Introduction to Fungi, Third Edition

ERYSIPHE
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that B. graminis survives mainly in the vegetative
state on overwintering host plants, especially
winter varieties of cereals (Jenkyn & Bainbridge,
1978). To survive a single growing season,
B. graminis may have to switch four times between
winter barley and summer barley main
crops and their volunteers germinating after
harvest (Limpert et al., 1999). The availability of
living shoots for infection throughout the year is
called the ‘green bridge’. In contrast, in hot and
arid regions such as the Mediterranean, chasmothecia
play a role in the oversummering of the
pathogen on wild grasses such as Hordeum
spontaneum, discharging ascospores when the
host seeds germinate in autumn (Clarke &
Akhkhra, 2002). Since B. graminis seems to have
its centre of origin in the Middle East, it is
possible that the chasmothecia are primarily
oversummering rather than overwintering
structures.
13.4 Erysiphe
The genus Erysiphe is currently subject to
major taxonomic rearrangements. Erysiphe has
traditionally been defined by chasmothecia
with undifferentiated mycelioid appendages
(Fig. 13.8a), and was later distinguished from
Blumeria by its knob-like haustoria and a cylindrical
(non-swollen) conidial foot cell (Fig. 13.8b).
This anamorph gives rise to one conidium at a
time, i.e. it is non-catenate. It is called Pseudoidium.
Erysiphe spp. now fall into several branches of
phylogenetic trees, and they are interspersed by
species which have similar anamorphs but chasmothecia
with uncinate or lobed appendages
(Saenz & Taylor, 1999a; Mori et al., 2000). Braun
et al. (2002) therefore proposed the absorption of
genera such as Microsphaera and Uncinula into
Erysiphe. The most important species of Erysiphe in
an agricultural context (Spencer, 1978; Smith
et al., 1988) are mentioned below. They seem to
share the fundamental biological principles of
infecting by wind-dispersed conidia which do not
require or even tolerate free water, and causing
disease symptoms as a superficial mycelium
producing haustoria only in epidermal cells.
13.4.1 Erysiphe sensu stricto
Erysiphe cruciferarum (formerly part of E. polygoni
sensu lato or E. communis) is a pathogen of
Fig13.7 Blumeria graminis. (a) Mat of superficial hyphae with
a sectioned chasmothecium containing several asci. (b) Ascus.