Introduction to Fungi, Third Edition

RUSSULOID CLADE
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Fig19.26 Basidiocarps in the russuloid clade. (a) Russula atropurpurea.(b)Heterobasidion annosum, the cause of butt rot of conifers.
(c) Stereum hirsutum basidiocarps growing on an oak branch viewed from above. Note the white-rot at the broken end of the
wood. (d) As (c) but viewed from below to show the smooth hymenium. (e) Auriscalpium vulgare basidiocarps growing from a
buried pine cone.The hymenium is borne on spines on the lower side of the cap.
the family Bondarzewiaceae (Larsson & Larsson,
2003).
Biology of Heterobasidion
Heterobasidion annosum (Fig. 19.26b) is the cause of
heart rot or butt rot of managed conifer
plantations, and occasionally of deciduous trees
such as birch in North-temperate regions
(Korhonen & Stenlid, 1998; Asiegbu et al., 2005).
It is the most important pathogen of conifers
in these areas. The disease is especially common
on alkaline soils. The fungus is a necrotrophic
parasite whose mycelium extends downwards
into the root system and upwards into the stem,
causing a stringy heart rot which damages the
strength and affects the saleability of the wood.
Root decay is often followed by wind throw. The
fungus may survive in the root system, especially
if it is resinous, for over 60 years. In Europe, three
somatic incompatibility groups have been distinguished,
an ‘S’ group (S for spruce) confined to
Norway spruce (Picea abies), a ‘P’ group which