperms are attacked. It was rarely found on standing<br />

trees, infrequently on felled logs and stumps, on structural timber outdoors<br />

such as in mills, lumber yards, on shingles, on bridge timber, posts, but is common<br />

on moist wood or wood located near a permanent or intermittent water<br />

supply if the wood is untreated (Palmer and Eslyn 1980). Some characteristics<br />

ofwooddecaybythisfungusaresimilartothoseofS. lacrymans, notably<br />

its sensitivity to dryness by mostly dying in pure culture tests with southern<br />

pine blocks of 30% wood moisture at 90% RH at 27 ◦ C(PalmerandEslyn<br />

1980), and its ability to transport nutrients and water from a feeding source to<br />

the advancing mycelial front spreading over non-wooden mortar and bricks.<br />

Pictures of mycelium and strands are by Zabel and Morrell (1992).<br />

The Serpula and Leucogyrophana speciesaswellasM. incrassata can be<br />

differentiated by their fruit bodies and strands (Appendix 1). Molecular techniques<br />

separate the vegetative mycelia (Chap. 2.4.2). The following description<br />

is based on observations and measurements in buildings and on results from<br />

wood samples in laboratory tests (Huckfeldt and Schmidt 2005; Schmidt and<br />

Huckfeldt 2005) and is supplemented especially for M. incrassata from Palmer<br />

and Eslyn (1980), Gilbertson and Ryvarden (1987), and Burdsall (1991).<br />

Serpula lacrymans, (True) Dry rot fungus<br />

Fruit body (Fig. 8.21a, b): annual to perenniell, resupinate to effused-reflexed<br />

and imbricate, sometimes stalactite-like, rust-brown, old: black; bulging,<br />

white-yellowish, sharp margin; fleshy-thick (to 12 mm), to 2 m wide, hymenophore<br />

merulioid; first monomitic, later dimitic containing fibers; yellowbrown,<br />

thick-walled spores 9−12 × 4.5−6µm; tetrapolar;<br />

Strands (Fig. 8.21d): young: white; old: grey-brown; to 3 cm in diameter,<br />

audibly breaking when dry, embedded in flabby mycelium; fibers 3–5 µm<br />

thick, hardly septate, without buckles, straight, rigidly, refractive; vessels to<br />

60µm thick, with bar-likes or warty wall thickenings, not or rarely branched.<br />

Serpula himantioides, Wild merulius<br />

Fruit body (Fig. 8.21e): annual, resupinate, sometimes membrane-like, rustbrown;<br />

white, sharp, not bulging margin, < 2 mm thick, hymenophore smooth<br />

to merulioid; yellow-brown, thick-walled spores 9−12 × 5−6µm; tetrapolar;<br />

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228 8 Habitat of <strong>Wood</strong> Fungi<br />

Strands: white to grey-brown, about 1 mm in diameter, microscopic characteristics<br />

similar to S. lacrymans.<br />

Leucogyrophana mollusca, Soft dry rot fungus<br />

Fruit body (Fig. 8.21k): resupinate, orange to yellow-brown; old: grey-blackish;<br />

white, cottony-frayed margin; 1–2 mm thick, to a few decimeters wide, easily<br />

separable; hymenophore merulioid, tooth-like elevations; uneven, brownviolet<br />

to grey-black sclerotia (Fig. 8.21m), 1–6 mm, often in groups; yellowishbrown<br />

spores 6−7.5 × 4−6µm;<br />

Strands (Fig. 8.21l): hair-like, first cream-yellow, soon brown-black, below<br />

1 mm thick, separated from mycelium (“barked”), flexible when dry, fragile<br />

when old; no fibers; vessels up to 25µm thick, numerous, in groups, with<br />

bar-thickenings.<br />

Leucogyrophana pinastri, Mine dry rot fungus, Yellow-margin dry rot fungus<br />

Fruit body (Fig. 8.21f, g): resupinate, first yellow-orange, then olive-yellow to<br />

brown, grey-black when old, to 1 m wide, hymenophore merulioid to irpicoid<br />

to hydnoid; round-oval, brown-black sclerotia to 2–3 mm thick; hyaline to<br />

yellowspores5−6×3.5−4.5µm;<br />

Strands: first yellowish, then grey-brown (Fig. 8.21h), hair-thin, separated<br />

from mycelium; no fibers; vessels to 15µm thick, numerous, in groups, with<br />

bar-thickenings.<br />

Leucogyrophana pulverulenta, Small dry rot fungus<br />

Fruit body: resupinate, first sulphur-canary yellow, then (Fig. 8.21n) oliveyellow<br />

to cinnamon-brown, also grey-black when old, white, indistinct margin,<br />

to 20 cm wide; hymenophore smooth to merulioid, no sclerotia; hyaline to<br />

yellow, thick-walled spores 5−6 × 3.5−4.5µm;<br />

Strands (Fig. 8.21o): white, to 2 mm thick, not clearly separated; no fibers;<br />

vessels to 20µm thick, numerous, in groups, bar-thickenings indistinct or<br />

absent.<br />

Meruliporia incrassata, American dry rot fungus<br />

Fruit body: similar to S. lacrymans, annual, resupinate to effused, 20 cm or<br />

more in length, thin, easily separable, whitish to buff margin, grey center,<br />

becoming darker as it matures; 1 to 12 mm thick, fleshy, brittle when dried;<br />

first appearing as a felted pad of mycelium with formation of pores beginning at<br />

the center, subsequent fertile to the margin; hymenophore poroid, occasionally<br />

merulioid; whitish to buff or ochre-grey when fresh, grey-brown to black when<br />

drying, unequally circular to angular pores, 1–3/mm; monomitic; thick-walled<br />

oblong to ellipsoid spores, variable in size, 8−16 × 4−8µm;<br />

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8.5 Damage to Structural Timber Indoors 229<br />

Strands: first as vein-like structures in the mycelium, often extending into<br />

soil or masonry, appearing whitish when young, browny-black with age (Eaton<br />

and Hale 1993), 0.3–5.1 cm in diameter, length up to 9 m (Palmer and Eslyn<br />

1980).<br />

Recognition characteristics of S. lacrymans (Fig. 8.21)<br />

<strong>Wood</strong>: The relatively large cubes of the brown-cubical rot (Fig. 7.1a) are no<br />

reliable characteristic. Painted doorframes or baseboards first show blisters<br />

and fine tears in the lacquer and after longer infestation, wavy surfaces.<br />

Fruit body: The brownish, to 12 mm thick and 2 m size, mostly resupinate<br />

fruit body growing on wood or masonry (Fig. 8.21a) is conspicuous. From<br />

shakes and vertical planes grow pad and bracket-like fruit bodies. The gyrosoreticulate<br />

hymenophore is traditionally named “merulioid” (Fig. 8.21b), which<br />

derives from the former generic name Merulius. The margin is whitish, often<br />

bulging and always with a sharply limited front. Particularly at the margin,<br />

as also with the mycelium, arise liquid drops of neutral pH value due to<br />

guttation, which led to the naming lacrymans (watering). Fresh fruit bodies<br />

have a pleasant smell like fungi, but putrefy after sporulation and then easily<br />

stink (from the ammonia). The old, dry, then black-brown fruit bodies hardly<br />

show the merulioid structure. Fruit bodies develop over the whole year, with<br />

an amassment in the late summer until winter (Nuß et al. 1991).<br />

Affected areas are often widely covered with brown, elliptical, yellow-brown<br />

spores with small, pointed extension at an end and partly with up to five intracellular<br />

oil droplets (Hegarty and Schmitt 1988; Pegler 1991; Nuß et al. 1991).<br />

Falck (1912) calculated the spore release by a 1-m 2 fruitbodyto3×10 9 spores<br />

per hour.<br />

First, however, inconstant fructification in the laboratory culture was obtained<br />

by Falck (1912), Cymorek and Hegarty (1986b) stimulated fructification<br />

by 12 ◦ C incubation and by natural temperature change in the open (cool)<br />

(Hegarty and Seehann 1987; Hegarty 1991). Fruit bodies relatively often developed<br />

in pure cultures, if the mycelium was first incubated for about 4 weeks at<br />

25 ◦ Conmaltagarandthenatabout20 ◦ C and natural daylight (Schmidt and<br />

Moreth-Kebernik 1991b; Fig. 3.1).<br />

Mycelium (Fig. 8.21c) and biology: During initial growth, with sufficient humidity<br />

and standing air, often a white, woolly thick aerial mycelium develops,<br />

which is rapidly interspersed by the typical strands. Yellow to wine-red (also<br />

violet) discolorations (“inhibition colors”) by restraining influences [light,<br />

accumulation of toxic metabolites, increased temperature: Zoberst (1952),<br />

Cartwright and Findlay (1958)] are characteristic and led to the former generic<br />

name Merulius, going back to the yellow beak of the male blackbird Turdus<br />

merula (Coggins 1980). Older mycelium collapses to removable, dirty grey to<br />

silvery skins, in which the branched strand system is embedded. The match-<br />

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230 8 Habitat of <strong>Wood</strong> Fungi<br />

to pencil-thick, up to 2 to 4-m-long, grey-brown and on their surface fibrously<br />

roughened strands (Fig. 8.21d, Table 2.4; Falck 1912) break when being dry with<br />

audible cracking. Strands are formed only in aerial mycelium, and there as well<br />

by dikaryotic as by monokaryotic mycelium, and not in substrate mycelium<br />

and reach (at 20 ◦ C) 5 mm length increase per day (Nuß et al. 1991).<br />

The fungus is tetrapolar heterothallic. Only dikaryons show clamps (Harmsen<br />

et al. 1958), while only monokaryons form plentifully arthrospores<br />

(Schmidt and Moreth-Kebernik 1991c). Contrary to Antrodia sinuosa and<br />

Coniophora puteana, the clamps are as large as the hyphal diameter (Nuß<br />

et al. 1991). Matings between different isolates of S. lacrymans revealed physiological<br />

differences between the different mycelial types, but also constancy<br />

of the characteristics over several generations (Schmidt and Moreth-Kebernik<br />

1989b, 1990, 1991a): The dikaryons (parents and F1 and F2 generation) grew<br />

significantly faster than the mycelia of the two appropriate monokaryons and<br />

the two heterokaryon types (A# B=, A= B#). Regarding wood decay, dikaryons<br />

and monokaryons showed greater activity than the heterokaryons (also Elliott<br />

et al. 1979). Monokaryons and heterokaryons however tolerated higher temperature<br />

than the dikaryons, by growing still at 28 ◦ C. Monokaryons also endured<br />

higher protective agent concentrations and this was also proven for Antrodia<br />

vaillantii and Gloeophyllum trabeum (Da Costa and Kerruish 1965). Related to<br />

practice, such physiological differences between the different mycelial types<br />

could become relevant, since dikaryons can revert under adverse conditions<br />

to the monokaryotic stage, as for example G. trabeum by arsenic (Kerruish<br />

and DaCosta 1963) and S. lacrymans by relatively high temperature (Schmidt<br />

and Moreth-Kebernik 1990). The more tolerant monokaryons would survive<br />

and can mate under again favorable conditions to dikaryons and thus have<br />

overcome the adverse environment.<br />

The vegetative hyphae in the aerial mycelium are thicker (about 6µm) than<br />

the hyphae within woody tissue, with about 2µm. Within wood, medallion<br />

clamps also occur. The distance between the two clamps is shorter than in<br />

aerial mycelium, and often almost right-angled hyphal branching occurs. Morphologic<br />

characteristics of mycelium, fruit body, and spores were described by<br />

Nuß et al. (1991).<br />

Conifers are preferred. Hardwoods with dark heart like oak and chestnut<br />

are more resistant than light species (Wälchli 1973). Beside wood and masonry,<br />

composite woods (chipboards, fiberboards), carpets, and textiles are attacked<br />

and insulating materials (Grinda and Kerner-Gang 1982) like mineral wool are<br />

through-grown and damaged (Bech-Andersen 1987b).<br />

Because of the relatively low optimal temperature range of 17 to 23 ◦ C, the<br />

mycelium grows preferentially in the cooler cellar and ground floor areas. The<br />

total span reaches from 0 to 26–27 ◦ C, and growth stops at 27–28 ◦ C, which<br />

differentiates the species from the similar S. himantioides. The mycelium died<br />

on agar at 55 ◦ C for 3 h (Table 3.8, also Mirič and Willeitner 1984). In dried<br />

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8.5 Damage to Structural Timber Indoors 231<br />

wood samples, however, only 70 ◦ C for 4 h were lethal (Huckfeldt et al. 2005).<br />

The spores were killed after 1 h at 100 ◦ C (Hegarty et al. 1986). Thus, hotair<br />

treatment procedures of attacked buildings (see below), as they are used<br />

in Denmark and also proposed for Germany, kill neither the spores nor the<br />

hyphae growing within large-dimensioned timbers and masonry.<br />

The minimum wood moisture for initial colonization is 21% u (Huckfeldt<br />

2003). The opinion has it that this infection of wood below the fiber saturation<br />

range of about 30% is possible, because the Dry rot fungus is particularly<br />

effective to transport nutrients and water by means of mycelium and strands,<br />

and here particularly by the vessel hyphae, from a moist nutrient source [wood<br />

over fiber saturation or wet masonry: Dickinson (1982)] to the infestation of<br />

“dry wood” (Wälchli 1980; Jennings 1987, 1991; Coggins 1991; Savory 1964).<br />

Not to stamp out, even in recent publications, is the erroneous opinion that<br />

S. lacrymans is extraordinary to colonize dry timber by the exclusive water<br />

production via its own enzymatic wood decay (Chap. 3.3). Also incorrect is<br />

that it takes up the necessary water from the air humidity.<br />

Compared to Cellar fungus and the indoor polypores, the Dry rot fungus<br />

was considered to be sensitive to high wood moisture content (Cartwright<br />

and Findlay 1958). There is an older reference that it even reduced high wood<br />

moistures by guttation in favor of higher air humidity (Miller 1932). The<br />

optimal wood moisture for initial decay is about 30–40% u and shifts with<br />

longer decomposition rather to 40–60% (Wälchli 1980). The maximum of<br />

about 90% (Wälchli 1980) was higher than the 55% moisture content often<br />

cited in the older literature. In piled wood samples (Table 8.7), the optimum<br />

wood moisture was between 45 and 140%, and even samples with initial values<br />

of 240% wood moisture were decayed with wood mass loss over 2% (Huckfeldt<br />

and Schmidt 2005), so that the total span reached from 21 to 240%. The common<br />

term in English “Dry rot fungus” (Savory 1964; Coggins 1980; Bravery et al.<br />

2003) and in German “Trockenfäule-Erreger” is paradoxical, since the Dry rot<br />

fungus also (like all other decay fungi) needs free water in the cell lumina<br />

for the enzymatic wood decay and is susceptible to desiccation. By means<br />

of mycelium (and strands), the fungus transports beside nutrients and water<br />

also minerals, e.g., the wood-decay limiting nitrogen (Watkinson et al. 1981)<br />

from the soil under a house to wood decay in the interior (Doi 1989; Doi<br />

and Togashi 1989; also Weigl and Ziegler 1960; Jennings 1991). After Savory<br />

(1964), the main significance of the strands lies in the nutrient translocation<br />

and not in the water transport (also Bravery and Grant 1985). Literature data<br />

to the requirements for temperature and humidity are also by Viitanen and<br />

Ritschkoff (1991a).<br />

The mycelium of S. lacrymans is said to show dryness resistance of many<br />

years. However, the few experiments available revealed that it can reach at least<br />

under laboratory the dryness resistance only by a slow moisture removal. Assumably,themyceliumneedstimetorevertfirstintothemonokaryoticstage<br />

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232 8 Habitat of <strong>Wood</strong> Fungi<br />

with its resistant arthrospores. Furthermore, the resistance at 20 ◦ Camounted<br />

only about 1 year. Only at low temperature (7.5 ◦ C), the fungus survived several<br />

years (Theden 1972; also Savory 1964). Nevertheless, the remaining infected<br />

areas form a danger potential for new growth. Infected timber parts can exhibit<br />

just so much moisture to enable a slight growth and thus a longer survival<br />

than by means of dryness resistance (Grosser 1985). Furthermore, the danger<br />

of re-infection may derive from the dryness-resistant spores, whose duration<br />

of germ ability was said to amount to 20 years. In infected buildings, S.<br />

lacrymans frequently produces basidiospores, and basidiospores seem to be<br />

the main agent of dispersal (Falck 1912; Langendorf 1961; Schultze-Dewitz<br />

1985). Vegetative spread by mycelium and strands seems to be restricted to<br />

within buildings or the soil in subfloor space (Doi 1991). However, according<br />

to Wälchli (1980) the infection occurs instead by mycelium that is brought in<br />

with timber from other remedial treatments and via wooden boxes or shoes.<br />

Beside the requirement for low temperature, the preferential indoor occurrence<br />

of S. lacrymans was attributed to the intensive synthesis and secretion of<br />

oxalic acid (Jennings 1991; cf. Table 3.9), whose excessive production was said<br />

to be neutralized as calcium oxalate by calcium from masonry or by chelating<br />

with iron from girders (Bech-Andersen 1985, 1987a, 1987b; cf. Palfreyman<br />

et al. 1996). Oxalic acid is also implicated in copper tolerance of fungi. Although<br />

a single isolate of S. lacrymans was only able to grow on agar at a low<br />

concentration of copper sulphate (Table 3.10), Haustrup et al. (2005) showed<br />

