Introduction to Fungi, Third Edition

EXAMPLES OF MUCORALES
193
distribution of these fungi (Kirk, 1993). The
zygospores proper, when extruded from their
zygosporangia, also have striate walls.
Choanephora
Choanephora cucurbitarum is a weak pathogen
causing soft rot and wet rot diseases of a wide
range of tropical and subtropical plants such as
okra, chilli pepper, cowpea and Amaranthus. It
also grows on decaying flowers of various kinds.
Infection of male inflorescences of Artocarpus
integer (Moraceae) by Choanephora attracts gall
midges which feed on the mycelium and build
up large populations on the decaying flesh of the
inflorescence. The gall midges are probably
involved in pollination of the female inflorescences
of Artocarpus (Sakai et al., 2000).
Asexual reproduction is by two types of
structure, drooping multisporous sporangia and
monosporous sporangiola (‘conidia’) borne on
separate sporangiophores (Fig. 7.26). The development
of sporangia is stimulated by growth on
carbon-limited media and temperatures around
30°C, whilst the optimum temperature for
sporangiolum formation is around 25°C. Light
is essential for sporulation. The sporangia are
columellate or non-columellate and dehisce into
two halves along a line of weakness. The
sporangiospores have brown walls with longitudinal
grooves appearing as striations, and
bear a group of hyaline tapering appendages at
each pole. These appendages may play a role in
the dispersal of the spores in water films since
they only become extended if the sporangium
dehisces in water (Higham & Cole, 1982).
Sporangiola develop on globose vesicles at the
tips of separate sporangiophores, each of which
may bear about 100 sporangiola. The sporangiolum
is multinucleate and the spore within
it develops a separate thick, brown, ridged
Fig 7.26 Choanephora cucurbitarum.
(a) Sporangiophore with drooping sporangium.
(b) Sporangiophore (‘conidiophore’) with
numerous monosporous sporangiola (‘conidia’).
(c) Apex of conidiophore showing swollen
vesicles bearing conidia. (d) Dehisced
sporangium showing striate spores with
terminal appendages. (e) Conidium.
(f) Sporangiospore. (c) and (d) to same scale.