STUDIES IN MYCOLOGY 50: 471–479. 2004.
Passalora perplexa, an important pleoanamorphic leaf blight pathogen of
Acacia crassicarpa in Australia and Indonesia
Vyrna C. Beilharz1*, Ian G. Pascoe1, Michael J. Wingfield2, Budi Tjahjono3 and Pedro W. Crous4
1
Primary Industries Research Victoria, Department of Primary Industries, Knoxfield, Private Bag 15, Ferntree Gully Delivery Centre, Victoria 3156, Australia; 2Forestry and Agricultural Biotechnology Institute, Faculty of Natural and Agricultural
Sciences, University of Pretoria, Pretoria, South Africa; 3PT Riau Andalan Pulp and Paper, P.O. Box 1080, Pekanbaru-Riau,
Sumatra, Indonesia; 4Centraalbureau voor Schimmelcultures, Fungal Biodiversity Centre, Uppsalalaan 8, 3584 CT Utrecht,
The Netherlands
*Correspondence: Vyrna C. Beilharz, vyrna.beilharz@dpi.vic.gov.au
Abstract: Passalora perplexa is described from lesions on blighted phyllodes of Acacia crassicarpa growing in northern
Australia and Indonesia. The fungus develops two distinct conidiomatal synanamorphs from the same stroma in nature, one
external and sporodochial (Type 1), the other internal and coelomycetous (Type 2). A third synanamorph (Type 3) develops
as resting spores within cells of Type 2 conidia in culture. Type 1 conidiophores and conidia are consistent with Passalora
sensu lato, with pigmented conidiophores and conidia and thickened, darkened, refractive scars. The conidiophores are
initially caespitose and stromatal, but later sporodochial and generated by the outer cell layer of more or less protuberant
stromata. Type 2 conidia are smaller, paler, cylindrical and mostly 1-septate. They have unthickened scars and are formed on
short, 0–1-septate conidiophores which line a central cavity that develops within the same stroma. In culture, conidial cells of
Type 2 conidia may eventually release an inner, hyaline propagule (Type 3 conidia) that possibly acts as a resting spore. The
connection between Type 1 and Type 2 synanamorphs has been confirmed in culture via single-conidial isolates. Sequence
data derived from the ribosomal DNA ITS region (ITS1, ITS2) and the 5.8S gene, show that P. perplexa is an anamorph of
Mycosphaerella, closely allied with other species of Passalora. Passalora perplexa is a severe pathogen of Acacia crassicarpa in Indonesian plantations and has become a serious constraint to plantation development with this species.
Taxonomic novelty: Passalora perplexa Beilharz, Pascoe, M.J. Wingf. & Crous sp. nov.
Key words: Acacia crassicarpa, Mycosphaerella, Passalora, phyllode blight, synanamorph, systematics.
INTRODUCTION
Acacia crassicarpa Benth. (Leguminosae, Mimosaceae) is indigenous to New Guinea and the tropical
northern regions of Australia, including the coastal
areas of far north Queensland, the off-shore islands to
the north of Cape York Peninsula, and Melville Island
near Darwin, NT. Along with A. aulacocarpa A.
Cunn. ex Benth., A. auriculiformis A. Cunn. ex Benth.
and A. mangium Willd., A. crassicarpa has become an
important plantation species in South-East Asia. Thus,
plantations have been established in northern Australia
to meet the demand for seed of particular provenances
of these three species (Old et al. 1997).
During an investigation into diseases which might
pose a threat to these plantations, an unidentified
cercosporoid pathogen was found on blighted phyllodes of A. crassicarpa (Old et al. 1997, 2000) (Figs
1–6). A similar collection from Melville Island had
earlier been referred to by Yuan (1996) as Pseudocercospora sp., based on his observations of the external
sporulation. It was similarly referred to as an “undescribed sp. aff. Pseudocercospora” by Old et al.
(1997) and, following the first sighting of a putative
synanamorph, as a “gen. indet., aff. Pseudocercospora” by Cannon et al. (1997). This sporodochial,
cercosporoid conidial type is referred to as Type 1.