11outof12isolatestobetolerantagainstcoppercitrate.Theimplicationof<br />

calcium in oxalate precipitation was also shown for M. incrassata (Jellison et al.<br />

2004). Thus, dry rot attack in buildings is often found in the ends of beams,<br />

which are not separated from the masonry.<br />

During controversies, e.g., in the context of house buying, frequently the<br />

question of the infection date plays a role, for whose determination the daily<br />

average mycelial growth is often used. According to Jennings (1991), the linear<br />

mycelial extension on wood, masonry and insulants ranges from 0.65 to<br />

9mm/d. Assuming a 5-mm radial increase per day on malt agar at optimal<br />

temperature (Table 2.2), 15 cm follow per month. Due to the changing and<br />

not always optimal conditions in buildings and because different isolates of<br />

the fungus exhibited considerable differences in growth rate [1.5–7 mm/d: Cymorek<br />

and Hegarty (1986a); Seehann and v. Riebesell (1988)], an exact age<br />

determination on the basis of the mycelial extension is impossible. Similarly,<br />

the decay of pine sapwood samples varied among 25 isolates from 12 to 56%<br />

in 6 weeks of cultivation (Cymorek and Hegarty 1986a; Thornton 1991), and<br />

different isolates differed likewise in their sensitivity to wood preservatives<br />

(Abou Heilah and Hutchinson 1977; Cymorek and Hegarty 1986a; Wa˙zny and<br />

Thornton 1989a, 1989b, 1992; Wa˙zny et al. 1992). Important is also the decision<br />

if the mycelium in a building is alive or dead. Subculturing on malt agar is<br />

possible, but isolations from mycelium are often contaminated by molds. Vital<br />

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8.5 Damage to Structural Timber Indoors 233<br />

staining with fluorescein diacetate is suitable (Huckfeldt et al. 2000; also Koch<br />

et al. 1989; Bjurman 1994).<br />

The possibilities to identify S. lacrymans cover the classical methods of fruit<br />

body investigation (Grosser 1985; Pegler 1991), strand diagnosis (Falck 1912;<br />

Table 2.4, Appendix 1), and mycelium analysis by identification key (Stalpers<br />

1978). As modern techniques, protein polyacrylamide gel electrophoresis<br />

(Schmidt and Kebernik 1989; Vigrow et al. 1989; Palfreyman et al. 1991;<br />

Fig. 2.19) and immunological tests (Palfreyman et al. 1988; Vigrow et al. 1991c;<br />

Toft 1992, 1993; Glancy and Palfreyman 1993) were tested for suitability. DNA<br />

techniques have been established (Schmidt 2000) and are already used commercially.<br />

MALDI-TOF mass spectrometry was capable of differentiating the<br />

mycelium of the True dry rot fungus and its closest relative the Wild merulius<br />

(Schmidt and Kallow 2005; Fig. 2.24). Measurement of microbial volatile organic<br />

compounds (MVOCs) may identify wood-decay fungi (Bjurman 1992b).<br />

Pinenes, acrolein, and ketones were found in Serpula lacrymans, Coniophora<br />

puteana, and Oligoporus placenta (Korpi et al. 1999). Mono- and sesquiterpenes,<br />

aliphatic alcohols, aldehydes and ketones, and some aromatic compounds<br />

were emitted by Fomitopsis pinicola, Piptoporus betulinus, and further<br />

species (Rosecke et al. 2000). Blei et al. (2005) showed that MVOC analysis<br />

was able to distinguish pure cultures of Antrodia sinuosa, C. puteana, Donkioporia<br />

expansa, Gloeophyllum sepiarium, S. lacrymans, and S. himantioides.<br />

Field experiments, however, were influenced by the distance of sampling from<br />

the infested and/or destroyed wood and also by the rates of air changes.<br />

To improve the technique of MVOC analysis, Keller et al. (2005) measured<br />

volatile compounds in non-infested living and bedrooms as a background<br />

reference for infestation. Trained sniffer dogs can also detect S. lacrymans<br />

(Koch 1991).<br />

If S. lacrymans is proven, the fungus is (beside longhorn beetle and termites)<br />

the only biological damage causer for which there is the obligation in<br />

some German states (Hamburg, Hessen, Sachsen, Thüringen, and Saarland)<br />

to become registered. Since costs of refurbishment can be considerable (to<br />

e3,000 per m 2 living space), the determination of the extent of the damage and<br />

theremedialtreatmentsshouldbedonebyarenownedcompany.InGermany,<br />

refurbishment has to follow the standard DIN 68800 part 4. In the case of a lawsuit,<br />

§459 of the German Civil Code regarding “regress for material defects”<br />

takes effect.<br />

8.5.4<br />

Prevention of Indoor Decay Fungi and Refurbishment of Buildings<br />

All decaying fungi need water for wood decay. Elimination of the source of<br />

moisture and drying of wood and masonry after prolonged wetting are the<br />

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234 8 Habitat of <strong>Wood</strong> Fungi<br />

most important remedial treatments. Since S. lacrymans can transport water,<br />

it cannot be excluded that sources of dampness are overlooked during repair,<br />

and thus more-extensive measures are necessary for its control.<br />

The first remedial treatment of dry rot infestation is described in the Bible<br />

in Leviticus 14:33–48. Preventive measures against all house-rot fungi are<br />

avoidance of general building defects and of those during refurbishment of old<br />

buildings: moisture ascending in the masonry, seeping rain water, insufficient<br />

ventilation, installation of wet or infested timber and wet fillers, allside walled<br />

beam ends, lack of building drainage, condensation water by wrong thermal<br />

insulation and inappropriate vapor barriers, unsatisfactory underside blockage<br />

of buildings without cellars, wrong structure of floors, reuse of attacked<br />

building debris, leakages in bathrooms and insufficient wood protection.<br />

To the common causes belong also unrepaired building damage: leaky roofs,<br />

shattered windowpanes, leaky or sweating water and heater lines, clogged or<br />

defective rainwater and drainage facilities as well as water damage caused by<br />

burst piping, defective washing machines and dishwasher water pipelines, cellar<br />

floodings and fire-fighting water (Thornton 1989a; Paajanen and Viitanen<br />

1989; Bricknell 1991; Doi 1991; Wälchli 1991).<br />

Particularly regarding cellar fungi, flooring in new buildings should not<br />

done too early. Damp bulk goods in ceilings shall be avoided.<br />

The danger of infestation exists via spores and by infected timber and<br />

wooden boxes, which are stored as firewood in damp cellars, and by mycelium<br />

viatheshoesofworkers.<br />

If a fungus is found, it should be first determined whether it concerns S.<br />

lacrymans or another fungus, as this decision may require the obligation to<br />

register the fungus and influences the extent of remedial treatments. In cases of<br />

doubt, laboratory identification should be performed by appropriate institutes,<br />

national testing institutions, offices for plant protection or in the laboratories of<br />

wood preservative manufacturers. The German standard DIN 68800 demands<br />

that if an exact species identification is not possible, then refurbishment is to<br />

be proceeded in such a way, as if the True dry rot fungus were present.<br />

Then the extent of the damage has to be established. German guidelines for<br />

control measures are listed in Table 8.8 (Grosser et al. 2003).<br />

Table 8.8. German guidelines for control measures during refurbishment<br />

DIN 68800 Part 4: <strong>Wood</strong> preservation; control measures against wood-destroying fungi<br />

and insects, issue 1992<br />

Part 3: <strong>Wood</strong> preservation; protective chemical wood preservation, issue 1990<br />

Part 2: <strong>Wood</strong> preservation in building construction; protective structural measures,<br />

issue 1984<br />

DIN 52175: <strong>Wood</strong> preservation; term, fundamentals, issue 1975<br />

Concretization rule for building work (VOB part B)<br />

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8.5 Damage to Structural Timber Indoors 235<br />

Refurbishment methods are described by Grosser (1985), Blow (1987),<br />

Wälchli (1991), Bech-Andersen (1995), Gründlinger (1997), Sutter (2003),<br />

Bravery et al. (2003) and Grosser et al. (2003), briefly: Elimination of the<br />

source of moisture, removal of all infected timber 1 m beyond the last evidence<br />

of fungus or decay, disposal of the attacked timber and the other infected<br />

building materials, physical (heat) and chemical treatment (boron, quaternary<br />

ammonium compounds) of infested masonry with certified preservatives<br />

for those species that colonize brickwork, use of preservative-treated<br />

timbers for replacement following DIN 68800, and providing adequate ventilation.<br />

Eradication in the roof space with hot air as it is used against insects (Paul<br />

1990) is already done or is being considered to fight fungi in some European<br />

countries (Koch 1991; Sallmann 2005). However, first these treatments are<br />

technically wrong in view of a safe killing of mycelium and spores of house-rot<br />

fungi in wood and in masonry, since the necessary heat (Schmidt and Huckfeldt<br />

2005; Huckfeldt et al. 2005; Table 3.8) is not obtained, particularly not in the<br />

inside of thick timber. Second, heat treatment is economically doubtful due<br />

to the endangerment of the structural fabric and third, from an ecological<br />

viewpoint, enormous energy is needed.<br />

Microwaves are also used or being considered as an alternative method.<br />

Irradiation tests with microwaves from 1990 to 1992 in Denmark in about 100<br />

cases of fungal infestation killed the mycelium of S. lacrymans that previously<br />

had been inserted into the brickwork within 10 min (Bech-Andersen and Andersen<br />

1992; Kjerulf-Jensen and Koch 1992). However, microwave treatment<br />

is a fire risk if metal fastenings are present in the timber (Bravery et al. 2003)<br />

and there are general doubts on the suitability of the technique for buildings<br />

(Sallmann 2005).<br />

For registered historical buildings and wood artifacts, the suitability of fumigants<br />

was tested mainly for the control of insects, but also to control decay<br />

fungi. Against fungi, bromomethane and ethylene oxide have been used (Unger<br />

et al. 2001). Fumigants, however, do not provide protection against new infestations.<br />

In the laboratory, aminoisobutyric acid, which is analogous to the amino<br />

acid alanine, reduced the decay of wood samples by S. lacrymans from 22 to<br />

1% (Elliott and Watkinson 1989). An intervention in the trehalose metabolism<br />

of S. lacrymans was suggested to influence the internal translocation processes<br />

(Jennings 1991). The binding of iron by chelating agents inhibited mycelial<br />

growth, EDTA prevented decay of pine samples by Coniophora puteana, Gloeophyllum<br />

trabeum and Oligoporus placenta (Viikari and Ritschkoff 1992), and<br />

tellurium acid wood decay by C. puteana (Lloyd and Dickinson 1992). Polyoxin<br />

acted as inhibitor of the chitin synthase of several fungi (Johnson and<br />

Chen 1983). Particularly the Trichoderma species display a wide arsenal of<br />

antagonistic mechanisms that make these fungi attractive as biological control<br />

agents (Highley and Ricard 1988; Giron and Morrell 1989; Doi and Yamada<br />

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236 8 Habitat of <strong>Wood</strong> Fungi<br />

1991; Rattray et al. 1996; Bruce 2000). Bacteria decreased wood decay by O.<br />

placenta (Murmanis et al. 1988; Benko and Highley 1990).<br />

From a biological point of view, there is no reason that all indoor wood<br />

decay fungi should be a problem. The biological requirements of the common<br />

species are known. Control measures are straightforward. Even once a fungus<br />

is established, it is mainly only necessary to change the conditions in the<br />

building to a long-term removal of moisture. There was only slight wood decay<br />

by some house-rot fungi below the fiber saturation range of about 30% u. The<br />

lower limit for decay of pinewood samples (mass loss slightly over 2% within<br />

5 months) was 22% (Table 8.7). This also applies to the feared S. lacrymans.<br />

This fungus turned out in many laboratory tests on temperature and drying<br />

effects to behave rather sensitively when compared to the cellar fungi and<br />

the indoor polypores. The only biological specific features of S. lacrymans are<br />

its more highly developed strand system to transport nutrients from a moist<br />

feeding source over considerable distances and to colonize new substrate, its<br />

formation of thick surface mycelium that prevents the colonized wood from<br />

drying, and its ability to grow through masonry.<br />

The most important measure against all fungi in buildings is to detect and<br />

eliminate the cause of the increased moisture content of wood and masonry<br />

that is in contact with wood as well to exclude any re-moistening, including<br />

throughcondensationandfaultsbythehomeuser.Ifthedestroyedtimber<br />

has been replaced and lasting dryness of the wood can be guaranteed, there is<br />

no need for further provision, from the biological view, as there is no fungus<br />

known which destroys dry wood (below 22% u), not even S. lacrymans.Since<br />

practice, however, shows that in many cases a lasting dryness cannot be ensured<br />

in buildings, there are specific recommendations (and in Germany regulations)<br />

forthecaseofS. lacrymans infestation.<br />

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9<br />

Positive Effects of <strong>Wood</strong>-Inhabiting<br />

Microorganisms<br />

Particularly after the OPEC oil embargo of the 1970s, research turned towards<br />

the utilization of renewable resources like wood, yearly plants, and lignocellulosic<br />

waste from forestry and agriculture instead of oil as raw material for<br />

chemical and biological processes (“biotechnology of lignocelluloses”) (Eriksson<br />

et al. 1990; Dart and Betts 1991).<br />

Among the substantial causes that make the biological conversion of lignocelluloses<br />

difficult (Table 4.2), the most serious obstacle is the incrustation<br />

of the degradable carbohydrates cellulose and hemicelluloses by the lignin<br />

barrier, which is not surmountable by most microorganisms. Table 9.1 groups<br />

some bioconversions that have been done in the past or are recently investigated<br />

or already performed into those microbial processes, which go well<br />

directly with lignocelluloses, and into those, which need a pretreatment of the<br />

substrate. Only the wood-degrading white, brown, and soft-rot fungi, and the<br />

wood-degrading bacteria can degrade the native woody cell wall without any<br />

pretreatment of the substrate. Whereas brown and soft-rot fungi and assum-<br />

Table 9.1. Biotechnological procedures with lignocelluloses without and after substrate<br />

pretreatment<br />

conversion without substrate pretreatment<br />

– “myco-wood”<br />

– production of edible mushrooms<br />

– biological pulping<br />

pretreatment of the substrate and subsequent microbial conversion<br />

biological pretreatment<br />

– “palo podrido” and “myco-fodder”<br />

chemical pretreatment<br />

– hydrolysis of wood with acids and use of glucose for yeast production, ethanol<br />

fermentation and microbial transformations to amino acids, antibiotics, enzymes,<br />

vitamins<br />

– sulphite pulping process and use of hardwood pentoses in the spent liquor for yeast<br />

production and of softwood hexoses for ethanol fermentation<br />

– pulping and subsequent use of enzymes for deinking of waste paper<br />

physical pretreatment<br />

– grinding of lignocelluloses to improve accessibility to enzymes<br />

– steam explosion methods to open the wood structure for bioconversions<br />

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238 9 Positive Effects of <strong>Wood</strong>-Inhabiting Microorganisms<br />

ably also the wood-degrading bacteria only clear the hurdle of lignification,<br />

exclusively the white-rot fungi and their ligninolytic system additionally use<br />

the lignin as a carbon source and are therefore predestined for bioconversions<br />

(Table 4.3). All other microorganisms as well as their isolated enzymes need<br />

first a pretreatment of the substrate wood, which loosens the chemical/physical<br />

association of carbohydrates and lignin or reduce the lignin content or improve<br />

the physical accessibility of the degrading agents to the substrate. The various<br />

possibilities of a pretreatment can be grouped into biological, chemical,<br />

and physical methods (Dart and Betts 1991). Saddler and Gregg (1998) distinguished<br />

four main pretreatment methods currently being researched and<br />

commercialized to make lignocelluloses more easily digestible to hydrolytic<br />

enzymes while preserving the yield of the original carbohydrates for bioconversions:<br />

organosolv, steam explosion, dilute-acid prehydrolysis, and ammonia<br />

fiber explosion. Some of the bioconversions described below like “myco-wood”<br />

or “palo podrido” may occur a little strangely to some readers, but are examples<br />

that wood bioconversion can work.<br />

9.1<br />

“Myco-<strong>Wood</strong>”<br />

In Eberswalde, Germany, around 1930, J. Liese started to cultivate edible mushrooms<br />

on wood like Flammulina velutipes, Kuehneromyces mutabilis, Lentinula<br />

edodes (Fig. 2.17a) and Pleurotus ostreatus to improve the food situation<br />

of the population (Liese 1934). Due to the import stop of wood from overseas<br />

into the German Democratic Republic (GDR) at that time which was<br />

needed for pencils etc., his student, W. Luthardt thought about a possible<br />

use of the wood substrate remaining after mushroom production to produce<br />

pencils and other form-stable products. In 1956, Luthardt got the patent for<br />

“myco-wood” for the GDR and in 1957 under license for the Federal Republic<br />

of Germany: “Myco-wood is a wood that is loosened through the controlled<br />

action of certain wood-inhabiting fungi and which has changed its technological<br />

characteristics to a large extent or may obtain defined technical qualities”<br />

