6 Wood Discoloration

232 8 Habitat of Wood Fungi
with its resistant arthrospores. Furthermore, the resistance at 20 ◦ Camounted
only about 1 year. Only at low temperature (7.5 ◦ C), the fungus survived several
years (Theden 1972; also Savory 1964). Nevertheless, the remaining infected
areas form a danger potential for new growth. Infected timber parts can exhibit
just so much moisture to enable a slight growth and thus a longer survival
than by means of dryness resistance (Grosser 1985). Furthermore, the danger
of re-infection may derive from the dryness-resistant spores, whose duration
of germ ability was said to amount to 20 years. In infected buildings, S.
lacrymans frequently produces basidiospores, and basidiospores seem to be
the main agent of dispersal (Falck 1912; Langendorf 1961; Schultze-Dewitz
1985). Vegetative spread by mycelium and strands seems to be restricted to
within buildings or the soil in subfloor space (Doi 1991). However, according
to Wälchli (1980) the infection occurs instead by mycelium that is brought in
with timber from other remedial treatments and via wooden boxes or shoes.
Beside the requirement for low temperature, the preferential indoor occurrence
of S. lacrymans was attributed to the intensive synthesis and secretion of
oxalic acid (Jennings 1991; cf. Table 3.9), whose excessive production was said
to be neutralized as calcium oxalate by calcium from masonry or by chelating
with iron from girders (Bech-Andersen 1985, 1987a, 1987b; cf. Palfreyman
et al. 1996). Oxalic acid is also implicated in copper tolerance of fungi. Although
a single isolate of S. lacrymans was only able to grow on agar at a low
concentration of copper sulphate (Table 3.10), Haustrup et al. (2005) showed
11outof12isolatestobetolerantagainstcoppercitrate.Theimplicationof
calcium in oxalate precipitation was also shown for M. incrassata (Jellison et al.
2004). Thus, dry rot attack in buildings is often found in the ends of beams,
which are not separated from the masonry.
During controversies, e.g., in the context of house buying, frequently the
question of the infection date plays a role, for whose determination the daily
average mycelial growth is often used. According to Jennings (1991), the linear
mycelial extension on wood, masonry and insulants ranges from 0.65 to
9mm/d. Assuming a 5-mm radial increase per day on malt agar at optimal
temperature (Table 2.2), 15 cm follow per month. Due to the changing and
not always optimal conditions in buildings and because different isolates of
the fungus exhibited considerable differences in growth rate [1.5–7 mm/d: Cymorek
and Hegarty (1986a); Seehann and v. Riebesell (1988)], an exact age
determination on the basis of the mycelial extension is impossible. Similarly,
the decay of pine sapwood samples varied among 25 isolates from 12 to 56%
in 6 weeks of cultivation (Cymorek and Hegarty 1986a; Thornton 1991), and
different isolates differed likewise in their sensitivity to wood preservatives
(Abou Heilah and Hutchinson 1977; Cymorek and Hegarty 1986a; Wa˙zny and
Thornton 1989a, 1989b, 1992; Wa˙zny et al. 1992). Important is also the decision
if the mycelium in a building is alive or dead. Subculturing on malt agar is
possible, but isolations from mycelium are often contaminated by molds. Vital
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