Introduction to Fungi, Third Edition

ZOOPAGALES
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5 families and 20 genera but we shall study only
the Piptocephalidaceae, earlier classified in the
Mucorales.
7.4.1 Piptocephalidaceae
This family includes Piptocephalis and Syncephalis,
both mycoparasites. DNA sequence analysis
suggest that these two genera are not closely
related (Tanabe et al., 2000). Piptocephalis is a
biotrophic haustorial parasite which needs the
presence of a susceptible host for good growth
and reproduction (Manocha, 1975), although on
certain agar media Piptocephalis spores will
germinate and give rise to a limited mycelium
producing dwarf sporangiophores. The spores so
formed are unable to germinate if transferred to
fresh agar, but they do germinate and infect a
suitable host fungus if one is present. Syncephalis
develops intrahyphal hyphae within the host
mycelium and can be grown more readily in
culture if supplied with appropriate nutrients
(Jeffries & Young, 1994).
Piptocephalis
Most of the 20 or so known species of Piptocephalis
(Gr. pipto ¼ to fall, kephale ¼ head) parasitize the
mycelium of Mucorales, with P. xenophila exceptional
in its ability to infect members of the
Ascomycota. Species of Piptocephalis are most
abundant in the surface layers of soils where
there is a rapid recycling of organic matter,
such as in woodland and in grazed grassland
(Richardson & Leadbeater, 1972). They also parasitize
Mucorales on dung. A characteristic habitat
for P. freseniana is herbivore dung towards the
end of the fruiting phase of Mucor and Pilaira.
From an infected host mycelium Piptocephalis
develops an erect dichotomous sporangiophore
(Fig. 7.33a). Swollen nodulose (knobbly) head
cells form at the tips of the branches (see
Fig. 7.33c), and from these cylindrical merosporangia
radiate outwards. The merosporangia are
thin-walled and usually contain from one to
several multinucleate merospores, arranged in
a single row. Piptocephalis unispora is unusual in
that its merosporangia contain only a single
sporangiospore. Its merosporangial wall encloses
the sporangiospore which has a two-layered wall
and may contain 1 3 nuclei (Jeffries & Young,
1975). At maturity Piptocephalis merosporangia
behave in two different ways (Ingold & Zoberi,
1963). In some species the thin sporangial wall
collapses around the spores which remain
attached together as spore rods, appearing as
short chains (see Fig. 7.33c). Alternatively, as in
P. freseniana, the merosporangial wall becomes
diffluent and all the spores in a head collapse
to form a spore drop. In some species the whole
head cell with its attached merospores becomes
detached at maturity. All types of propagule can
be dispersed by wind.
On germination sporangiospores swell and
emit one to several germ tubes (McDaniell &
Hindal, 1982). There is a chemotropic attraction
Fig 7.33 Piptocephalis virginiana. (a) Habit
sketch to show dichotomous sporangiophore.
(b) Head cell and intact merosporangia.
(c) Head cells showing breakdown of
merosporangia to form chains of spores.
(d) Spore germination and formation of
appressorium on a host hypha.
(e) Appressorium and branched
haustorium on host hypha.The parasite
mycelium is branched and extending to other
host hyphae. (f) Zygospore.The fungus is
homothallic. (b e) to same scale.