bia webeta begir age doost dari

Bremia Plasmopara

MILDÚS.

1.- Describa las características de signos y síntomas en las muestras proporcionadas.

Cucumis sativus (pepino).Síntomas: manchas circulares rodeadas por un halo clorótico. Signos: en el envés de la hoja aspecto velloso.

'Mildius'

Lactuca sativa (lechuga).Síntomas: manchas cloróticas. Signos: aspecto vellosos por el envés de la hoja.

'Mildius'

Espinaca. Síntomas: manchas cloroticas circulares. Signos: aspecto vellosos por el lado del envés.

'Mildius'

Maleza. Síntomas: manchas circulares rodeadas por un halo clorotico. Signos: en el envés de la hoja aspecto velloso.

2.- Describa las características microscópicas de los esporangios observados.

Bremia presenta haustorios globosos y ramificación en una sola dirección, los esporangios germinan de forma directa o indirecta.
Perosnospora las terminaciones de las ramas de los esporangios son agudos, no presenta papila apical, presenta haustorios claviformes.
Plasmopara presenta haustorios piriformes, las ramificaciones de los esporangios son en ángulo recto, presenta una papila apical.
Pseudoperonospora la ramificación de los esporangios es dicotomica, presenta papila, las puntas son romas, presenta haustorios claviformes.

3. - ¿Cuál es la forma y color de los esporangios de los hongos observados?

Son hilanos.

Forma: Bremia Plasmopara

'Mildius'

Peronospora Pseudoperonospora

'Mildius'

4.- ¿Por qué no se emplea un medio de cultivo para el aislamiento de los hongos que producen Mildiús?

Por que son parásitos estrictos.

5. - ¿Qué estructura fungosa nos permiten establecer la identificación a nivel de género de los Mildiús?

Los haustorios.

6.- ¿Qué estructuras son las encargadas de adsorber los nutrientes de las células vegetales?

Los haustorios y el micelio intracelular.

7.- ¿Por qué no es conveniente usar lactófenol con azul de algodón para observar las estructuras fúngicas?

Por que el azul de algodón va a teñir las estructuras del hongo y no se va a poder apreciar si el hongo presenta color por si mismo, además que el color de las estructuras es un criterio para la identificación del hongo, sobretodo si las oosporas o conidios presentan color.

8.- Comentarios y discusión.

Los mildiús son parásitos estrictos por lo cual no se van a aislar en medios de cultivo por lo que va a ser necesario que se realicen cortes de los tejidos infectados para la observación de esporangioforos y esporangios para su identificación.

Para una buena identificación se hace uso del material vegetal ya que se tiene establecido que patógenos son los más frecuentemente encontrados en el material vegetal que nos interesa o que estamos trabajando.

El diagnostico de mildiús es rápida ya que como se menciono anteriormente son parásitos estrictos y con una observación microscópica en fresco se realiza la identificación.

Para la diferenciación de los mildiús se hace uso de sus estructuras tales como: esporangios, el tipo de ramificaciones y la presencia de papila apical en los esporangios.

En cuanto el tipo de lesiones producidas por los diferentes hongos son similares, por lo que no se puede hacer un diagnostico diferencial como lo es con las bacterias que algunas de ellas presentan lesiones características en el hospedante.

De los aspectos más importantes para la identificación del parásito en el tejido vegetal es saber diferenciar las células vegetales de las estructuras fungosas y para que se realice una buena observación se necesita de un buen corte vegetal que sea delgado y representativo.

+ نوشته شده در یکشنبه ۲۲ اردیبهشت ۱۳۸۷ ساعت 4:9 AM توسط مریم |

ائوميست

PPT]

ائوميست1

ساختار فايل: Microsoft Powerpoint - نسخه HTML
به صورت توليد زئوسپور در زئوسپورانژيوم ( Zoosporangium) ميباشد که بر روي ... بيماري بادزدگي يا سفيدک دروغي سيب زميني وگوجه فرنگي در اثرPhytophtora infestans ...
www.cua.ac.ir/agric/Moosawi-Jorf/Moosawi-Jorf_files/PLPLectures_files/PLP4.ppt - صفحات همسان

PPT]

ائوميست2

ساختار فايل: Microsoft Powerpoint - نسخه HTML
قارچهاي اين خانواده , عامل بيماري سفيدک کرکي يا دروغي يا داخلي (Downy mildew) در تعداد زيادي .... در اين جنس معمولا اسپورانژيومها مانند كنيديوم عمل ميكنند. ...
www.cua.ac.ir/agric/Moosawi-Jorf/Moosawi-Jorf_files/PLPLectures_files/PLP5.ppt - صفحات همسان

+ نوشته شده در یکشنبه ۲۲ اردیبهشت ۱۳۸۷ ساعت 3:51 AM توسط مریم |

Erysiphe syringae)

First Report of Powdery Mildew of Ligustrum japonicum (Japanese Privet) Caused by Microsphaera syringae (Erysiphe syringae) in North America

Jennifer S. Falacy, Irrigated Agriculture Research and Extension Center, Washington State University, Prosser 99350-8694; and Dean A. Glawe, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup 98371-4998

The woody shrub Ligustrum japonicum Thunb. (Japanese privet) is used widely as a landscape plant. The only published report (4) of powdery mildew on this host in North America was based on an anamorphic fungus in Louisiana regarded as a possible species of Microsphaera. The Plant Clinic at Oregon State University houses an unpublished record, dated August 30, 1961, of a powdery mildew on this host in Portland, Multnomah County, Oregon (Jay Pscheidt, personal communication); that fungus was recorded as Microsphaera alni but no voucher specimen or morphological description exists. In August 2002, powdery mildew was collected by Master Gardener Marilyn Tilbury from L. japonicum in Seattle, King County, Washington. The authors determined the causal agent to be Microsphaera syringae (Schw.) Magn. The present report documents for the first time the occurrence of M. syringae on L. japonicum in North America, and presents information on the taxonomy and identification of this fungus.

Signs of the fungus included white mycelium consisting of hyphae, conidiophores bearing single conidia, and brown to black ascocarps. Distinguishing characteristics included lobed appressoria (Fig. 1); ascocarps (85-) 90-113 (-116) µm with dichotomously branched appendages (Fig. 2), short-stipitate asci (Fig. 3) 50-60 (-64 ) × 27-42 (-45) µm each with 4 to 8 oval to phaseoliform ascospores 18-22 (-23) × 10-11 (-12) µm; conidiophores with short cylindrical foot cells and cylindrical conidia (Fig. 4) (26-) 27-35 (-41) × (11-) 12-14 (-15) µm. A voucher specimen (WSP 70743) was deposited with the Mycological Herbarium, Department of Plant Pathology, Washington State University.


	Fig. 1. Appressorium of Microsphaera syringae formed on Ligustrum japonicum.		Fig. 2. Ascocarp appendages of Microsphaera syringae formed on Ligustrum japonicum.


	Fig. 3. Asci with ascospores formed by Microsphaera syringae on Ligustrum japonicum.		Fig. 4. Conidium of Microsphaera syringae formed on Ligustrum japonicum.

+ نوشته شده در یکشنبه ۲۲ اردیبهشت ۱۳۸۷ ساعت 3:46 AM توسط مریم |

A Survey of Ascomycetous Holomorphs

A Survey of Ascomycetous Holomorphs

New Phylogenetic System: * = covered in this treatment

Phylum 6 Ascomycota -- with three Subphyla
    Subphylum Taphrinomycotina
         Class Taphrinomycetes
               Order Taphrinales*
          Class Schizosaccharomycetes*
          Class Pneumocystidiomycetes
          Class Neolectomycetes
     Subphylum Saccharomycotina
            Class Saccharomycetes
               Order Saccharomycetales* - see Chapter 6
     Subphylum Pezizomycotina
          Class Pezizomycetes (operculate discomycetes)
                Order Pezizales*
          Class Dothideomycetes
                Order Dothideales*
                Order Capnodiales*
                Order Myriangiales
                Order Pleosporales*
                Order Botryosphaeriales
                Order Hysteriales
                Order Patellariales
           Class Eurotiomycetes
                Order Eurotiales*
                Order Onygenales*
                Order Coryneliales
                Order Mycocaliciales
                Order Chaetothyriales
                Order Pyrenulales
                Order Verrucariales
           Class Laboulbeniomycetes
                Order Laboulbeniales*
                Order Pyxidiophorales
           Class Lecanoromycetes
                many orders of Lichens - see Chapter 7
           Class Arthoniomycetes
                Order Arthoniales
           Class Leotiomycetes
                Order Helotiales*
                Order Erysiphales*
                Order Rhytismatales*
                Order Cyttariales*
                Order Thelebolales
           Class Sordariomycetes
                Order Sordariales*
                Order Ophiostomatales*
                Order Diaporthales*
                Order Coniochaetales
                Order Chaetosphaeriales
                Order Hypocreales* (includes Clavicipitales*)
                Order Microascales
                Order Melanosporales
                Order Coronophorales
                Order Xylariales*
                Order Trichosphaeriales
                Order Phyllachorales
                Order Meliolales*
                Order Lulworthiales
                Order Calosphaeriales

click on this line to see a new page explaining the classification

Hotlinks to Traditional Orders: Taphrinales - Pezizales - Elaphomycetales
Sphaeriales - Sordariales - Diatrypales - Hypocreales
Diaporthales - Leotiales - Cyttariales - Rhytismatales - Clavicipitales
Erysiphales - Onygenales - Eurotiales - Ophiostomatales
Meliolales - Laboulbeniales - Dothideales

Now to put anamorph and teleomorph together, and talk about the whole fungus (the holomorph). If you have any queries about anamorph-teleomorph connections in ascomycetes, there is now a web site at which you can look them up. Here is the URL - http://www.cbs.knaw.nl/databases/anateleo.html
Enter Peziza and see how many different connections you retrieve. Try Acremonium (a hyphomycete with single, generalized phialides) and see how many holomorphs come up. Why do you think there are so many?

I will briefly survey the more important orders of ascomycetes, linking the different life-forms together in as many cases as possible. Although 50 orders of ascomycetes (quite a few of them almost entirely lichenized) were recognized in one recent classification, you may be relieved to discover that I will show examples of only 19, and provide a key to only 17 (mainly non-lichenized orders - see Chapter 7 for some of the others)

I have also added a page (click here) which is essentially copied from the Myconet Web page established and maintained by Dr. Ove Eriksson. This gives the most recent classification of Ascomycetes, which is (of course) much more complex than the one I use in this chapter. Students should at least be aware of the full complexity of the situation, even if they - or their professors - choose not to expose them(selves) to its full rigour.

(1) Order Taphrinales Subphylum Taphrinomycotina: 9 genera, 120 species. This is an outlying group which causes serious diseases of some plants in the Rosaceae (e.g., Taphrina deformans causing peach leaf curl) and the Amentiferae (e.g., Taphrina populina on poplar).

Here is Taphrina deformans attacking peach leaves in New Zealand. But the same picture could also have been taken in North America or Europe. The leaves become thickened, distorted and often yellow or reddish in colour.

This fungus has four unique or unusual features.

(A) The assimilative mycelium is dikaryotic -- this would immediately distinguish it from most other ascomycetes (and indeed raises questions about the taxonomic position of this order).

(B) It produces an exposed layer of asci on the surface of the host leaf (right). Since there is no surrounding or supporting fungal tissue, there is nothing we could call an ascoma.

(C) The ascospores often bud in a rather yeast-like manner, even while still inside the ascus (right and bottom right).

(D) When the asci open to release their spores, they tend to split across the tip, rather than around it (bottom, left), so they are not like the rest of the operculate group -- compare them with the asci of the Pezizales, the next order. As you may have guessed by now, this group sits uneasily among the other ascomycetes, and one eminent authority grouped the Taphrinales with the smut fungi (see order Ustilaginales in Chapter 5c); both are yeast-like when grown in axenic culture.
The anamorph of Taphrina, the phase in which it grows in culture, is a single- celled budding yeast named Lalaria.

Compare its features for yourself with some of the orders that follow.

WEB IMAGES

Taphrina populina (left) attacks leaves of poplar.

Taphrina amentorum (below) attacks the green fruits of Alnus (alder), turning them bright red. This illustration is from a wonderful book, Fungi of Switzerland - Volume 1 - Ascomycetes by Breitenbach and Kraenzlin. I recommend this book to all mycologists. The series is undoubtedly the best of its kind, with excellent illustrations of macroscopic and microscopic features, as you see here, plus detailed descriptions on the facing pages. Check it out...

Pneumocystis carinii, Class Pneumocystidiomycetes, the causal agent of a lung disease that affects many AIDS sufferers, fits into the Subphylum Taphrinomycotina.

Series Unitunicatae-Operculatae

(2) Order Pezizales Class Pezizomycetes Subphylum Pezizomycotina: 150 genera, 900 species. The 'operculate discomycetes' -- we'll look at 7 of the 15 families currently recognized.

(a) Family Pezizaceae. Classic 'cup-fungi' producing apothecial ascomata that are usually shaped more like saucers or goblets, usually without stalks, and found growing on wood, dung or soil. They vary so much in colour, texture and ornamentation that most discomycete specialists split the Pezizaceae into several tribes or even families. Their asci have a diagnostic pop-open lid or operculum, and the tips of the asci are amyloid (sometimes expressed as I⁺ -- this means giving a blue, starch-like reaction in an iodine solution known as Melzer's reagent).

A small species of Peziza (right, as seen through the dissecting microscope) often crops up on soil in greenhouses, frequently preceded by its blastic-synchronous Chromelosporium anamorph (the whitish fuzz at lower left).

Microscopic detail of both reproductive phases is given in the diagrams (right).

The Chromelosporium anamorph of Peziza is shown here under phase-contrast illumination.

Larger species of Peziza, producing thin, rather brittle apothecial ascomata several centimetres across, with light brown or orange hymenia, can be found on the ground in Spring and Fall (right).

(b) Family Sarcosomataceae.

	This family contains wood-inhabiting fungi with apothecia that are often stalked (stipitate), relatively tough, and brightly coloured. The asci are sub-operculate, and non-amyloid. The scarlet cups of Sarcoscypha coccinea (left), growing from buried hemlock branches, brighten up the early Spring in Canadian woodlands.

Urnula (below) is another striking example of the Sarcosomataceae.

(c) Family Pyronemataceae.

Aleuria aurantia, the orange peel fungus (below),
is common along the edge of logging roads on Vancouver Island.

The picture above is from Fungi of Switzerland Volume 1 by Breitenbach and Kraenzlin. Note how the field picture is flanked by details of the diagnostic microscopic features. This book is the best of its kind, and belongs on every mycologist's shelf.

Another example of the Pyronemataceae from this magnificent book is Humaria hemisphaerica (above),

Scutellinia scutellata (right), [Pyronemataceae] its orange apothecia rimmed with dark hairs (which give it the common name 'eye-lash fungus', and with non-amyloid asci, is one of the commonest cup-fungi, growing on rotten wood. Anamorphs don't seem to be produced by many members of this family.