Subsequent examination of some of this material
confirmed the presence of a coelomycetous synanamorph occupying a central locule within the stromata
of sectioned sporodochial conidiomata, which is
subsequently referred to as Type 2. Both morphs were
clearly derived from cells of the same stroma, and the
connection was confirmed via cultural studies, so the
possibility of hyperparasitism was ruled out. DNA
sequence data of the ITS region (ITS1, ITS2) and the
5.8S gene confirmed that this species is a Mycosphaerella Johanson anamorph. More recently, the pathogen
was recollected from plantation-grown A. crassicarpa
in Indonesia, where it causes a severe foliar blight
disease. Sequence data derived from the ITS region
confirmed that it is the same pathogen as that occurring in Australia (Crous et al. 2004, this volume).
Numerous pleoanamorphic fungi have been described. The provision of names for these fungi with
multiple states has been discussed in some detail
(Carmichael 1981, Gams 1982, Hennebert 1987,
Minter 1987, Seifert & Samuels 2000). We have been
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unable to find any combination of synanamorphs that
would equate with the cercosporoid fungus infecting
phyllodes of A. crassicarpa and described here. The
correct or most logical means of treating the nomenclature of pleoanamorphic fungi remains somewhat
subjective, and has not been defined in the Code of
Botanical Nomenclature. The well-known generic
name Passalora Fr. sensu Crous & Braun (2003) is
correct for the hyphomycetous synanamorph, and it is
particularly useful in this case because most colonies
of the fungus show liberal and conspicuous sporulation of this morph, whereas the cryptic Type 2 synanamorph is less likely to be observed, and is
unlikely to be found in isolation. Gams (1982) suggested that the anamorph form with the greatest differentiation should have priority (unless it is rare), a
view which further supports the application of the
name Passalora to the fungus on A. crassicarpa.
The conidia of the Type 1 and Type 2 synanamorphs of the cercosporoid fungus from A. crassicarpa, although easily distinguished, show some
similarity in morphology. The Type 2 conidia are
somewhat cercosporoid in type and reminiscent of
some species of Colletogloeum Petr., but the conidiomata do not fit with the acervular conidiomata of that
genus. Critical differences between the two types of
conidia, including pigmentation, can be linked to their
relative positions in relation to the host tissue. For
example, the thickened hila of Type 1 conidia are
probably associated with their readiness to secede
(Beilharz 1994). In contrast, the broader, unthickened
hila of Type 2 conidia are more appropriate to passive
release following breakdown of overlying fungal and
host tissues.
Acacia crassicarpa is a species that has become
increasingly important in plantations in various parts
of South-East Asia, where it is grown specifically for
the production of pulp. The relatively recent outbreak
of a serious leaf blight disease caused by a cercosporoid fungus has demanded an appropriate taxonomic
treatment of this organism. This study represents a
collaborative effort by a number of research groups
who have an interest in this fungus and the disease
with which it is associated. Here, we describe a potentially devastating, newly recognised disease of A.
crassicarpa, and describe the causal organism, a novel
pleoanamorphic species of Passalora.
MATERIALS AND METHODS
Isolates
At VPRI, cultures were derived from the Australian
specimen VPRI 21125 by the following means. Naturally-produced Type 1 conidia were lifted from lesions
en masse with a fine needle and jab-inoculated on to 2
% potato-dextrose agar (PDA; Difco) plates emended
with achromycin (0.05 mg/mL) (PDA+A). Similarly
472
harvested Type 1 conidia were also suspended in a
drop of water containing a trace of Tween 80, streaked
out on to 2 % tap water agar and transferred individually to PDA+A the following day, after germinating.
Type 2 conidia formed in vitro in PDA cultures derived from individual Type 1 conidia were used to
provide single-conidial isolates as described above. In
addition, whole, pale, smooth protuberant stromata
lacking external conidiophores and putatively containing Type 2 conidia, were lifted from the phyllode
surface with a fine, sterile needle and placed directly
onto PDA+A. All PDA+A cultures were transferred to
PDA after 3–7 d and grown on for up to 2 mo in the
dark at 22 °C. The choice of the various forms of
inoculum was determined by the ease with which they
could be harvested from infected phyllodes or cultures. For example, Type 1 conidia were abundant on
the natural subtrate, but occurred in comparatively
small numbers in culture, where they were liable to be
contaminated with Type 2 conidia. Type 2 conidia
were abundant in wet masses in culture; in nature,
however, they tended to remain aggregated and often
could not be completely freed from excised conidiomata, despite the application of pressure on coverslips
or attempts to tease the elements apart in a drop of
water on a microscope slide. Type 3 conidia were not
seen in 2-mo-old cultures on PDA, and Type 2 conidia
from these cultures germinated normally on fresh agar
plates. The Australian specimens and a dried culture
of VPRI 21125 have been deposited in herb. VPRI,
Knoxfield, Victoria, Australia.
