Introduction to Fungi, Third Edition

RUSSULOID CLADE
571
Fig19.28 The bow-tie reaction between incompatible monospore isolates of Stereum hirsutum. (a) General appearance during
early development; w, watery exudation; b, bow-tie region. (b,c) Abnormal branching of hyphae in the bow-tie region.From
Coates et al. (1981), with permission from Elsevier. Photograph kindly provided by A.D.M. Rayner.
Chondrostereum purpureum
There are several species superficially resembling
Stereum but falling outside the core group
currently placed in the russuloid clade. One
such fungus is Chondrostereum purpureum
(formerly known as Stereum purpureum), with
purplish leathery bracket-like or resupinate
basidiocarps (Plate 10d). Its exact placement in
the Homobasidiomycetes remains to be determined.
It is a wound pathogen of numerous
genera of deciduous trees but especially of
members of Rosaceae, including plum and
cherry trees in which it causes ‘silver leaf’
disease. The silver sheen on the leaves is due to
the separation of the epidermis from the
mesophyll induced by secretions of toxic secondary
metabolites (Strunz et al., 1997) and/or
cellulase- and pectinase-type enzymes (Simpson
et al., 2001) from mycelium in the branches
below the leaves. Although C. purpureum is
of considerable economic importance as a
pathogen of fruit trees, it has been proposed as
a biocontrol agent in forest situations where
coniferous trees are to be grown and broadleaved
trees, such as alder or birch, occur as
weeds (Shamoun, 2000).
Amylostereum
There are several species of Amylostereum related
to each other, but of uncertain placement within
the Homobasidiomycetes (Slippers et al., 2003).
They are necrotrophic wood-rotting wound
pathogens of Pinus spp. and have entered a
species-specific relationship with wood wasps
of the genus Sirex, which distribute conidial
(arthrosporic) inoculum in their internal glands
and deposit it with mucilage surrounding
their eggs, thereby providing the fungus with a
suitable entry route into host trees.
Decomposition of the wood by Amylostereum
spp. facilitates feeding by the Sirex larvae,
which take up inoculum prior to pupation