Caloscypha fulgens is a common spring discomycete in western North America. It is easily recognized by its brilliant orange apothecia which soon become externally tinged blue or greenish-blue. These specimens grew in May along a trail in John Dean Park near my home.

The phase contrast photomicrograph below shows asci and ascospores of
Caloscypha fulgens.

There are 8 globose, uniseriate ascospores.

Some genera, such as Genea (right), produce closed but hollow ascomata. The asci are cylindrical or clavate, and are arranged in an extensive flat hymenium lining the ascoma, but they do not shoot their spores. These apparently contradictory features show that members of this family are becoming sequestrate (their fruit bodies do not liberate spores at maturity) and hypogeous (they produce their ascomata underground).

Geopora cooperi, here seen bisected, is also sequestrate and hypogeous, but now the air space inside the fruit body is much less than in Genea: another step on the way to becoming a truffle (see below, and Family Tuberaceae).

This evolutionary process is diagrammatically illustrated here. The fourth and final step sees the elimination of air spaces altogether, and is a solid truffle of the genus Tuber, Family Tuberaceae -- see family (g) below.

Evolution toward the sequestrate and hypogeous condition is not restricted to the Pyronemataceae, but can also be seen operating in several other families of the operculate discomycetes.

4 sequestrate evolution.gif (27453 bytes)

(d) Family Ascobolaceae.

Students who have followed the succession of fungal fructifications appearing on horse dung will be familiar with the two most important genera of this largely coprophilous (dung-inhabiting) family -- Ascobolus and Saccobolus. Both produce minute, translucent apothecia (seen under the low power of the dissecting microscope, top right; higher power, lower right).

The dark dots are mature asci, which are broad, and project from the hymenium when mature, so that their tips may become oriented toward the light.

The 8 ascospores have a purple or brown outer wall layer. Ascobolus (left), like most other ascomycetes, shoots ascospores individually. Saccobolus (right) atypically sticks all eight together in a bundle, and they are expelled as a single projectile, which gives them extra range. I haven't seen any anamorphs in this family, though a few are known.

(e) Family Helvellaceae.
These mostly spring-fruiting fungi have large and unusually configured apothecial ascomata. All are stalked, with beige to brown, hymenium- covered caps. Helvella species (H. elastica, below, left; H. crispa, below, right) have a drooping flap on either side, and are called saddle fungi. Abbott and Currah (1997) gave a good revision of this family.

This is Helvella lacunosa...

...and this is a cross section of its stipe - surely one of the most interesting of any fungus. Its structure gives it a lot of the stiffness of a girder, for a minimal investment in materials.

The ascomata of Gyromitra species (left), are among the largest ascomycete fructifications, and some species contain the toxin gyromitrin, a precursor of the deadly monomethylhydrazine.
By causing some fatal poisonings, the Spring-fruiting Gyromitra esculenta (far left) has earned its place in Chapter 22 on poisonous mushrooms.

It is vital for morel-hunters to be able to distinguish the convoluted head of Gyromitra, the false morel, from the ridged and pitted head of the delicious true morel (see below)

...and here's a March 2000 collection we made of Gyromitra infula on a rotten log (note that superficially, it looks more like a Helvella, but is distinguished by its spores, which have an apiculus at each end.

Occasionally you may find a specimen that looks as if a mould is growing on it. Sometimes there really is a mould attacking it, but it's also likely that what you're seeing is a deposit of the fungus's own ascospores, as is the case with the Gyromitra esculenta below, which was sitting in very still air (the beautifully ellipsoidal spores, each containing polar oil droplets, are shown in the second photo).

(f) Family Morchellaceae.
While Gyromitra is one of the few lethally toxic fungi, its cousin, Morchella, the true morel (below, left) is one of the finest of all edible fungi. The left-hand picture below is of my first morel of the year 2000 (Morchella angusticeps, found near Lake Wenatchee, Washington State). Species of Morchella have a broad, hollow stalk, and a pitted and ridged, sponge-like, more or less conical or ellipsoidal head. Since the hymenium doesn't cover the ridges (as you can see in the transverse section, below centre), it seems likely that a morel is a compound ascoma, each pit representing an individual apothecium. The anamorph of the morel is a blastic-sympodial hyphomycete, Costantinella, which I have often found in the Fall growing on soil beside trails in Algonquin Park, Ontario (below, right).

Morels have a broad geographic range, but are common in relatively few areas, of which Michigan is perhaps the best-known. People throng to the woods in May to hunt this elusive delicacy, and Boyne City holds an annual morel-hunting championship. When Dutch elm disease was killing millions of elm trees, morels sometimes fruited profusely around recently dead trees. In recent years they have also been collected in large numbers on burned over areas of western forests. Morels are discussed as a a delicacy in Chapter 18.

Just to confuse the issue, a second genus of Morchellaceae, Verpa, also fruits in May. Species of Verpa aren't toxic, but neither are they good to eat. Verpa bohemica (left), found at Lake Wenatchee, like the morel above, is called the wrinkled thimble-cap.

Verpa bohemica (above, and far left), looks like a morel, but it is easy to tell the difference by bisecting the fruit bodies vertically. While the cap and stalk of the true morels (the two right-hand specimens in each picture) are firmly united, the cap of Morchella semilibera (first from left, next to the Verpa) is, as its name implies, half-free, and that of Verpa is attached only at the apex, as you can see in the sectioned fruit bodies in the lower photograph. In addition, the stipe of Verpa (far left) is 'stuffed' with cottony mycelium, while those of the Morchella species are completely hollow.

(g) Family Tuberaceae Order Pezizales Class Pezizomycetes...

...the truffles. Here, the evolutionary process still active in the Geneaceae, Otideaceae, etc. has run its course. The ascomata are sequestrate, hypogeous and solid (no air spaces any more -- as you can see in this bisected specimen of Tuber aestivum, which a truffle dog brought to me at Scheggino in Italy)

The asci, produced in a highly convoluted hymenium, are rounded and thin-walled (those of Tuber albidum are shown at left) with no trace of an operculum or other shooting mechanism, and usually contain only 1-3 spores.

The ascospores of truffles have complex, highly ornamented walls. They come in two basic patterns - spiny (left) and lacunose (right). These SEM pictures show single ascospores of (left) the black truffle, Tuber melanosporum (the French favourite) and (right) the white truffle, Tuber magnatum (which the Italians prefer). You might be interested in my own ratings, given in Chapter 18).

Only by examining a series of microscopic characters, and considering some intermediate forms that trace the probable course of evolution in the group (a set of diagrams given earlier) can we tell that these fungi are related to the 'operculate discomycetes.'

Although it doesn't make taxonomy any easier, we must now logically place these hypogeous (underground) families with their epigeous (above-ground) forebears in the order Pezizales. The hypogeous habit has necessitated the evolution of new methods for passive spore dispersal, in which some agency other than the fungus supplies the energy for dispersal. Members of the Tuberaceae, especially species of the genus Tuber (the true truffles), have achieved this by developing what can only be called fascinating smells. These odours are released when the ascospores are mature, and lead many mammals unerringly to the ascomata, which they unearth and consume, subsequently depositing the still-viable spores elsewhere. Tuber is dependent, not only on mammalian vectors, but on the roots of oak and hazelnut trees, with which it establishes a symbiotic ectomycorrhizal relationship (see Chapter 17). Tuber melanosporum and Tuber magnatum are, respectively, the black and white truffles of French and Italian haute cuisine, perhaps the most highly esteemed (and certainly the most expensive) of all edible fungi, and so are discussed in detail in Chapter 18.

Molecular studies (Urban et al., 2004) have shown that certain species of Tuber have previously unknown hyphomycetous anamorphs resembling Geniculodendron, with branched conidiophores and blastic-sympodial conidiogenesis.

(3) Order Elaphomycetales:

1 family, 2 genera, 21 species. At first sight the hypogeous ascomata of Elaphomyces (left) look just like truffles; and they're even called 'deer truffles'...

...but they have no hymenium - the basically spherical, non-shooting asci (two stained asci are shown here) are produced randomly throughout the interior of the ascoma. Elaphomyces no longer offers much in the way of visual clues about its possible epigeous ancestors, so only molecular techniques can help us decide its relationships. These techniques are what placed a strange new fungus from the forests of Guyana right next to Elaphomyces...

The two pictures on the left [from Miller et al. (2001) Mycol. Res. 105: 1268-1272] show a fungus that clearly has a volva and a stipe (stalk). It was discovered only in 1998 and described in 2001. It doesn't look like Elaphomyces (see picture above), and was almost described as a basidiomycete, a member of the Tulostomataceae (the stalked puffballs). But repeated molecular results from different collections showed that it is in fact an ascomycete very closely related to Elaphomyces, and has apparently evolved major new characters as a way of dealing with a very wet environment -- it needed to get its spores not only out of the soil, but above it. We welcome Pseudotulostoma to the known fungi.

Series Unitunicatae-Inoperculatae

Although none have lids (opercula), the asci of this group are not as uniform in appearance or structure as we might like (below). Most have thicker walls at their tips, pierced by a fine pore. Inside the apices, many have diagnostic sphincter-like rings, which control the expulsion of the spores. Some of those rings are amyloid (they stain blue in iodine), others don't react with iodine, and are called chitinoid. Some asci don't have rings at all, and in the lichenized Lecanorales (G) (now placed in the Class Lecanoromycetes), the ascal apex is extremely thick and pierced by a narrow canal. The true relationships among these orders have yet to be fully worked out.

4 inoperc asci.gif (21448 bytes)

(4) Order Sphaeriales Class Sordariomycetes: 225 genera, 1300 species. Many members of this group produce dark, brittle, globose to pear-shaped individual perithecial ascomata with prominent ostioles. Others have many perithecial cavities immersed in a single stroma to form a compound fructification, as in Xylaria below The asci often have an apical ring or sphincter, which is usually, though not always, amyloid (stains blue in iodine). Thread-like, sterile elements called paraphyses are present between the asci in the hymenium of some members, absent from others. Ascospores can be light or dark, simple or septate, with or without germ pore or slit, sometimes with gelatinous sheaths or appendages.

The compound fructification of Xylaria, a common wood-inhabiting genus, has hundreds of perithecial ascomata just below the surface, as a you can see in the transversely cut specimen (below, left). Each perithecium contains many asci, as you can see in the section (below, centre).

xylaria1.jpg (11976 bytes)

inoperc2.jpg (2203 bytes)

The asci are inoperculate, with an amyloid apical ring (stained blue - above, right) and contain 8 darkly pigmented, asymmetrical spores, which will eventually be shot out through the ostiole.

Xylaria hypoxylon is another common and easily recognized species. The upper part of the compound ascoma is covered with the whitish conidia of the blastic-sympodial anamorph (which, strange to say, has not been named). This species is often seen on fallen, rotting branches.

This order also includes such pathogens as Entoleuca mammata (formerly Hypoxylon pruinatum) (below), which causes poplar canker, a disease that kills millions of trees every year. The extensive, more or less elliptical cankers (below, left) develop groups of perithecial ascomata (light circular patches, below, right) after the tree cambium has been killed.

For more information about the Xylariaceae, please consult the web site built by Jack Rogers, an authority on this group, at http://mycology.sinica.edu.tw/Xylariaceae/
This deals with all the main genera, and has many useful illustrations and keys.

The genus Annulohypoxylon has recently (2005) been erected for species of Hypoxylon distinguished by molecular characteristics and by the presence of: (1) a discrete carbonaceous layer enclosing each perithecium, and (2) ostiolar discs.

(5) Order Sordariales Class Sordariomycetes: 5 families, 75 genera, 600 species. This is a generally saprobic group producing solitary perithecial ascomata, and found on dung or decaying plant remains. Their asci sometimes have non-amyloid apical sphincters, and sometimes lack any apical apparatus. Several members of this order are important tools in fungal genetics and biochemistry. First and foremost is Neurospora, which has justifiably been called the 'Drosophila of the fungus world'. It was on Neurospora crassa that the science of haploid genetics was founded. The uses of Neurospora and Sordaria mutants are explored in Chapter 10.

Neurospora has Chrysonilia anamorphs (left) that closely resemble the Monilia anamorphs of Monilinia (Sclerotiniaceae, Leotiales).

When I was in China some years back, I noticed the vivid yellow-orange fruiting of Chrysonilia on the husks of corn cobs thrown away near the great wall at Badaleng.

This slide prep. shows the branched blastic-acropetal chains of conidia formed by this fungus (stained blue).

Many species of Sordaria and Podospora fruit on herbivore dung, and shoot their ascospores from perithecial ascomata whose necks, like that of the Sordaria on the left, are phototropic (point toward the light). Look for the apical ring mechanism in the Sordaria asci (right), seen under phase contrast illumination.

Different species of Podospora have 4, 8 (as on the left), 16, 32, 64, 128, 256, 512, 1024 or 2048 ascospores per ascus.

How many do you think there are in each of the two asci of Podospora tarvisina on the right?

The various combinations of tubular and gelatinous ascospore appendages in Podospora not only help in species identification, but also stick the spores to grass after they have been shot away from the dung on which the ascomata develop. Some species of Podospora have Phialophora anamorphs.

Podospora has been analyzed from the molecular point of view and found to be a polyphyletic genus. Species bearing plates of agglutinated hyphae (see middle left-hand photo above) were found to be monophyletic, and have been moved to Schizothecium.

Chaetomium (left) is an important cellulolytic genus that damages fabrics and paper, especially in the tropics. It differs from most other Sordariales in that its asci, though cylindrical, deliquesce or autolyse at maturity. Since they don't shoot their spores, they have no apical ring mechanism, and the mucilaginous, lemon-shaped ascospores ooze out of the ascoma into a characteristic mass of coiled (left) or dichotomously branched hairs that develop on the top of the ascoma. Dispersal must be by rain or arthropods. Chaetomium has Botryotrichum anamorphs

(6) Order Diatrypales Class Sordariomycetes: 20 genera, 125 species. The bark on dead branches of trees often develops eruptions that mark the extensive immersed stromata (compound ascomata) and the grouped ostioles of such common genera as Diatrype (in surface view, right, and cut away, below, left, to show the perithecial cavities) and Quaternaria. Diatrypalean asci (seen in a squash, below, right) have a tiny amyloid apical ring, and the ascospores, also very small, are characteristically sausage-shaped (allantoid).

Another informative pair of illustrations, of Diatrype disciformis (above), from the highly recommended Fungi of Switzerland. The reference is at the end of the chapter.

(7) Order Hypocreales Class Sordariomycetes: 80 genera, 550 species.
This order is recognized by its brightly coloured, simple or compound, perithecial ascomata -- usually yellow, orange or red -- which are fleshy or waxy in texture, and usually borne on supporting layers of mycelium (subicula) or in stromata. Four genera are especially well-known.

1) Nectria (27 species) has bright red, superficial perithecia (right) containing 2-celled (didymosporous) ascospores. Some species cause cankers and die-backs of trees.

Nectria sensu lato has a variety of conidial anamorphs, all of them phialidic. The erumpent sporodochia of one commonly encountered phialidic anamorph, Tubercularia, cause a condition known as coral spot (below, left).

