Introduction to Fungi, Third Edition

466 LOCULOASCOMYCETES
Fig17.7 Phoma betae. (a) L.S. pycnidium. (b) Portion of
pycnidium wall, showing conidiogenous cells and conidia.
develops a thickened rim which resembles a
phialide or an annellophore (annellide). Sutton
(1980) has interpreted these spores as
phialoconidia.
Phoma epicoccina is an unusual species because
it possesses a hyphomycetous synanamorph,
Epicoccum nigrum (Fig. 17.8), which is very
common on decaying plant material and in the
soil. The Epicoccum state takes the form of
cushion-shaped sporodochia, which are black or
purplish-red in colour and covered with roughwalled,
warted, segmented, brownish-red conidia
(Fig. 17.8a). The conidia may be violently
projected from the sporodochium, probably by
the rounding off of the two turgid cells on either
side of the septum which separates the conidium
from its conidiophore (Fig. 17.8c; Webster, 1966).
It is possible that conidial discharge is stimulated
by drying because the peak concentration
of Epicoccum spores in air occurs shortly before
noon (Meredith, 1966). The synanamorphic
nature of P. epicoccina and E. nigrum has been
conclusively demonstrated only relatively
recently (Arenal et al., 2000).
17.2.4 Pleospora
Estimates of the number of species of Pleospora
vary, and Kirk et al. (2001) suggested that there
are about 50. Most species form fruit bodies on
moribund herbaceous stems apparently as saprotrophs,
but some are weak pathogens. Of these,
P. bjoerlingii (¼ P. betae) is the cause of blackleg
of sugar beet. Pleospora scirpicola forms its pseudothecia
on the underwater parts of the culms
of the bulrush, Schoenoplectus lacustris, and was
the first fungus in which the ‘jack-in-the-box’
mechanism of discharge of bitunicate asci was
illustrated (see Fig. 17.1).
Pleospora herbarum attacks a wide range of
cultivated hosts, causing such diseases as net
blotch of broad bean and leaf spot of clover,
lucerne and other hosts. It may be seed-borne.