Introduction to Fungi, Third Edition

440 HYMENOASCOMYCETES: HELOTIALES (INOPERCULATE DISCOMYCETES)
Fig15.7 Development of Pyrenopeziza brassicae ascocarps. (a) Immature apothecium,10 days old on oilseed rape.The apical
pore has just formed. (b) 14-day-old apothecium on oilseed rape.The opening is widening due to the expansion of the basal disc.
(c) Mature apothecium 46 days after inoculation onto agar. Reprinted from Gilles et al. (2001), with permission from Elsevier.
Images kindly provided by N. Evans.
(Salamati et al., 2000). The mating type idiomorphs
have been characterized for all species
except Tapesia acuformis (Foster & Fitt, 2004), and
they are of the usual heterothallic/bipolar type.
The biology of the two sister species Tapesia
yallundae on wheat and T. acuformis on rye
(formerly called T. yallundae W and R pathotypes,
respectively) is very similar and has been
reviewed by Fitt et al. (1988) and Lucas et al.
(2000). Eyespot is a major disease in winter
cereals growing in cool climates. Infection is
probably mainly by the needle-shaped conidia
which are formed on overwintered stubble and
spread by rain splash. However, ascospores
released from apothecia (Fig. 15.8a) in early
spring are also infectious. If a spore lands on
the coleoptile of a host plant, it germinates and
produces an aggregate of hyphae termed an
infection plaque (Fig. 15.8b). Numerous melanized
appressoria are formed at the interface
of this structure with the host epidermis, so that
infection of susceptible hosts occurs at several
points (Fig. 15.8c). Penetration is probably
mediated by a combination of turgor pressure
and hydrolytic enzymes. The typical eyespot
(Fig. 15.8d) develops as a greyish-brown lesion
around clusters of infection plaques which may
be visible as the ‘pupil’ of the eyespot. Detailed
studies of infection mechanisms have been
published by Daniels et al. (1991, 1995). The presence
of eyespots at the haulm bases renders the
cereal shoots prone to collapsing. Further infections
can affect the vascular system, resulting
in poorly developed ‘whiteheads’ containing
inferior grain.
Resistance breeding seems to be a promising
strategy for the control of eyespot in cereals
(Lucas et al., 2000). Chemical control is also practised,
but Tapesia spp. have developed resistance
against several types of fungicide (Leroux &
Gredt, 1997).
15.4 Rhytismataceae
The taxonomy of this family is still in a state of
flux (Gernandt et al., 2001). It is sometimes given
ordinal status (Rhytismatales or Phacidiales).
The apothecia are immersed in host tissue or
embedded in a flat stroma. Individual apothecia
become evident when the upper surface breaks
open to reveal the hymenium. There are
219 species in this group at present (Kirk et al.,
2001). Most of them are associated with broadleaved
trees or conifers (Cannon & Minter, 1986;
Johnston, 1997). Particularly difficult genera