(Luthardt 1969). For myco-wood production, 50-cm-long stem sections of Fagus<br />

sylvatica were inoculated on the crosscut surface with a mycelium paste of<br />

Pleurotus ostreatus or Trametes versicolor, respectively, and were incubated in<br />

the constant climate of former air-raid shelters for different periods. Through<br />

the controlled white rot, a white and porous raw material free from tension<br />

was obtained that showed improved carving and sharpening ability to be used<br />

for form-constant products like pencils, rulers, and drawing boards. For example,<br />

after 3 months of incubation, the wood showed 30% mass loss, was<br />

completely colonized by mycelium, and was now suitable for rulers. One of<br />

these rulers is still used in our laboratory and looks like newly manufactured.<br />

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9.2 Cultivation of Edible Mushrooms 239<br />

About 120 million myco-wood pencils were produced in the GDR from 1958<br />

to 1961. The microbially modified wood also showed faster water absorption<br />

and desorption and was thus used for wood forms of the glass industry. Due<br />

to water-vapor film between wood and glass, it was possible to produce 12,000<br />

goblets using a myco-wood form instead of 800 glasses using normal wood<br />

(Luthardt 1963). Attempts to produce myco-wood also took place with tropical<br />

woods (Eusebio and Quimio 1975; Arenas et al. 1978) and bamboo (W. Liese,<br />

pers. comm.).<br />

9.2<br />

Cultivation of Edible Mushrooms<br />

Although actual data could not be obtained, the worldwide production of edible<br />

mushrooms cultivated on straw and wood may be in the range of 2 million t<br />

(fresh weight basis) per year (Table 9.2), so that the cultivation of mushrooms<br />

represents the economically most important microbial conversion of lignocelluloses<br />

(Chang and Hayes 1978).<br />

Without knowledge of the biological background, about 2,000 years ago,<br />

the Shii-take, Lentinula edodes, (Fig. 2.17a) was already cultivated on wood<br />

Table 9.2. Production of edible mushrooms (after various reports in the journal “Der<br />

Champignon”)<br />

Year (× 1,000 t) (%)<br />

Mushrooms worldwide 1991 4,273 100<br />

Agarics (Agaricus spp.) 1,590 37.2<br />

Oyster mushrooms (Pleurotus spp.) 917 21.5<br />

Auricularia spp., Tremella spp. 605 14.2<br />

Shii-take (Lentinula edodes) 526 12.3<br />

Enoki (Flammulina velutipes) 187 4.4<br />

Nameko (Pholiota nameko) 40 0.9<br />

Grifola frondosa 2005 35<br />

Mushrooms worldwide 1997 6,344 100<br />

China 4,000 63.1<br />

Japan, Taiwan, Korea, etc. 1,005 15.8<br />

EU 908 14.3<br />

North America 431 6.8<br />

Shii-take worldwide 1997 1,322 100<br />

China 1,125 85.1<br />

Japan 133 10.0<br />

Taiwan, Korea 44 3.4<br />

EU 0.995<br />

France 0.450<br />

Germany 0.150<br />

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240 9 Positive Effects of <strong>Wood</strong>-Inhabiting Microorganisms<br />

in Asia. The name Shii-take means “Pasania-fungus”, because the mushroom<br />

was grown on the “Shii-tree” (Castaneopsis (Pasania) cuspidata, Japanese chinquapin).<br />

For the cultivation of this excellently tasting mushroom (compared<br />

to the Shii-take, the commercially produced agarics taste like nothing) as “natural<br />

log cultivation”, originally in China, and later in Japan, logs and branch<br />

sections were exposed to natural, passive inoculation by wind-borne spores<br />

and were stacked in the forest for fruit-body formation. About 300 years ago,<br />

the Shii-take was cultivated by farmers for extra income to be sold on local<br />

markets. The bark surface of logs, particularly from Quercus serrata or other<br />

fagaceous trees, was broken with an axe to improve the chances of inoculation.<br />

Since the 1920s, pure spawn culture was placed (“spawning”) into holes<br />

drilled into the logs. For the colonization phase of the substrate by mycelium,<br />

the inoculated logs were first placed as stacks in the forest or in greenhouses<br />

until the mycelium grew out. The colonized woods were then set up individually<br />

or stacked crosswise in the forest (“growing yard”) or in greenhouses for<br />

fruit body formation. Eight to 12 months after inoculation, there is the first<br />

flush of mushrooms, and cropping of logs occurs over about 5 years. Since<br />

the 1970s in Taiwan, Japan, and China, the Shii-take is produced commercially<br />

on chopped wood (chips) and wood waste like sawdust under controlled<br />

conditions such as defined substrate composition, temperature, light conditions,<br />

relative humidity, and wood moisture content. The big breakthrough<br />

for sawdust substrates was the use of plastic bags, in which the substrate can<br />

be compressed, sterilized, inoculated, and grown out (Fig. 9.1). The woody<br />

substrate is supplemented with amendments (bran, whole meal, urea etc.),<br />

watered for a suitable moisture content, and inoculated with special isolates.<br />

In this “bag” or “artificial log” culture, the mycelium knits the substrate into<br />

a solid block. The methods for Shii-take production have been recently summarized<br />

by Miller (1998). In the local experiments (Schmidt and Kebernik<br />

1986; Schmidt 1990), different wood wastes such as chips (Fig. 9.1), sawdust,<br />

Fig.9.1. Shii-take (Lentinula edodes)<br />

fruit-bodies grown on wood waste chips<br />

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9.2 Cultivation of Edible Mushrooms 241<br />

leaves and needles from some hardwoods and also from spruce and pine were<br />

used. A short colonization phase of the substrate was done at about 24–28 ◦ C<br />

in closed plastic bags or similar containers. Readiness of the Shii-take to fruiting<br />

became visible in the closed bag, when brown-black wet spots occurred<br />

between the white mycelial mat along the outer surface of the artificial log<br />

and the bag. Then the substrate was a solid block, and the substrate containers<br />

were opened or removed for fruiting at lower temperature of about<br />

12–20 ◦ C. After bag removal, the outer mycelial surface becomes brown and<br />

leathery. Then the logs were sprayed with water once a day, and natural daylight<br />

in a greenhouse was used to stimulate primordia formation. The artificial<br />

light–dark cycle requires light in the 3,700 to 4,200-nm range and intensity<br />

of 400–500 lux (Miller 1998). Several flushes occur within 1 year. After each<br />

cropping, the dry substrate may be re-wetted e.g., by soaking in cold water.<br />

This soaking both replaces the water that has been lost by the growth of<br />

the fruit bodies and the cold stimulates the development of the next primordia.<br />

The yields amounted to about 100% biological efficiency (fungal fresh<br />

weight: dry weight wood; Royse 1985). In Taiwan, for example, 516 companies<br />

produced about 24,000 t of fresh fungi on chopped substrates in 1985,<br />

and a similar quantity was obtained, however, by over 5,000 farmers on wood<br />

sections.<br />

The Shii-take was for a long time the most common mushroom cultivated<br />

on wood worldwide. Altogether, the fungus was the second most frequent<br />

cultivated mushroom with its main production in Japan after the Agaricus<br />

species, which are traditionally cultivated on wheat straw that is composted<br />

with manure or some other nitrogen-rich additive. The Shii-take has been<br />

however overhauled through the increased production of Pleurotus species<br />

particularly in China. Worldwide 526,000 t Shii-take were harvested in 1991<br />

and 1.3 million t in 1997 (Table 9.2). Beside Asia, some Shii-take cultivation<br />

is performed in the USA, Canada, and Europe. In Germany, there is a handful<br />

of commercial Shii-take growers producing some hundreds of tons. A great<br />

part of Chinese and Japanese Shii-take is exported in dry condition to Taiwan,<br />

Singapore, USA, Canada, Australia, and Europe. In Germany, 100 g of dry,<br />

imported Shii-take cost about e10. The local market price varies for outdoorgrown<br />

fungi due to seasonal influences from e10 to 40 per kg fresh weight.<br />

Because of the slow growth of the Shii-take mycelium during the colonization<br />

phase, the cultivation on shopped substrates is endangered by contaminations,<br />

partly leading to parasitism, particularly by Trichoderma species like T. hamatum,<br />

T. harzianum, T. parceramosum,T. pseudokoningii, T. reesei and T. viride<br />

(Albert 2003). Thus, the colonization phase is commonly performed with<br />

pasteurized (60–100 ◦ C) ore autoclaved substrates in plastic bags (Schmidt<br />

1990).<br />

The fundamentals of Shii-take production are known outside of Asia. The<br />

first cultivations in Europe were performed by Mayr (1909) and Liese (1934;<br />

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242 9 Positive Effects of <strong>Wood</strong>-Inhabiting Microorganisms<br />

Fig. 2.17a), and research on the biological and physical demands of the fungus<br />

were done in the USA (e.g., Leatham 1982; Royse 1985) and in Europe (e.g.,<br />

Zadraˇzil and Grabbe 1983; Rohrbach 1986; Müller and Schmidt 1990; Lelley<br />

1991; Kalberer 1999). Basically, the procedure consists of four main steps as<br />

shown in Fig. 9.2: pre-culture of a certain isolate, propagation of the mycelium<br />

for inoculation by growth on sterile grains (spawn production), colonization<br />

phase of the sterilized substrate in plastic bags, and fruiting phase on the<br />

opened containers.<br />

The reasons why the Japanese and Chinese in particular have been so successful<br />

in Shii-take cultivation are not known. Generally, the cultivation of<br />

so-called “alternative or exotic mushrooms” has got to have the right feel for<br />

it. The Shii-take belongs to “demanding mushrooms” while the Oyster mushroom,<br />

Pleurotus ostreatus, is easily satisfied through its fast growth ability on<br />

several substrates such as lignocellulosic waste (Pettipher 1987) and is thus<br />

lesser sensitiveness to contamination. In North America and Europe, particularly<br />

in Italy and Hungary, frequently Pleurotus species such as P. ostreatus are<br />

grown on chopped wheat straw, but also stem sections (Fig. 9.3) or chopped<br />

waste is used by hobby breeders and commercially. The market price of this<br />

lesser-tasting fungus in Germany amounts to e5–10/kg fresh weight. Further<br />

fungi that are cultivated on lignocelluloses are e.g., Agrocybe aegerita,<br />

Auricularia auricula-judae, Flammulina velutipes, Grifola frondosa, Hericium<br />

erinaceus, Kuehneromyces mutabilis, andPholiota nameko (Miller 1998). Research<br />

results and practical tips for mushroom culturing occur in the German<br />

Fig.9.2. Main steps of Shii-take production: a Maintenance of a selected isolate on agar.<br />

b Mycelial growth on grains for inoculation. c Substrate colonization in closed plastic bags.<br />

d Fruiting phase after removal of plastic bag (from Schmidt 1990)<br />

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9.2 Cultivation of Edible Mushrooms 243<br />

Fig.9.3. Pleurotus ostreatus cultivation<br />

on beech wood billets in Germany in<br />

1936 (photo J. Liese)<br />

journal “Der Champignon”. The international work is treated at the meetings<br />

of the International Mycological Society.<br />

Concerning the nutritional value of fungi, it may be considered that a fresh<br />

fruit body contains predominantly water and only about 10% dry matter.<br />

For 100 g of fresh Shii-take, 92.6 g water, 4.3 g carbohydrates, 1.9 g protein,<br />

0.3 g lipids, 0.7 g ballast material, and 0.5 g minerals have been measured,<br />

corresponding to 109 kJ. Minerals in decreasing order were K, P, chloride, Ca,<br />

Mg, Na, Zn, fluoride, Fe, and Cu. The vitamins comprised C, pantothenic acid,<br />

nicotine amide, E, B1, folic acid, and D (Schulz 2002; also Spiegel 2001). Thus,<br />

considering the high price of the tasty mushrooms species, their significance<br />

as food lies rather in culinary appeal.<br />

For thousands of years, mushrooms have been known as a source of medicine,<br />

particularly in Asia. Among these non-culinary mushrooms, e.g., Ganoderma<br />

species are grown on wood waste to obtain medically active compounds<br />

(Miller 1998). For example, he has shown that the methanol extract of the G.<br />

lucidum fruitbodyhasastronginhibitoryactivityofthe5α-reductase that<br />

is involved in the benign prostatic hyperplasia of older men (Liu et al. 2005).<br />

Those “medicinal mushrooms” are widely sold as a nutritional supplement<br />

and are touted as being beneficial to health. Asian people believe that the Shiitake<br />

has antivirus, antibactericidal, antitumour (e.g., Mori et al. 1989) and<br />

cholesterol-decreasing effects. In view of the possibly increased heavy metal<br />

content and radiation load that had been measured in some forest mushrooms,<br />

indoor-cultured fungi are harmless, but are usually lesser tasty than outdoorgrown<br />

fungi. In Asia, the quality of mushrooms grown in a bag or bottle culture<br />

is considered inferior.<br />

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244 9 Positive Effects of <strong>Wood</strong>-Inhabiting Microorganisms<br />

9.3<br />

Biological Pulping<br />

Mechanical and chemical processes for pulp and paper production consume<br />

energy and chemicals. Their wastes have to be controlled in view of environmental<br />

aspects. Biotechnological processes have thus been successfully<br />

implemented in the pulp and paper industry during the last decade driven<br />

by the objective to reduce manufacturing costs using new delignification processes<br />

and by environmental considerations (Messner et al. 2003). The application<br />

of white-rot fungi, or their ligninolytic systems, was one option for<br />

this. The aim was termed as biological pulping or briefly biopulping. In its<br />

strict sense, biopulping was defined as the pretreatment of wood chips with<br />

selectively delignifying white-rot fungi prior to mechanical or chemical pulping<br />

(Messner 1998). In a broader sense, the term biopulping is also used for<br />

any biochemical assistance to the pulping process such as the application of<br />

blue-stain fungi for resin reduction or the use of enzymes for bleaching and<br />

deinking.<br />

Nilsson had found Sporotrichum pulverulentum (first termed Chrysosporium<br />

lignorum) in chip piles in Sweden, where it caused serious damages (Bergman<br />

and Nilsson 1966). In 1972, Henningsson et al. described the fungus as the<br />

thermophilic white-rot basidiomycete Phanerochaete chrysosporium (teleomorph<br />

of S. pulverulentum) causing defibration of wood. In the late 1960s,<br />

Eriksson in Stockholm had already started research to decrease the lignin<br />

content in the wood microbially by treatment of wood chips with white-rot<br />

fungi (Eriksson 1985; Eriksson et al. 1990). Mechanical pulp was produced<br />

from chips pretreated with P. chrysosporium by Ander and Ericksson (1975).<br />

Because white-rot fungi of the “selective delignification type” would also attack<br />

the carbohydrates sooner or later, cellulase-less mutants such as Cel 44 of S.<br />

pulverulentum have been produced by UV irradiation of conidia (Ander and<br />

Eriksson 1976) and later by crossing of Cel − -mutants with monokaryons of<br />

high ligninolytic activity (Johnsrud 1988).<br />

Phanerochaete chrysosporium has also been isolated in the USA in the Arizona<br />

desert (Burdsall and Eslyn 1974). Also in the late 1960s, Kirk in Madison<br />

began research on P. chrysosporium with the isolation of lignin peroxidase (Tien<br />

and Kirk 1983; see Chap. 4.5), and since the 1980s, biopulping is investigated<br />

in the USA (Kirk et al. 1993).<br />

There were masses of investigations and publications on various aspects<br />

of biopulping during the past four decades. They report on the successful reduction<br />

of chemicals and manufacturing and energy costs as well as on the<br />

application of further white-rot fungi such as Ceriporiopsis subvermispora,<br />

Dichomitus squalens, Merulius tremellosus, and Phlebia brevispora. For example,<br />

when biopulped chips are used to produce mechanical pulp, energy for<br />

refining was reduced from 25 to 35% and the sheet strength properties are<br />

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9.3 Biological Pulping 245<br />

typically improved 20 to 40% (Hunt et al. 2004). A 20% reduction was obtained<br />

in the total pulping time necessary for achieving pulp and paper properties<br />

comparable to those from controls (Chen et al. 1999). Körner et al. (2001)<br />

showed that non-sterile incubation of wood chips with Coniophora puteana<br />

yielded energy savings of about 40% during refining of wood chips, a three<br />

times higher bending strength and more than half reduced water absorption<br />

and swelling of fiber boards. The topic of biological treatment of chips of was<br />

reviewed by Messner (1998).<br />

Despitethemassiveamountofmoneyandworkdevotedtobiopulping,<br />

a sweeping success seems however vague. The difficulties involved are mainly<br />

microbiological problems: It is generally difficult to scale-up small-sized laboratory<br />

experiments with fungal pure cultures via medium-sized rotating fermentors<br />

with controlled aeration and temperature to the final aim of obtaining<br />

the same result in chip silos or even in large-sized chip piles under natural outdoor<br />

conditions. During controlled biopulping, the different white-rot fungi<br />

may be grown on wood chips for 10 to 15 days. In a wood chip pile, available<br />

nutrients, humidity, and temperature are, however, favorable to contamination<br />

by many fungi. Most common are Trichoderma species, of which some<br />

excrete antibiotics against other fungi. Uneven distribution of the inoculum,<br />

unsuitable or uneven oxygen and carbon dioxide amounts, unfavorable or uneven<br />

wood moisture content, and increase of the temperature to 50 ◦ Coreven<br />

to the incineration point are common problems of large-sized outdoor bioconversions<br />

in piled substrates. An example with respect to brown-rot fungi<br />

is the successful laboratory and pilot-scale experiments by Leithoff (1997) to<br />

bio-leach chromium, copper and other elements from treated waste wood by<br />

means of Antrodia vaillantii (Chap. 7.4) and the failure of the method using<br />

larger chip piles under practical conditions. Nevertheless, it has been stated<br />

that development of the biopulping process has reached the pilot scale as far as<br />

the use of white-rot fungi for mechanical and sulphite pulping is concerned, has<br />

already been tested on a commercial scale with Ophiostoma piliferum for craft<br />

pulping (Messner 1998) and that “biopulping ... is close to mill application”<br />