At CBS, single Type 1 conidial isolates were
derived from Indonesian specimens and cultivated on
2 % malt extract agar (MEA; Difco) as described by
Crous (1998). Colonies sporulated on MEA after 1–2
mo incubation on the laboratory bench in daylight at
room temperature, forming conidiomata containing
Type 1 and Type 2 conidia. After 3 mo incubation on
MEA, conidiomata with Type 2 conidia were observed to also give rise to Type 3 conidia, a form
observed only in culture. Specimens and cultures have
been deposited in the herbarium and culture collection
of CBS in Utrecht, the Netherlands.
A phylogeny of the cercosporoid fungi occurring
on Acacia, including Passalora perplexa, is presented
elsewhere in this volume (Crous et al. 2004).
Morphology
Slide preparations were made in lactic acid and 50
examples of each structure were measured under a
×100 oil immersion lens using Olympus BH–2 (VPRI)
or Zeiss Axioskop (CBS) light microscopes. The 95 %
confidence intervals were also determined for conidial
dimensions, with the extremes in conidium length and
width given in parentheses. Colony colour was determined on 2 % MEA after 3 mo at 25 °C in the dark
using the colour designations of Rayner (1970).
PASSALORA PERPLEXA AND ITS SYNANAMORPHS
Figs 1–6. Passalora perplexa. 1. Trees showing defoliation. 2–6. Symptoms associated with Crassicarpa leaf blight.
RESULTS
Disease symptoms
Lesions occur primarily on the phyllodes of A. crassicarpa but they can also form on the petioles and
young shoots. Phyllode lesions are initially small and
typically elliptical, and are surrounded by a distinct
chlorotic halo (Figs 1–6). On freshly formed lesions,
fascicles of grey-brown conidiophores and dense
olivaceous spore masses can easily be seen. Lesions
formed at the edges of phyllodes or abutting primary
veins can cause severe malformation and curling of
the phyllodes (Figs 2–6). Infections are often severe,
causing the dramatic malformation of the apical
portions of young (1–2-yr-old) trees (Fig. 1).
Taxonomy
Sequences obtained for the ITS region in the laboratories of both VPRI and CBS, confirmed that the Australian and Indonesian specimens represented the same
taxon. The DNA sequence analyses also showed that
the fungus is an anamorph of Mycosphaerella, clustering with Cercospora loranthi McAlpine (Crous et al.
2004, fig. 1), which is a species of Passalora. These
relationships have been discussed elsewhere (V.C.
Beilharz, in press). Sequences of P. perplexa have
been deposited in GenBank, and the alignment of
sequence data in TreeBASE (Crous et al. 2004).
The habit, morphology, pigmentation and scar
characteristics of Type 1 conidiophores and conidia
are characteristic of the genus Passalora. This observation is consistent with the results of the DNA-based
comparisons. Currently there are no species of Passalora known from Acacia (Crous & Braun 2003), and
hence this species with its pigmented Type 1 conidia
and thickened, darkened, refractive conidial hila can
be described as new. Prior to the discovery of additional coelomycetes resembling the Type 2 synanamorph and their affiliations being established, it would
be inappropriate to provide a separate generic name
for the Type 2 synanamorph or to name this synanamorph.
Passalora perplexa Beilharz, Pascoe, M.J. Wingf.
& Crous, sp. nov. MycoBank MB500123. Figs
7–27.
Etymology: Named because of the unusual combination of conidial synanamorphs.
Fungus pleoanamorphicus conidia generis Passalorae et
coelomycitica formans. Conidiophora solitaria vel laxe
aggregata, pallide vel medio-brunnea, levia vel verruculosa,
subcylindrica, ramosa vel simplicia, pluriseptata, sympodialiter proliferentia, 15–80(–116) µm longa, 3–5 µm lata.
