6 Wood Discoloration

7.2 White Rot 139
tarius, T. versicolor and some other fungi shows black demarcation lines (zone
lines) (Fig. 7.2a), by which different species, or incompatible mycelia of the
same species separate themselves from each other, or mycelia dissociate themselves
from not yet colonized wood (“marble rot”, in German: “Marmorfäule”).
The lines result from fungal phenol oxidases, whereby fungal compounds or
also host-own substances are transformed to melanin (Li 1981; Butin 1995).
As a function of the moisture distribution in wood, or between different fungal
species or incompatible genotypes, a compartmentalization of individual
decay centers can result from black pseudosclerotic layers of firmly structured
mycelium (Rayner and Boddy 1988; Eriksson et al. 1990).
Cell wall decay can start by microhyphae producing holes in the secondary
wall (Schmid and Liese 1966), which flow together to larger wall openings with
advancingdecay.Usually,however,thehyphaegrowinsidethelumenwithclose
contact to the tertiary wall. The hypha surrounded by a slime layer (Table 2.1)
excretes the degrading agents, which are active only in direct proximity of the
hypha. Thus, a lysis zone develops under the hypha, and the hypha produces
groovesinthewallwhichisgraduallyreducedinthickness,likearivererodes
the ground (Schmid and Liese 1964; Liese 1970; Fig. 7.2b).
Fig.7.2. White rot. a Simultaneous white rot by Trametes versicolor in beech wood with black
demarcation lines. b Clamped hypha of T. versicolor digging into the cell wall (TEM, from
Schmid and Liese 1964). c Successive white rot by Ganoderma adspersum in the Chilean
“palo podrido” (photo J. Grinbergs). d White pocket rot (photo W. Liese)
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