(Messner et al. 2003).<br />

As a “by-product”, the biotechnological attempts of using fungi or their<br />

enzymes in the pulp and paper industry in processes as biopulping, biobleaching,<br />

and fiber modification have spurred the understanding of the mechanisms<br />

of wood decay (Chap. 4). It may however be mentioned that the most often<br />

investigated fungus with respect to enzyme mechanisms, P. chrysosporium,has<br />

beside chip piles no relevance for wood, neither for trees nor for constructional<br />

timber.<br />

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246 9 Positive Effects of <strong>Wood</strong>-Inhabiting Microorganisms<br />

9.4<br />

“Palo Podrido” and “Myco-Fodder”<br />

In the evergreen temperate rainforests of southern Chile, Philippi (1893) found<br />

in the heartwood of dying and fallen hardwoods (Eucryphia cordifolia, Nothofagus<br />

spp. and other trees) a white, spongy-wet wood tissue (Fig. 9.4a, also<br />

Fig. 7.2c), which may occupy the entire interior of logs. This white-rotted<br />

wood, called “palo podrido” (rotted wood) or “huempe”, develops by the action<br />

of Ganoderma species like Ganoderma adspersum (Martínez et al. 1991a,<br />

1991b; Barrasa et al. 1992; Bechtold et al. 1993) and other white-rot Basidiomycetes,<br />

associated yeasts and bacteria (González et al. 1986), in the moist<br />

forest climate during a long time. Environmental factors such as a lack of<br />

desiccation and frost during the year in tropical forests may have reduced<br />

the mechanical stress on the wood and maintained conditions that promote<br />

delignification (Eriksson et al. 1990). Low nitrogen content of the wood was<br />

considered to be a major factor that contributed to this selective delignification<br />

(Dill and Kraepelin 1986). Black manganese deposits indicating the correlation<br />

to manganese peroxidase have been found in palo podrido by Barrasa et al.<br />

(1992) and others. Rodriguez et al. (2003) detected several iron-chelating catechol<br />

compounds in palo podrido samples, whose relation to lignin or fungal<br />

metabolites remained however unclear.<br />

Palo podrido has been used by rural population as feed for foraging cattle.<br />

Healthywood,eveningrindedform,hasaverylowrumendigestibility.Thus,<br />

the development of palo podrido by the action of fungi may be termed as<br />

“biological wood pretreatment”. Due to the fungal delignification particularly<br />

in the area of the middle lamella/primary walls, the woody tissue is loosened<br />

and now edible by cattle. Figure 9.4b demonstrates that the Chilean cow prefers<br />

the pineapple-like palo podrido (Fig. 9.4a) to the surrounding grass. Mainly<br />

through the opening of the wood structure, now the anaerobic rumen bacteria<br />

cangetaccesstothedigestiblewoodcarbohydrates.Thereductionofthelignin<br />

content from 22% of healthyNothofagus wood to about 6%in the corresponding<br />

palo podrido sample (Dill and Kraepelin 1986) may have promoted bacterial<br />

activity, but is probably no premier factor, as it has also been stated for the<br />

bacterial degradation of chemically pretreated wood (Chap. 5.2). The rumen<br />

bacteria convert the wood carbohydrates in palo podrido to fatty acids like<br />

acetic, propionic, and butyric acid. This fermentation is the “biotechnological”<br />

part of palo podrido. Last, the cow uses the fatty acids and also the continually<br />

dying bacteria to produce meat and milk.<br />

Lignocelluloses which have been specifically treated with fungi to improve<br />

the digestibility and protein content for use as ruminant feed have been termed<br />

as “myco-fodder” (Heltay 1999; also Eriksson et al. 1990). For example, the<br />

digestibility of straw that was treated with Lentinula edodes for 2 months<br />

showed increased digestibility by 28% (Zadraˇzil 1985; Zadraˇzil and Brunnert<br />

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9.5 <strong>Wood</strong> Saccharification and Sulphite Pulping 247<br />

Fig.9.4. “Palo podrido” caused by Phlebia chrysocreas (a) andaChileancoweating“palo<br />

podrido” (b) (photos J. Grinbergs)<br />

1980). As a by-product, production of edible mushrooms may increase the<br />

economy of fungal straw treatment.<br />

9.5<br />

<strong>Wood</strong> Saccharification and Sulphite Pulping<br />

Both wood saccharification with acids and sulphite pulping may be termed<br />

“chemical wood pretreatment” when the obtained sugars are subsequently<br />

used for microbial or enzymatic conversions.<br />

The acid wood saccharification yields monosaccharides from the wood carbohydrates.<br />

Hydrolysis of lignocelluloses either with diluted or concentrated<br />

acids has been practiced on a large commercial scale for many years. This technique<br />

was used in the USA in the 1910s and in Germany and in Switzerland<br />

during the Second World War. About 10 million m 3 of wood were saccharified<br />

by acid hydrolysis with up to 48% sugar yield of the possible 70% yield in<br />

the former Soviet Union around 1983 (Wienhaus and Fischer 1983). The main<br />

product is glucose, which is the universal sugar for the majority of organisms.<br />

Glucose can by either converted by yeasts, e.g., Candida utilis, aerobically<br />

to fodder yeast (single cell protein, SCP; Dart and Betts 1991) or for human<br />

feed, or glucose is anaerobically fermented to ethanol to be used as chemical<br />

feedstock or as petrol substitution (Decker and Lindner 1979). Glucose fermentation<br />

to ethanol was one of the first complex biological processes mastered by<br />

man and became an important fuel and chemical feedstock in the mid-19th<br />

century. However, with the rapid growth of the petroleum and petrochemical<br />

industry following World War I, fermentation has been restricted primarily<br />

to the brewing and distilling industries (Saddler and Gregg 1998). Ethanol<br />

can be also obtained from xylose by the xylose-fermenting yeast Pachysolen<br />

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248 9 Positive Effects of <strong>Wood</strong>-Inhabiting Microorganisms<br />

tannophilus. Other fungi, e.g., molds, as well as aerobic and/or anaerobic bacteria<br />

can produce amino acids, antibiotics, enzymes, organic acids, solvents,<br />

and vitamins from glucose or glucose-containing wastes. Technical problems<br />

of acid hydrolysis, such as corrosion of the reaction vessels and formation of<br />

noxious by-products, led to research on enzymatic hydrolysis processes, which<br />

promised, for example, higher sugar yields (Saddler and Gregg 1998).<br />

Spent sulphite liquors contain at about 50% of the employed wood as lignin<br />

sulphonic acids and simple sugars from the hemicelluloses. A number of applications<br />

for lignosulphonates or the entire spent sulphite liquors have been<br />

developed in the past (e.g., Faix 1992). Since the early past century, the hexoses<br />

in spent softwood liquors were converted by yeasts to alcohol and the pentoses<br />

in hardwood liquors to fodder or feeding yeast, respectively. For example, a mill<br />

in Switzerland produced (in 1980) in two tanks (320 m 3 ) 82,000 hL alcohol and<br />

7,000 t of yeast cells, respectively. In Sweden, 1.2 million hL of alcohol was produced<br />

in 33 plants in 1945 (Herrick and Hergert 1977). In the 1980s, the sugars<br />

in spent sulphite liquor were converted by means of the soft-rot deuteromycete<br />

Paecilomyces variotii for use as animal feed in Finland (“Pekilo-process”; Forss<br />

et al. 1986). Han et al. (1976) cultured Aureobasidium pullulans on straw hydrolysate<br />

for production of single cell protein. Ek and Eriksson (1980) used<br />

Sporotrichum pulverulentum for water purification and protein production.<br />

Anaerobic treatment of pulp mill effluents by bacteria was reviewed by Guiot<br />

and Frigon (1998).<br />

9.6<br />

Grinding and Steam Explosion<br />

Among the physical pretreatment methods, grinding of lignocelluloses increases<br />

the inner surfaces of the wood cell wall and thus improves the accessibility<br />

for enzymes to the cell wall components. The particle size must be<br />

reduced to 50µm to maximize the effect. The energy costs become prohibitive<br />

at particle sizes of 200µm (Dart and Betts 1991).<br />

Steam explosion methods saturate the lignocellulose with steam and then<br />

allow it to undergo explosive decompression. The treatment releases acids<br />

that contribute to the disruption of the cell wall (Dart and Betts 1991). In the<br />

steaming-extraction process, chopped wood was treated in watery or alkaline<br />

solution for a few minutes at 185–190 ◦ C (1,100–1,200 kPa). Subsequent washing<br />

with water or thin sodium hydroxide solution separated the wood into<br />

a solid component containing lignin and cellulose and a liquid phase of the<br />

hemicelluloses (Dietrichs et al. 1978). In vivo digestibility of wood in a test<br />

cow increased from about 5% of natural wood to 80% for steam-treated wood<br />

(Puls et al. 1983). The hemicellulose fraction was used to produce Paecilomyces<br />

variotii mycelium and enzymes (Schmidt et al. 1979).<br />

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9.7 Recent Biotechnological Processes and Outlook 249<br />

9.7<br />

Recent Biotechnological Processes and Outlook<br />

Several new applications of enzymes have reached, or are approaching, the<br />

stage of commercial use in the pulp and paper industry. These include e.g.,<br />

enzyme-aided bleaching with xylanases, direct delignification with oxidative<br />

enzymes, energy-saving refining with cellulases, pitch removal with lipases,<br />

slime control (Klahre et al. 1996) in the paper machine, removing contaminants<br />

in the recycle stream, as well as deinking (Kenealy and Jeffries 2003; Messner<br />

et al. 2003).<br />

A colorless mutant of the blue-stain fungus Ophiostoma piliferum was used<br />

to control pitch problems (Blanchette et al. 1992b; Farrell et al. 1993; Brush et al.<br />

1994; also Fischer et al. 1994), and chip treatment with O. piliferum decreased<br />

energy consumption and increased strength properties in mechanical pulps<br />

(Forde Kohler et al. 1997).<br />

Enzymes used in pulping can increase the yield of fiber, decrease further<br />

refining energy requirements, or provide specific modifications to the fiber.<br />

Cellulases, hemicellulases, and pectinases allowed for better delignification of<br />

the pulp and savings in bleaching chemicals without altering the strength of<br />

the paper (Kenealy and Jeffries 2003). Laccase and protease reduced energy<br />

requirements in mechanical pulping. Cellulases and hemicellulases have been<br />

used in the refining of virgin fibers. Agricultural residues like wheat and rice<br />

straw have been mechanically pretreated followed by treatment with enzymatic<br />

cocktails from Lentinula edodes for pulp production (Giovannozzi-Sermanni<br />

et al. 1997).<br />

The initial studies on the use of enzymes in bleaching were performed with<br />

a goal of imitating the wood-decaying action of fungi in nature (Iimori et al.<br />

1998; Viikari et al. 1998). However, different mixtures of lignin and manganese<br />

peroxidases did not consistently delignify unbleached craft pulp. The use of<br />

xylanases in bleaching can improve lignin extraction, alter carbohydrate and<br />

lignin association, or cleave redeposited xylan. Recently, laccases or manganese<br />

peroxidases, either alone or combined with low molecular weight mediators,<br />

have been examined. In the laccase-mediator concept, laccase is combined with<br />

a low molecular weight redox mediator resulting in generation of a strongly<br />

oxidizing co-mediator, which then specifically degrades lignin (Jakob et al.<br />

1999; Sealey et al. 1999). “Novel xylanases” deriving from thermophilic and<br />

alkaline sources are of importance due to the prevailing conditions in pulp processing.<br />

Progress in the knowledge of the xylanase-encoding DNA sequences<br />

and the expression of xylanases in other microorganisms may lead to further<br />

development in this area (Kenealy and Jeffries 2003).<br />

Waste paper is the primary raw material of the European paper industry.<br />

For Germany, the amount of waste paper for paper production has been<br />

forecasted to about 14 million t in 2005. In 1995, the average composition of<br />

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250 9 Positive Effects of <strong>Wood</strong>-Inhabiting Microorganisms<br />

waste paper in a deinking plant consisted of 41% newspapers, 39% magazines,<br />

9% wood-free paper, 6% unusable paper and board, 4% other bright papers,<br />

and 1% non-paper components (Hager 2003). More than 70% of mixed office<br />

waste paper consists of uncoated papers that are printed with copy or<br />

laser printer toners, which may be difficult to remove by conventional, alkaline<br />

deinking (Kenealy and Jeffries 2003). Fibers may be treated by hydrolyzing<br />

enzymes to remove print (deinking). Cellulases are particularly effective in<br />

the removal of toners from office waste papers. It was concluded that the primary<br />

role of cellulases in deinking involves separating ink-fiber agglomerates<br />

and dislodging or separating ink particles and fibrous material in response<br />

to mechanical action during disintegration (Kenealy and Jeffries 2003). Few<br />

experiments have used oxidative enzymes for deinking. The missing potential<br />

for the reduction of specks that derive from residual ink and the observed<br />

lignin modification rendered laccase either alone or combined with the mediator<br />

1-hydroybenzotriazole unsuitable for practical ink elimination of wood<br />

containing waste paper (Hager et al. 2002). Recycled paper sludge generated<br />

during repulping was simultaneously hydrolyzed with fungal cellulase and fermented<br />

with the yeast Kluyveromyces marxianus to convert cellulose fibers to<br />

ethanol (Lark et al. 1997).<br />

Papers made from secondary fibers often show a higher microbial load<br />

which is of disadvantage for some applications, e.g., as hygienic papers (Cerny<br />

and Betz 1999).<br />

Anaerobic treatment of pulp mill effluents was reviewed by Guiot and Frigon<br />

(1998).PhanerochaetechrysosporiumandTrametes versicolor havebeenusedto<br />

degrade the chlorolignins in the effluents produced during chlorine bleaching<br />

(Eriksson et al. 1990). The ligninolytic systems of white-rot fungi, particularly<br />

P. chrysosporium, was used to degrade several persistent environmental<br />

pollutants such as benzo(a)pyrene, DDT, and dioxin. Bacteria metabolized<br />

dibenzo-p-dioxin (Wittich et al. 1992). Aerobic bioremediation techniques<br />

for the cleanup of creosote and PCP-contaminated soils were reviewed by<br />

Borazjani and Diehl (1998) (also Prewitt et al. 2003). Aerobic PCP transformation<br />

initially produced small amounts of pentachloroanisole; however more<br />

than 75% of both chemicals disappeared in 30 days from the test soil. Under<br />

methanogenic conditions, PCP was reductively dechlorinated to tetra-, tri-,<br />

and dichlorophenols (D’Angelo and Reddy 2000). Bioremediation of wood<br />

treated with preservatives using white-rot fungi was treated by Majcherczyk<br />

and Hüttermann (1998). The peroxidases of white-rot fungi unspecifically oxidize<br />

aromatic compounds by generating such a high redox-potential that they<br />

“burn down” all available aromatics present in the proximity of the mycelia.<br />

Phanerochaete laevis transformed polycyclic aromatic hydrocarbons (Bogan<br />

and Lamar 1996). Tubular bio-filters filled with straw, which were previously<br />

colonized with Pleurotus ostreatus mycelium was used to filter out ammonia<br />

from the waste air of cattle sheds (Majcherczyk et al. 1990). Experiments on the<br />

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9.7 Recent Biotechnological Processes and Outlook 251<br />

biodegradability of coal tar oil (creosote) by 16 bacterial species and six fungi<br />

using IR-spectra as an indicator for attack have been unsuccessful, assumably<br />

due to the complex mixture of some hundred toxic compounds in the tar oil<br />

(Schmidt et al. 1991).<br />

Bark extracts of Acacia spp. (wattle or mimosa bark extract) and wood extracts<br />

of Schinopsis spp. (quebracho wood extract) are rich sources of tannins.<br />

Tannins are used for a long time in leather tanning and for the production of<br />

adhesives (Pizzi 2000; Roffael et al. 2002). Copper tannate was tested as a possible<br />

wood preservative (Pizzi 1998). In 1950, worldwide about 300,000 t of<br />

tannin extracts were produced (Herrick and Hergert 1977). Main commercial<br />

producers are Argentina, South Africa, Brazil, Paraguay, Zimbabwe, Indonesia,<br />

