Introduction to Fungi, Third Edition

682 ANAMORPHIC FUNGI
Fig 25.8 Endoparasitic
nematophagous fungi. (a c)
Drechmeria coniospora. (a) Dead
nematode containing hyphae, and
bearing emergent conidiophores.
(b) Conidiophores. (c) Mature
conidia showing terminal adhesive
bulbs. (d,e) Harposporium anguillulae.
(d) Dead nematode showing the
extent of internal mycelium, and
external conidiophores.
(e) Enlargement to show details
of conidiophores which bear
subglobose phialides and
sickle-shaped phialoconidia.
and congregate at the bottom of the tube,
from which they can be collected onto tapwater
agar plates and observed by microscopy.
After a few hours’ incubation, non-motile nematodes
may be found, some of them infected with
endoparasitic fungi. These may develop reproductive
structures. Bailey and Gray (1989)
have discussed various isolation techniques for
nematophagous fungi.
25.1.4 Nematode fungus interactions
Stimulation of trap formation
Many nematophagous fungi do not produce
trapping organs in pure culture, but the addition
of nematodes or nematode extracts will
induce their development within 24 48 h. The
inducing molecules include small oligopeptides
containing non-polar and aromatic amino
acids, such as the phenylalanyl-valine dipeptide
(Friman et al., 1985). These are present in
exudates from nematodes (Nordbring-Hertz,
1977). Other substances, such as horse serum or
yeast extract, are also effective in inducing trap
formation, and in natural substrates such as soil
or dung conidia may germinate directly by
formation of a trap (Persmark & Nordbring-
Hertz, 1997).
In general terms, the readiness to form
traps has been found to differ between various
genera and is inversely correlated with their
saprotrophic capacity (Cooke, 1964; Barron,
1992). Nordbring-Hertz and Jansson (1984) have
categorized nematophagous fungi into three
groups. Thus, the net-forming genus Arthrobotrys