Introduction to Fungi, Third Edition

208 ZYGOMYCOTA
Fig 7.37 The eventful life cycle of Basidiobolus ranarum, not to scale. A beetle with attached or ingested ballistoconidia and
capilliconidia is eaten by a frog. In the gut of the frog, both conidial types can undergo cleavage to form endospores, which germinate
by enlargement to form the gut stage. After defaecation, gut-stage cells germinate to produce ballistoconidia or cleave to give the
Palmella stage. Discharged ballistoconidia may germinate by repetition, by forming capilliconidia, or by emitting a hypha. Zygospore
formation is initiatedby conjugation between two adjacent hyphal cells. Small open circles represent haploid nuclei; diploid nuclei are
larger and split. Basidiobolusranarum is homothallic. Key events in the life cycle are plasmogamy (P), karyogamy (K) and meiosis (M).
infections. In horses, infection of the nasal
mucosa is again most probably from soil.
7.5.2 Ancylistaceae: Conidiobolus
There are about 30 species of Conidiobolus, the
‘conidium thrower’. King (1977) has given keys
and descriptions. Most of them grow saprotrophically
in soil and litter and can be readily
isolated by the canopy technique described for
Basidiobolus (see p. 203) because they forcefully
project their conidia. Several species have been
isolated from basidiocarps of the Jew’s Ear
fungus, Auricularia auricula-judae. Some are pathogenic
to insects such as aphids and termites, and
certain species cause disease in mammals
including man. The characteristic feature of
Conidiobolus is the formation of globose multinucleate
primary conidia surrounded by a twolayered
wall whose layers do not separate (Latgé
et al., 1989). The primary conidia are projected
by an eversion mechanism in which the inner
wall of the double-walled conidiophore apex
(‘columella’) suddenly rounds off because of
different mechanical properties of the two wall
layers. The force responsible is turgor pressure.
After discharge, the tip of the columella can be
seen projecting outwards as a conical papilla,
and the base of the discharged conidium ends
in a similar projection (Fig. 7.39b). Spores may
be shot away for up to 4 cm. Germination of
primary conidia may be by repetition producing
the same spore type, by germ tubes (direct