Introduction to Fungi, Third Edition

ASCOSPHAERALES
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ascocarps, and it is thus an exception to the
generalization which places such fungi in the
Archiascomycetes (Chapter 9) or Hemiascomycetes
(see Eremothecium, Galactomyces, Saccharomycopsis;
Chapter 10). Support for the inclusion of
Eremascus in the Euascomycetes comes not only
from molecular data (Berbee & Taylor, 1992a;
Anderson et al., 1998) but also from the presence
of typical Euascomycete septa with one central
pore and associated Woronin bodies (Kreger-van
Rij et al., 1974). Further, the arthroconidia are
delimited by a double-septum (Harrold, 1950)
and are released by rhexolytic secession, which is
typical of certain Plectomycetes (see Fig. 11.3f).
Two species are known, E. albus and E. fertilis
(Fig. 11.1). Both are associated with sugary substrates
such as mouldy jam, but several collections
of E. albus have been made from powdered
mustard. Harrold (1950) has shown that both
fungi grow best on media with a high sugar
content (e.g. 40% sucrose), but do not grow well
in a water-saturated atmosphere. The mature
mycelium consists of uninucleate segments.
Both species are homothallic. On either side of
a septum, short gametangial branches arise
which are swollen at their tips and, in the case
of E. albus, coil around each other. The gametangial
tips of E. albus are usually uninucleate and,
following breakdown of the wall separating the
tips of adjacent gametangia, nuclear fusion
occurs. This is followed by meiosis and mitosis
so that eight nuclei result, each one being
surrounded by cytoplasm to form a uninucleate
ascospore (Fig. 11.1m). The ascospores are
dispersed passively following breakdown of the
ascus wall. On germination a multinucleate germ
tube emerges, but the uninucleate condition is
soon established by the formation of septa.
11.2.2 Ascosphaera
Ascosphaera spp. are associated with bees and
related insects, growing saprotrophically in their
nests on the gathered pollen and nectar. They can
be maintained in pure culture but commonly
Fig11.1 Eremascus.(a d) Eremascus fertilis, stages in the development of asci. (e g) Eremascus albus, stages in the development
of asci. Note the coiling of the gametangia and the globose ascospores of E. albus.(h m) Eremascus albus, nuclear behaviour
during ascus formation (after Harrold,1950). (h) Uninucleate gametangia. (i) Plasmogamy and karyogamy. (k m) Nuclear divisions
preceding ascospore formation.