Introduction to Fungi, Third Edition

GLOMALES
217
become infected with E. muscae, making it a
sexually transmitted pathogen. Although it was
previously generally accepted that there are no
rhizoids in E. muscae, Balazy (1984) has shown that
rhizoids do develop from hyphal bodies within
the head, growing through the proboscis and
forming a network of branched hyphae with
short irregular holdfasts. A few days after infection
the fly dies and the hyphal bodies within
the abdomen then grow out into coenocytic
hyphae which penetrate between the abdominal
segments and develop into conidiophores.
Discharge of primary conidia begins within
about 5 h, reaching a maximum about 10 12 h
after death. Over 8000 conidia may develop from
a single cadaver (Mullens & Rodriguez, 1985).
The primary conidia remain viable for only
3 5 days. If they fail to penetrate a fly, they may
produce secondary conidia within 3 h. The
secondary conidia are released from the tips of
short conidiophores by septal eversion. They may
germinate by a germ tube or by producing the
same type of conidium by repetition.
Within the body of the dead fly, multinucleate
spherical resting bodies (azygospores) are formed.
In the wheat bulb fly Leptohylemia coarctata it has
been observed that a much higher proportion of
infected female flies contain resting bodies as
compared with infected males. This is probably
associated with the longer lifespan of females
than males (Wilding & Lauckner, 1974). Resting
bodies may develop terminally or in an intercalary
position from short hyphae, or by budding
from hyphal bodies. They germinate by developing
a germ conidiophore. Germination is stimulated
by the action of chitin-decomposing
bacteria on the resting spore wall. It is from
such resting bodies that infection probably
begins each year (Goldstein, 1923).
The onion fly Delia antiqua has maggots which
pupate in the soil and overwinter there. Adults
become infected as they emerge through the
soil the following season, presumably from germ
conidia which develop from resting spores
(Carruthers et al., 1985). In some members of
the Entomophthorales, e.g. Entomophthora sepulchralis,
zygospores develop following conjugation
between hyphal bodies (see Fig. 7.44).
Entomophthora muscae, like many other
entomopathogenic Entomophthorales, can be
grown in complex media such as those used in
tissue culture (Wolf, 1981; Papierok & Hajek,
1997). Yeast extract and ingredients of animal
origin such as egg yolk, fat and serum or blood
are also used. Growth is markedly stimulated by
glucosamine, a breakdown product of chitin.
Successful cultures have also been established
on a medium containing wheat grain extract,
peptone, yeast extract and glycerol (Srinivasan
et al., 1964).
Furia
Some of the species formerly placed in the
genus Entomophthora have features distinct
from E. muscae and have been re-classified into
different genera. An example is Furia americana
(Plate 3h, Fig. 7.45), a fungus found on blowflies
in the autumn, especially around corpses of dead
animals or stinkhorns. In wet weather severe
epidemics may occur, greatly affecting the
blowfly population. Distinctive features are the
conidiophores which branch close to the conidiogenous
cells; uninucleate, bitunicate clavate
conidia with a rounded apex and basal papilla;
and discharge by septal eversion. Dead flies are
often attached to adjacent plants by filamentous
rhizoid-like hyphae. The conidiophores form
yellowish pustules between the abdominal
segments and the branched tips bear conidia.
The two layers of the conidium wall are
frequently separated from each other by liquid
(Figs. 7.45a c). These conidia are projected for
several centimetres from the host and, on germination,
may form germ tubes, or may produce
secondary conidia which are projected by the
rounding off of a two-ply septum. Within the dry
body of the dead fly numerous smooth hyaline
thick-walled resting spores (azygospores) are
formed by budding from the lateral walls of
parent hyphae (Fig. 7.45f).
7.6 Glomales
The roots of most terrestrial plants grow in
a mutualistic symbiosis with fungi, i.e. an
association in which both partners benefit.