Introduction to Fungi, Third Edition

196 ZYGOMYCOTA
sporangiospores, each with 1 3 nuclei. The
cleavage process is similar to that found in
other Mucorales (Fletcher, 1972). The sporangial
wall shrinks at maturity so that the spores
appear in chains reminiscent of Aspergillus.
Occasionally the merospores may lie in more
than a single row. The spore heads remain dry
and entire rows of spores (spore rods) are
detached by wind (Ingold & Zoberi, 1963).
Syncephalastrum racemosum is heterothallic and
forms zygospores resembling those of other
Mucorales.
7.3.7 Cunninghamellaceae
In this family, asexual reproduction is entirely by
means of monosporous sporangiola. Sporangia
are not formed. There is a single genus.
Cunninghamella
There are about 12 species of Cunninghamella,
found in soil in the warmer regions of the world,
e.g. the Mediterranean and subtropics (Domsch
et al. 1980; Zheng & Chen, 2001). Cunninghamella
elegans and C. echinulata are saprotrophs but C.
bertholettiae is a serious, sometimes fatal, human
pathogen. Cunninghamella echinulata may also be
a destructive mycoparasite of Rhizopus arrhizus.
Cunninghamella elegans and C. echinulata have been
used in a wide range of biotransformations of
pharmaceutical products (Kieslich, 1997). DNA
sequence studies have grouped C. echinulata with
some of the genera traditionally classified in
Mucoraceae (O’Donnell et al., 2001), but comparisons
of fatty acid and cell wall composition of
Cunninghamella japonica and Blakeslea trispora
have suggested that Cunninghamella is related to
members of the Choanephoraceae, a conclusion
reached also on morphological criteria by some
other workers.
The sporangiola of Cunninghamella are hyaline
and clustered on globose vesicles (ampoules)
on branched or unbranched sporangiophores
(Fig. 7.29). They are sometimes referred to as
conidia, but details of their development indicate
that they are best interpreted as one-spored
sporangiola. Khan and Talbot (1975) have studied
sporangiolum development in C. echinulata. The
ampoules are club-shaped, globose or pearshaped
and bear spherical sporangiola, each
arising from a tubular denticle. Localized areas
of weakness in the ampoule wall, yielding to
turgor pressure, blow out to form the denticles.
The wall is two-layered in the ampoule and
denticle, but single in the developing sporangiolum
where it develops hollow spines all over the
surface. Within the sporangiolum wall a twolayered
wall develops around the multinucleate
protoplast. Hawker et al. (1970) have studied the
structure and germination of sporangiola in
a species of Cunninghamella. Here, too, the wall
Fig 7.29 Cunninghamella echinulata. (a) A
simple and a branched sporangiophore.
(b,c) Apices of sporangiophores showing
expanded vesicles developing
sporangiola. (d) Apex of mature
sporangiophore with cluster of
attached and two detached
spiny-walled sporangiola. Scale bar (a) ¼
25 mm, (b d) ¼ 10 mm.