6 Wood Discoloration

194 8 Habitat of Wood Fungi
violet striping), then a “bright hard rot” (light brownish, wood still firm), later
a “dark hard rot” (brownish-red, only wood structure remaining) and finally
a “soft rot” (Fig. 8.14B; Zycha 1964), where the wood is fibrously dissolved
and interspersed with small, white spindle-like nests with a black center of
manganese deposits (Fig. 8.14C) (Hartig 1978; see Chap. 7.2).
Imperiled for H. annosum are first plantings on formerly agriculturally
used pasture soils and arable lands (“field-dying”, German: “Ackersterbe”).
Conifers on base-rich and compacted ground, and on sites with very variable
moisture content suffer more from the disease than those on acidic, more open
soils with a more uniform water supply (Butin 1995; Schönhar 1997; Heinsdorf
and Heydeck 1998). The inhibition of acidophilic, antagonistic mycorrhizas
may play a role. A direct control is difficult, and only preventing measures are
used (Schönhar 1990, 2002b). Rooting out and removing the infected stumps
as well as isolating the infected sites by ditches are difficult and not always
successful (Schönhar 1989). The most effective measure is to perform thinnings
during the wintertime, as spore infection decreases during frost (Korhonen
and Holdenrieder 2005). In not-yet-infected first plantings, the stumps which
are the starting point for a propagation of the fungus via root grafts, have
been coated on the fresh surface with carbolineum, which however delays the
stumpdecomposition.Immediatetreatmentofthefreshsurfacewithasodium
nitrite solution prevented spore germination of H. annosum.Aschemical,also
urea (Schönhar 2002b) and boron compounds are used (Pratt 1996). Originally
in the U.K and later in Scandinavia and further European countries, a spore
solution of the antagonistic fungus Phlebiopsis gigantea is immediately applied
to the fresh stump surface of pines (Meredith 1959; Rishbeth 1963; Schwantes
et al. 1976; Lipponen 1991; Gibbs et al. 2002) and spruce (Korhonen et al. 1994;
Holdenrieder et al. 1997). There are spore preparations, which are specifically
suited for spruce, but generally, P. gigantea is more suitable for pines. The
wood can be automatically inoculated with spores through holes in the saw
blade of the harvester (Metzler et al. 2005). The antagonist overgrows the
stump cross surface, so that H. annosum cannot colonize it by spores. Thus, an
infection of neighboring trees over root grafts is prevented. Further antagonists
to H. annosum are treated by Holdenrieder and Greig (1998) and compiled by
Woodward et al. (1998).
Root graft transmission can be reduced by far planting faces and admixture
of hardwoods. Lesser sensitive hardwoods as well as fir or larch should be
selected for particularly endangered sites instead of spruce and pine. In vitro,
mycelial growth was inhibited by stilbenes, flavonoids and lignans (Zycha et al.
1976; Shain and Hillis 1971; Yamada 1992). Breeding attempts with the aim of
red-rot resistant tree clones were performed, but did yet not reach a practical
use. Recent resistance research mainly deals with the genetic mechanisms of resistance
and the physiology of defense reactions (Korhonen and Holdenrieder
2005). Viruses in the root rot fungus, which are morphologically similar to the
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