Introduction to Fungi, Third Edition

402 HYMENOASCOMYCETES: ERYSIPHALES
Fig13.8 Erysiphe polygoni. (a) Chasmothecium showing dark, free-ended equatorial appendages, and the hyaline superficial
mycelium anchoring the chasmothecium to the host leaf. (b) T.S. host leaf showing simple haustorium, superficial mycelium and
conidial chain arising from a foot cell which does not appear bulbous.
crucifers, causing severe infections on cabbage
and Brussels sprouts. It is morphologically
similar to E. betae which is a specialized pathogen
of sugar beet and related hosts (Beta spp.). Erysiphe
polygoni is now considered a separate species of
no commercial interest, forming powdery
mildew on Rumex and Polygonum. Erysiphe pisi is
a cosmopolitan pathogen of leguminous plants
including peas and lucerne. There are several
formae speciales. This species is of particular
interest because much physiological work has
been done on its haustoria which can be isolated
from infected leaves (Gil & Gay, 1977). Another
powdery mildew fungus on Leguminosae is
Erysiphe trifolii infecting mainly clover and with
formae speciales on Trifolium, Lathyrus, Melilotus
and Lotus. Erysiphe heraclei (¼ E. umbelliferarum)
infects umbellifers such as carrot and celery
and is of limited importance in winter crops in
the Mediterranean. It is exceedingly common
on hogweed (Heracleum sphondylium).
All the above species belong to the redescribed
genus Erysiphe, possess a Pseudoidium
anamorph and cluster together in phylogenetic
analyses (Saenz & Taylor, 1999a; Mori et al., 2000).
13.4.2 Microsphaera and Uncinula
Both these genera group together with the main
Erysiphe cluster around E. pisi, E. cruciferarum and
other species described above (Saenz & Taylor,
1999a) and will in due course be called Erysiphe
(Braun et al., 2002) possibly with the addition of
further names reflecting distinct phylogenetic
sub-groups rather than characteristics of chasmothecial
appendages. Anamorphic states belong to
Pseudoidium.
Microsphaera
Chasmothecia of Microsphaera (now Erysiphe sect.
Uncinula) contain several asci, but they carry
appendages with tips showing a highly diagnostic
dichotomous branching (see Fig. 13.10a).
Microsphaera (now Erysiphe) alphitoides is the
cause of oak mildew which is extremely
common, especially on Quercus robur. It appears
from June onwards, infecting mainly leaves
which are produced on sucker shoots and
seedlings, and causing distortions to growing
shoots until growth finally stalls for the rest of
the growing season (Fig. 13.9). The chasmothecial
stage is not always present but may be more