Cellulae conidiogenae terminales, verruculosae vel rugosae,
simplices, subcylindricae, apicem rotundatum versus
angustatae, 15–20 × 3–4 µm; cicatrices modice inspissatae
et fuscatae, refringentes, 1–2 µm diam. Conidia solitaria,
pallide olivacea vel medio-brunnea, levia vel eximie verruculosa, recta vel curvata, anguste obclavata vel subcylindri-
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BEILHARZ ET AL.
ca, sursum obtusa, ad basim longe obconice subtruncata,
(1–)3–9(–13)-septata, (16–)50–100(–153) µm longa, 2.5–
5.5 µm lata, hilo modice inspissato et fuscato, refringente,
1–2 µm diam.
Holotype: Indonesia, South Sumatra, Kerinci, Herb. CBS
9907 holotype, on phyllodes of Acacia crassicarpa, Feb.
2004, M.J. Wingfield, ex-type cultures CBS 116363 = STEU 11147–11149.
Pleoanamorphic, producing stromatic conidiomata on
phyllodes of Acacia crassicarpa. Leaf spots hologenous, initially pale brown, orbicular and non-necrotic,
becoming medium brown, necrotic, elongated, narrowly ellipsoidal to sub-circular, with an inconspicuous border, often distorted and wrinkled and causing
distortion of the phyllode, limited by main secondary
veins, to at least 15 mm long, 2–5 mm wide. Mycelium internal, consisting of smooth, branched, septate,
brown hyphae, 3–4 µm wide. Stromata medium
brown throughout or ranging from brown in the exposed apical cells to hyaline or sub-hyaline in the
deeper tissues, initiated in the substomatal cavity,
usually becoming erumpent, protuberant and pulvinate, composed of textura angularis, 50–80 µm wide,
50–90 µm high. Conidiomata amphigenous, eustromatic, comprising either (a) pale-yellowish, fleshy,
protuberant stromata containing Type 2 conidia but, at
least initially, bearing no Type 1 conidiophores; (b)
brown immersed or erumpent stromata bearing Type 1
conidiophores but, at least initially, containing no
Type 2 conidia, or (c) mature brown conidiomata, up
to 80 µ m diam, 60 µm high, bearing numerous Type 1
conidiophores and containing numerous Type 2 conidia.
Type 1 synanamorph: Conidiophores occasionally
solitary, usually aggregated in loose fascicles arising
from the upper cells of a brown stroma, up to at least
62 in number, pale to medium brown, smooth towards
the base and often becoming rugose towards the apex
with age, subcylindrical, branched or unbranched,
walls slightly thickened, straight to variously curved
or geniculate-sinuous, having a basal septum and 0–11
additional septa; proliferation sympodial, with endohyphal regeneration or proliferation also commonly
exhibited, 15–80(–116) µm long, 3–5 µm wide. Conidiogenous cells terminal, verruculose or rugose,
unbranched, subcylindrical, tapering to
rounded
apices proliferating sympodially, 15–20 × 3–4 µm.
Conidiogenous scars slightly thickened and darkened,
refractive, flat against the side of the conidiophore, on
short pegs or on sloping shoulders following proliferation of the conidiogenous cell, sometimes protruberant, often somewhat disguised by the dark, rugose
wall of mature conidiophores but clearly seen on
paler, more newly generated conidiogenous cells, 1–2
µm diam. Conidia solitary, pale olivaceous to medium
brown, dry, smooth, rarely finely verruculose, straight
or curved, narrowly obclavate to sub-cylindrical,
474
tapering gradually to an obtuse apex and to a rounded
or long-obconically-subtruncate base, often constricted at one or more septa or with an otherwise
uneven edge-line, (1–)3–9(–13)-septate, (16–)50–
100(–153) µm long, and 4–4.5(–5.5) µm wide in vivo
(Australian specimens), or (2.5–)3–4 µm wide (Indonesian specimens). Secondary conidiation was occasionally seen. Hila slightly but distinctly thickened
and darkened, refractive, 1–2 µm diam.
Fig. 7. Conidia of Passalora perplexa in vivo. Scale bar =
10 µm.
Fig. 8. Type 2 conidia and conidiophores of Passalora
perplexa in vivo. Scale bar = 10 µm.
