Introduction to Fungi, Third Edition

PLEOSPORALES
475
Fig17.14 Curvularia spp. (a) Curvularia lunata, the conidial state of Cochliobolus lunatus.Conidiophores showing sequence of conidial
development. (b) Mature detached conidia of C. lunata. Note the paler end cells. (c) Mature detached conidia of C. cymbopogonis
showing the protuberant hilum.
The pathology of Cochliobolus
Cochliobolus has been examined by DNA sequencing
methods (Berbee et al., 1999), which revealed
two separate groups. All important pathogens
belong to one group and have Bipolaris
anamorphs. In general, the teleomorphs are
rare or absent in nature, and the diseases are
carried mainly by the thick-walled conidia,
which can survive in the soil but can also infect
seeds. Cochliobolus sativus (B. sorokiniana) is the
cause of a variety of root and leaf necroses of
cereals (especially wheat and barley) in warm
humid climates of South East Asia, Australia,
North and South America. A good review of its
biology has been written by Kumar et al. (2002).
It is a typical hemibiotrophic pathogen which
forms quiescent infections in the first-infected
epidermal cell, followed by a necrotrophic phase
in which the surrounding tissue is aggressively
invaded. This pathogen shares with Botrytis
cinerea (see p. 435) the ability to evade the
oxidative burst launched as a defence response
by the newly infected host (Kumar et al., 2001).
Several sesquiterpene-type toxins are produced
and contribute to a weakening of the host;
prehelminthosporol (Fig. 17.15a) seems to be
the most potent. These toxins act in a nonspecific
manner on several different cellular
processes. Interestingly, barley cultivars possessing
the mlo-type resistance against powdery