Kenya, and Chile. The hot water extract of spruce and larch bark contains a high<br />

amount of carbohydrates and was thus unsuitable for adhesives. The soft-rot<br />

fungus Paecilomyces variotii reduced the carbohydrate content, so that the tannins<br />

were suitable as adhesives (Schmidt et al. 1984; Schmidt and Weißmann<br />

1986). Wagenführ (1989) used a commercial pectinolytic enzyme preparation<br />

to reduce the carbohydrate content.<br />

Despite the massive amount of money and effort devoted over the past<br />

decades to the microbiological or enzymatic conversions/treatments of lignocelluloses,<br />

several of the projects started with enthusiasm have suffered success<br />

or practical utilization or even loss of interest. Oil has remained the premier<br />

raw material for chemicals of all types (Little 1991). However, the foreseeable<br />

limitation of oil resources and thus the probable increase in the cost of<br />

petroleum-derived feedstock will provide the necessary incentive to further<br />

research. But, the development and utilization of alternative processes also<br />

depend on political interests and geographical aspects. As an example for the<br />

latter, the use of biofuels (rapeseed oil methylester, RME) may be a possible<br />

substitute for fossil fuels, which also contribute substantially to the increase in<br />

CO2 in the atmosphere. In Germany, the share of RME on the whole consumption<br />

of diesel fuel however is 4.3% and cannot exceed 7% due to the limited<br />

arable acreage. In the end, economy and subsidization will decide on future<br />

research.<br />

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Appendix 1<br />

Identification Key for Strand-Forming House-Rot Fungi<br />

(According to Huckfeldt and Schmidt 2004)<br />

All key points must be considered before a decision. Numbers in parentheses refer to<br />

the preceding key point. The question mark points out that only few samples have been<br />

investigated.<br />

1 fungus causes (intensive) rot 2<br />

1∗ fungus does not cause (intensive) rot – possible error: rotten wood is<br />

overgrown or infection is in initial stage; no vessel hyphae (if vessels then<br />

usually within strands, forward to 3)<br />

34<br />

2(1) brown-cubicalrot;nosetae;sporesalwayseven(alsoinoil-immersion) 3<br />

2∗ white rot; vessels always less than 15 µm in diameter 24<br />

3(2) strands clearly recognizable, but often overgrown by mycelium 4<br />

3∗ strands indistinct (microscopic investigation necessary; start at (4) if<br />

vessels are present)<br />

16<br />

4(3) strands over 5 mm in diameter, removable from the substrate, frequently<br />

surrounded by thick mycelium or hidden in masonry, wood etc.; dry<br />

strands break with clearly audiblecracking; fiber (skeletal) hyphae refractive;<br />

vessels with internal wall thickenings (bars), to 60 µm indiameter;<br />

vegetative hyphae with clamps see (12) Serpula lacrymans<br />

4∗ strands under 5 mm in diameter or firmly attached to the substrate 5<br />

5(4,16) strands hair-like, often branched and clearly defined (with “bark”), below<br />

0.5mm in diameter and often below mycelium, removable; no fibers; or<br />

strands/mycelium with sclerotia<br />

6<br />

5∗ strands not hair-like, not clearly defined (without bark); no sclerotia;<br />

fibers present or absent<br />

7<br />

6(5) sclerotia large, to 6 mm in diameter, round, often somewhat irregular,<br />

sometimes absent; strands hair-like, with bark, cream to yellow, redbrown<br />

to black when old, under 0.5 mm in diameter, somewhat flexible<br />

when dry; no fibers; vessels to 25 µm in diameter, numerous, in groups,<br />

withbars,cellwallto1µm thick; some vegetative hyphae bubble-like<br />

swollen to 10–25 µm in diameter and according literature with medallion<br />

clamps, always with clamps; strands also in masonry; only on softwoods<br />

Leucogyrophana mollusca<br />

6∗ sclerotia small and oblong, to 2.5 mm long, brown to grey, sometimes<br />

absent; strands hair-like, with bark, yellowish, grey to brown, probably<br />

darker when old, covered by lighter mycelium or exposed, under 0.5 mm<br />

in diameter, somewhat flexible when dry; no fibers; vessels to 25 µm in<br />

diameter, but often partly thickened, numerous, in bundles, with bars;<br />

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254 Appendix 1<br />

vegetative hyphae with clamps, 2.5–4.5 µm in diameter; strands also in<br />

masonry; probably only on softwoods Leucogyrophana pinastri<br />

7(5) strands with vessels (sometimes rare; search; wood fibers may be mistaken<br />

for vessels)<br />

8<br />

7∗ strands without vessels 9<br />

8(7) strands without fibers, however usually with vessels and vegetative hyphae<br />

with clamps<br />

10<br />

8∗ strands with fibers, vessels and vegetative hyphae with clamps 11<br />

9(7) strands with fibers and vegetative hyphae 16<br />

9∗ juvenile strands only with vegetative hyphae (old strands sometimes with<br />

vessels and fibers)<br />

22<br />

10(8) vessels rare, often narrowed at the septa; fibers absent or indistinct; veg- 15<br />

etative hyphae with clamps<br />

10∗ vessels numerous, to 21 µm in diameter, often in bundles, with septa, bars<br />

indistinct or absent, cell wall to 1 µm thick; no fibers; vegetative hyphae<br />

with clamps, 1–4µm in diameter, small hyphae partly with thickened<br />

cell wall; strands indistinct, just as embedded as those of S. lacrymans,<br />

somewhat flexible when dry, white, cream-yellow to grey, always brittle,<br />

to 2 mm in diameter, also in masonry Leucogyrophana pulverulenta<br />

11(8) vessels with bars (sometimes absent in very young strands), to 60 µm<br />

in diameter, fibers straight-lined, not flexible (with aqueous or ethanol<br />

preparation, may be flexible in KOH)<br />

11∗ vessels without bars, but with clearly defined septa, rarely over 30 µmin<br />

diameter; mycelium not silver grey (if molds absent), fibers flexible or not<br />

12(11) fibers refractive, (2–) 3–5 (–6.5) µm in diameter, fibers within strands<br />

near fruit body to 12 µm in diameter, straight-lined, septa not visible,<br />

no clamps, thick-walled, lumina often visible; vessels at least partly numerous<br />

(in groups), 5–60 µm indiameter,notorrarelybranched;with<br />

bars, these up to 13 µm high; vegetative hyphae hyaline, partly yellowish,<br />

brown when old, with large clamps, 2–4 µm in diameter, near fruit body<br />

to 4 µm in diameter; strands white, silver-grey, greytobrown,to3cm<br />

wide, usually with flabby mycelium in between, dry strands breaking<br />

with clearly audible cracking (strands contaminated with molds often<br />

not cracking any more); aerial mycelium cotton-woolly, soft, white, lightgrey<br />

to silver-grey, with yellow, orange or violet spots (“inhibition color”),<br />

often several square meters on walls, ceilings and floors, in the draught<br />

collapsing fast; on hardwoods and softwoods; strands often in masonry;<br />

(S. himantioides can be excluded, if strands thicker than 2 mm and at least<br />

some fibers more than 4.5 µmindiameter) Serpula lacrymans<br />

12 ∗ see before, but fibers (1.5−) 2–3.5 (−4) µm (sometimes not clearly distinguishable<br />

from S. lacrymans); strands to 2 mm in diameter, root-like<br />

branched and not as surrounded by thick mycelium as S. lacrymans;fruit<br />

body to 2 mm thick Serpula himantioides<br />

13(11) vegetative hyphae partly swelling up to 5–10 (−20) µm, fibers up to 2.5<br />

(−3) µm, vessels up to 40 µm; mycelium white, sometimes going yellow<br />

(if vessels swelling up: see 15)<br />

13 ∗ vegetative hyphae not swelling, ± regular diameter, at septa sometimes<br />

smaller; strands and aerial mycelium predominantly consisting of fibers,<br />

12<br />

13<br />

22<br />

14<br />

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Appendix 1 255<br />

thesebrighttobrown;vesselssolitary;vegetativehyphaepresent,however<br />

partly rare (search)<br />

14(13) fibers light to dark-brown, flexible or not, older strands not snow-white;<br />

on hardwoods and softwoods<br />

14 ∗ fibers hyaline or pale yellow, flexible; strands whitish to cream, partly<br />

somewhat yellowing or rarely infected by molds, also ice flower-like,<br />

flexible when dry, up to 7 mm in diameter; fibers numerous, 2–4µm<br />

in diameter (in Antrodia xantha partly somewhat yellowish, hyphal tips<br />

with tapering ending cell walls), narrow lumina, straight-lined, mostly<br />

unbranched, insoluble in 3% KOH, [if dissolving, see Diplomitoporus<br />

lindbladii (31), check rot type, if fibers missing], but in KOH swelling,<br />

sometimes with ‘blown up’ hyphal segments; vessels not rare but in old<br />

strands difficult to isolate, up to 25 µm in diameter, thick-walled with<br />

middle lumen, without bars; vegetative hyphae with few clamps, 2–4 (–7)<br />

µm in diameter, sometimes medallion clamps, often somewhat thickwalled;<br />

surface mycelium white to cream, thin, aerial mycelium in nodraught<br />

or under-floor areas partly some square meters large, white<br />

to cream, later also stalactite-like growth from above; strands also in<br />

masonry(?);probablyonlyonsoftwoods;genusAntrodia (species not<br />

surely distinguishable on the basis of their strands/mycelia)<br />

Antrodia vaillantii, A. sinuosa, A. xantha, A. serialis<br />

15(10,14) vegetative hyphae with clamps; strands first cream to loam-yellow, then<br />

brownish to ochre, up to 3 mm wide, root-like branches, similar to those<br />

of Coniophora puteana, however not becoming black; surface mycelium<br />

first dirty-white to yellowish, then loam-yellow, brownish to ochre, near<br />

fruit body partly violet; vegetative hyphae refractive, (1.5−) 2.5–3–5 (−5)<br />

µm in diameter, partly thickened; fibers indistinct, 1.5–5 µmindiameter<br />

(often only in darker strands); vessels hyaline, sometimes with ‘blown up’<br />

hyphal segments, up to 15 (−25) µm in diameter, without bars, but with<br />

septa, with clamps; on and within (?) masonry and wood, often in damp<br />

cellars; brown rot Paxillus panuoides<br />

15 ∗ vegetative hyphae without or rarely with clamps, rarely multiple clamps<br />

(more often at margin of fruit body, often indistinct, since branched),<br />

2–6 (–9) µm indiameter;strandsfirstbright,thenbrowntoblack,up<br />

to 2 mm wide, to 1 mm thick, root-like, hardly removable (not so with C.<br />

marmorata), when removed usually fragile, partly with brighter center,<br />

underlying wood becoming partly black; fibers pale to dark brown, 2–4<br />

(−5) µm in diameter, somewhat thick-walled, however with relatively<br />

broad, usually visible lumen, also branched, to be confused with vegetative<br />

hyphae; drop-shaped, hyaline to brownish secretions (1–5 µm in<br />

diameter) often to be found on hyphae; vessels in strands surrounded and<br />

interwoven by fine hyphae (0.5–1.5 µm in diameter), therefore preparation<br />

with H2SO4 and KOH solution, due to preparation irregularly formed<br />

or distorted, up to 30 µm in diameter, thin-walled (or slightly thick-walled<br />

with C. marmorata), without bars, but with septa; often also in masonry<br />

etc., genus Coniophora (species not surely distinguishable on the basis of<br />

their strands/mycelia) e.g., Coniophora puteana, C. marmorata<br />

16(3,9) mycelium on masonry, concrete etc.; vessels possibly not visible or missing,<br />

untypical or small; if star-shaped setae present see (25)<br />

15<br />

5<br />

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256 Appendix 1<br />

16∗ mycelium not on or in masonry 17<br />

17(16) fibers present; vessels absent; vegetative hyphae with clamps (in older<br />

parts rare); mycelium and strands only on wood<br />

18<br />

17∗ fibers missing or very rare; vegetative hyphae present (see (5) if vessels<br />

present, search for vessels, being rare in young strands)<br />

22<br />

18(17) fibers partly with swelling and partly with regular diameter, 2.5–4.5 µm<br />

in diameter (in fruit body sometimes larger), flexible,luminasmall,often<br />

visible, sometimes punctually larger; vegetative hyphae thin-walled, 1–2<br />

(−2.5) µm in diameter, with clamps, but no medallions; cystidia possible;<br />

myceliumcreamtocorky,firmandtough,oftenincavitiesandshakesin<br />

wood below fruit body; on oak, half-timbering; brown rot<br />

Daedalea quercina<br />

18∗ fibers not swelling, ± regular in diameter; hyphae in wood usually possess<br />

clamps of medallion type<br />

19<br />

19(18) mycelium rough-velvet; usually two-layered, at least two-colored: white<br />

mycelium close to wood and covered by yellow, reddish to brown aerial<br />

mycelium; fibers 1.5–5 µm in diameter, discolored at darker mycelial areas;<br />

vegetative hyphae with clamps; grey mycelia cannot be differentiated;<br />

often at windows<br />

20<br />

19∗ mycelium fine-velvet to silky; not distinctly two-layered; fibers 1.5–2<br />

(−2.5) µm in diameter, hyaline, straight, rarely branched; vegetative hyphae<br />

always with clamps, 1.5–2 µm in diameter; if hyphae wider see (14);<br />

mycelium firm and tough, first white, then with yellow, ochre to violet<br />

spots; covering cavities and shakes in wood, easy to remove; mycelia and<br />

strands so far only proven for wood; monstrous “dark fruit bodies”, sometimes<br />

with little caps; usually on softwoods; brown rot; genus Lentinus<br />

(species not surely distinguishable on the basis of their strands/mycelia)<br />

e.g., Lentinus lepideus<br />

20(19) fibers up to dark-brown (examine dark areas); aerial mycelium cream,<br />

ochre to dark-brown, underneath white to cream mycelium (not always<br />

clearly visible, use pocket-lens); colored fibers 1.5–3 (–4.5) µm in diameter;<br />

vegetative hyphae 2–4.5 µm in diameter, with clamps; strands rare,<br />

then forming structures of a few centimeters, these first bright, reddish,<br />

then red-brown to grey; in cavities dark, monstrous tap-, pin-, antlers- or<br />

cloud-like “dark fruit bodies”; only on softwoods<br />

Gloeophyllum abietinum<br />

20∗ colored fibers and surface mycelia not so dark, 2–5 µm indiameter;<br />

sometimes also “dark fruit bodies”<br />

21<br />

21(20) mycelium white, cream to light brown; rarely short strands of few centimeters<br />

of length, these first bright, then yellowish to ochre-brown and usually<br />

covered by mycelium; colored fibers light to dark yellow, light-brown to<br />

brown, 2–4.5 µm in diameter (partly broader); vegetative hyphae hyaline,<br />

2–4µm in diameter, with clamps; arthrospores rare, 3−4 × 10−15 µm,<br />

cylindrical; often in shakes; tap-, pin-, antlers- or cloud-like “dark fruit<br />

bodies”; only on softwoods Gloeophyllum sepiarium<br />

21∗ mycelium white, beige, yellow-orange to light grey-brown; strands under<br />

1 mm in diameter and not clearly defined; surface mycelium whiteyellow<br />

to grey and usually covered by mycelium; colored fibers very light<br />

yellow, gold-yellow to light-brown, 1–4 µm in diameter, septa clearly<br />

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Appendix 1 257<br />

22(13,17)<br />

recognizable; vegetative hyphae hyaline, 2–4 µm in diameter, thin-walled,<br />

with clamps; ‘dark fruit bodies’ also antlers-shaped, often with brighter<br />

tips; often in shakes; only on wood (softwoods and hardwoods)<br />

Gloeophyllum trabeum<br />

vegetative hyphae without clamps 23<br />

22∗ vegetative hyphae with clamps, partly with swellings, 1–2 µmindiameter;<br />

fibers and vessels only in older strands; fibers 0.5–2 (−3) µm, hyaline,<br />

straight-lined, thick-walled, septa not visible, no clamps, no reaction in<br />

KOH; vessels 6–40 µm in diameter, thin-walled or slightly thick-walled,<br />

hyaline, vessels in strands surrounded and interwoven by fine hyphae<br />

(0.5–1.5 µm in diameter); mycelium pure white or pink, if being undisturbed<br />

lasting so, easily removable, but sensitive; strands often sunk in<br />

mycelium; on softwoods, rarely on hardwoods; brown rot; genus Oligoporus<br />

and similar fungi (species indistinguishable by strands/mycelia)<br />

e.g., Oligoporus placenta<br />

23(22) arthrospores thin-walled, cylindrical 1.5−2.5 × 5−12 µm; vegetative hyphae<br />

hyaline, thin-walled or slightly thick-walled, 2–3 (−4) µmindiameter,<br />

without clamps, but with primordial clamps; vessels indifferent, septa<br />

present, thin-walled, to 12 µm in diameter; in older parts sometimes small<br />

fibers(comparewith12);myceliumwhitetoyellow,easilyremovable,but<br />

sensitive; strands often sunk in mycelium<br />

monokaryon of Serpula lacrymans<br />

23∗ arthrospores absent or different 34<br />

24(2) setae present, simple setae or stellar setae, within white to cream 25<br />

mycelium, partly only very small nests of setae (search)<br />

24 ∗ setae absent 28<br />

25(24) stellar setae present; vegetative hyphae without clamps 27<br />

25 ∗ setae not clearly stellar-shaped or simply branched, partly rooted 26<br />

26(25) simple, dark-brown, to 180 µm long setae within mycelium, strand and<br />

fruit body; fibers pale yellow, thin-walled, 2–3 µm in diameter, rarely<br />

branched; vegetative hyphae hyaline, 1.5 µm in diameter; mycelium<br />

downy, loam-yellow to brown, also white when young; strand-like structures<br />

up to 4 mm wide and 0.5 mm thick, firmly attached, often fingershaped<br />

branched; usually on hardwoods (often on framework), very rare<br />

on softwoods; so far proven for oak, ash, false acacia, elm, beech, fir and<br />

spruce; white rot Phellinus contiguus<br />

26 ∗ simple, dark-brown setae in fruit bodies and mycelium, under 100 µm;<br />

other species of the genus Phellinus known to occur in buildings (species<br />

not surely distinguishable on the basis of strands/mycelia)<br />

Phellinus nigrolimitatus, P. pini, P. robustus<br />

27(25) stellar setae dichotomously branched, to 90 µm in diameter, in fruit body,<br />

mycelium and strand, partly rare; vegetative hyphae with septa, 2–4 µmin<br />

diameter; strands cream to red-brown, fibrous surface; partly embedded<br />

in white mycelium or fruit body; spores subglobose, smooth; strands on<br />

and in masonry; white rot Asterostroma laxum<br />

27 ∗ stellar setae only rarely branched, up to 190 µm in diameter, in fruit body,<br />

mycelium and strand; vegetative hyphae with septa, 1.5–3 µm indiameter;<br />

strands cream-brown, up to 1 mm in diameter; surface mycelium<br />

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258 Appendix 1<br />

first white, then brown, partly small mycelial plugs; spores subglobose,<br />

tuberculate; strands on and in masonry; white rot<br />

Asterostroma cervicolor<br />

28(24) fibers absent (also in aqueous preparation); sometimes strands with vessels<br />

