6 Wood Discoloration

116 5 Damages by Viruses and Bacteria
In logs, which were stored for protection from decay fungi, staining and
insect attack in the open (v. Aufseß 1986; Schmidt et al. 1986) or were sprinkled
(sprayed) or water-stored (ponded) (Karnop 1972a, 1972b; Berndt and Liese
1973; Schmidt and Wahl 1987), bacteria degraded in situ within a few weeks
the non-lignified margo fibrils of the sapwood bordered pits (Fig. 5.4). Several
bacterial isolates were obtained (Schmidt and Dietrichs 1976). The increased
wood porosity may cause wood cracks during artificial drying and an irregular
over-uptake of preservative solutions, varnishes, stains, or paints resulting in
uneven finishes (Willeitner 1971). Wood spots due to increased permeability
and bad smell of bacterial metabolites are current problems when wet-stored
wood is used for indoor wood paneling.
Timber in service is colonized by bacteria, if the wood is very wet and thus
less suitable for fungi due to reduced oxygen content. Early reports (Liese
1950; see Fig. 5.3a) on bacterial degradation refer as to wood in long-lasting
ground contact (Levy 1975b), as in foundation piles, sleepers, or to wood
in water, like in cooling towers, harbor constructions and boats (Liese 1955).
Cell wall degradation even occurred in chromium-copper-arsenic-treated piles
and poles (Willoughby and Leightley 1984; Singh and Wakeling 1993). The
bacteria dissolved the toxic components and thus favored wood degradation
by soft-rot fungi (Daniel and Nilsson 1985). Wood samples impregnated with
chromium-copper-arsenate and incubated with bacterial pure cultures showed
increased wood mass loss during subsequent incubation with Coniophora
puteana (Willeitner et al. 1977).
Bacteria are often found in archaeological woods from buried and waterlogged
environments (Blanchette 1995; Björdal et al. 1999; Kim and Singh 1999,
2000; Singh et al. 2003; Björdal et al. 2005; Schmitt et al. 2005). In those wet
conditions, bacterial wood degradation is often associated with soft-rot fungi
(Willoughby and Leightley 1984; Singh et al. 1991; Singh and Wakeling 1993).
Fig.5.4. Destruction of a pine sapwood
bordered pit showing the detachment of
the torus(T) by bacterial (B)degradation
of the margo fibrils. (REM, from Peek
and Liese 1979)
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