PASSALORA PERPLEXA AND ITS SYNANAMORPHS
Type 2 synanamorph: Conidiophores reduced, hyaline
to sub-hyaline, 0–1-septate, lining a single, initially
ill-defined cavity, which develops within either a
substomatal or protuberant stroma exactly as described above. Conidia initially hyaline and inconspicuous, later pale olivaceous, ± cylindrical, barely if
at all tapering to the apex or the base, sometimes
swollen at the apex or broadening to the base, occasionally constricted, smooth, (0–)1(–3) septate,
(12–)15–21(–25) µm long, 2.5–4 µm wide; hila broad,
truncate to slightly convex, not darkened, unthickened, non-refractive, 2–2.5 µm diam. No pore or slit
has been detected that would allow ready release of
Type 2 conidia. On the other hand, the contents of
certain old conidiomata have become exposed by the
apparent breakdown and peeling back of both fungal
and host tissues. These conidiomata eventually resemble acervuli, although they are no longer actively
sporulating. It is possible that Type 2 conidia depend
on tissue breakdown for their dissemination, and that
insects or other animals may aid their dispersal.
Type 3 synanamorph: After 1 mo, Type 2 conidia
from 3-mo-old MEA cultures exposed to daylight
develop thick-walled hyphal swellings (reminiscent of
chlamydospores that develop in conidial cells of
certain Fusarium spp.); these inner propagule cells
eventually burst free from the cells of the Type 2
conidia, frequently still having pigmented remnants of
the conidial wall attached to their hyaline walls. Type
3 conidia are 6–20 x 4–6 µm, 0(–1)-septate, ellipsoid
and hyaline. Type 3 conidia did not develop in 2-moold PDA cultures grown mostly in the dark.
Cultural characteristics: Colonies slow-growing,
reaching up to 20 mm diam after 3 mo on 2 % MEA at
25 °C under near-UV light; colonies erumpent, margins feathery, irregular; outer region (surface) sepia
(15”k) due to submerged, radiating mycelium; inner
region whitish to cream, with slimy sporodochial
spore masses, fuscous black (7””k); central region
with moderate hazel (17”’i) aerial mycelium; reverse
brown-vinaceous (5”’m).
(ex DFR 162), VPRI 20901; Melville Island, plantation
provenance, 17 Sept. 1992, K.M. Old (ex DFR 138), VPRI
20903.
Fig. 9. Type 1 conidiophores of Passalora perplexa in vivo.
A. Conidiophores emerging from stomata. B. Sporodochial
conidiophores. C. Conidiophores arising from a subcuticular hypha. Scale bar = 10 µm.
Substrate and distribution: Pathogenic to phyllodes of
Acacia crassicarpa; Australia, Indonesia.
Additional specimens examined: All on phyllodes of Acacia
crassicarpa, Indonesia, Southern Sumatra, Kerinci, Feb.
2004, M.J. Wingfield, herb. CBS 9908, 9909, 9911, cultures derived from CBS 9911, CBS 116364 = STE-U
11150–11151. Australia, Queensland, Cooktown–Cape
Tribulation Hwy, 4 km W of Bloomfield, 8 Apr. 1995,
K.M. Old (ex DFR 257) (CSIRO Forestry and Forest
Products herbarium, Canberra Australia), VPRI 20902; 5
km W of Bloomfield, 8 Apr. 1995, K.M. Old (ex DFR 252),
VPRI 20904; Ingham, Shell trial site, Lannercost State
Forest, 3 Apr. 1995, K.M. Old (ex DFR 255), VPRI 20905;
Edmund Kennedy National Park, K.M. Old (ex DFR 305),
4 Apr. 1995, VPRI 20906; Ingham, Shell trial site, Lannercost State Forest, K.M. Old (#6), 9 Apr. 1996, VPRI 21125
; N.T., Yapilika, Melville Island, 17 May 1994, Z.Q. Yuan,
Fig. 10. Conidia of Passalora perplexa in vitro on PDA.
Type 1 conidia (top), and Type 2 conidia (bottom). Scale
bar = 10 µm.
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BEILHARZ ET AL.