The picture on the right shows the yellow-orange Tubercularia anamorph growing beside the dark red Nectria perithecial ascomata. It is interesting and a little unusual to see both phenotypic expressions of the genome being produced simultaneously.

However, the most economically important of the nectriaceous anamorphs are certain Fusarium species (below, right), many of which cause destructive wilt diseases of higher plants, or produce mycotoxins.

(2) *Gibberella* *also has Fusarium* anamorphs, which are producing the reddish pigment seen in the picture (near right)** Fusarium (far right) produces curved phragmoconidia, frequently with an angled 'foot cell,' from clusters of phialides.
*The picture on the right shows Gibberella* (the dark bodies are its perithecia) and its Fusarium anamorph (reddish-orange) growing together on a corn cob.**

One species of Gibberella causes a disease of rice called 'foolish seedling' in which seedlings grow too rapidly and consequently fall over. The active principle, a plant growth hormone called gibberellic acid, has been extracted and is now widely used to stimulate plant growth.

(3) Hypomyces. In this series of five pictures, we zoom in on Hypomyces lactifluorum, an orange fungus which, like other species of the genus, parasitizes basidiiomycetes, in this case the agaric genera Lactarius and Russula...

...producing a layer of tissue that completely covers the gills and suppresses their development...

...then developing thousands of bright orange-red perithecial ascomata all over the surface of the subiculum.

The Hypomyces completely envelops the aborted mushroom and its colour gives the host-parasite combination the name 'lobster fungus'. Strangely enough, this monstrosity is edible, though I regret to have to tell you that it does not taste like the divine crustacean.

Here is the ostiolar region of one Hypomyces perithecial ascoma.

Note the pseudoparenchymatous wall of the perithecium, and some of the narrow asci which have been squeezed out during the preparation of the slide...

...and here are two of the extremely characteristic spindle-shaped, 2-celled, colourless ascospores. If you look carefully you'll see the septum in the lower spore, and that the spores are rather rough-walled or verrucose.

Twenty-one species of Hypomyces that grow on fruit bodies of various basidiomycetes produce anamorphs belonging to the hyphomycete genus, Cladobotryum, which has an unusual blastic-retrogressive method of forming conidia
(see Chapter 4a).

If you need to identify a species of Hypomyces, there is now a fine new fully illustrated resource on the web, at: http://nt.ars-grin.gov/taxadescriptions/hypomyces/

(4) Hypocrea forms fleshy stromata on wood (right). The dark spots are the ostioles of the embedded perithecial cavities.

The asci are typically 16-spored, the ascospores uniseriate, as you can see in the second picture

The teleomorph of Hypocrea is recorded far less often than its green-spored, phialidic anamorph, Trichoderma (lower right) which, because some species are broad-spectrum mycoparasites, and others produce cellulases and antibiotics, is one of the most important genera of moulds in forest soils. It is now being exploited in biological control of pathogenic fungi (see Chapter 14), and in the production of enzymes which can convert cellulose to glucose (Chapter 24)

Chaverri and Samuels (2003)give a detailed treatment of Hypocrea species with Trichoderma anamorphs.

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The diagrams below show the wide range of anamorphs found in the Nectria-like members of the Hypocreales. They all have phialides as their conidiogenous cells, though the different ways in which these are arranged, and the varying shape and septation of the conidia, place them in many different anamorph-genera (named in the drawing).

(8) Order Diaporthales, Class Sordariomycetes: 90 genera, 500 species. Here several beaked, perithecioid ascomata are usually immersed in a single stroma (as in Diaporthe impulsa, right).
Paraphyses are often absent; and the asci become free inside the ascoma, and then autolyse. This rather paradoxical situation suggests that evolution is in active progress here. Two important genera stand out. Cryphonectria (Endothia) parasitica causes chestnut blight, which has almost extinguished an important species of North American tree in about 50 years: you can read the full story in Chapter 12. Because of this near-extinction, you will probably not be able to find specimens of Cryphonectria, but another member of this order, Gaeumannomyces graminis, which causes 'whiteheads' or, take-all' of wheat, is common. It rots the roots of afflicted plants, and causes premature drying out of the plant, sometimes reducing yields to zero. Anamorphs are coelomycetous.

Leucostoma niveum (above), as illustrated in Fungi of Switzerland - Volume 1 - Ascomycetes, is another member of the Diaporthales.

(9) Order Leotiales Class Leotiomycetes: 13 families, 400 genera, 2000 species. (Note that the Geoglossaceae have now been removed from this Class). A large assemblage termed the 'inoperculate discomycetes.' The apothecial ascomata are superficially similar to those of the Pezizales, but the asci are inoperculate, and usually have amyloid apical rings. This suggests to me that the two major kinds of apothecial ascomata are examples of parallel or convergent evolution. Several of the families in this order are common and well-known, so four of them are dealt with below.

(a) Family Sclerotiniaceae.
Class Leotiomycetes
As the name implies, these fungi often form sclerotia, which may be solid masses of fungal tissue, or may be of mixed origin -- fungal hyphae riddling a mummified host such as a peach, plum, cherry or blueberry, or a catkin (right and below, in Ciboria amentacea). Having overwintered in this guise, they germinate in spring and use the stored energy to produce stalked apothecial ascomata (right). Ascospores (primary inoculum) are shot when the host is in flower, and gain entrance through the stigma.

The illustration above is from Fungi of Switzerland, which I recommend to you all.

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The anamorphs are generally responsible for secondary dispersal, and some cause serious plant diseases. For example, the soft brown rot of peaches (above, left) is produced by a Monilia anamorph of Monilinia. The greyish powder on the surface of the peach (above, left) and the cherry (below) is made up of masses of branched blastic-acropetal chains of conidia (above, right).

The longer I leave the ripe cherries on my cherry tree, the more of them will succumb to the Monilinia soft brown rot, as the conidia being produced on one cherry (far right) infect others
(see Chapter 12).

Monilinia vaccinii-corymbosi causes mummyberry, a serious disease of cultivated blueberry. Shoots infected by this fungus become ultraviolet-reflective, and release a fragrance and sugars - three features that attract pollinators.

These insects then transfer the Monilia conidia to the flowers, initiating new infections.

[Oregon State University has a good web page about this problem: check it out at:
http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=182]

The mummified berries that result from these infections are pseudosclerotia (a mixture of plant and fungal tissue).

The mummified berries overwinter, then germinate to produce Monilinia apothecia that release the primary inoculum (ascospores) to start the cycle again.

Another Monilinia produces spur blight of wild cherry (left), killing back young shoots and forming new conidia on the leaves.

Grey mould of strawberry (left) is caused by Botrytis cinerea, the anamorph of Botryotinia fuckeliana.

Botrytis cinerea (holomorph = Botryotinia) is a very common mould that can also be seen fruiting on dead flower heads and overripe blackberries (below) during damp weather in late summer and fall.

And a bright red flower head of geranium (Pelargonium) (below, left) can turn into a rather sorry looking mess (below, right) in about a week. Botrytis cinerea at work.

Here is a young, branched conidiophore of Botrytis, highly magnified, showing the development of blastic-synchronous conidia on small terminal vesicles.

Many members of the Sclerotiniaceae have distinctive anamorphs (see above and
Chapter 4a), while the teleomorphs are relatively uniform. So some of the holomorph genera erected for the teleomorphs have atypically been distinguished by characters of their anamorphs -- and even named after them. So we have Sclerotinia with Sclerotium (sclerotial) anamorphs, Monilinia with Monilia anamorphs (blastic-acropetal), Botryotinia with Botrytis anamorphs (blastic-synchronous), and Streptotinia with Streptobotrys anamorphs (blastic-sympodial).

Sclerotium, Monilia and Botrytis cause several serious plant diseases (see above and Chapter 12), but when Botrytis grows on overripe grapes in certain areas of France, Germany, Hungary, and South Africa it is called the 'noble rot' in several languages ('pourriture noble', 'edelfaule') because the small quantities of sweet dessert wine that can be made from such shriveled grapes have intense and exquisite flavour, and can be sold for very high prices. Find out what a bottle of Chateau d'Yquem sauternes from France (or a 'Trockenbeerenauslese' from Germany, or a good Tokay from Hungary) costs at your local wine store: be prepared for a shock. The full story and some pictures can be found in Chapter 19.

(b) Family Phacidiaceae Class Leotiomycetes. Some Phacidium spp. cause snow blight diseases of conifers, as these two photos of extensive damage to Abies foliage demonstrate.

If we look more closely, we will see that this family is not typical of discomycetous fungi in general, since the ascomata develop inside host tissue, and are at first covered by a thick roof of dark fungal tissue, as in the diagram (left).

But at maturity the roof splits open and exposes the hymenium. The apical ring in the asci is amyloid (I⁺). Compare this family with the order Rhytismatales, a little lower on the page...How do these orders differ?

Phacidium has coelomycetous anamorphs: those of pathogenic species such as P. coniferarum belong to Apostrasseria (upper left)...

...while those of saprobic species like P. betulinum belong to Ceuthospora (lower left).

The two sets of photomicrographs show vertical sections through the pycnidial conidiomata, and details of the conidiogenous cells and conidia under phase contrast illumination.

Can you tell from these pictures how the two anamorph genera, Apostrasseria (above) and Ceuthospora (below), can be differentiated?

(c) Family Geoglossaceae Now (surprise) placed in a separate Class Lichinomycetes.
The family name means 'earth-tongues' - they produce unusual stalked, somewhat flattened and tongue-like, or sometimes pileate, ascomata which emerge from the ground. The hymenium doesn't line a cup or saucer, but covers the convex upper surface of the ascoma, which is fleshy and yellow in Spathularia (right), tough and black in Microglossum, Trichoglossum and Geoglossum (below, left).

If you squash a tiny piece of the hymenium of a mature Geoglossum ascoma, you will see the asci, each of which contains a bundle of 8 long, parallel, phragmoseptate brown ascospores (below, centre). A single 7-septate (phragmosporous) ascospore is shown in the right-hand picture (The number of septa in the ascospore is diagnostic).

Cudonia (left and below) is a pileate (bearing a well-differentiated beret-like cap) genus of the Geoglossaceae. C. grisea (left) is common in spring on decaying wood on the Pacific Northwest.

The illustration of Cudonia circinans (below) is from Fungi of Switzerland Volume 1, a work all those who are interested in the ascomycetes should consult regularly. Note its admirable inclusion of both macroscopic and microscopic characters.

Mitrula produces what looks like a small version of Spathularia. One of the common species, Mitrula paludosa (left, approx 3x), grows on dead leaves in bogs or other wet places. This one was in a shallow stream beside the trail to Botanical Beach, Vancouver Island, B.C.

(d) Family Leotiaceae Class Leotiomycetes contains some more normal-looking 'discomycetes' such as Bisporella, which produces those small yellow discoid apothecia so common on fallen, decorticated tree-trunks...

...while Chlorociboria, also fairly common, stains wood a deep green and forms small, vivid green apothecia on rotten logs.

Another rather spectacular member of this order is Bulgaria inquinans, found on wood of deciduous trees. The apothecial ascomata have a rubbery texture, and the hymenium is jet black.

(This picture is from "The Wild Mushroom" by George McCarthy, which I recommend to those with an eye for fine photographs of macrofungi).

Less typical are the spectacular ascomata of Leotia: these are much larger, stalked, jelly-like, and have beret-like convex fertile heads (Leotia lubrica below, left and the beautiful velvety green and translucent yellow Leotia viscosa below, right).

(e) Family Dermateaceae includes Diplocarpon rosae (which, with its Marssonina anamorph, causes black spot of roses - see illustration in Chapter 12), and a common but interesting fungus, Trochila ilicicola, that fruits on dead leaves of holly (Ilex) in our garden. Here are several illustrations that will put you in the picture. Below, left, a scan of a dead holly leaf showing numerous fruit bodies all over the upper surface. Below, right, the closed fruit bodies under the dissecting microscope.

These ascomata have a hinged lid, which opens when the leaf is kept in a damp chamber (below, left). The exposed hymenium contains thousands of asci like that shown below, right.

(f) Family Vibrisseaceae is a small family with filiform (thread-like), multiseptate, fragmenting ascospores. It has interesting stream-dwelling anamorphs (Anavirga).
This illustration of Vibrissea truncorum (below) is from the highly recommended Fungi of Switzerland.

(10) Order Cyttariales Class Leotiomycetes: 1 genus, 10 species.

	The globose compound ascomata appear on the branches of the Southern Beech (Nothofagus) in Chile, Argentina and New Zealand. They seem to be made up of many apothecial ascomata packed together, as the photographs (left and below) show. In South America they are eaten and used to make an alcoholic beverage (see Chapter 18) (photos courtesy M. Wingfield, D. Minter)

(11) Order Rhytismatales Class Leotiomycetes: 70 genera, 400 species.
The ascomata develop immersed in host tissue or a fungal stroma, which ultimately ruptures to expose the hymenium. The asci often have apical rings, but these are small and chitinoid (do not stain blue in iodine). The ascospores are usually long and thin

The genus Lophodermum (right) is sometimes endophytic and asymptomatic in pine needles for much of its life, but eventually fruits after the needles die (see Chapter 11).

The lower picture (right) is of a transverse section of a pine needle that has been colonized by Lophodermium -- the section passes through two ascomata. Note the built-in thin-walled area in the roof of each ascoma, at which it will split open in order to shoot its ascospores.

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Rhytisma acerinum (below) causes 'tar spot' of red maple leaves in Eastern N. America...

...while Rhytisma punctatum (below) produces a similar syndrome on big-leaf maple in Western North America, but the small, individual stromata do not fuse. In this photo, the fungus appears to be prolonging the life of the leaf tissue surrounding its colony.

(12) Order Clavicipitales: 27 genera, 270 species. Now placed in Order Hypocreales, Class Sordariomycetes

This order comprises a group of highly evolved and sophisticated, obligately parasitic fungi with: (a) frequently stalked, all-fungal stromata (below, A,B,D,E), (b) long asci without apical rings, but with thickened tips (below, right, F), and (c) long, thread-like ascospores that in some taxa fragment at or following release (below, right, F). They have some interesting anamorphs, including Tolypocladium, Polycephalomyces, and Neotyphodium (which used to be called Acremonium, until it was realized that the holomorphs were in different Orders).

Three bizarre and spectacular genera, Claviceps, Cordyceps and Epichloë, will give us a snapshot of this fascinating order.

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(1) Claviceps purpurea (A,B,C above) discharges its ascospores when its main host, rye, is in flower, and infection takes place through the stigma. As the infection progresses, the fungus takes over the food being channeled into seed-production by the host. The ovarian tissues are replaced by a mycelial mat that produces masses of conidia of the Sphacelia anamorph in a sweet-smelling nectar. Insects are attracted to the nectar, and spread the conidia to other host plants. The mycelial mat hardens and becomes a purplish sclerotium -- the ergot -- which replaces the grain (drawings A and B above, and scan below).

