Introduction to Fungi, Third Edition

322 HYMENOASCOMYCETES: PYRENOMYCETES
Fig12.4 Podospora anserina, ascospore development (based on Beckett et al.,1968). (a) Binucleate ascospore initial enclosed by two
membranes, between which the primary spore wall develops. (b d) The secondary spore wall develops within the primary wall,
and the secondary appendages develop towards each end of the spore by outpushing of the spore membrane. (e g) Development of
tertiary, pigmented wall layer. A further mitotic nuclear division occurs.The uninucleate tail of the spore is cut off from the body of
the spore, and its cytoplasm degenerates, but the tail persists as the primary appendage. Note that the tertiary wall layer does not
extend into the primary appendage. At the opposite pole, a thinner area in the tertiary wall marks the position of the germ pore.
the end of the spore opposite the primary
appendage marks the position of the germ pore
(Fig. 12.4f). The secondary appendages of many
species of Podospora are very elaborate branched
structures.
Mating systems of Podospora
Anamorphs of Podospora species, where known,
consist of dark-celled phialides which produce
small, sticky, unicellular, uninucleate, hyaline
phialoconidia assigned to the anamorph genera
Phialophora and Cladorrhinum. These do not
germinate and are presumed to function as
spermatia (Bell & Mahoney, 1997; Lundqvist
et al., 1999).
The sexual compatibility within the genus
varies. Most species for which information is
available are homothallic, including species with
eight-spored asci such as P. decipiens, and species
with more than eight spores in the ascus, e.g.
P. pleiospora (Lundqvist et al., 1999). Podospora
anserina and S. tetrasporum are pseudohomothallic
(Esser, 1974; Raju & Perkins, 1994). Podospora
anserina normally has four-spored asci, each
ascospore eventually becoming quadrinucleate
following two post-meiotic mitotic nuclear divisions
(see Fig. 12.6). During the final stages of
development three nuclei remain in the main
body of the spore and one nucleus passes into
the primary spore appendage, where it