Notes: In culture, colonies sporulate on MEA after 1–
2 mo, forming sporodochia situated on globose conidiomata that are pycnidioid but lacking a clear
ostiole. Conidia formed on sporodochia are of Type 1.
A conidial type intermediate between Type 1 and
Type 2 was also observed. These conidia were initially hyaline, becoming medium brown, smooth,
cylindrical to subcylindrical, apex obtuse, base obconically subtruncate with a darkened (not thickened
and refractive as in Type 1) scar, and a minute marginal frill, 20–35 × 3–6 µm, (1–)3(–4)-septate. Inside
the conidiomata Type 2 conidia were formed. After 3
mo, these conidia were observed to give rise to Type 3
conidia which were 0(–1)-septate, ellipsoid and hyaline.
Both Type 1 and Type 2 conidia were also generated in cultures on PDA held in the dark for 2 mo.
When the superficial mycelium was lifted away from
2.5-mo-old colonies, wet, dark masses of Type 2
conidia were found in small, well-defined cavities in
the mycelium. The conidia resembled naturally produced Type 2 conidia in shape, pigmentation and scar
characteristics, but were longer, broader, and up to 5septate. Type 2 conidia were sparsely present in
mounts of both superficial hyphae and the fine, feathery mycelium at the more or less flat colony margins.
They had been produced terminally on lateral conidiophores or hyphae of indeterminate length. Type 1
conidia produced in vitro were smooth to verruculose
(the latter especially towards the base), occasionally
verrucose, shorter and fewer-septate than those produced in vivo, but similar in shape and width and
exhibiting the narrow, darkened, slightly thickened
hila of conidia produced in vivo. The outer wall layer
of these Type 1 conidia was often slightly retracted
from the hilum. Cottony mycelium from the colony
surfaces often contained a few small, dense hyphal
aggregates composed largely of clusters of short
conidiogenous cells producing Type 2 conidia. These
conidia tended to be straighter than Type 2 conidia
produced en masse, whether in vivo or in vitro.
DISCUSSION
In this study, we have provided a name for the important fungal pathogen that causes leaf blight specifically on Acacia crassicarpa. Passalora perplexa is
present both in Australia, where it is apparently native,
and in the extensive plantations in Indonesia to which
it has spread. In plantations, the disease associated
with this fungus can be very severe and it is likely to
provide significant challenges for forestry companies
that plant A. crassicarpa. Having a name for the
476
pathogen that causes Crassicarpa leaf blight is an
important step towards the recognition of the disease
and the development of management strategies to deal
with it.
Crassicarpa leaf blight was first noted on Melville
Island, Northern Territory, Australia in 1996 (Yuan
1996). There has been some confusion regarding the
taxonomy of this fungus, particularly because very
little work has been done on the taxonomy of leaf
pathogens of tropical Acacia spp. Thus two fungi, a
species of Pseudocercospora and a species of Cercospora, were recorded on the leaves of A. crassicarpa
and A. mangium respectively. Although the fungi are
readily distinguished, there has been confusion in the
field regarding the causes of the two diseases. Passalora perplexa, described in this study, may be specific
to A. crassicarpa, and certainly appears unable to
infect A. mangium, which shows no signs of the
disease even when planted in close proximity to
heavily infected A. crassicarpa trees.
The pleoanamorphy displayed by P. perplexa is
unusual in that one form could be characterised as a
hyphomycete, a second form represents a coelomycete, and a third morph appears to represent a resting
spore form. Because of this, care was taken to demonstrate unequivocally that Type 1 and Type 2 conidia
did indeed belong to the same fungus. Careful characterisation of the relationship between morphs included
single-spore culturing and connection of the various
forms based on DNA sequence data. The conidiophores of the Type 1 and Type 2 morphs are generated, often concurrently, by cells of the same stroma.
This appears to be a unique feature. Type 3 conidia
were only observed in certain cultures, and we suspect
that this conidial form is associated with the growth
medium or conditions of incubation.
Different anamorphs in single fungal taxa often
develop on conidiogenous cells having distinctly
different morphological forms. These are often associated with different functions such as, for example, rain
dispersal (conidia in wet slimy masses), winddispersal (conidia thin-walled, dry) and survival
(conidia less numerous, larger, pigmented and thickwalled) (Carmichael 1981, Seifert & Samuels 2000).
