Introduction to Fungi, Third Edition

DERMATEACEAE
439
Further, B. cinerea is known to produce laccase
and other enzymes which can degrade or
detoxify phytoalexins (Prins et al., 2000). ABC
transporters capable of excluding phytoalexins
from the hyphal cytoplasm have also been
reported from B. cinerea (Schoonbeek et al., 2001;
see also p. 278). Hence, Govrin and Levine (2000)
have suggested that the hypersensitive response
launched by the host actually facilitates, rather
than represses, infection by B. cinerea.
Fungicide resistance
Although biological control strategies against
B. cinerea are being attempted, especially in the
greenhouse and in post-harvest storage of certain
fruit crops, control in agricultural situations
relies chiefly on the application of fungicides.
This is especially the case for the control of grey
mould on grapevines. Botrytis cinerea has developed
resistance against almost all fungicides in
current use, and this may be due to several
factors, e.g. the occurrence of sexual reproduction
in the field, the existence of at least two
genetically distinct ‘species’, and the presence
and spread of transposable genetic elements in
one of them (Giraud et al., 1999). All of these
factors enhance the genetic diversity of populations
of the pathogen, and thus the chances of
development of fungicide resistance. Mechanisms
of resistance of B. cinerea to fungicides
have been discussed by Leroux et al. (2002) and
seem to involve strategies also described from
other fungi, i.e. reduced fungicide penetration
into or enhanced export from the hyphae by
means of ABC transporters, enzyme-mediated
detoxification and degradation of fungicides,
and mutations leading to a reduced binding of
the fungicide to its modified target protein.
15.3 Dermateaceae
This family (385 species) is almost certainly
polyphyletic and it will take some time and
numerous further name changes before the
genera are circumscribed to the phylogeneticists’
satisfaction. The species included here produce
their apothecia directly on the substratum.
Stromata are absent. The apothecia are small
(less than 1 mm in diameter) and rather inconspicuous,
being coloured in grey, brown or black
tones. The development of apothecia has been
described by Gilles et al. (2001) for Pyrenopeziza
brassicae (Fig. 15.7). Apothecia are formed from
hyphae aggregating into small globular structures
resembling sclerotia or cleistothecia. Later
a pore develops at the apex (Fig. 15.7a), and this
increases in diameter by lateral expansion of the
basal disc (Fig. 15.7b) Meanwhile the asci mature
in the hymenium. Ultimately, a flat apothecium
is formed which possesses a clearly defined
margin typical of the Dermateaceae (Fig. 15.7c).
This developmental pattern has been termed
hemiangiocarpic by Corner (1929). The anamorphs
of Dermateaceae are variable. One very
common form (Cadophora) is Phialophora-like,
i.e. the phialides bear an apical collarette
(Harrington & McNew, 2003). Other forms do
not have phialides, and instead long and transversely
septate conidia are produced more or less
directly from vegetative hyphae.
One large genus (Mollisia) is chiefly saprotrophic
and forms apothecia on dead leaves
and fallen twigs, as exemplified by the ubiquitous
Mollisia cinerea which fruits on dead wood
(Plate 7d). Other members of the family are
hemibiotrophic plant pathogens causing limited
lesions on agricultural crops. Pyrenopeziza
brassicae (anamorph Cylindrosporium concentricum)
causes light leaf spot on winter oilseed rape
(Fig. 15.7) whereas Tapesia yallundae (anamorph
Pseudocercospora herpotrichoides) is the cause of
eyespot at the base of cereal stems, especially
winter wheat, and its sister species, T. acuformis,
causes a similar disease especially on rye. The
conidial Rhynchosporium secalis is the agent of
leaf blotch on a range of cereals. All of these
pathogenic species are phylogenetically closely
related (Goodwin, 2002).
15.3.1 Tapesia yallundae and T. acuformis
Apothecia have been found only recently for
both Tapesia species (see Lucas et al., 2000) and
Pyrenopeziza brassicae (see Gilles et al., 2001). They
have not yet been found for Rhynchosporium
secalis, although the high genetic diversity of
field isolates of this species indicates that
sexual reproduction should occur in nature