Introduction to Fungi, Third Edition

ONYGENALES
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Fig11.7 Friesian cattle showing
typical symptoms of Trichophyton
verrucosum infections. Lesions are
indicated by arrows.The circular
lesion around the eye is
particularly large because the
animal has spread the infection
by rubbing.
culture media, in addition to the clinical
symptoms (see Weitzman & Summerbell, 1995).
All Arthrodermataceae appear to be heterothallic.
Different strains of A. simii can induce enhanced
growth but not complete mating and
gymnothecium formation in strains of opposite
mating type of a range of other species
(Stockdale, 1968). Using this feature as a test
system, it has been found for most anthropophilic
species that all known isolates are of only one
mating type, e.g. ( ) for T. rubrum. Since the
Arthroderma state of dermatophytes is found only
on substrates in contact with soil (Summerbell,
2000), the lack of sexual reproduction in most
anthropophilic species may be the result of
adaptation to a highly patchy and specialized
habitat (Howard et al., 2003).
Geophilic members of the Arthrodermataceae
are best isolated from soil or other substrata
enriched in hair, skin or feathers (e.g. rodent
burrows or birds’ nests) using horse hair or
human hair as bait. Gymnothecia can be picked
up with the aid of a dissection microscope,
and transferred to a suitable medium such as
Sabouraud agar (Sharma et al., 2002).
11.3.3 Gymnoascaceae
The Gymnoascaceae are a small family (10 genera,
23 species; Kirk et al., 2001). A recent phylogenetic
study is that by Sugiyama et al. (2002). Members
of the Gymnoascaceae are isolated mainly from
soil and are saprotrophic, degrading keratin and
also cellulose. The genus Gymnoascus has
been described by von Arx (1986). Gymnoascus
reessii is a species commonly encountered on
herbivore dung, producing strikingly coloured
gymnothecia which are at first yellow, then red
and finally brown as the ascospores mature. The
reticulo peridium consists of branched, recurved,
thick-walled hyphae loosely enclosing a mass of
asci (Fig. 11.8). Ascocarp development can be
followed readily in culture and begins from
paired gametangia which arise from the same or
different hyphae. The antheridium is club-shaped
and the ascogonium coils around it (Fig. 11.9a).
The ascogonium then becomes septate and its
cells give rise to ascogenous hyphae (see Fig.
11.9b), whose tips develop into croziers. Asci
develop from the penultimate cells of the croziers
(Kuehn, 1956). The branched reticulo peridial
hyphae arise from vegetative hyphae in the
region of the gametangium (Figs. 11.9b,c). The
asci do not discharge violently; the ascus wall
disappears and the spores escape through the
loose envelope. There is no conidial stage.
11.3.4 Myxotrichaceae
This family contains 4 genera (12 species).
Anamorphs are Oidiodendron or Malbranchea.
The genus Oidiodendron may have important