The conidia of the synanamorphs of P. perplexa differ
in pigmentation and wall thickness, as well as in their
mode of liberation. The hyphomycetous (Type 1)
conidia are ideally suited to wind dispersal, and are
typical of cercosporoid fungi. The coelomycetous
(Type 2) conidia probably require moisture for dispersal, and the Type 3 conidia, which can form inside the
conidial cells of Type 2 conidia in culture, are probably associated with longer term survival.
PASSALORA PERPLEXA AND ITS SYNANAMORPHS
Figs 11–24. Passalora perplexa. 11. Vertical section through an array of conidiomata. 12. Particularly long Type 1 conidiophores on excised sporodochial conidioma. 13. Type 1 conidiophores on sporodochial conidioma. 14, 15. Vertical section
through substomatal conidiomata showing Type 1 conidiophores and Type 2 conidia. 16–17. Vertical sections through conidiomata containing Type 2 conidia but lacking Type 1 conidiophores. 18. Vertical section through conidioma. 19. Type 1
conidium in vivo. 20–22. Type 1 conidia in vitro. 23, 24. Type 2 conidia in vitro. Scale bars = 10 µm.
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BEILHARZ ET AL.
Figs 25–27. Type 2 conidia of Passalora perplexa forming Type 3 conidia (arrows) in vitro. Scale bars = 5 µm.
There appears to be only one previously described
pleoanamorphic cercosporoid fungus. Alcorn (1992)
described Parapithomyces clitoriae Alcorn, which
produced a Pseudocercospora Speg. synanamorph
sporulating from epigenous, erumpent stromata on
leaves of Clitoria sp. In contrast, the Parapithomyces
morph sporulated from conidiophores borne on hypogenous, superficial hyphae. Both spore types of this
fungus were produced in culture from single Pseudocercospora sp. conidia. Intermediate spore types were
also found, as indeed occurred in P. perplexa, in both
instances emphasising the validity of the link between
the respective synanamorphs. In contrast to Passalora
perplexa, both anamorphs of Parapithomyces clitoriae
were hyphomycetes and their conidiophores were
indistinguishable from each other.
Acacia crassicarpa has become one of the most
widely planted plantation tree species in the tropics
and various forestry companies depend on it for the
production of pulp. Early plantings of this tree were
virtually free of disease. Thus the wide-scale appearance of leaf blight caused by P. perplexa, particularly
in Sumatra, is of considerable concern. Earlier records
of Australian collections were referred to Pseudocercospora (Yuan 1996, Old et al. 1997), as the Type 2
synanamorph had not been observed. The present
study represents the first detailed taxonomic evaluation of the causal agent of Crassicarpa leaf blight.
The distribution of P. perplexa on native A. crassicarpa in Australia suggests that it may be indigenous
across the humid tropical north of Australia (Old et al.
1997) and that it has been accidentally introduced into
Indonesia. Although there is no direct proof that this is
the case, we believe that the pathogen has been moved
with seed. This appears to be typical of Mycosphaerella spp. such as those on Eucalyptus leaves that have
been widely distributed throughout the world, largely
in the absence of any movement of plants. The fungi
478
might not specifically occur on seeds, but seed consignments often include fragments of leaves and fruits
that bear fruiting structures of the pathogens. Great
care should thus be taken in the future to prevent the
movement of additional new and devastating pathogens of forest trees (Wingfield et al. 2001).
Virtually nothing is known regarding the biology
of P. perplexa, and this alone represents an important
constraint to efforts to control the leaf blight disease
that it causes. The epidemiology of Crassicarpa leaf
blight will need to be elucidated in order that management strategies to reduce its impact may be implemented. The presence of healthy trees alongside
severely blighted individuals suggests that substantial
opportunity exists to breed and select for tolerance to
this disease.
ACKNOWLEDGEMENTS
James Cunnington, Rebecca Mills (VPRI) and Ewald
Groenewald (CBS) are thanked for valuable assistance in
providing the sequence data for specimens from Australia
and Indonesia, respectively. Mark Dudzinski, Division of
Forestry and Forest Products, CSIRO, Canberra, Australia,
is thanked for kindly providing VPRI with the Australian
specimens. Walter Gams is also thanked for providing the
Latin diagnosis.
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