Introduction to Fungi, Third Edition

ENTOMOPHTHORALES
209
Fig 7.38 Basidiobolus ranarum. Successive
stages in the formation of zygospores.
(a) Progametangia. (b) Young zygospore.
(c) Mature zygospore.
germination), by the formation, in some species,
of numerous microconidia, or by the development
of capilliconidia resembling those of
Basidiobolus. Zygospores or azygospores have
been reported and all species which reproduce
sexually in this way are homothallic. It is
believed that the cytological condition of the
nuclei is haploid, as it is in other Zygomycota,
and that karyogamy and meiosis are involved in
the formation of zygospores and azygospores
(McCabe et al., 1984).
The best-known species of Conidiobolus is the
cosmopolitan C. coronatus, a fungus which has
been referred to under various names, e.g.
Entomophthora coronata, Delacroixia coronata and
Conidiobolus villosus. It grows readily and rapidly
in agar culture, forming a septate mycelium and
numerous phototropic conidiophores (Fig. 7.39)
which shoot off conidia onto the lid of the Petri
dish. Conidial discharge takes place both in the
light and in the dark, but is enhanced by light
(Callaghan, 1969a).
The behaviour of a conidium on germination
depends on pH, humidity, availability of light,
and nutrients. If the conidium falls on a medium
containing nutrients, it germinates by means of a
germ tube, but on nutrient-poor media, such as
water agar, it may develop into a secondary
conidiophore, forming a slightly smaller conidium
(Fig. 7.39c). The secondary conidiophore
develops from the illuminated side of a primary
conidium, and the conidiophore which develops
is phototropically orientated, but not very
precisely (Page & Humber, 1973). Under conditions
of reduced humidity the primary conidia
may develop a cluster of globose microconidia
(Fig. 7.39f). The entire cytoplasm of the primary
conidium is evacuated by the expansion of a large
vacuole into numerous buds formed by localized
softening of the primary conidium wall. At