I found the ergots shown above at Whiffin Spit, Sooke, Vancouver Island, on Elymus mollis, a large grass that grows along the shore in the Pacific NorthWest. The largest ergot in the scan above is 4 cm long and almost 5mm wide. These sclerotia fall to the ground in Autumn, overwinter, and germinate the following Spring, each producing several stalked stromata (drawings B and C above, and photos below). Each stroma has a spherical head within which many perithecia develop around the periphery just below the surface.

Because this fungus has a small target, the stigma of the grass flower, which is available only during a narrow time-window, and because spores reach it only by chance, the fungus must disperse a large number of ascospores in a short time. A rough calculation suggests that a single ergot can give rise to 5 stromata, and each of those may contain 100 perithecial cavities, each cavity with 50 asci, and each ascus producing eight ascospores: a total of 5 X 100 X 50 X 8 = 200,000 propagules per ergot.

If the sclerotia are accidentally consumed by cattle, or if rye bread made from ergoty rye is eaten by humans, a large number of alkaloids found in the ergot cause a form of poisoning known as ergotism, or, more picturesquely, St. Anthony's Fire. Human victims frequently hallucinate and feel that they are burning (see chapter 21 for a fuller account of this mycotoxicosis). The alkaloids ergotamine and ergotaline cause contractions of the smooth muscles, and the ensuing restriction of the peripheral blood supply can lead to gangrene and even death. St. Anthony's Fire was fairly common in the Middle Ages, and sporadic outbreaks occurred until recently. Ergot, the only fungal structure in the British Pharmacopoeia Codex, has been used in obstetrics both to induce childbirth and to control post-partural bleeding. Another species of Claviceps brought the genus renewed fame, or perhaps I should say notoriety, as the prime source of LSD (lysergic acid diethylamide), one of the most powerful psychedelic drugs (it is a hundred times more potent than psilocybin, the active ingredient of `magic' mushrooms).

(2) Cordyceps species (drawings D and E, above, and several illustrations below) are bizarre: they generally parasitize insects, spiders and mites, or hypogeous fungi, and their large stromata spring up directly from their victims. These perithecial stromata, arising from an insect larva or pupa (below), are known as vegetable caterpillars, in recognition of the fact that they always incorporate elements from more than one kingdom.

"These strange 'two Kingdom' structures are used in traditional Chinese medicine (right), as a treatment for "general debility after illness, weakness, spitting of blood caused by TB ...chronic coughing and asthma ...night sweating ...anaemia ... malignant tumour."

Cordyceps sinensis (above, right) traditionally bundled with red thread, can be purchased in many Chinese pharmacies, but most people do not know where it comes from. You may be surprised to learn that most of the supply is collected at high altitudes in Tibet.

Yartsa Gunbu, as Tibetans call it, parasitizes the larvae of small white butterflies of the genus Thitarodes (formerly Hepialus). It occurs in alpine pastures at altitudes of 3000-5000 m, but most commonly from 3800 m to 4500 m. In Litang County, collectors are allowed to gather these fungi only in their legal grazing areas. Outsiders have to pay a fee to the local government for the right to collect. Not surprisingly, there are reports of conflicts between locals and unlicensed intruders.

The harvest of Cordyceps sinensis, which is collected in early spring in all grasslands across the Tibetan Plateau, is substantial. Estimates for the present annual harvest in Litang range up to 5,000 kg, representing 5 to 10 million specimens. For comparison, old statistics for Xikang Province report a Cordyceps harvest of 15,000 kg in 1939. Between 1949 and the mid-1980s the annual Cordyceps harvest ranged between 5,000 and 20,000 kg in Ganzi Prefecture. Cordyceps sinensis makes up about 95% of the fungal market in Tibet. Considering that it is worth $30,000/kg retail, this is not surprising. This one fungus contributes about 40% of the rural income in Tibet.

I am grateful to Daniel Winkler (link to his webpages) , who has spent much time working in Tibet, for this first-hand information, and for the picture (left) of a "bu" (Tibetan, short for yartsa gunbu, meaning worm) hunters' camp in Tibet.

During my recent visit to Japan, this specimen of Cordyceps neovolkiana arising from a beetle larva was spotted in a rotten log at Kikuchi Glen near Kumamoto by my guide, Dr. Hitoshi Neda.

For me, this find maintained Japan's reputation as the world centre for Cordyceps. I took two photos through the dissecting microscope with my digital camera and stitched them together after I got home to produce the result seen here.

Before I left Japan I obtained a copy of the classic Japanese book on Cordyceps and related genera, by Shimizu and Kobayasi (ISBN 4-259-53866-7) Its English title is "Illustrated Vegetable Wasps and Plant Worms in Colour" and it contains literally hundreds of superb colour paintings of these fungi. It is a mycologist's and a bibliophile's delight. Some of the paintings could clearly inspire the makers of science fiction movies. Seek it out!

To see some pictures from it, click here

	A few species of Cordyceps don't pick on arthropods, but cannibalistically attack another fungus - actually, it's even another ascomycete - the deer truffle (Elaphomyces). (Left) the large, stalked stroma of Cordyceps capitatus can be seen emerging from the host truffle. (Right) a close-up of the head shows the ostioles of hundreds of perithecial cavities, and a slice of the head (below) reveals their orientation.

Here is another species, Cordyceps ophioglossoides, that also attacks Elaphomyces. Every September for many years, during our mycology field course, we found this species parasitizing Elaphomyces along one of the hiking trails in Algonquin Park, Ontario. Once one of the students had spotted the club-shaped stroma of the parasite, excitement ensued as we dug down, following the yellow rhizomorphs of the fungus, until we finally excavated the host. This find was often dubbed - and with good reason - "fungus of the day," though perhaps that title should have been pluralized.

I am a member of a small group of Canadian west-coast mycologists, supported by a grant from the Mellon Foundation, who have been compiling an inventory of the macrofungi of Clayoquot Sound. On our November 2001 collecting trip, we made an exciting find -- a species of Cordyceps previously unreported from the west coast, arising from coleopteran pupae buried in the sand dunes on a rarely visited beach at the northern end of Pacific Rim National Park. The two photographs below document that find. In the first, you can see the head of a compound ascoma emerging from the sand between the two digging hands.

The second picture shows several excavated stromata and the sand-covered hosts.

I took the next picture in a cloud forest in Ecuador during April 2002. We were excited to find a spectacular Cordyceps that had killed a huge bird-eating spider (Mygale).

The next picture gives you some idea of the size of the spider...

Cordyceps species, which must infect target organisms that are clearly far scarcer than rye flowers, go a big step further than Claviceps in the multiplication of propagules. In some species, each of the 8 long ascospores breaks up into 128 part-spores, often while still in the ascus (below). I estimate that the usually single large stroma produced by some species bears more than 3000 perithecial ascomata, each containing at least 200 asci (seen in squash, below, left), each ascus containing 8 spores, and each of them fragmenting into 128 part-spores (look at the beaded appearance of the asci, below, centre, and at the single ascospore, below, right), for a total of 3000 X 200 X 8 X 128 = 614,400,000 propagules -- all from a single stroma.

A recent paper (Hywel-Jones (2002) Mycological Research 106: 2-3) points out that the number of part-spores in Cordyceps varies. Since there are about 300 species described in Cordyceps, there is a need for some subdivision. Neocordyceps is restricted to attacking Hymenoptera (wasps, ants, bees). The ascospores of Neocordyceps always break up into 64 part-spores. In Eucordyceps, some species also produce 64 part-spores, but others, like C. militaris and other species that are parasites of Lepidoptera (butterflies and moths) and in some cases Coleoptera (beetles), always produce 128 part-spores. Ascospores of species attacking cicadas (Homoptera) commonly break up into 32 part-spores, some species attacking spiders (with Akanthomyces anamorphs) produce only 16 part-spores. Only one known species produces fewer than 16 part-spores -- a recently described species from Coleoptera that has spores which divide into 4. At the other extreme, no species has been observed to produce 256 part spores. Perhaps at that point they would be getting too small to carry the necessary nucleus and food reserves.

Hywel-Jones ends his article with the statement: 'Molecular phylogenetics, classical morphology and field observation must be used together to provide a holomycological approach to fungal classification. Without this approach, confusion can...ensue, especially in...megagenera such as Cordyceps.' Recent molecular studies (2005) show that the large genus Cordyceps is not monophyletic, and that species occur throughout the Clavicipitaceae, which consists of three major clades. The morphological characters most consistent with phylogeny are: (1) colour and texure of stromata, (2) presentation of perithecia, and (3) anamorphs.

Here is a series of pictures that zoom in, starting with a tangle of long asci from a squashed perithecial cavity (below, left) and ending with a single spore (below, right).

Many of the anamorphs of the Clavicipitales are in the Acremonium-like genus Neotyphodium, with simple, tapered phialides, but in 1996 one species of Cordyceps, C. subsessilis, was discovered to be the holomorph of Tolypocladium inflatum. So what, you might say, until you realized that Tolypocladium inflatum is the fungus that produces the medically important, selective immunosuppressant, Cyclosporine, which has made the organ transplant revolution possible. For the story of that amazing pharmaceutical, and some pictures, go to Chapter 24.

(3) Epichloë causes 'choke' disease of grasses. On the left, a grass called Glyceria growing normally - with open, nodding inflorescences. On the right, the energy for the inflorescences has been stolen by the fungus, and used to produce a perithecial stroma that surrounds the stalk of the grass (the vertical whitish lines).

On closer inspection, these lines are seen to be creamy yellow fungal stromata (left), each incorporating many perithecia. A transverse section (below, left) reveals the peripheral perithecial ascomata, and the sheathing grass blades entirely encased in fungal tissue. Individual long, narrow asci can be seen in one of the perithecial ascomata (below, right).

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In a recently discovered twist to this story, this apparently damaging parasitic fungus has been found to have a mutualistic symbiosis with the grass. The simple, phialidic anamorph of Epichloë (which used to be called Acremonium, but has recently been segregated into a new anamorph genus, Neotyphodium), grows systemically throughout the grass plant without producing any disease symptoms, and actually protects the grass from herbivores by producing a virulent neurotoxin. A more detailed discussion of this relationship is given in Chapter 21.

To enjoy several wonderful paintings of members this bizarre group, taken from the superb Japanese book mentioned earlier, please click here. Don't miss them!
A wide-ranging book about the group, entitled 'Clavicipitalean Fungi', edited by White et al., has been published (September 2003). The full reference is given at the end of the chapter.

(13) Order Erysiphales Class Leotiomycetes: 28 genera, 100 species.
All members of this order are obligate parasites on leaves and fruits of higher plants, causing diseases called powdery mildews. These fungi have superficial mycelium which extracts nourishment from the host plant through specialized hyphae that penetrate the epidermal cells of the host and develop special absorbing organs called haustoria. You should have no difficulty spotting a few powdery mildews in summer; their whitish colonies growing on living leaves are unlike anything else (on squash, below, left). In dry summers, they are particularly common on grass in shady parts of lawns, on squash plants (below, left), on perennial Phlox, on Alnus rugosa, and many other angiosperms (over 1,000 species).

Basauxic chains of conidia of the Oidium anamorphs (SEM picture, left, and light micrograph below), whose powdery, whitish appearance gives these diseases their name (far left), arise from the mycelium in early summer.

(Oidium on grass: picture courtesy of Jose Rodriguez)

Airborne conidia spread the disease from plant to plant, and are later succeeded by dark-coloured ascomata (right) - of Uncinula in this case -which mature slowly in fall, and release ascospores the following spring. The order Erysiphales parasitizes well over 1,000 higher plant species, and the powdery mildews of grapes, hops, gooseberries and cereals are economically important diseases.

The generic concepts in this order are unusually straightforward and easy to apply; they depend on two major features of the ascoma -- the number of asci within it, and the kind of appendage growing out from it (see table below). In one way, the Erysiphales are the antithesis of the Sclerotiniaceae. There, the anamorphs were far more distinctive and diverse than the teleomorphs; here, the reverse is true. Most anamorphs of the Erysiphales belong to the hyphomycete genus Oidium, though a few other anamorph genera have been recognized - see below (from Boesewinkel 1980)

Although the order Erysiphales is very easy to characterize and recognize, its systematic position is controversial. Some mycologists insist that its asci are bitunicate, which would place it alongside the Dothideales (see below), but many mycologists do not accept this, and place the order among the unitunicate ascomycetes. The asci are sometimes rather thick-walled, but one of the world experts on the group, Dr. Zheng Ru-yong, of Beijing, tells me that she has seen distinctive inner and outer wall layers only in an undescribed taxon from Tibet, and has never seen the "Jack-in-a-box" mechanism so typical of the bitunicatae. The asci seem to have neither an operculum, nor an apical ring apparatus. This information, plus their strange arrangements for dispersal and dehiscence (see chapter 8), their unique anamorphs, and their obligately parasitic yet strangely superficial lifestyle, make them a rather peripheral (though important and interesting) group.

Key to Some Common Genera of Erysiphales

Appendage type	One ascus per ascoma	More than one ascus per ascoma
Appendages like assimilative hyphae	*Sphaerotheca*	Erysiphe
Appendages dichotomously branched at end	Podosphaera	Microsphaera
Appendages curled at end		Uncinula
Appendages needle-shaped, with bulbous base		Phyllactinia

Use the key given above to determine which genus is represented by the three photomicrographs below.

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(large photomicrograph above, courtesy of Jose Rodriguez)

Use the key again to identify the genus shown in the two photos above. Can you be sure of your identification? If not, why not?

It's easy to identify the genus illustrated below, since there's only one in the key with needle-like appendages with a bulbous base. Phyllactinia has some interesting adventures, which I will try to explain with the aid of several pictures.

Here is an alder leaf with several extensive colonies of Phyllactinia. Below, under the dissecting microscope you can see some developing ascomata with unique appendages. The bulbs, which have differentially thickened walls, develop first, then the needle-like extensions grow out. At maturity, as they dry out and collapse, the bulbs distort, causing the appendages to bend downward and lever the ascoma off the leaf surface, breaking its connections with the mycelium (below).

It is then free to fall away, the appendages acting as stabilizing vanes so that the ascoma will fall straight downward, and become attached to a new substrate by the large blob of mucilage on its top. This has been secreted by specialized hyphal cells with fine apical branches. These cells and the mucilage can be seen in the drawings below.

This new position leaves the asci, which are designed to shoot their spores, facing downward (the third drawing above). The final chapter is written when the ascoma splits around the equator at a built-in line of weakness, and hinges open so that the spores can be shot away.

Here is a wonderful photomicrograph of Cystotheca wrightii (below). Cystotheca is a genus not included in the key given above. Note that there is only one ascus per ascoma, with 8 ascospores. How would you change or add to the key to incorporate this genus?
This picture was very kindly provided by Jose Rodriguez.

If you would like to see more of the genera that are placed in the Erysiphales (and some of them are pretty weird-looking), I have inserted a separate page of illustrations.
Click here to see it.

Series Prototunicatae

In the following four orders, the walls of the asci break down when the ascospores mature, and therefore the spores cannot be forcibly ejected. This has led to the evolution of new ways of dispersing the spores.