28∗ fibers present; strands without vessels; mycelium sometimes with vessel-<br />

like hyphae<br />

29(28) crystalline asterocystidia in fruit body and strand, up to 20 µm indiameter,<br />

cystidia stipe to 11 µmlong,2µmindiameter; vegetative hyphae<br />

with clamps, 1.5–3 µm; vessels thin-walled, to 15 µmindiameter,without<br />

bars, but with septa; no fibers; strands snow-white to cream, 0.2–1 mm<br />

in diameter (?), mostly short und near fruit body; fruit body smooth; to<br />

date only found on softwood; white rot Resinicium bicolor<br />

29∗ without asterocystidia 30<br />

30(29) vegetative hyphae with clamps, partly with bubble-like swellings, 1–2<br />

(−4) µm; no fibers (if fibers present, see 31); sometimes with vessels (then<br />

no swellings), small clamps, 4–9 (?) µm in diameter; strands snow-white<br />

to cream, 0.2–1(?) mm in diameter, fragile, often only short and near<br />

fruit body; fruit body resupinate, thin, poroid, grandinioid or smooth,<br />

fragile; spores warty, translucent and small, 4−5.5×3−4.5 µm; so far only<br />

found directly on damp wood; white rot; genus Trechispora (species not<br />

distinguishable on the basis of strands/mycelia);<br />

in buildings Trechispora farinacea, T. mollusca<br />

30∗ other characteristics 34<br />

31(28) fibers insoluble in 3% KOH, sometimes slightly swelling, partly under 32<br />

3 µm in diameter; mycelium partly with brown crust<br />

31 ∗ fibers completely soluble in 3% KOH, 2–4.5 (−8?) µm in diameter, thickwalled<br />

to solid (‘filled’), similar to A. vaillantii (14); no vessels; vegetative<br />

hyphae with few clamps, 1–2.5 µm indiameter;surfacemycelium<br />

without crust, usually meager, partly forming compact plates, white to<br />

light-brown; strands white, partly somewhat yellowing, root-like, richly<br />

branched, radiate or ice flower-like, fibrous, up to 2 mm in diameter; so<br />

far mycelium only proven to occur on wood; white rot<br />

Diplomitoporus lindbladii<br />

32(31) arthrospores often lemon-shaped, hyaline, thick-walled, 5−7×7−12(−?)<br />

µm, in surface mycelium, which lies close to the wood, and in substrate<br />

mycelium; in white mycelium: fibers hyaline to brown, to 2 µmindiameter,<br />

not very thick-walled and hardly separable from vegetative hyphae; vegetative<br />

hyphae hyaline with clamps, these often difficult to find, 1–2 µmin<br />

diameter; vessels not proven; in colored mycelium: fibers light-brown to<br />

brown, 1.5–3 (−4.5) µm in diameter; vegetative hyphae hyaline to brown,<br />

thick-walled, rarely clamps, 2–6 (−7)µm in diameter, branched; vessels to<br />

11 µm in diameter; strands usually absent or short and under mycelium;<br />

mycelium first white to cream, then yellowish, grey to brown, when old<br />

often luxuriant, firm and tough, frequently with paper-like, firm, brown<br />

crust, predominantly in shakes and cavities, usually with amber guttation<br />

drops or with brown to black spots (remainders of dried guttation),<br />

in constructions white to cream; surface mycelium partly with distinct<br />

29<br />

31<br />

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Appendix 1 259<br />

margin; sometimes with poroid fruit bodies within surface mycelium<br />

(1–90 mm thick), then also wider hyphae; white rot, preferential sapwood<br />

decay,hardwoodandsoftwood,nooronlysomegrowthonmasonry<br />

Donkioporia expansa<br />

32 ∗ arthrospores, strands or mycelia different 33<br />

33(32) strands black, very clear, with separate crust layer, often also hollow<br />

when old (32), clearly thicker than 1 mm, only on wood with bark rests<br />

or in wood in the area of in-growing roots, examine for in-growing roots;<br />

hardwood and softwood; white rot rhizomorphs of Armillaria spp.<br />

33 ∗ strands or mycelia different 34<br />

34(1,23,<br />

30,33)<br />

on masonry, rough-casting etc.; no or slightwood decay: e.g., species of the<br />

genera Coprinus, Peziza (white strands), Scutellinia, Pyronema, molds<br />

(e.g., Cladosporium) and slime fungi (Enteridium, Fuligo, Trichia)<br />

34 ∗ further species on wood which so far were rarely found in buildings: e.g.,<br />

species of the genera Daldinia, Fomitopsis, Hyphodontia, Phanerochaete,<br />

Phlebiopsis, Pleurotus, Polygaster, Trametes; see also Table 8.6<br />

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Appendix 2<br />

Fungi Mentioned in this Book<br />

(see also Tables 8.1–8.3; most English names according to Larsen and Rentmeester 1992,<br />

Rune and Koch 1992, some names suggested as new by the author)<br />

Scientific name, English name Significance in this book<br />

Agaricus bisporus (J.E. Lange) Pilát agaric mushroom<br />

Agrocybe aegerita (Brig.) Singer edible mushroom on wood<br />

Alternaria alternata (Fr.) Keissl. toxic mold, blue stain<br />

Amanita caesarea (Scop.: Fr.) Pers. mycorrhizete<br />

Amanita muscaria (L.: Fr.) Hook. mycorrhizete<br />

Amylostereum areolatum (Chaill.: Fr.) Boid. red streaking<br />

Amylostereum chailletii (Pers.: Fr.) Boid. red streaking<br />

Antrodia serialis (Fr.: Fr.) Donk, Effused tramete indoor wood<br />

Antrodia sinuosa (Fr.: Fr.) P. Karsten, White polypore indoor wood<br />

Antrodia vaillantii (DC: Fr.) Ryv., Mine polypore indoor wood<br />

Antrodia xantha (Fr.: Fr.) Ryv., Yellow polypore indoor wood<br />

Armillaria borealis Marxm. & K. Korh., Nordic honey fungus tree parasite<br />

Armillaria cepistipes Velen. tree parasite<br />

Armillaria gallica Marxm. & Romagn. tree parasite<br />

Armillaria luteobubalina Watling & Kile parasite<br />

Armillaria mellea (Vahl: Fr.) Kummer, Honey fungus tree parasite<br />

Armillaria ostoyae (Romagn.) Herink, Dark honey fungus tree parasite<br />

Arthrographis cuboides (Sacc. & Ellis) Sigler pink stain<br />

Aspergillus flavus Link cancerogenic mold<br />

Aspergillus fumigatus Fres. cancerogenic indoor mold<br />

Aspergillus niger van Tieghem, Black mold mold<br />

Aspergillus versicolor (Vuill.) Tiraboschi mold on poplar wood,<br />

indoor mold<br />

Asterostroma cervicolor (Berk. & Curtis) Massee indoor wood<br />

Asterostroma laxum Bres. indoor wood<br />

Aureobasidium pullulans (de Bary) Arn. blue stain<br />

Auricularia auricula-judae (Fr.) Quélet edible mushroom on wood<br />

Auricularia polytricha (Mont.) Sacc. protoplasts<br />

Bispora monilioides Corda black streaking of beech<br />

logs<br />

Bjerkandera adusta (Willd:Fr.)P.Karsten,Smokeypolyporetreerot Boletus edulis Bull.: Fr. mycorrhizete<br />

Botrytis cinerea Pers. noble rot of wines, seedling<br />

shoot tip disease<br />

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262 Appendix 2<br />

Candida utilis (Henneberger) Lodder & Kreger yeast, glucose conversion<br />

Cantharellus cibarius Fr. mycorrhizete<br />

Ceratocystis adiposa (E.J. Butler) C. Moreau blue stain<br />

Ceratocystis coerulescens (Münch.) B.K. Bakshi blue stain<br />

Ceratocystis fagacearum (Bretz) Hunt Oak wilt disease<br />

Ceratocystis fimbriata (Ellis & Halstead) Davidson f. platani<br />

Walter<br />

Plane canker stain disease<br />

Ceratocystis minor (Hedgc.) J. Hunt blue stain<br />

Ceratocystis pluriannulata (Hedgc.) C. Moreau blue stain<br />

Cerinomyces pallidus Martin indoor wood<br />

Ceriporiopsis subvermispora (Pilát) Gilb. & Ryv. lignin degradation,<br />

biopulping<br />

Cerocorticium confluens (Fr.: Fr.) Jül. & Stalp. indoor wood<br />

Chaetomium globosum Kunze: Fr. soft rot<br />

Chlorociboria aeruginascens (Nyl.) Kan. Small-spored green<br />

wood-cup<br />

‘green rot’<br />

Chlorociboria aeruginosa (Pers.: Fr.) Seaver (large-spored) ‘green rot’<br />

Chondrostereum purpureum (Pers.: Fr.) Pouzar, Silver-leaf tree rot, stored and exterior<br />

fungus<br />

wood<br />

Ciboria batschiana (Zopf) Buchwald acorn rot<br />

Cladosporium cladosporioides (Fres.) de Vries blue stain<br />

Cladosporium herbarum (Pers.) Link mold, blue-stain<br />

Cladosporium sphaerospermum Penz. blue stain, indoor mold<br />

Climacocystris borealis (Fr.)Kotl&Pouzar treerot<br />

Coniophora arida (Fr). P. Karsten, Arid cellar fungus indoor wood<br />

Coniophora marmorata Desm., Marmoreus cellar fungus indoor wood<br />

Coniophora olivacea (Fr.) P. Karsten, Olive cellar fungus indoor wood<br />

Coniophora puteana (Schum.: Fr.) P. Karsten, (Brown) Cellar<br />

fungus<br />

indoor wood<br />

Coprinus comatus (O.F. Müller: Fr.) S.F. Gray light influence<br />

Cryphonectria parasitica (Murr.) Barr Chestnut blight<br />

Cryptostroma corticale (Ellis & Everh.) P.H. Greg & S. Waller mold, woodworker’s lung<br />

Cylindrocarpon destructans (Zins.) Scholten oak root parasite<br />

Dacrymyces stillatus Nees: Fr., Orange jelly indoor wood<br />

Daedalea quercina (L.: Fr.) Fr., Maze-gill stored and exterior wood<br />

Daedaleopsis confragosa (Bolton: Fr.) J. Schröter white rot<br />

Dichomitus squalens (P. Karsten) D.A. Reid successive white rot,<br />

biopulping<br />

Diplomitoporus lindbladii (Berk.) Gilb. & Ryv. indoor white wood<br />

Discula pinicola (Naum.) Petrak blue stain<br />

Donkioporia expansa (Desm.) Kotl. & Pouzar, Oak polypore indoor white-wood<br />

Emericella nidulans (Eidam) Vuill. toxic mold<br />

Earliella scrabosa Gilb. & Ryv. mine timber<br />

Fistulina hepatica (Schaeffer: Fr.) Fr., Beef-steak fungus tree rot<br />

Flammulina velutipes (Curtis: Fr.) Singer edible mushroom on wood<br />

Fomes fomentarius (L.: Fr.) Kickx, Tinder fungus tree rot<br />

Fomitopsis palustris (Berk. & M.A. Curtis) Gilb. & Ryv. cellulose degradation<br />

Fomitopsis pinicola (Swartz: Fr.) P. Karsten, Red-belted<br />

polypore<br />

brown rot<br />

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Appendix 2 263<br />

Fuligo septica Gmelin indoor wood<br />

Fusarium oxysporum (Schlecht.: Fr.) ssp. cannabis herbicide, oak root parasite<br />

Ganoderma adspersum (Schulzer) Donk “palo podrido”<br />

Ganoderma applanatum (Pers.) Pat. white rot<br />

Ganoderma lipsiense (Batsch) G.F. Atk., Artist’s conk white rot<br />

Ganoderma lucidum (Curtis: Fr.) P. Karsten medicinal mushroom<br />

Gliocladium roseum Bainier antagonism<br />

Gloeophyllum abietinum (Bull.: Fr.) P. Karsten, Fir gill<br />

polypore<br />

stored and exterior wood<br />

Gloeophyllum sepiarium (Wulfen: Fr.) P. Karsten, Yellow-red<br />

gill polypore<br />

stored and exterior wood<br />

Gloeophyllum trabeum (Pers.: Fr.) Murr., Timber gill stored and exterior wood<br />

polypore<br />

Grifola frondosa (Dicks.: Fr.) S.F. Gray white rot, edible mushroom<br />

Hebeloma cylindrosporum Romagn. mycorrhizete<br />

Hebeloma velutipes Bruchet mycorrhizete<br />

Helicobasidium brebissonii (Desm.) Donk seedling smothering<br />

Hericium erinaceus (Bull.: Fr.) Pers. edible mushroom on wood<br />

Heterobasidion abietinum Niemelä & Korhonen, Fir root<br />

rot fungus<br />

tree parasite<br />

Heterobasidion annosum (Fr.: Fr.) Bref. s.s., Pine root<br />

rot fungus<br />

tree parasite<br />

Heterobasidion parviporum Niemelä & Korhonen,<br />

tree parasite<br />

Spruce root rot fungus<br />

Hormonema dematioides Melin & Nannf. blue stain<br />

Hyphoderma praetermissum (P. Karsten) J. Eriksson & Strid indoor wood<br />

Hyphodontia spathulata (Schrader) Parm. indoor wood<br />

Inonotus dryadeus (Pers.: Fr.) Murrill white rot<br />

Inonotus dryophilus (Berk.) Murrill successive white rot<br />

Inonotus hispidus (Bull.: Fr.) P. Karsten white rot<br />

Kluyveromyces marxianus (E.C. Hansen) Van der Walt yeast, ethanol production<br />

Kretzschmaria deusta (Hoffman) P.M.D. Martin white-rot ascomycete<br />

Kuehneromyces mutabilis (Schaeff.: Fr.) Singer & A.H. Sm. edible mushroom on wood<br />

Laccaria bicolor (Maire) Orton mycorrhizete<br />

Laetiporus sulphureus (Bull.: Fr.) Murrill, Sulphur polypore tree rot<br />

Laurelia taxodii (Lentz & H.H. McKay) Pouzar brown pocket rot<br />

Lecythophora hoffmannii (van Beyma) W. Gams soft rot<br />

Lecythophora mutabilis (J.F.H. Beyma) W. Gams & McGinnes soft rot<br />

Lentinula edodes (Berk.) Pegler, Shii-take edible mushroom on wood<br />

Lentinus lepideus (Fr.: Fr.) Fr., Scaly Lentinus stored and exterior wood<br />

Leucogyrophana mollusca (Fr.: Fr.) Pouzar, Soft dry<br />

rot fungus<br />

indoor wood<br />

Leucogyrophana pinastri (Fr.: Fr.) Ginns & Weresub,<br />

Mine dry rot fungus<br />

indoor wood<br />

Leucogyrophana pulverulenta (Sow.: Fr.) Ginns, Small indoor wood<br />

dry rot fungus<br />

Loweporus lividus (Kalchbr.: Cooke) J.E. Wright mine timber<br />

Macrophomina phaseolina (Tassi) Goid. conifer seedling parasite<br />

Melanomma sanguinarum (P. Karsten) Sacc. red spotting of beech wood<br />

www.taq.ir


264 Appendix 2<br />

Memnoniella echinata (Rivolta) Galloway toxic mold<br />

Meria laricis Vuill. Meria needle-cast of larch<br />

Meripilus giganteus (Pers.: Fr.) P. Karsten, Giant polypore tree rot<br />

Meruliporia incrassata (Berk. & Curtis) Murr., American indoor wood<br />

dry rot fungus<br />

Merulius tremellosus Schrader successive white rot,<br />

biopulping<br />

Monodictys putredinis (Wallr.) Hughes soft rot<br />

Nectria coccinea var. faginata Lohmann, Watson & Ayers Beech bark disease<br />

Nectria galligena Bres. Beech bark disease<br />

Nematoloma frowardii (Speg.) E. Horak lignin degradation<br />

Oligoporus amarus (Hedgc.) Gilb. & Ryv. brown pocket rot<br />

Oligoporus placenta (Fr.) Gilb. & Ryv., (Reddish)<br />

indoor wood<br />

Sap polypore<br />

Oligoporus stipticus (Pers.: Fr.) Kotl. & Pouzar brown rot<br />

Ophiostoma novo-ulmi Brasier Dutch elm disease<br />

Ophiostoma piceae (Münch) H. and P. Sydow blue stain<br />

Ophiostoma piliferum (Fr.) H. and P. Sydow blue stain<br />

Ophiostoma setosum Uzunovic, Seifert, S.H. Kim & Breuil blue stain<br />

Ophiostoma ulmi (Buisman) Nannf. Dutch elm disease<br />

Oudemansiella mucida (Schrad.) Höhn competition<br />

Pachysolen tannophilus Boidin & Adzet yeast, xylose fermentation<br />

Paecilomyces variotii Bain. soft rot<br />

Paxillus involutus (Batsch: Fr.) Fr. mycorrhizete<br />

Paxillus panuoides (Fr.: Fr.) Fr., Stalkless Paxillus stored and exterior wood<br />

