6 Wood Discoloration

190 8 Habitat of Wood Fungi
(pine), S-group (spruce), and F-group (fir) (Holdenrieder 1989; Siepmann
1989; Capretti et al. 1990; Stenlid and Karlsson 1991; Korhonen et al. 1992). In
North America occur the P- and S-type. The Asian forms are lesser characterized
(e.g., Dai and Korhonen 1999). The three European forms show significant
differences in their distribution and host preference and have been attributed
to three distinct species (Niemelä and Korhonen 1998; Korhonen and Holdenrieder
2005):
Heterobasidion annosum s.s. corresponds to the European P-type of H.
annosum s.l. and may named pine root rot fungus, as it typically occurs
in pine forests. In addition, the fungus attacks Juniperus communis, Picea
abies, P. sitchensis, Pseudotsuga menziesii, Larix decidua, L. x eurolepsis, and
L. kaempferi. The distribution area covers the whole of Europe except for the
most northern forests and possibly the great parts of Siberia.
Heterobasidion parviporum (European S-type of H. annosum s.l.; Spruce
root rot fungus) occurs in Europe nearly exclusively on Picea abies, but as it
seems, it is not found in Western Europe. In Russia, it attacks also Abies sibirica
and in East Asia further Picea and Abies species.
Heterobasidion abietinum (European F-type of H. annosum s.l.; Fir root
rot fungus) occurs in fir forests from the Pyrenees to South Polonia and the
Caucasus, particularly on Abies alba, but also on A. borisii-regis, A. cephalonica
and A. nordmanniana.
The three closely related species can be differentiated by cultural studies,
mating tests and DNA techniques. The hymenium of H. parviporum has small
pores (up to 5 pores/mm) and the upper side shows short hairs, while H. annosum
s.s. has bigger pores and a bald upper side. The features of H. abietinum
often overlap with those of the two former species, but its occurrence on firs
is a suitable clue (Korhonen and Holdenrieder 2005). Hybridization of the
species occurs in the laboratory. A natural hybrid between S- and P-type has
been found in North America, but generally, hybrids occur more easily between
forms from different continents. Regarding the evolution of H. annosum
s.l., the origin of H. parviporum and H. abietinum seems to be East Asia, as
there occurs a form that showed high compatibility with all three species. Assumably,
H. annosum s.l. spread from the eastern Himalayas and has thereby
increasingly differentiated via different routes: H. abietinum arrived in Europe
via the South Asian conifer forests, H. parviporum via northern Asia, and the
American S-type reached North America over the Bering Strait. Not much is
known on the P-types (Korhonen and Holdenrieder 2005). Molecular analyses
have shown a close relation of the genus Heterobasidion to the Russulales.
The following description concerns H. annosum s.l.
Occurrence: common in Europe, North America; predominantly conifers; in
heartwood and rootwood of spruce, larch and Douglas fir; in pine restricted to
the root area due to greater resin content; broad host range of over 200 woody
plants (Heydeck 2000); largest diameter of a genet smaller than 30 m, only in
www.taq.ir