(14) Order Onygenales Class Eurotiomycetes: 40 genera, 120 species.
Here belong some unusual fungi which cause skin diseases in people (below, left), and can digest hair, horn and feather (below right, a picture of Onygena fruiting on what was once a robin - photo courtesy of Paul Kroeger) -- all because they have the unusual ability to metabolize that rather resistant protein, keratin.

Onygena equina (above - from Fungi of Switzerland - Volume 1 - Ascomycetes ) producing its stalked mazaedia on shed horns and hooves.

This Order has traditionally been divided into 4 families: Arthrodermataceae, Gymnoascaceae, Myxotrichaceae and Onygenaceae. Many members are keratinophilic, producing simple thallic-arthric conidia, and some genera in each family have ascomata with reticuloperidia - loosely-woven, mesh-like 'walls', though which ascospores can easily escape at maturity - look at the pictures below.

Auxarthron, with 12 species, is a member of the Onygenaceae. The scanning electronmicrograph below (Skinner et al. 2006) shows very beautifully the groups of ornamented ascospores and some of the hyphae of the reticuloperidium,

The members of one family, the Myxotrichaceae (genera Myxotrichum, Pseudogymnoascus and Gymnostellatospora) are atypical, partly because they are cellulolytic, and partly because they have more complex thallic-arthric anamorphs classified in genera like Oidiodendron. Developmental and molecular information now suggests that this family is more closely related to the inoperculate discomycetes (Tsuneda and Currah 2004). The two pictures below are of Myxotrichum ascomata.
Note that in addition to having a reticuloperidium, they develop long, barbed appendages adapted to dispersal by hitching rides on passing arthropods.

Family Arthrodermataceae contains the genera Arthroderma (anamorphs in Trichophyton) and Nannizzia (anamorphs in Microsporum), the infamous dermatophytes which cause superficial mycoses ranging from the inappropriately named ringworm of the scalp to another misnomer, athlete's foot (you certainly don't need to be athletic to catch it) - see Chapter 23.

Other members of the Onygenales can degrade cellulose, and yet others are coprophilous (dung-inhabiting). They all produce ascomata, but although these are theoretically cleistothecial, their walls, as mentioned above, may be very loosely woven, and in some the ascospores can simply fall out through the gaps. The asci are always more or less spherical, never shoot their spores, and tend to break down at maturity. Because of my earlier conclusion that asci evolved as spore-shooting devices, I assume that the ascoma and asci in the Onygenales are 'reduced' forms, simplified during evolution from an earlier spore-shooting design. The ascomata often bear highly characteristic coiled or branched appendages that can make identification easy -- if the teleomorph is present. The ascoma illustrated below is that of Ctenomyces, which has comb-like appendages that are adapted for dispersal by attachment to small animals or to the hairs of larger ones.
(picture courtesy of Dave Spero).

If you isolate dermatophytes in pure culture, they may or may not produce teleomorphs. But they will develop characteristic thallic conidial anamorphs (left). Sometimes these produce small, thallic-arthric conidia (Chrysosporium or Malbranchea), sometimes large, spindle-shaped, transversely septate, solitary thallic conidia (Trichophyton or Microsporum), and sometimes the same culture will produce both kinds of conidia. When a fungus has two or more different anamorphs, these are called synanamorphs. The three most important anamorph genera of dermatophytes are Epidermophyton, Microsporum and Trichophyton. Of these, Epidermophyton has no known teleomorph, 9 species of Microsporum have teleomorphs in Nannizzia, and 7 species of Trichophyton have teleomorphs in Arthroderma.

Can you identify the anamorph shown below by comparing the photomicrographs with the named illustrations above? The left-hand photo shows the fungus growing on a horse hair. Note that the photo on the right shows several stages in the development of the conidia. If necessary, check back to the developmental section in Chapter 4

(15) Order Eurotiales Class Eurotiomycetes: 50 genera, 140 species.
This largely cleistothecial order contains the teleomorphs of some of the most successful of all conidial fungi -- the common green and blue moulds of the hyphomycete genera Penicillium and Aspergillus (colonies of both are illustrated in the left-hand picture below: the granular colony is of Aspergillus flavus. Aspergillus conidiophores with their apical vesicles are shown under high power in the centre picture, the brush-like conidiophores of Penicillium on the right).

These ubiquitous and almost omnivorous anamorphs are blastic-phialidic, and produce masses of dry, wind-dispersed conidia. These moulds aren't just extremely successful, they are of considerable importance to us because they produce antibiotics and mycotoxins, and cause a lot of food spoilage. Species of Aspergillus have teleomorphs in Eurotium (a section through a cleistothecial ascoma is shown below, left, and stained ascospores below, centre) or Emericella, while many penicillia have teleomorphs in the rather similar Talaromyces or Eupenicillium. The cleistothecial ascomata of the teleomorphs have impermeable walls one or more cells thick. The asci are scattered throughout the cavity of the ascoma (i.e., never in a hymenium, as the left-hand picture below shows); they are spherical, thin-walled, and break down when the spores mature. The ascospores often have a pulley-wheel shape (as shown in the centre and right-hand pictures below). Again, it is thought that these fungi are 'reduced' derivatives of spore-shooting ancestors.

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(16) Order Ophiostomatales Class Sordariomycetes: 15 genera, 130 species. The ascomata of this order have long, tubular necks, with the ostiole at the tip (below, left). The asci are not arranged in a hymenium, and autolyse early. The spores ooze out of the ostiole and form a slimy droplet that is supported by a ring of specialized, hair-like ostiolar hyphae at the top of the neck (below, centre). These fungi often fruit in bark beetle tunnels, and the elevated spore drop has evolved to ensure that the beetle carries spores with it when it flies off in search of another tree.

The most important genera in this order are Ophiostoma and Ceratocystis. Ophiostoma novo-ulmi causes Dutch elm disease (below), which was introduced into the U.S. in 1930, to Canada in 1944, has since spread right across the continent, and has much more than decimated the American elm.

This beetle-transmitted fungus has a Pesotum anamorph (below) that produces many tall, synnematal conidiomata (below, left) each bearing a slimy droplet of conidia at its tip (below, right). In producing this stalked spore drop, the anamorph is completely analogous to the teleomorph; both are trying to ensure that beetles don't leave home without them.

As of October 2003, there is a huge mountain pine beetle infestation in the interior of British Columbia - it covers an area of more than 700 x 400 km, and affects 72 million cubic metres of wood. One probably unsuccessful way of controlling it is to cut newly infested trees, since the beetles are killed by the sawmill processes. However, the salvaged wood is stained blue by a fungus that is introduced to the tree by the beetle, and such wood, even though sound, will not be accepted by the Japanese, so loses value. The fungus is often a species of Ophiostoma, and this is what blue stain looks like.

This is clearly a major challenge to the British Columbia lumber industry, but Lynn Pont, a female entrepreneur, hopes she has the answer: instead of calling the wood 'bug-killed', call it 'Denim pine' and make a variety of trendy products under this label. She flew off to China in September 2003 with a suitcase full of samples, in a game attempt to open the markets there. Since the truth is that the blue-stained wood has lost little or none of its strength, the problem being largely cosmetic, we wish her luck. Watch out for 'Denim wood' in your neck of the woods...

Ceratocystis fagacearum and its Chalara quercina phialidic anamorph (left) are the cause of another widespread and serious tree disease, oak wilt. The teleomorphs of Ophiostoma and Ceratocystis are very similar, but the genera are easily distinguished by their anamorphs: the Chalara anamorph of Ceratocystis has solitary phialides with long, tubular collarettes (left), and forms long, cylindrical conidia (one is emerging from the left-hand phialide); Ophiostoma has several different anamorphs, none of them anything like Chalara.

(17) Order Meliolales
Class Sordariomycetes: 24 genera, 1600 species. This obligately biotrophic, largely tropical order has black, superficial hyphae with lateral appressoria, and black, superficial, cleistothecial ascomata containing evanescent, 2-spored asci. Ascospores usually 4-septate. I found this colony growing on a leaf of salal (Gaultheria shallon) on Vancouver Island.

(18) Order Laboulbeniales Class Laboulbeniomycetes: 75 genera, 1700 species. This group has recently been intensively studied in New Zealand, increasing its representation from 26 taxa to 190 taxa, including about 100 undescribed taxa, which goes to show how much potential there is for increasing our knowledge of many fungal groups. This group is so distinct from the other ascomycetes that some people put it in a separate Class, Laboulbeniomycetes. While that might be justifiable, it would also complicate our classification and make life a little more difficult for you. So, having noted the possibility of such elevated status, I will press on. All 1700 species are invariably found attached to the exoskeleton of insects, or occasionally, millipedes and mites. The left-hand picture below shows a gyrinid beetle with small spiny outgrowth protruding from its upper left quarter. These are shown more highly magnified in the centre, and revealed as ascomata of the Laboulbeniales. The development of Stigmatomyces baerii, which is found on houseflies, is followed in the diagrams below, right. An ascospore (A) becomes attached to the animal, germinates, and sends a foot into the exoskeleton to absorb nutrients. Although haustoria may penetrate as far as the epidermal cells, there is never any real invasion of host tissues. The ascospore develops a median septum, and the upper cell becomes differentiated into a male organ, with several phialide-like cells (B) that produce spermatia. The lower cell then develops an ascogonium with a trichogyne, which is fertilized by the spermatia (C). Several asci then develop from the ascogonium, and eventually deliquesce. The mature ascoma is spine-like, projecting from the exterior of the host, and can be seen with a hand-lens (D). Other genera exhibit the same basic features (Hesperomyces - E and Corethromyces - F).

Newly described Laboulbenialean taxa in Diphymyces (A,D,E,F), Cucujomyces (B) and Rhacomyces (C), found on beetles in subantarctic islands of New Zealand

The Laboulbeniales apparently don't produce anamorphs, so are presumably spread from animal to animal by adhesive ascospores during mating of the hosts, or when insects form dense swarms. This goes some way toward explaining the almost incredible site-specificity of many Laboulbeniales. Various species are restricted to one part of the insect, for example, one side of a particular left limb; or even to one sex of their host, though most species are not quite so limited.

Series Bitunicatae

These all produce bitunicate asci.
(Again, if you don't remember what these are, look back at the beginning of Chapter 4a)

(19) Order Dothideales Class Dothideomycetes: 50 families, 650 genera, 6300 species. This is an extremely large and diverse order, which will obviously need to be subdivided when its taxonomy is better understood: I will mention only a few common examples, from 7 families.

(a) Family Venturiaceae. Venturia inaequalis causes apple scab, an economically important disease. You'll find the Spilocaea pomi anamorph causing large brownish spots on the leaves (below, right), and disfiguring blackish scabs on the fruit (below, left).

It produces its blastic-annellidic conidiogenous cells (below, left -- you can see the rings clearly) and obclavate conidia on those spots and scabs. But you won't find the teleomorph during the growing season. Its pseudothecial ascomata (seen in section, below, right) develop slowly in the dead apple leaves over the winter, and the ascospores are shot in spring when the susceptible young leaves appear.

Apiosporina morbosa (below) causes the extremely common and disfiguring black knot of some rosaceous trees, especially wild cherry and damson plum, its pseudothecial ascomata (below, left) developing on conspicuous black fungal stromata (below, right).

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(b) Family Leptosphaeriaceae The illustration of Leptosphaeria acuta (below) is from the superb Fungi of Switzerland - Volume 1. This fungus is common on dead stems of nettle (Urtica dioica) in Spring. Note that the ascospores are phragmosporous. The anamorph is a Phoma (Coelomycetes), which looks like the teleomorph, but produces unicellular conidia.

(c) Family Pleosporaceae Now placed in
Order Pleosporales,
Class Dothideomycetes.
Lewia has anamorphs in Alternaria (whose beaked, catenate dictyoconidia are shown at right).

Alternaria conidia are among the most common spores in the atmosphere (see Chapter 8)

Species of Pleospora (above) are common on dead herbaceous stems, and have anamorphs in the dictyosporous hyphomycete genus Stemphylium (left), and the pycnidial coelomycete genus Phoma (right), among others.

Ascospores and conidia in Pleosporaceae are, as you can see above, commonly both dictyoseptate. Phragmoseptate or dictyoseptate ascospores are common throughout the Dothideales; in fact, if a fungus has ascospores of this kind, the odds are about 9 to1 that it is a member of the Dothideales.

(d) Family Botryosphaeriaceae.
Now placed in
Order Botryosphaeriales,
Class Dothideomycetes

Guignardia aesculi and its Phyllosticta coelomycetous anamorph cause a leaf scorch of Aesculus (horse chestnut, buckeye) ubiquitous in eastern North America that defoliates many ornamental chestnut trees a month or so before they would normally lose their leaves. It doesn't kill the trees, but it is unsightly, and significantly shortens the trees' growing season. This disease seems to

be absent from the west coast, since the Aesculus in my neighbourhood is not afflicted.

(e) Family Capnodiaceae. Now placed in Order Capnodiales,
Class Dothideomycetes
Commonly known as 'sooty moulds,' these fungi grow on the sugary excreta of various insects such as mealy bugs and scale insects. I have found their thick black mycelia producing spectacular black coatings on the trunks and leaves of southern beech (Nothofagus) in the forests of South Island, New Zealand. It's hard to believe that the tree trunks in the left-hand picture would normally appear whitish. The black, feathery branches of some of the numerous and diverse anamorphs can be seen in the picture on the right. Molecular evidence suggests that the Capnodiaceae do not belong in the Dothideales.

(f) Family Dothioraceae Dothiora pyrenophora (below), which fruits on dead branches of Sorbus (Mountain ash), is shown here in an illustration from the highly recommended Fungi of Switzerland - Volume 1. The ascospores are dictyosporous, and anamorphs of this family, where known, are coelomycetous.

(g) Family Hysteriaceae Now placed in Order Hysteriales,
Class Dothideomycetes.
Ascomata opening by a longitudinal split, and sometimes called hysterothecia. The illustration below, of Hysterium pulicare, is again drawn from the renowned and unique Fungi of Switzerland, by Breitenbach and Kraenzlin, in which macroscopic and microscopic features are always elegantly illustrated side by side.

Mytilidion mytilinellum (below) with superficial ascomata, also opening by a longitudinal slit, is also from the superb Fungi of Switzerland.

Now I will provide a dichotomous key to 17 of the traditional orders just discussed. But you will see at the very beginning of the key that this chapter has by no means dealt with all fungi that produce asci. Many thousands of fungi are always found in intimate relationships with algae, and are called lichens (Chapter 7). Many more never produce ascomata, often have unicellular thalli, and are chemically rather different from other ascus-producing fungi. These are known as yeasts (see Chapter 6). I have treated yeasts and lichens separately because each group is phylogenetically diverse, and includes non-ascomycetous fungi (notably basidiomycetes).

+ نوشته شده در یکشنبه ۲۲ اردیبهشت ۱۳۸۷ ساعت 3:32 AM توسط مریم |

plant pathogens

The Microbial World:
Biotrophic plant pathogens

Produced by Jim Deacon
Institute of Cell and Molecular Biology, The University of Edinburgh

Biotrophic plant pathogens

Quite a lot of plant-pathogenic fungi establish a long-term feeding relationship with the living cells of their hosts, rather than killing the host cells as part of the infection process. These pathogens are termed biotrophic [from the Greek: bios = life, trophy = feeding].