Penicillium aurantiogriseum Dierckx indoor mold<br />

Penicillium camemberti Thom cheese mold<br />

Penicillium brevicompactum Dierckx indoor mold<br />

Penicillium chrysogenum Thom indoor mold<br />

Penicillium glabrum (Wehmer) Westling mold, suberosis<br />

Penicillium implicatum Biourge mold on poplar wood<br />

Penicillium nalgiovense Laxa salami-sausages mold<br />

Penicillium roqueforti Thom cheese mold<br />

Penicillium spinulosum Thom indoor mold<br />

Peziza repanda Pers. indoor wood<br />

Phaeolus schweinitzii (Fr.:Fr.)Pat.,Dyepolypore treerot<br />

Phanerochaete chrysosporium Burds. ligninase, biopulping<br />

Phanerochaete laevis (Fr.) J. Eriksson & Ryv. detoxification<br />

Phanerochaete sordaria (P. Karsten) J. Eriksson & Ryv. fatty acid profiles, lignin<br />

degradation<br />

Phellinus chrysoloma (Fr.) Donk white rot<br />

Phellinus contiguus (Pers.) Pat. indoor white-rot<br />

Phellinus hartigii (Allesch. & Schnabl) Pat. white rot<br />

Phellinus igniarius (L.: Fr.) Quélet, False tinder fungus white rot<br />

Phellinus nigrolimitatus (Romell) Bourdot & Galzin,<br />

Black-edged polypore<br />

tree rot<br />

Phellinus pini (Brot.: Fr.) A. Ames, Ochre-orange<br />

hoof polypore<br />

tree rot<br />

Phellinus pomaceus (Pers.: Fr.) Maire white rot<br />

www.taq.ir


Appendix 2 265<br />

Phellinus robustus (P. Karsten) Bourdot & Galzin white rot<br />

Phellinus tremulae (Bondartsev) Bondartsev & Borrisow parasite<br />

Phellinus weirii (Murrill) Bilb. parasite<br />

Phialophora fastigiata (Lagerb. & Melin) Conant grey stain of poplar<br />

Phlebia brevispora Nakasone specific PCR, biopulping<br />

Phlebia chrysocreas (Berk. & M.A. Curtis) Burds “palo podrido”<br />

Phlebia radiata Fr. lignin degradation<br />

Phlebiopsis gigantea (Fr.) Jül., Conifer parchment antagonism<br />

Pholiota carbonica A.H. Sm. competition<br />

Pholiota highlandensis (Peck) Hesler & A.H. Sm. competition<br />

Pholiota nameko (T.Itô)S.Ito&S.Imai ediblemushroom<br />

Pholiota squarrosa (Pers.: Fr.) Kummer white rot<br />

Phoma exigua Sacc. blue stain<br />

Physisporinus vitreus (Pers.: Fr.) P. Karsten, Pole fungus manganese deposits<br />

Phytophthora cactorum (Lebert & Cohn) Schröter Beech seedling disease<br />

Phytium debaryanum Hesse conifer seedling parasite<br />

Piptoporus betulinus (Bull.: Fr.) P. Karsten, Birch polypore tree rot<br />

Pleurotus ostreatus (Jacq.: Fr.) Kummer, Oyster fungus edible mushroom on wood<br />

Pleurotus ostreatus ssp. florida edible mushroom on wood<br />

Pluteus cervinus (Schaeffer) Kummer indoor wood<br />

Polyporus squamosus (Hudson: Fr.) Fr., Scaly polypore tree rot<br />

Pycnoporus cinnabarinus (Jacq.) Fr. lignin degradation<br />

Ramariopsis kunzei (Fr.) Corner indoor wood<br />

Resinicium bicolor (Alb. & Schwein.: Fr.) Parm. indoor white-rot<br />

Reticularia lycoperdon Bull. indoor wood<br />

Rhinocladiella atrovirens Nannf. blue stain<br />

Rhizina undulata Fr. root-decay ascomycete<br />

Rhizoctonia solani Kühn beech nut rotting<br />

Rigidoporus lineatus (Pers.) Ryv. mine timber<br />

Rigidoporus vinctus (Berk.) Ryv. mine timber<br />

Rosellinia aquila (Fr.) de Not. seedling smothering<br />

Rosellinia minor (Höhn) Francis seedling smothering<br />

Rosellinia quercina R. Hartig oak root parasite<br />

Saccharomyces cerevisiae Meyen: E.C. Hansen yeast<br />

Schizophyllum commune Fr.: Fr., Split-gill stored and exterior wood<br />

Sclerophoma pithyophila (Corda) v. Höhn. blue stain<br />

Scutellinia scutellata Lambotte indoor wood<br />

Serpula himantioides (Fr.: Fr.) P. Karsten, Wild merulius indoor wood<br />

Serpula lacrymans (Wulfen: Fr.) Schroeter apud Cohn, indoor wood<br />

(True) Dry rot fungus<br />

Sirococcus conigenus (DC.) P.F. Cannon & Minter tree parasite<br />

Sirococcus strobilinus Preuss Sirococcus shoot dieback<br />

Sistotrema brinkmanni (Bres.) J. Eriksson stored and exterior wood<br />

Sparassis crispa Wulfen: Fr. tree rot<br />

Sphaeropsis sapinea (Desm.) Dyko & Sutton Conifer seedling shoot tip<br />

disease<br />

Sphaerotheca lanestris Harkn. virus vector<br />

Stachybotrys chartarum (Ehrenb.) Hughes toxic mold<br />

Stereum hirsutum (Willd.: Fr.) S.F. Gray, Hairy Stereum stored and exterior wood<br />

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266 Appendix 2<br />

Stereum rugosum (Pers.: Fr.) Fr. white rot<br />

Stereum sanguinolentum (Alb. & Schwein.: Fr.) Fr.,<br />

red streaking, Wound rot of<br />

Bleeding Stereum<br />

spruce<br />

Strasseria geniculata (Berk. & Broome) Höhn blue stain, Conifer seedling<br />

shot tip disease<br />

Thekopsora areolata (Fr.) Magnus spruce inflorescence<br />

damage<br />

Thelephora terrestris Erh. seedling smothering<br />

Thielavia terrestris (Apinis) Malloch & Cain. soft rot<br />

Trametes hirsuta (Wulfen: Fr.) Pilát white rot<br />

Trametes multicolor (Schaeffer) Jül. indoor wood<br />

Trametes pubescens (Schum.) Pilát fatty acid profile<br />

Trametes versicolor (L: Fr.) Pilát, Many-zoned polypore stored and exterior wood<br />