Typically, these fungi grow between the host cells and invade only a few of the cells to produce nutrient-absorbing structures termed haustoria. By their feeding acitivities, they create a nutrient sink to the infection site, so that the host is disadvantaged but is not killed. This type of parasitism can result in serious economic losses of crop plants, and in natural environments it can reduce the competitive abilities of the host; indeed, a few biotrophic pathogens have been used successfully as biological control agents of agricultural weeds.

In many ways, this type of parasitism is very sophisticated - keeping the host alive as a long-term source of food. This has led some people to suggest that biotrophic parasitism is evolutionarily advanced. But this is clearly not the case in general, because an almost identical type of parasitism is found in the arbuscular mycorrhizal fungi (see Mycorrhizas) which are thought to have developed on the earliest land plants.

Here we consider the two most important groups of biotrophic plant pathogens:

the rust fungi (Basidiomycota)
the powdery mildew fungi (Ascomycota).

A parallel can be made between the behaviour of these fungi and the biotrophic mycoparasites (see Verticillium biguttatum)

1. Powdery mildew fungi Powdery mildew of roses, caused by the fungus Sphaerotheca pannosa. This is a very common disease, familiar to most gardeners, and it is typical of many powdery mildews, where the fungus forms a powdery coating of white spores on the leaf surface. Other common examples in Britain are powdery mildew of hawthorn (Podosphaera oxyacanthae), gooseberry (Sphaerotheca mors-uvae), and cereals and grasses (Erysiphe graminis). All these fungi grow superficially on the host, only penetrating the leaf epidermis. But they extract considerable amounts of plant nutrients through their haustoria, and these nutrients are used for sporulation, leading to rapid epidemic spread of these diseases.

The powdery mildew pathogens are in the fungal group Ascomycota (ascus-forming fungi). They produce chains of asexual spores (conidia) for aerial dispersal, and at the end of the growing season they can produce small fruiting bodies (ascocarps) containing the sexual spores (ascospores) that serve for dormant survival. Figure A (above) shows many separate, localised lesions of Erysiphe graminis on wheat leaves. The conidia from these lesions (C, D, stained with trypan blue) are produced continuously in chains, maturing at the tip of the chain and being wind-dispersed. They are large enough (about 30 micrometres) to impact onto cereal leaves at normal wind speeds (typically 1-2 metres per second) in field conditions (see Airborne Microbes). Figure B shows similar lesions near the end of the growing season. The small black flecks are the ascocarps. The ascocarps of a different fungus (Podosphaera, the powdery mildew fungus of hawthorn) are seen at higher magnification in Figure E. This type of ascocarp is termed a cleistothecium - a closed body containing one or more asci (each with 8 ascospores inside it). The ascospores are released when the cleistothecium wall is ruptured. (For another example, see Thermoascus)
The haustorium of Erysiphe graminis is highly distinctive (Figure F), consisting of a rounded body with finger-like projections in a wheat epidermal cell. The fungus in this Figure was stained with trypan blue, which also shows the host cell nucleus (n). The haustoria of E. graminis, like those of all biotrophic fungi, are not in direct contact with the host cell contents, because they are surrounded by a membrane - the extrahaustorial membrane - which represents a modified form of the host cell membrane (Fig. G). From Deacon (1997) Modern Mycology By digesting the host cell walls with enzymes, it has been possible to isolate "haustorial complexes" consisting of the haustorium and its encasing membrane. Experimental studies on these haustorial complexes of pea powdery mildew have shown that the extrahaustorial membrane lacks ATPase activity (see Figure G) and thus lacks the ability to control the movement of nutrients across this membrane. In contrast, both the haustorial membrane (of the fungus) and the plant cell membrane have normal ATPase activity for driving nutrient uptake. The consequence is that the fungus can take up nutrients from the host cell, with little or no resistance, while the infected host cell can take up nutrients from its neighbours. So there is a one-way flow of nutrients into the haustorium, and from there to the fungal hyphae on the plant surface, where the fungus uses the nutrients for spore production.

2. Rust fungi

The infection behaviour of rust fungi is broadly similar to that of the powdery mildews, involving nutrient absorption by haustoria to support abundant sporulation for epidemic spread. These fungi also get their name from the characteristic sporing stage - in this case the (usually) rust-coloured uredospores which develop in pustules where the fungus erupts through the plant surface.

Figure H. Wheat leaf infected by the rust fungus, Puccinia graminis var tritici, showing individual lesions (light coloured haloes on the leaf) with pustules of uredospores in their centres. [Image taken by placing an infected leaf on a flat-bed scanner]

The life cycle of rust fungi (basidiomycota, related to the toadstool-producing fungi) is often more complex than that of powdery mildews, because some rust fungi need two different types of host to complete their cycle. These hosts are termed the main host and the alternate host.

For example, Puccinia graminis var. tritici has wheat as its main host and barberry plants (Berberis species) as its alternate host. There is a correspondingly large number of sporing stages - up to 5 in some cases, as shown below.

Figure I. Life cycle of Puccinia graminis var tritici.

On wheat:

P. graminis produces uredospores from a bed of tissue that erupts through the leaf or stem surface (Figures J, K). These uredospores can reinfect another wheat plant (see Fungal tip growth), leading to multiple cycles of infection during the cropping season. They are binucleate spores, containing nuclei of different mating types, and they germinate to produce hyphae that have 2 nuclei in each hyphal cell. In this condition, the fungus is termed a dikaryon (i.e. with two nuclear types).
Near the end of the growing season, the same pustules produce a different type of spore - the teliospore, which consists of two cells with heavily thickened and darkly pigmented walls (Figure L). The teliospores also are dikaryons, with two nuclei in each cell.
The teliospores overwinter, and in spring the nuclear pairs fuse to form diploid nuclei. This is followed immediately by meiosis, then the spore germinates from each cell to form a short hypha that produces 4 uninucleate, haploid basidiospores (see Figure I).

Figures J-L. Puccinia graminis on the cereal host. (J) Pustules of uredospores on a cereal stem. (K) Section of a leaf showing eruption of uredospores through the leaf epidermis (stained with safranin). (L) Section of a leaf later in the season, showing teliospores in place of the uredospores that were produced earlier.

On barberry:

The basidiospores can only infect a barberry plant. They give rise to haploid hyphae of different mating types, which grow through the barberry leaf. These hyphae produce flask-shaped sexual structures termed spermogonia on the upper surface of the barberry leaf (Figures M and N). Small "male" sexual spores (spermatia) are formed within the spermogonia, and "female" flexuous hyphae project from the neck of the spermogonium, among the stiffer hairs (arrowhead in Figure N).
Fertilisation of flexuous hyphae by spermatia of a different mating type is brought about by insects. Then the nuclei pair in the hyphae, forming a dikaryon which gives rise to sporing pustules on the lower surface of the barberry leaf (Figures O and P).
The spores from these pustules are termed aeciospores. They can only infect a cereal host, thereby completing the life cycle.

Figures M-P. Puccinia graminis on the alternate host, barberry. (M) Small lesions on the upper surface of a barberry leaf, with spermogonia in their centres. (N) Section of a spermogonium, showing the minute spermatia (male sexual cells) and the position (arrowhead) where flexuous (female) hyphae arise. (O) Close-up of lower surface of the leaf, showing cup-shaped pustules of aeciospores. (P) Cross section of a leaf showing the aeciospores developing in tightly packed chains from a pad of fungal tissue.

Some common rust fungi

Rust fungi are remarkably common on both crop plants and wild, native plants. On crops they cause serious economic damage, necessitating the use of fungicides. Although Puccinia graminis (black stem rust of cereals) is most important in the USA, Puccinia striiformis (yellow rust) and P. recondita (brown rust) are more important on cereals in Britain.

Several other rusts are common in Britain.

Phragmidium violaceum produces pustules of violet teliospores on the leaves of blackberry bushes (Rubus fruticosus) (Figures Q, R). The stalked teliospores of this fungus are highly distinctive (R). There is no alternate host in this case, only the main host.
Puccinia punctiformis (thistle rust) is also commonly seen (Figure S). It grows systemically in the thistle Cirsium arvense, overwintering as mycelium in the rootstock, and producing chocolate-brown aeciospores. This fungus also has no alternate hosts.
Another common species is birch rust, Melampsoridium betulinum, which forms abundant uredospores (Figure T) and aeciospores on birch leaves. Larch trees are the alternate host of this fungus.
Further common species include mint rust, groundsel rust (Coleosporium tussilaginis; Figures U, V), dandelion rust, hollyhock (mallow) rust and snapdragon (Antirrhinum) rust.

Figure Q-R. Blackberry rust, showing pustules of aeciospores on the leaf surface (Q) and the stalked, multicellular aeciospores under a microscope (R). Figure S. Thistle rust. Figure T. A mass of uredospores of birch rust, each about 30 micrometers long and easily impacted onto leaf surfaces during wind-dispersal.

Figures U,V. Groundsel (Senecio vulgaris), a common weed of open ground. U, whole plant (about 15 cm tall) with rust infection at the base; V, close-up of base, showing uredospore pustules of Coleosporium tussilaginis on the stem and leaves.

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Oidium

Tomato plants showing typical signs of powdery mildew were received in April 2006 from a hydroponic greenhouse situated in western Turkey. Dense, irregular white patches observed on the upper surfaces of the leaves and on the stems of the plants (Fig. 1) could be easily differentiated from the symptoms caused by Leveillula taurica. L. taurica is known as the unique agent of tomato powdery mildew in Turkey up to now and causes white powdery masses appearing just under the chlorotic spots that are produced on the adaxial surface of the leaves.


Figure 1: Symptoms of powdery mildew on stalks and upper leaf surfaces of tomato	Figure 2: Conidiophore with false chain of conidia (A), conidium developing singly on conidiophore (B), and germinating conidia (C) of Oidium neolycopersici (bar represents 30 µm)

To determine the morphological characteristics of the pathogen, surface mycelium was removed with small strips of clear adhesive tape and examined using light microscopy. Microscopic observations revealed ellipsoid-ovoid or doliform conidia that measured 31-57 x 15-27 µm (mean: 33.7 x 17.4 µm; n=50) germinating with one short germ tube terminating in simple apices. Conidiophores were straight, with cylindrical foot-cells measuring 47-78 µm (mean: 53.8 µm), followed by two or three short cells. The total length of the conidiophores measured 73-104 µm (mean: 87.4 µm). Conidia were solitary or sometimes in short pseudo-chains of 2-4 conidia (Fig. 2). Based on these characteristics the fungus was identified as Oidium neolycopersici (Kiss et al., 2001).

To confirm the pathogenicity of the fungus, disease free tomatoes plants (20 plants of each cultivars SC 2121 and H 2274) were inoculated at the five to six true-leaf stage with conidia falling from diseased tomato leaves hanging above them. Plants were kept in a polyethylene chamber placed in a greenhouse cabinet at 21 ± 1⁰C and a 14-h photoperiod for five days. The polyethylene chamber was then removed and the plants were grown in the greenhouse. The first white fungal colonies appeared on the leaves of the inoculated plants 7 days after inoculation and after 14 days, a powdery mildew, exhibiting the same morphological features, was observed on all of the tomatoes plants.

This is believed to be the first report of powdery mildew caused by Oidium neolycopersici on tomatoes in Turkey. This disease has the potential to cause economic losses (Jones et al., 2001) and may become a problem in greenhouse-grown tomatoes in the near future.

Figure 2: Conidium, mycelium and conidiophore of Oidium piperis. Top left: close-up of conidium; Top right: close-up of mycelium showing the indistinct to slightly nipple-shaped apressoria; Bottom: close-up of conidiophore. Note that oil droplets attached to the surface of the fungal structures originated from the host-plant tissue.

Based on these characteristics the fungus was identified as Oidium piperis. A specimen was deposited in the herbarium of the Universidade Federal de Viçosa (VIC 27825). The description of O. piperis provided in Braun (1987) states that conidia of this fungus are 20–74 x 6–23 µm (mostly 34–47 x 13–20 µm). Although our specimen had smaller conidia it was otherwise identical to Braun’s description. Previously reported only in India on Piper betle (Uppal et al., 1946) and in Denmark on Peperomia verticillata (Anon., 1981), there is no previous record of this fungus occurring in Brazil. This new finding suggests a much wider distribution and perhaps a more common occurrence than previously thought. Only minor was observed damage on isolated plants and the threat to medicinal use of P. aduncum appears small.

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Oidiopsis haplophylli

Fungi

Powdery Mildew
Oidiopsis haplophylli (Magnus) Rulamort (teleomorph: Leveillula taurica (Lév.) G. Arnaud (Ascomycetes, Erysiphales)

Status
Exotic (but present in Australia)

Conidiophore

Caption: Oidiopsis haplophylli on Euphorbia cyathophora. Conidiophores arising through the stomata (st) with primary (pc) and secondary conidium (sc) (BRIP 16890).
Source: Dr Jose Liberato DPI&F

Anamorph

Mycelium hemiendophytic (partly external and partly internal), amphigenous, evanescent to persistent. Superficial hyphae entering the leaves through stomata, branched, septate, hyaline, smooth. Conidiophores produced from the internal mycelium, arising through the stomata, rarely from the external mycelium, isolate or in groups, long and fairly slender, mostly about 100-350 mm, simple or occasionally branched, cylindrical, septate, hyaline; foot-cells not twisted or sinuous. Conidia formed singly at the apex of conidiophores, hyaline, morphologically distinguished: primary conidia roughly lanceolate, usually apically pointed, 30-80 x 9-28 mm and secondary conidia roughly ellipsoid to cylindrical, sometimes somewhat irregular, rounded or truncate at the apex, not pointed, approximately the same size like the primary conidia, (Braun 1987).

Teleomorph:

Cleistothecia gregarious to subscattered, often immersed in the dense mycelial felt, 120-280 x mm in diameter, cells obscure, irregularly shaped, 8-20 mm in diameter, appendages usually well developed, numerous, seldom few, poorly developed, arising from the lower half of the ascocarp, mycelioid, simple or irregularly branched, septate, thin-walled, hyaline to light brown, smooth to rough, mostly shorter than the cleistothecial diameter, often very short, occasionally longer, up to 1.5 times as long as the cleistothecial diameter, 4-11 mm wide, mostly interlaced with each other and with the mycelium, asci very numerous, on an average more than 20 per ascocarp, clavate-ovoid to nearly cylindric, stalked, 60-120 x 20-50 mm, 1-4 spored, spores ellipsoid-ovoid, 20-45 x 12-23 mm (Braun 1987).

Notes:

1. L. taurica is a complex of more or less genetically divergent isolates, comprising several biological species for which a clear morphological separation of species is impracticable.

2. Records describing the actual observation of the teleomorph are scanty.

3. The emergence of conidiophores through the stomata, typical of Oidiopsis, is the main difference between Oidiopsis and Streptopodium and has already been the cause of misidentifications. This feature is well observed under scanning electron microscopy. Moreover, leaf clearing and staining techniques (Liberato et al. 2005) enable for observation of this feature with a light microscope.

4. Additional synonyms are given by Braun (1987). Many authors have used the name Oidiopsis taurica for the anamorph of L. taurica (≡ Erysiphe taurica), which was introduced as a new combination (comb. nov.): Oidiopsis taurica (Lév.) E.S. Salmon. It is considered a formal error by the rules of the International Code of Botanical Nomenclature (Art. 59.6) and O. taurica must be attributed to Salmon alone as new name for the anamorphic state, i.e., O. taurica E.S. Salmon, introduced in 1906. Oidium haplophylli Magnus (1900) is the oldest name for the anamorph, with Oidiopsis haplophylli (Magnus) Rulamort as correct combination in Oidiopsis. The latter name should be used for the anamorph of L. taurica.

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PHYLUM ASCOMYCOTA

INTRODUCTION TO THE ASCOMYCOTA

The Ascomycota (as-ko-mi-KO-ta) is derived from two Greek roots that mean wineskin or bladder (aski -ασκί); and fungus (mykes -μύκης). The reference is to the structure (ascus) within which the sexual meiospores are formed.

The ascus-bearing fungi include a very diverse and economically-important collection of organisms. Asci (Figure A) and ascocarps (Figure B), the structures that bear the asci, are among the important structural themes in this phylum. Asci contain the sexual meiospores, which may be agents of dispersal, but most taxa disperse themselves asexually by means of conidiospores contained on conidia (Figure C). The phylum itself is extraordinarily diverse formed of free-living, parasitic, and symbiotic taxa (Figures D-T). Many are parasites of agricultural plants and cause diseases like: apple scab, apple bitter rot, brown stone rot, strawberry stem rot, etc. Some, like Endothia parasitica, have by their introduction altered the Eastern Deciduous Forest in North America by the effective elimination of one of its dominant plants, the American Chestnut (Castanea dentata). Similarly, American Elms (Ulmus americana) have disappeared due to the introduction of another ascomycete that causes Dutch Elm Disease.

Ascomycete-caused diseases are not restricted to plants. For example, skin ailments (e.g. ringworm, athlete's foot), and histoplasmosis, a pneumonia-like disease, are caused by ascomytogenous fungi. Household molds (toxic molds, black molds, and green molds) tend to be from this phylum, though many have lost the ability to produce sexual spores. Ergot, a disease brought on by ingesting rye infected with Claviceps purpurea, causes hallucinations and uncontrolled contractions of certain muscles, especially the uterus. The active agent in ergotized grain seems to be a compound similar to LSD.

All ascomycetes are not dangerous or detrimental. Truffles and morels produce much-prized edible ascocarps. Yeast (Saccharomyces and related taxa) is perhaps the most economically-important fungus of all and is responsible for the alcoholic fermentation of beer, wine, etc. as well as the fermentation necessary for the production of leavened bread.

Some species of the Orbiliomycetes are associated with dry wood and are the causative agents of dry rot. These thrive in the xeric environments of dry dead wood on a tree (where they can be exposed to drying winds and sun) or the semi-arid soil associated with plants like Yucca. However, when the hyphae of their sparse mycelia come into contact with nematodes, they begin to elaborate hyphal loops, which function as nematode traps. When a nematode sticks its head into a snare, the hydrostatic pressure of the hyphal loop increases suddenly, and the worm is caught. The fungus then elaborates a feeding haustorium into the nematode and quickly digests the animal. The fungus, with the added nutrition from the nematode, elaborates conidia for dispersal. Not only do they lead a double life as wood eaters and nematode trappers, but some have lost the ability to make asci. The most well-known nematode-eating fungus, Arthrobotrys, is the anamorph (asexual form) of some taxa within the sexual genus Orbilia. Thus, these same fungi can consume the trim wood on my garden shed door, recycle wood and its elements in the brush pile at the bottom of my yard, and consume soil nematodes in the garden bed where I grow tomatoes. Clearly, the benefits to me far outweigh the costs.

Many species of the ascomycetes perform ecological functions that are quite valuable in the long run. Indeed, the environmental role of most ascomycetes cannot be overstated. Apart from their roles as "decomposers", many of them enter into symbiotic relationships with plants to form a fungus-plant mycorrhizal associations. Similar fungus chimeras include the lichens, most of which have an ascomycete as the mycobiont.

The typical ascomycete life cycle involves the association of haploid, monokaryotic branched filaments. In the case of morel (Morchella), hyphae of two compatible mating types associate and begin to weave the ascocarp. Then, in the hymenial layer, each filament has cells that enlarge. The functional female grows a long structure called a trichogyne that fuses with an enlarged cell in the compatible filament. The result is the emergence of a filament that remains haploid with two distinct nuclei (dikaryotic). As it divides, the terminal end makes a crook (called a crozier) that sequesters one of the nuclei to insure that each daughter cell has the full complement of haploid nuclei. This dikaryon is short-lived and after a few cell divisions leads to the development of the ascus, within which the haploid nuclei fuse and then undergo meiosis to form the ascospores on the surface of the ascocarp.

One of the oddest members of this phylum is Laboulbenia, an obligate parasite of insects, especially beetles, with a distinctive non-mycelial and determinate growth pattern. The fungus body, the receptacle, attaches to the host by a basal cellular holdfast and a single, simple haustorium penetrates the insect. Lateral filamentous appendages and one or more sessile or stalked perithecia arise on the receptacle after feeding on the insect. The ascus wall deliquesces (begins to gelatinize) prior to spore discharge.

*A. Asci of Peziza* with ascospores (opaque linear structures)**	B. The types of ascocarps found in the Ascomycota.	C. An SEM micrograph illustrating the structure of an ascomycete conidium.		*D. The ascocarps of Neolecta, a symbiont (parasite?) of spruce.*	*E. Spores of Pneumocystis* from a lung tissue of a person who was immune compromised by HIV.**
*F. Schizosaccharomyces, a non-budding yeast.*	*G. Asci of Taphrina* are scattered over the host tissue rather than being united into an ascocarp.**	*H. An SEM image of Saccharomyces* showing a developing bud and bud scars.**		*I. Arthonia, an ascomycete fungus in lichenized form.*	*J. Sooty mold caused by Chaetotherium.*
*K. Capnodium* forming a perithecium on Pinus. This is the causative agent of sooty mold on pine.**	*L. Perithecia of Venturia* in the leaf tissue of apple (causing apple scab).**	*M. An SEM micrograph of a Eurotium* cleistothecium. This is the perfect stage of the mold that produces aflatoxins in peanuts and grain.**		*N. Cladonia, a common lichenized fungus known as British Soldier.*	*O. The cleistothecium of Microsphaera, the agent responsible for powdery mildew on lilac leaves.*
*P. Apothecia of Peziza.*	*Q. Ascocarps of Morchella, a prized delicacy for mushroom pickers.*	*R. Perithecia of Claviceps* growing in rye. This is the agent responsible for ergot.**		*S. An SEM micrograph of the perithecium of Neurospora.*	*T. The receptacle of Laboulbenia* attached to the body of an ant.**
Images taken from: A: http://www.humboldt.edu/~dll2/bot105/fungi/ascos.htm B: Bold et al. (1987) C: http://staff.vbi.vt.edu/pathport/pathinfo_images/Aspergillus_flavus/23293C.jpg D: http://www.uoguelph.ca/~gbarron/SAC%20FUNGI/ascokey.htm E: http://www.dpd.cdc.gov/dpdx/HTML/Pneumocystis.asp?body=Frames/M-R/Pneumocystis/ F: http://www.umassmed.edu/bmp/graphics/rhindfig1.jpg G: http://botit.botany.wisc.edu/images/332/Ascomycota/Hemiascomycetes/ H: http://www.bath.ac.uk/bio-sci/wheals2.gif I: http://www.pnl.gov/ecology/Gallery/lichens/arun.html			J: http://www.min.pcarrd.dost.gov.ph/pest/fruit/fruit_sootymold.html K: http://www.cals.ncsu.edu/course/pp318/profiles/fdc/fdc.htm L: http://biodidac.bio.uottawa.ca/thumbnails/filedet.htm M: http://schimmel-schimmelpilze.de/download-1/eurotium-herbariorum.gif N: http://web.uvic.ca/ail/bibliography.html O: http://sorrel.humboldt.edu/~dll2/bot359/htmfiles/erysipha/microsp1.gif P: http://www.uni-greifswald.de/~mycology/gallery/Seiten/Peziza%20micropus.htm Q: http://fungi.umn.edu/gallery/725058a.jpg R: http://www.pmf.unsa.ba/biologija/talofiti/asco6b.jpg S: http://pmb.berkeley.edu/~glass/Glasslab_site/ T: http://www.bsu.edu/classes/ruch/msa/blackwell/9-4.jpg

SYNOPTIC DESCRIPTION OF THE ASCOMYCOTA

The following description comes from Alexopoulos and Mims (1979), Alexopoulos et al (1996), Bold et al. (1987), and Scagel et al., (1984).

I. SYNONYMS: ascomycetes, sac fungi.

II. NUMBER: >15,000 species.

III. PHYLUM CHARACTERISTICS:

A. ASEXUAL REPRODUCTION: Conidia.

B. SEXUAL REPRODUCTION: Ascospores produced within an ascus and often enclosed within an ascocarp. Nuclear fusion followed by meiosis (and usually a mitosis) to produce 8 ascospores in an ascus. Distinctive gametangia and stages of ascospore formation.

C. VEGETATIVE HYPHAE: Haplophase dominant; dikaryophase produces ascogenous hyphae and ascus mother cells.

D. CELL WALLS: Chitin and glucan.

E. ECOLOGY: These are fungi that are free-living saprobes or parasites. Some of them make chimeroid entities like mycorrhizal associations and lichens.

SYSTEMATICS OF THE ASCOMYCOTA

The taxonomy of the Ascomycota has been in flux for some time ( e.g. Hudson 1984, Alexopoulos and Mims 1979, Bold et al. 1987, and Scagel et al. 1984). First, the practice of separating the lichens and imperfect fungi (those that do not exhibit sexual reproduction) was abandoned and more natural taxonomic systems began to appear. This trend can be seen in the systems of Margulis and Schwartz (1982, 1988, and 1998). Then, Nishida and Sugiyama (1994) discovered a distinct group that they called the Archiascomycetes according to their SSU rRNA analysis of fungi. Thus, they and others including Liu et al. (1999), defined the Ascomycota as having 3 classes: Archiascomycetes, Saccharomycetes, and the Euascomycetes. Both the Saccharomycetes and the Euascomycetes groups seemed to be well defined and monophyletic. The "Archiascomycetes" seemed to be paraphyletic and comprised the broad grouping from which the other two groups sprang. I feel that the diversity of the Ascomycota is too great to be reflected in a system of 3 classes. Thus, I have adopted the system of Eriksson et al (2001) which has 3 subphyla and 14 classes. The analysis of Lutzoni et al. (2004) confirms the monophyly of the Ascomycota but calls into question the monophyly of some of the Taphrinomycotina. Adl et al. (2005) seem to separate the ascomycotes into four taxa at the level of Taphrinomycotina (which I interpret as 4 subphyla). Thus, the system of Eriksson et al. (2001) likely will be modified.

HIERARCHICAL CLASSIFICATION OF THE ASCOMYCOTA

This system is a modification of Eriksson et al (2001) which has 3 subphyla and 14 classes.

SUBPHYLUM TAPHRINOMYCOTINA = CLASS ARCHIASCOMYCETES

This is the group that Nishida and Sugiyama (1994) called the class Archaeascomycetes. I have raised it to subphylum level according to the system of Ericksson (2000) who claims that they are the sisters to all of the other Ascomycota, and they appear to be the groups from which the other Ascomycotes arose. However, the following classes differ from each other structurally and, according to Ericksson (2000), on the basis of their SSU rRNA sequences. Thus, the diversity of the group of four classes really indicates that they are defined by exclusion from the well-defined and natural groupings: Saccharomycotina and Pezizomycotina. Also, I am troubled by their apparent primitiveness. All of these taxa (except the fission yeasts) are parasites and, therefore, may only appear to be primitive through reduction. Clearly, the book is not closed on the taxonomy of the Ascomycota.

CLASS NEOLECTOMYCETES

These are fungi that produce large fruiting bodies (ascocarps up to 9 cm tall). The ascogenous hyphae do not have crosiers. The asci open by a slit. The ascospores germinate to form yeast-like conidia. The mycelia and fruiting bodies are associated with spruce roots and may be parasitic.

ORDER NEOLECTIALES

Neolecta

CLASS PNEUMOCYSTIDOMYCETES

These live as parasites in the alveoli of certain vertebrates and, therefore, are of significant medical importance. They grow as yeasts that divide by fission (not budding). They fuse to form asci of 8 banana-shaped ascospores.

ORDER PNEUMOCYSTIALES

Pneumocystis

CLASS SCHIZOSACCHAROMYCETES = OCTOSPOROMYCES

These are the fission yeasts. They fuse to form asci of four or eight ascospores. They live as saprobes in fruit juice.

ORDER SCHIZOSACCHARIALES

Schizosaccharomyces

CLASS TAPHRINOMYCETES

Biotrophic parasites of seed plants and ferns causing galls, leaf curls, deformed fruits and witches brooms. Intercellular or subcuticular dikaryophase mycelium in parasitic phase with terminal chlamydospores or ascogenous cells, each forming a single ascus in a hymenium-like layer; after nuclear fusion and mitosis, ascogenous cells often divide to give a basal stalk cell with ascus at the apex; ascospores may bud within ascus so that it appears multispored; saprotrophic phase of budding monokaryotic cells; can be cultured in the yeast state.

ORDER TAPHRINALES)

Taphrina, Protomycetes.

SUBPHYLUM SACCHAROMYCOTINA = HEMIASCOMYCETES

These are the budding yeasts. Vegetative phase unicellular yeast-like or filamentous; asci one-walled, naked, not borne on ascogenous hyphae, produced singly, following karyogamy; no ascocarps.

CLASS SACCHAROMYCETES

ORDER SACCHAROMYCETALES = ENDOMYCETALES

Saccharomyces, Dipoascus.

SUBPHYLUM PEZIZOMYCOTINA

These comprise most of the ascomycota. The organisms form mycelia that make ascocarps (ascus-bearing structures also called ascomata) with hymenia. Some of the taxa are lichenized (enter into a symbiotic relationship with algae to form lichens). Some of the taxa have lost the ability to undergo meiosis and, although they might fuse, they can not produce ascospores or asci. Such taxa were once called the Fungi Imperfecti or Deuteromycota. Such a distinction is decidedly artificial. On the other hand, symbiotic entities like lichens do not easily fit into a natural system unless the fungal symbiont (mycobiont) is given complete preference. To be consistent with current fungal taxonomic systems, I will include the lichenized fungi in this system and describe the lichens in a separate page. This subphylum follows that of Ericksson (2000), but I have added a 9th class, Laboulbeiomycetes, a group of uncertain status in Ericksson's system.