Trechispora farinacea (Pers.) Liberta indoor wood<br />

Trechispora mollusca (Pers.) Liberta indoor wood<br />

Trichaptum abietinum (Dicks.: Fr.) Ryv., Fir Polystictus red streaking<br />

Trichoderma hamatum (Bonord.) Bainier mushroom parasite<br />

Trichoderma harzianum Rifai mushroom parasite<br />

Trichoderma parceramosum Bissett mushroom parasite<br />

Trichoderma pseudokoningii Oudem. mushroom parasite<br />

Trichoderma reesei E.G. Simmons enzymes<br />

Trichoderma viride Pers.: Fr. mold, antagonism,<br />

enzymes<br />

Tyromyces caesius (Schrader: Fr.) Murrill, Blue cheese<br />

polypore<br />

brown rot<br />

Tyromyces stipticus (Pers.: Fr.) Kotl. & Pouzar brown rot<br />

Volvariella bombycina (Schaeffer: Fr.) Singer indoor wood<br />

Xerocomus pruinatus (Fr.) Quélet IGS sequence<br />

Xylaria hypoxylon (L.) Grev. white-rot ascomycete<br />

Xylobolus frustulatus (Pers.: Fr.) Boidin, Ceramic parchment tree rot<br />

www.taq.ir


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www.taq.ir


Subject Index<br />

Abiotic wood discolorations 119<br />

Accessory compounds 57, 81, 90–1, 147,<br />

175–6, 194<br />

Acetylation of wood 156<br />

Acid production by fungi 70–4, 94, 97–8,<br />

104, 220, 232<br />

Actinobacteria 111<br />

Air 58–60, 174–5<br />

Algae on wood 119, 200<br />

Allergies through fungi 123–4<br />

Alternative wood protection 79–81, 156–9<br />

Amplified fragment length polymorphism<br />

(AFLP) 45<br />

Antagonisms 79–81, 124, 170, 194, 235<br />

Antrodia species 13–4, 23, 32, 38, 41, 44, 69,<br />

73–4, 77, 138, 156, 201, 207–11, 216–7,<br />

218–20, 230, 233, 255<br />

Archaea 110<br />

Archaeological wood 105, 116–7<br />

Armillaria root disease 187<br />

Armillaria species 6, 9, 14–5, 23, 32, 34–6,<br />

38–9, 41, 43–5, 60, 74, 80, 104, 118, 132,<br />

135, 173, 184, 186–189, 200–1, 224, 259<br />

Arthrospores 15, 17, 66, 69, 80, 103<br />

Ascomycetes 16, 18–20, 27, 31, 49–50, 70,<br />

84, 102, 120, 125, 137–8, 142, 184, 201<br />

Ascospores 19–20, 75<br />

Asexual development 10–6<br />

Aspergillus species 16–7, 50, 62–3, 70, 80,<br />

87, 121–5<br />

Asterostroma species 212–3, 257–8<br />

Aureobasidium pullulans 50, 80, 125,<br />

127–8, 248<br />

Bacteria 4, 47, 54, 58, 60, 63, 69–71, 75, 80,<br />

93–5, 98, 109–18, 132, 156, 200, 236, 246,<br />

251<br />

Bacteria and forest damages 110–3, 170<br />

Bacteria and wood used in kitchens 118<br />

Bacteria as antagonists 80, 118, 170, 189<br />

Bacteria as pathogens to trees 111, 114<br />

Bacterial degradation of pits 60, 93, 112,<br />

116, 132<br />

Bacterial wood degradation 55, 113–4<br />

Bacterial wood discoloration 56, 117<br />

Bark damages 163–8, 175–6, 199<br />

Bark extracts 251<br />

Basidiomycetes 16, 18, 21, 25, 27, 31, 47,<br />

49–50, 59, 64, 70, 84, 112, 129, 135, 137–8,<br />

182, 208, 222, 224<br />

Basidiospores 21, 23, 70, 193, 226, 229, 232<br />

Bavendamm test 32, 101–2<br />

Beech bark disease 163–5, 197<br />

Biological forest protection 80<br />

Biological influences on fungi 53, 79–85<br />

Biological pulping 140, 244–5<br />

Biological wood protection 80, 159<br />

Bioremediation of preservatives 74, 156<br />

Biotechnology of lignocelluloses 237–51<br />

Biotic wood discolorations 119–33<br />

Blue stain 80, 125–8<br />

Blue stain fungi 11–2, 21, 50, 54, 59, 65, 67,<br />

81, 125–8, 132, 200, 210<br />

Boron wood preservatives 74, 132, 151, 153,<br />

155, 194<br />

Brown pocket rot 136–7<br />

Brown rot 135–8, 184, 198–200, 202, 205,<br />

219–20, 223<br />

Brown rot fungi 32, 72, 96–7, 101, 129,<br />

135–8, 204, 207, 218<br />

Butt rot 189–90, 198<br />

Carbon dioxide 58–60, 66, 84, 158, 245<br />

Carbon sources for fungi 53–5<br />

Cavity bacteria 114<br />

Cavity formation 114, 135, 142–4, 199<br />

Cellar fungi 220–3, 234, 236<br />

Cellulases 87, 95–7, 121, 249–50<br />

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330 Subject Index<br />

Cellulose 54, 59, 66, 88, 90–2, 95–9, 237<br />

Cellulose degradation 72, 87–9, 92, 95–9,<br />

104, 113–4, 122, 135, 138, 145<br />

Ceratocystis fagacearum 32, 170–2<br />

Ceratocystis fimbriata 32–3, 167–8<br />

Ceratocystis minor 32, 125, 127<br />

Chaetomium globosum 26, 43, 60, 75, 81,<br />

123–4, 142, 145<br />

Chemical wood discolorations 117, 119, 133<br />

Chemical wood preservation 149–53<br />

Chestnut blight 165–7<br />

Chitin 4, 56, 156, 158, 183, 235<br />

Chitosan for wood protection 158<br />

Chlamydospores 15, 17, 60, 103, 125–6<br />

Chlorociboria species 119–20<br />

Chromium wood preservatives 74, 116–7,<br />

144–5, 151–2, 156, 220<br />

Cladosporium species 26, 50, 123, 125, 127<br />

Clamp formation 21–2<br />

Classification of fungi 47–52, 162–4<br />

Coal tar oil wood preservatives 146, 151,<br />

153<br />

CODIT model 175<br />

Collections of fungi 32<br />

Competitions 79–85<br />

Conidia 16–8, 25, 31, 52, 59, 75, 121, 123,<br />

191–2<br />

Coniophora species 9, 13–5, 22–3, 32, 35–6,<br />

38, 41, 44, 46–7, 59, 64, 66, 69, 77, 80,<br />

96–8, 116, 135, 138, 158, 182, 201, 205,<br />

207–11, 218, 220–3, 230, 233, 235, 245,<br />

255<br />

Copper tolerance 73, 220, 232<br />

Copper wood preservatives 74, 146, 151<br />

Cryphonectria parasitica 165–6<br />

Cubical rot 138, 145, 219, 229<br />

Dacrymyces stillatus 214<br />

Daedalea quercina 23, 74, 161, 184, 200–1,<br />

202, 208, 256<br />

Damage to buds, shoots and branches 163<br />

Damage to seeds and seedlings 161–2<br />

Dark fruit body 75, 203–4<br />

Deinking 250<br />

Demarcation lines in wood 79, 139, 197,<br />

199, 206<br />

Detection methods of tree and wood<br />

damages 179–83<br />

Deuteromycetes 16–8, 31, 47, 49–50, 52, 60,<br />

102, 120–1, 124–5, 142, 201<br />

Development of Ascomycetes 18–20, 27<br />

Development of Basidiomycetes 21–3<br />

Development of Deuteromycetes 16–8<br />

Diplomitoporus lindbladii 212, 258<br />

Discula pinicola 50, 127<br />

Disposal of preservative-treated wood 74,<br />

155–6, 250<br />

DNA-arrays 45<br />

DNA-based techniques 35–46, 233<br />

DNA-restriction 35, 37–9<br />

DNA-sequencing 39–44, 77, 210, 219<br />

Donkioporia expansa 15, 38, 44, 56, 67, 138,<br />

201, 207–8, 214–6, 233, 259<br />

“Dry rot” 231<br />

Dry rot fungi 207–8, 210, 219–20, 223–33<br />

Dutch elm disease 168–70<br />

Edible mushrooms 36, 68, 84, 188, 197,<br />

199–200, 206, 239–43<br />

Environmental concerns of wood<br />

preservation 150–6<br />

Environmental pollutants 84–5, 132, 153,<br />

155, 250<br />

Enzymatic bleaching 249<br />

Enzymes 57, 60, 87–107, 238, 249<br />

Enzymes in pulp and paper production<br />

249–50<br />

Erosion bacteria 114–5<br />

Ethanol production 59, 247–8<br />

Excessive preservative uptake 60, 93, 116<br />

Fatty acid profiles of fungi 47<br />

Felling time of trees 131, 147–8<br />

Fenton reaction 97–8, 105–6<br />

Fermentation of spent sulphite liquors 59,<br />

248<br />

Fiber saturation point 63–5, 231, 236<br />

Fixation of wood preservatives 151<br />

Flammulina velutipes 24, 76–7, 238, 242<br />

Fomes butt (root) rot 189–95<br />

Fomes fomentarius 4, 23, 25, 75–6, 138, 140,<br />

165, 184, 195, 200<br />

Force of gravity 25, 74–7<br />

Forest diseases 84–5, 109, 112, 114, 121,<br />

161–73, 184, 186–200<br />

Formal genetics of fungi 26–31<br />

Frost cracks 113<br />

www.taq.ir


Subject Index 331<br />

Fruit body formation 16, 19–25, 52, 74–7,<br />

102, 180, 229, 240–3<br />

Fruit body types of Ascomycetes 20–1, 31,<br />

49–50<br />

Fruit body types of Basidiomycetes 23–4,<br />

31, 50, 184<br />

Fumigation against fungi 172–3, 235<br />

Fungal cell wall 4, 16, 55<br />

Fungal dry matter 53, 56, 243<br />

Fungal protoplasm 5–9<br />

Fungi imperfecti 16, 121<br />

Fungi in cooling towers 60, 140–2, 201, 216<br />

Fungi in piled wood chips 107, 121, 201, 245<br />

Fungi in wood artifacts 235<br />

Fungi on hardwoods 137, 140, 142, 184,<br />

188, 195, 199, 202, 206, 212, 214<br />

Fungi on leaf litter 201<br />

Fungi on masonry 224, 227, 231–2, 235–6<br />

Fungi on mining timber 201, 204–6, 216–7,<br />

219–20, 222<br />

Fungi on monocotyledons 144, 206<br />

Fungi on poles 142, 201, 204–5, 217, 219,<br />

222<br />

Fungi on softwoods 137, 142, 184, 186, 188,<br />

190, 195, 198, 200, 202, 205, 207, 212–4,<br />

219–20, 230<br />

Fungi on stored wood 121, 128, 138, 145,<br />

200–7<br />

Fungi on structural timbers indoors 137,<br />

201–2, 204–5, 207–33<br />

Fungi on structural timbers outdoors 137,<br />

145, 200–7, 219, 226–7<br />

Fungi on stumps 80, 82, 187, 191, 200,<br />

204–6, 217, 219, 227<br />

Fungi on trees 65, 82, 121, 127–8, 137–8,<br />

145, 161–73, 183–200, 202, 206<br />

Fungi on urban tress 184, 189, 197, 199, 216<br />

Fungi on window joinery 202, 204, 207–8,<br />

214<br />

Fungi on wood in aquatic habitats 62, 142,<br />

145, 201, 205<br />

Ganoderma species 24, 80, 129, 135,<br />

139–40, 200, 246<br />

Gloeophyllum species 15, 23–4, 31, 35, 38,<br />

58, 66–7, 73–4, 98, 137–8, 155, 158, 200–1,<br />

202–05, 207–8, 211, 233, 235, 256–7<br />

“Green rot” 119–20<br />

Grouping of Bacteria 110–2<br />

Grouping of Deuteromycetes 16, 52<br />

Grouping of wood preservatives 150–1<br />

Growth rate of mycelium 9–10, 78, 98, 210,<br />

223, 232<br />

Guttation 56, 215, 229, 231<br />

Hazard classes of timber 148<br />

Heart rots 184, 193, 198–9, 202, 205, 216<br />

Heat treatment against fungi 70, 220, 231,<br />

235<br />

Hemicellulose degradation 89, 92–4, 122,<br />

135, 145<br />

Hemicelluloses 54, 87–8, 91–2, 237, 248<br />

Heterobasidion species 16, 21, 23, 25–6,<br />

30–4, 36, 38–9, 43, 57–9, 66, 80, 135, 138,<br />

140, 184, 189–95, 200–1<br />

Heterothallic (homothallic) fungi 26–7<br />

Hook formation 19<br />

House rot fungi 12–4, 32, 65, 68, 71, 73,<br />

77–8, 108, 138, 207–33<br />

Hypha 3–8, 11–2, 12, 55<br />

Hyphal zonation 8–9<br />

Identification keys for fungi 31–2, 101, 210,<br />

253–9<br />

Identification of Ascomycetes 31–2<br />

Identification of Bacteria 118<br />

Identification of Basidiomycetes 31–47,<br />

186, 210, 233<br />

Identification of Deuteromycetes 31, 52, 125<br />

Immunological methods for enzymes 35,<br />

98, 105<br />

Immunological methods for fungi 34–5,<br />

233<br />

Inspection methods for fungal activity<br />

179–83<br />

Interactions between microorganisms<br />

79–85<br />

Internal transcribed spacer of rDNA 37–44<br />

Intersterility groups 29–30, 35, 39, 186,<br />

189–90<br />

Isolate variation in fungi 9, 78, 220, 223, 232<br />

Isozyme analysis 34<br />

Laccase 32, 57, 101–2, 104, 106, 136, 158,<br />

249–50<br />

Laetiporus sulphureus 23, 25, 39, 59, 184,<br />

197, 201, 208<br />

Leaf diseases 109, 162–3<br />

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332 Subject Index<br />

Lentinula edodes 6, 9, 24, 31, 35, 43, 56, 69,<br />

74, 104–5, 135, 238–42, 246, 249<br />

Lentinus lepideus 35, 66, 74, 135, 201, 205,<br />

208<br />

Leucogyrophana species 41, 201, 223,<br />

225–7, 228, 253–4<br />

Lichens 85<br />

Light 24, 26, 74–5, 199, 241<br />

Lignin 54, 88–9, 91, 99–107, 113–4, 138,<br />

145, 183, 219, 237, 246<br />

Lignin carbohydrate complex 91–2, 94, 99,<br />

237, 249<br />

Lignin degradation 72, 89, 91–2, 99–107,<br />

136, 138<br />

Lignin peroxidase 57, 72, 89, 102–6, 249<br />

“Lower fungi” 48–9<br />

Low-molecular agents 72, 98, 104–6, 137–8,<br />

249<br />

MALDI-TOF mass spectrometry 46–7, 233<br />

Manganese deposits 57, 140–1, 246<br />

Manganese peroxidase 57, 72, 89, 104, 106,<br />

140, 246, 249<br />

Mannan 89, 94<br />

Mating of mycelia 26–30<br />

Melanin 125<br />

Meripilus giganteus 23, 135, 184, 197, 200<br />

Meruliporia incrassata 13, 33, 41, 138, 223,<br />

226–7, 228–9, 232<br />

Microbial volatile organic compounds<br />

(MVOCs) 124, 233<br />

Microsatellites 44–5<br />

Microscopic methods for fungi 183<br />

Microwaves against fungi 235<br />

Minerals in wood 56–7, 83, 97–8<br />

Molding 58, 121–5, 210<br />

Molds 16, 54, 58–9, 67, 120–1, 132, 200, 232<br />

Molds as pathogens 123–4<br />

Molecular genetics of enzymes 104–5, 249<br />

Molecular techniques for fungi 33–47, 183,<br />

190, 210, 227<br />

“Moon wood” 148<br />

Mushroom production on wood 237,<br />

239–42<br />

Mycelium 3, 6, 9–11, 32, 55, 189, 215, 223<br />

Mycoallergies 123–4<br />

“Myco-fodder” 246<br />

Mycoplasmas 112, 164, 173<br />

Mycorrhiza 36, 38–9, 41, 82–5, 189<br />

Mycoses 124<br />

Mycotoxicoses 123<br />

“Myco-wood” 206, 237–9<br />

Naming of enzymes 88<br />

Naming of fungi 47–8<br />

National regulations for wood preservation<br />

149–50<br />

Natural durability 58, 145–7, 182<br />

Nectria species 164<br />

Needle diseases 162–3<br />

Nitrogen in wood 56, 81, 246<br />

Nutrient uptake 55<br />

Nutrients for fungi 53–8, 81, 146<br />

Oak disease in Europe 173<br />

Oak wilt disease 170–3<br />

Oligoporus placenta 23, 27, 31, 35, 38, 64,<br />

77, 80, 94, 97–8, 137, 158–9, 201, 218,<br />

219–20, 233, 235–6<br />

Ophiostoma piceae 31–2, 120, 125, 127, 158,<br />

172<br />

Ophiostoma piliferum 32–3, 43, 81, 125,<br />

127, 245, 249<br />

Ophiostoma ulmi 25, 31–2, 80, 168–70<br />

Oxalic acid (oxalate) 71–3, 94, 97–8, 104,<br />

220, 232<br />

Oxygen 58–9, 103, 111–2, 116, 133, 145–6,<br />

245<br />

Paecilomyces variotii 50, 63, 75, 94, 120–1,<br />

132, 248, 251<br />

“Palo podrido” 139–40, 246–7<br />

Parasits 53–4, 59, 186–200, 219<br />

Paxillus panuoides 66, 74, 201, 205, 208, 255<br />

Pectin 92–3, 125<br />

Penicillium species 16, 50, 58, 75, 80–1,<br />

121–3, 161<br />

Pentachlorophenol 153, 155–6, 250<br />

Phaeolus schweinitzii 23, 184, 198, 200<br />

Phanerochaete chrysosporium 5, 31, 47, 67,<br />

87–8, 96, 102–4, 107, 201, 244, 250<br />

Phellinus pini 11, 23, 35, 39, 135, 137, 140,<br />

186, 198, 257<br />

Phenol oxidases 32, 102, 133<br />

Phlebiopsis gigantea 80, 194, 200–1, 208<br />

pH-value 26, 58, 70–2, 98, 117, 119, 145, 225<br />

pH-value of wood 70, 112<br />

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Subject Index 333<br />

Phylogenetic analysis 41–2<br />

Physical/chemical influences on fungi<br />

53–77<br />

Piptoporus betulinus 23, 25, 58, 184, 199,<br />

233<br />

Plane canker stain disease 167–8<br />

Pleurotus ostreatus 24, 30–1, 43, 56, 104,<br />

200, 238, 242, 250<br />

Polymerase chain reaction 35–45<br />

Polypore fungi 27, 66, 137, 184, 196–7, 219<br />

Polyporus squamosus 184, 199, 208<br />

Positive effects of wood microorganisms<br />

237–51<br />

Prerequisites for fungal activity 84, 90, 97,<br />

101, 105, 145–6<br />

Pretreatment of wood for fungi 99, 237–8,<br />

246–8<br />

Prokaryotes 4, 109–10, 112<br />

Protection measures against fungi 131–3,<br />

146–59, 166, 168, 170, 172–3, 178, 180,<br />

189, 194–5, 201–2, 216, 233–6<br />

Protein-based techniques for identification<br />

33<br />

Protoplast fusion 31<br />

Pruning 177–8<br />

Randomly amplified polymorphic DNA<br />

(RAPD) 36–7<br />

Red-streaking discoloration 129–31, 195<br />

Red-streaking fungi 54, 129–31, 200<br />

Relative air humidity 64, 68, 123, 226–7<br />

Relativity of experimental data 77–8<br />

Remedial measures of indoor rot 233–6<br />

Resistance to heat 15, 69–70, 111, 204–5,<br />

216, 220, 223, 231<br />

Resistance to dryness 15, 60, 66, 129, 145,<br />

204–6, 220, 223, 231–2<br />

Restriction fragment length<br />

polymorphism of DNA (RFLP) 35, 37–9<br />

Rhizomorphs 9, 12–5, 186–9<br />

Ribosomal DNA (rDNA) 37–44, 110, 118,<br />

210, 226<br />

Rickettsia 111<br />

Root graft transmission 169, 171, 188, 191,<br />

194<br />

Root rots 184–90, 197–8, 200<br />

Sap stain 125–8<br />

Saprobes 53, 59, 187, 195, 198<br />

Schizophyllum commune 24–5, 27, 60, 66,<br />

71–2, 77, 129, 168, 200–1, 206<br />

SDS polyacrylamide gelelectrophoresis<br />

(SDS-PAGE) 33–4, 233<br />

“Selective delignification” 140, 244<br />

“Selective white-rot” 107, 140<br />

Septum 6, 50<br />

Serpula species 3, 9, 11–5, 23–6, 28–30,<br />

32–8, 41–2, 44–7, 56–7, 59, 62–4, 66–9,<br />

73–5, 97–8, 138, 153, 201, 207–11, 218,<br />

223–8, 229–36, 253–4, 257<br />

Sexual development of fungi 16, 18, 26–9<br />

Simultaneous white rot 138–9, 191, 197<br />

Size of wood microorganisms 3<br />

Slime fungi 48–9, 200<br />

Slime layer around hyphae 5, 90, 105,<br />

138–40, 144<br />

Sniffer dogs 124, 180, 233<br />

Soft rot 135, 142–6, 184, 207<br />

Soft-rot fungi 50, 54, 60, 66, 70, 102, 116,<br />

142–6, 201<br />

Solvent-based preservatives 152<br />

Somatic incompatibility 30<br />

Sparassis crispa 184, 186, 200<br />

Species-specific priming PCR 43–4, 210<br />

Spore dispersal 25–6, 123–4<br />

Spore germination 26, 50, 232<br />

Spores 15–9, 21, 23–5, 81, 102, 123<br />

Sporotrichum pulverulentum 81, 96, 107,<br />

244, 248<br />

Stainings for fungi 183, 233<br />

Standards for wood preservation 148–9<br />

Steam explosion treatment 238, 248<br />

Stem decays 184–5, 193, 195, 199<br />

Stereum sanguinolentum 23, 66, 80, 129–30,<br />

131, 135, 161, 195<br />

Stereum species 9, 26, 28, 80, 82, 131, 168,<br />

195, 200–1<br />

Strand diagnosis 13–4, 210, 253–9<br />

Strands (cords) 12–3, 57, 204, 210, 212–3,<br />

216–9, 222–3, 227–31<br />

Succession 82<br />

Successive white rot 139–40<br />

Super critical fluid treatment 156, 168<br />

Surveys on occurrence of house-rot fungi<br />

207–9, 218, 220, 224<br />

Symbioses 82–5<br />

Synergisms 81<br />

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334 Subject Index<br />

Temperature 6, 24–6, 32, 67–70, 78, 110,<br />

121, 126, 145, 186, 210–1, 216, 223, 227,<br />

229–30, 245<br />

Test ratings of wood preservatives 150<br />

Thermal wood modification 157<br />

Trametes versicolor 23–4, 31, 35–6, 47–8,<br />

58, 64, 72–3, 79–80, 82, 90, 103–4, 129,<br />

138–40, 155, 157, 159, 200–1, 206–7, 208,<br />

238, 250<br />

Translocation of nutrients 15, 55–7, 189,<br />

225, 227, 231, 235–6<br />

Transpressorium 11–2, 126, 199<br />

Treatmentprocessesoftimberwith<br />

preservatives 153–4<br />

Tree care 177–8<br />

Tree defense against microorganisms<br />

174–7, 189, 193, 195<br />

Tree polypores 184<br />

Tree rots 82, 183–200<br />

Trichaptum abietinum 39, 66, 129, 131,<br />

201<br />

Trichoderma species 31, 33, 43, 50, 58, 80–1,<br />

87–8, 96, 121, 124, 170, 189, 235, 245<br />

Tunneling bacteria 114<br />

Tyrosinase 102<br />

UV light 1, 26, 75, 183, 244<br />

Vegetative development of fungi 7–14, 19,<br />

21<br />

Viruses 47, 109, 166, 170, 194–5<br />

Vitamins 25–6, 57, 81, 84, 87, 112, 243<br />

Water 53, 60–1, 146<br />

Water activity 62–3, 121, 123<br />

Water formation by fungi 58, 66, 231<br />

Water potential 56, 62–3<br />

Water storage of wood 60, 113, 116, 131–2,<br />

187<br />

Water transport by fungi 6, 231, 234<br />

Water-based preservatives 151<br />

Wet heartwood 70–1, 110, 112<br />

“Wet rot” 219, 222<br />

White pocket rot 137–8, 140<br />

White rot 129, 135, 137–42, 184, 191, 195,<br />

198–9, 206, 212–4, 216<br />

White rot fungi 32, 72, 88, 101–2, 129,<br />

138–42, 244, 246<br />

Wilt diseases 168–73<br />

<strong>Wood</strong> cell wall 92<br />

<strong>Wood</strong> damaging agents 1<br />

<strong>Wood</strong> decays 135–46, 186–200<br />

<strong>Wood</strong> discolorations 117, 119–32<br />

<strong>Wood</strong> dry weight 61, 182<br />

<strong>Wood</strong> hydrophobization 156–8<br />

<strong>Wood</strong> modifications 156–7<br />

<strong>Wood</strong> moisture 57, 60–7, 123, 127, 129,<br />

145–7, 201, 204, 210–1, 216, 219, 222, 224,<br />

226–7, 230–1, 233–6, 245<br />

<strong>Wood</strong> parenchyma 117, 119, 122, 125, 129,<br />

133, 175<br />

<strong>Wood</strong> preservation 117, 124, 133, 146,<br />

149–53, 178, 182, 234<br />

<strong>Wood</strong> protection 131–3, 146–59<br />

<strong>Wood</strong> saccharification 247–8<br />

<strong>Wood</strong> strength properties 183<br />

<strong>Wood</strong>-based composites 149, 155, 230<br />

<strong>Wood</strong>-decay fungi 10, 32–3, 40, 43, 47, 54,<br />

57, 82, 185<br />

<strong>Wood</strong>-inhabiting fungi 23, 32, 54, 82, 121,<br />

125<br />

<strong>Wood</strong>-plastic composites 155<br />

Wound dressings 178, 195<br />

Wound parasites 53, 174, 184, 206, 222<br />

Wound reaction in trees 112, 174–8<br />

Wound rot of spruce 195<br />

Wound treatment 178–80<br />

Xylan 89, 93, 249<br />

Xylan degradation 89, 93–4, 125<br />

Yeasts 4, 32, 47, 59, 201, 246–8<br />

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