CLASS ARTHRONIOMYCETES

This class appears to be monophyletic. Most of them are lichenized and produce asci with double walls and slits. The asci elongate to a rostrum when discharging spores. The ascocarps are apothecia with a naked hymenium.

ORDER ARTHRONIALES

Arthonia, Chrysothrix, Melaspilea, Roccella, Arthrophacopsis.

CLASS CHAETOTHYRIOMYCETES

This class appears to be monophyletic. Most species are saprobes on vascular plants, dead wood, lichens, etc. Some are human pathogens. The ascocarps are small perithecia that contains paraphyces.

ORDER CHAETOTHYRIALES

Chaetothyrium, Capronia, Adelococcus, Verrucaria.

CLASS DOTHIDIOMYCETES

Typically, these form bitunicate asci within perithecia (members of the order Patellariales produce apothecia). The asci usually are associated with paraphyses-like structures (pseudothecia). The spores are septate. This class and the Chaetothyriomycetes corresponds to Loculoascomycetes in some earlier systems and is often referred to as "bitunicate ascomycetes". Five orders are recognized in this system (after Ericksson, 2000). Some families will probably have to be transferred to the Chaetothyriomycetes when more molecular data are available.

ORDER CAPNODIALES

Capnodaria, Capnodium, Achaetobotrys, Antennulariella, Coccodinium, Metacapnodium.

ORDER DOTHIDIALES

Asci ovoid, club-shaped or cylindrical, grouped in small locules without pseudoparaphyses in pseudothecia; pseudothecia separate or grouped on or in stroma; ascospores usually uniseptate.

Dothidea, [Mycosphaerella, Guignardia both incertae sedis].

ORDER HYSTERIALES

On dead woody branches and bare wood; with distinct boat-shaped, carbonaceous pseudothecia opening by longitudinal slit and appearing apothecium-like when moist.

Hysterium.

ORDER MYRIANGIALES

Mostly tropical or subtropical, epiphytes, parasites or hyperparasites on fungi or scale insects on living leaves and stems; asci globose, scattered individually throughout ascocarp.

Myrangium, Elsinoe.

ORDER PATELLARIALES

Asci in apothecia.

Patellaria

ORDER PLEOSPORALES

Asci long, cylindrical, separated by pseudoparaphyses in relatively large, uniloculate, usually solitary pseudothecia; ascospores commonly phragmosporous or dictyosporous, pigmented.

Venturia, Delitschia, Leptosphaeria, Lophiostoma, Melanomma, Montagnula, Phaeosphaeria, Phaeotrichum, Pleospora, Sporormia, Teichospora.

CLASS EUROTIOMYCETES

This class appears to be monophyletic. Two orders are accepted. The Elaphomycetaceae form a monophyletic group with Eurotiales and are not treated as a separate order, but should perhaps be placed in a separate suborder in Eurotiales. Asci are small, evanescent and are produced at different levels within the ascocarp which may vary from a loose weft of hyphae bearing asci to a well organized structure with a definite wall; the ascocarp is often enclosed by a cleistothecium (but osteolate in some); conidia common; widespread and often associated with seeds, soils, and as animal parasites. "The blue and green molds". Some like Aspergillus and Penicillium are form-taxa. That is, sexual structures are not known. The class has 2 orders.

ORDER EUROTIALES

Eurotium, Eupenicillium.

ORDER ONYGENIALES

Gymnoascus, Eremascus, Onygena, Ascosphaera, Arthroderma

CLASS LECANOROMYCETES

This class contains most of the lichenized fungi. Most produce asci in apothecia with a naked hymenium. Asci usually thin-walled with a thicker wall at the distal end. Dehiscence is rostrate. This class is used for most of the discolichens, but it is not strongly supported in phylogenetic analyses. This is a large and diverse class of 5 orders and 500 genera.

ORDER AGYRIALES

Agyrium, Lithographa, Anamylopsora, Elixia.

ORDER GYALECTALES

Coenogonium, Gyalecta.

ORDER LECANORALES

Acarospora, Hymenelia, Anzia, Arctomia, Anthroraphis, Biatorella, Calicium, Calycidium, Catillaria, Cetradonai, Cladonia, Coccocarpia, Collema, Crocynia, Dactylospora, Gypsoplaca, Haematomma, Arctopeltis, Lecanora, Lecidea, Loxospora, Megalaria, Macarea, Miltidea, Micoblastus, Ophioparma, Pachyascus, Pannaria, Parmelia, Physcia, Porpidia, Psora, Ramalinia, Rhizocarpon, Sphaerophorus, Stereocaulon, Lobaria, Nephroma, Peltigera, Placynthium, Fuscidea, Letrouitia, Teloschistes.

ORDER LICHINALES

Gloeoheppia, Heppia, Lichina, Peltula.

ORDER PERTUSARIALES

Megaspora, Pertusaria.

CLASS LEOTIOMYCETES

They have thin-walled asci that are inoperculate. The mildews are part of this class (as indicated by molecular studies). Most produce apothecia (the mildews produce reduced cleistothecia).

ORDER CYTTARIALES

Cyttaria.

ORDER ERISIPHALES

Biotrophic parasites; ascocarps with 1 to several oval-shaped to club-shaped explosive asci; ascospores unicellular, colorless; chains of conidia arising in basipetal succession from mother cell on superficial colorless mycelium; penetration of host by haustoria confined to epidermal cells. "Powdery mildews."

Erysiphe, Microsphaera, Uncinula.

ORDER HELIOTIALES (HELOTIALES)

Asci inoperculate in distinct hymenium in apothecia of varying form; mostly saprotrophic but with a few plant pathogens.

Monilinia, Bulgaria, Dermea, Geoglossum, Hemiphacidium, Hyaloscypha, Leotia, Loramyces, Phacidium, Rustroemia, Sclerotinia, Vibrissea, Ascocorticium.

ORDER RHYTISMATALES

Ascodichaena, Cryptomyces, Cudonia, Rhytisma.

ORDER THELEBOLALES

Thelebolus.

CLASS ORBILIOMYCETES

This class contains dry rot fungi, as well as taxa that feed on other plants. When in the presence of nematodes, some will elaborate capture mechanisms with which they can significantly reduce the populations of soil nematodes. Arthrobotrys is the anamorph (asexual form) of small cup fungi, in the genus Orbilia.

ORDER ORBILIALES

Orbilia, Hyalorbilia

CLASS PEZIZOMYCETES

Thin-walled asci operculate in distinct hymenium. Most produce apothecia of varying shapes, large to minute; saprophytic on soils, dung, wood and plant debris. Others (truffels) produce subterranean (hypogeal) ascocarps that are modified apothecia in which the acsi have become inoperculate. This large class has a single order (PEZIZALES)

ORDER PEZIZALES

Anthracobia, Ascolobus, Ascodesmis, Caloscypha, Carbomyces, Gyromitra, Glaziella, Helvella, Karstenella, Acervus, Pyronema, Sphaerosoma, Peziza, Morchella, Rhizinia, Sarcoscypha, Sarcosoma, Tuber.

CLASS SORDARIOMYCETES

These have unitunicate asci in perithecia. The asci open by a pore This assemblage is supported by SSU rRNA as a natural group. The 8 orders are distributed among 3 subclasses: Hypocreomycetidae, Xylariomycetidae, and Sordariomycetidae. This is a large and diverse class of nearly 800 genera.

ORDER HALOSPHAERIALES

Halosphaeria.

ORDER HYPOCREALES

Perithecial fungi with unitunicate asci; perithecia usually in a well-developed stroma which is usually light-colored; asci are long and cylindrical, with a thickened apex; 8 ascospores which are filiform, hyaline, septate and break apart easily; mainly parasitic on grasses, insects, spiders and other fungi.

Bionectria, Melanospora, Claviceps, Hypocrea,Nectria, Niesslia.

ORDER MICROASCALES

Chadefaudiella, Microascus.

ORDER BOLINIALES

Endoxyla, Catabotrys.

ORDER DIAPORTHALES

Melanoconis, Valsa.

ORDER OPHIOSTOMATALES

Kathistes, Ophiostoma.

ORDER SORDARIALES

Perithecia are ostiolate with persistent, unitunicate asci; asci usually embedded in a stroma which may be composed of both host and fungus tissue or fungus tissue only: ascocarps are usually dark and carbonaceous.

Annulatascus, Batistia, Cephalotheca, Chaetomium, Chaetosphaeria, Coniochaeta, Helminthosphaeria, Lasiosphaeria, Nitschkia, Neurospora, Sordaria.

ORDER XYLARIALES

Amphisphaerella, Clypeosphaerella, Diatrype, Graphostroma, Hyponectria, Xylaria.

CLASS LABOULBENIOMYCETES

Mainly obligate parasites of insects, especially beetles, with distinctive non-mycelial and determinate growth pattern. With main body of the fungus, the receptacle, attached to host by basal cellular holdfast; single, simple haustorium penetrating host; receptacle varies in size and complexity, in some row of 3 cells, in others large number of cells superimposed in tiers. Lateral filamentous appendages and 1 or more sessile or stalked perithecia arise on receptacle; asci usually 4-spored; ascospores usually colorless, elongated and more or less spindle-shaped, 2-celled with large basal cell, each surrounded by a colorless envelope thickened at the lower end; ascus wall deliquesces prior to spore discharge.

ORDER LABOULBENIALES

Laboulbenia.

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Downy Mildew in Greenhouse Cucumber

Author:	Gillian Ferguson - Greenhouse Vegetable IPM Specialist/OMAFRA; Ray Cerkauskas - Plant Pathologist/Agriculture and Agri-Food Canada; Michael Celetti - Plant Pathologist/OMAFRA.
Creation Date:	03 April 2007
Last Reviewed:	03 April 2007

Introduction

Downy mildew is a disease caused by the fungus-like water mold, Pseudoperonospora cubensis, which attacks only cucumbers and related crop species (gourds, pumpkin, squash, melons) . This disease primarily affects the foliage and can cause severe yield losses in a short period of time.

Symptoms

Symptoms are usually seen first on the lower, older leaves. Initial symptoms of downy mildew typically consist of angular, yellow spots on the upper leaf surfaces (Figure 1). On the undersides of such spots, a purplish grey fungal (Figure 2) growth may be visible when there is high relative humidity or moist conditions. As the disease progresses, the yellow spots enlarge, become necrotic or brownish in the centre, with the browning spreading to the margins of the spots (Figure 3). Such spots may merge to form large brown areas on the leaves (Figure 4). This kills leaves if the disease is allowed to develop unchecked. Lack of photosynthetic tissue results in stunting of plants, reduced fruit size, and poor fruit set.

Yellow angular spots defined on upper surface of cucumber leaf

Figure 1: Yellow angular spots defined on upper surface of cucumber leaf

ungal growth of Pseudoperonospora cubenis on lower surface of cucumber leaf

Figure 2: Fungal growth of Pseudoperonospora cubenis on lower surface of cucumber leaf

Typical papery brown spots of downy mildew

Figure 3: Typical papery brown spots of downy mildew

Coalescing of many infected spots in downy mildew infection

Figure 4: Coalescing of many infected spots in downy mildew infection

Disease Cycle

Pseudoperonospora cubensis is an obligate parasite requiring living host tissue to survive and does not live in debris in the soil. The pathogen does not survive over winter in Canada. However, occasionally under optimum environmental conditions, the pathogen may develop thick-walled spores (called oospores) that are resistant to low temperatures and dry conditions, but this is rare and not considered an important source of inoculum. Infections in greenhouses likely originate from another type of spore (called sporangia), that enter the facilities from the outside. Local field infections are usually established by spores that are carried by moist air currents blowing northwards from southern regions during the summer.

Moisture on the leaf surfaces is necessary for infections to occur. When spores land on a wet leaf surface, they can either germinate and infect through the breathing pores (stomates) on leaves, or release many smaller spores (called zoospores) that swim in the film of water on leaves during humid or wet conditions, and infect leaves through stomates. Optimum temperatures for infection range between 16° to 22°C. Infection occurs more rapidly at the warmer temperatures. The period of wetness needed for infection on cucumber leaves are about 12 hours at 10 to 15°C, 6 hours at 15 to 19°C, and 2 hours at 20°C. About 4 to 5 days after infection, new spores are produced and released into the air primarily during the morning period. Spores can quickly spread within the greenhouse via moist air currents, contaminated tools, equipment, fingers, and clothing. Fortunately, the spores become less infective under conditions of high temperatures and low humidity in the greenhouse.

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Management Strategies

Cultural Practices

Management of the greenhouse environment - Avoid dew formation by providing adequate heating and ventilation. This is critical to reducing incidence of downy mildew. Special attention must be paid to purging moist air out of the greenhouses during the evenings, and keeping the plant foliage dry, particularly during the night. At normal greenhouse temperatures, relative humidity should generally not be allowed to exceed 70-75%.
Sanitation - All sources of infection should be removed and discarded away from the greenhouse so that spores are not blown back into the greenhouse. This could include burial of plant debris. Infected leaves or plants should be carefully removed and placed in a garbage bag before disposal to ensure that spores do not escape and infect nearby commercial cucurbit fields (pumpkin, zucchini, cucumber, squash). All cucurbit plants should be removed from the immediate surroundings of the greenhouse because they may serve as reservoirs for the downy mildew fungus. Surfaces in infested greenhouses should be thoroughly disinfected.
Adequate canopy aeration - Ensure that plants are sufficiently spaced and that the canopy is well pruned and thinned to provide for adequate air-circulation.
Avoid over watering - Over-watering not only leads to overly soft, more vulnerable plants, but also to guttation or production of droplets of moisture at the margins of leaves early in the morning. This moisture at the leaf margins provides perfect infection sites for the downy mildew pathogen.
Avoid overhead watering or humidification - Any cultural practice (e.g. misting) that increases leaf moisture will increase disease development when spores are present in the air.

Chemical Controls

Apply chemical controls in a timely manner - If only a few spots are evident on a few leaves of one plant, then the disease is in the early stages of development. Appropriate chemical control procedures should be implemented immediately because the spores are readily dispersed by air currents. Further disease development may be very rapid under favourable environmental conditions as previously described.

Rotate products - Where possible, it is best to rotate fungicides to reduce chances of development of resistance in the fungus to the material applied. Generally, systemic fungicides should be used in combination with protectant fungicides to reduce the chances of development of resistance in the fungus. As for all crop protection chemicals, growers must always read and follow label recommendations.

+ نوشته شده در شنبه ۲۱ اردیبهشت ۱۳۸۷ ساعت 3:26 AM توسط مریم |

مطالب جدیدتر مطالب قدیمی‌تر

bia webeta begir age doost dari

علمی

Bremia Plasmopara

ائوميست

ائوميست1

ائوميست2

Erysiphe syringae)

A Survey of Ascomycetous Holomorphs

plant pathogens

آزمون ارشد- بيماري ها 1383

آزمون ارشد- بيماري ها 1383

Oidium

Oidiopsis haplophylli

PHYLUM ASCOMYCOTA

Downy Mildew in Greenhouse Cucumber

Table of Contents

Introduction

Symptoms

Disease Cycle

Management Strategies

Cultural Practices

Chemical Controls

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