6 Wood Discoloration

246 9 Positive Effects of Wood-Inhabiting Microorganisms
9.4
“Palo Podrido” and “Myco-Fodder”
In the evergreen temperate rainforests of southern Chile, Philippi (1893) found
in the heartwood of dying and fallen hardwoods (Eucryphia cordifolia, Nothofagus
spp. and other trees) a white, spongy-wet wood tissue (Fig. 9.4a, also
Fig. 7.2c), which may occupy the entire interior of logs. This white-rotted
wood, called “palo podrido” (rotted wood) or “huempe”, develops by the action
of Ganoderma species like Ganoderma adspersum (Martínez et al. 1991a,
1991b; Barrasa et al. 1992; Bechtold et al. 1993) and other white-rot Basidiomycetes,
associated yeasts and bacteria (González et al. 1986), in the moist
forest climate during a long time. Environmental factors such as a lack of
desiccation and frost during the year in tropical forests may have reduced
the mechanical stress on the wood and maintained conditions that promote
delignification (Eriksson et al. 1990). Low nitrogen content of the wood was
considered to be a major factor that contributed to this selective delignification
(Dill and Kraepelin 1986). Black manganese deposits indicating the correlation
to manganese peroxidase have been found in palo podrido by Barrasa et al.
(1992) and others. Rodriguez et al. (2003) detected several iron-chelating catechol
compounds in palo podrido samples, whose relation to lignin or fungal
metabolites remained however unclear.
Palo podrido has been used by rural population as feed for foraging cattle.
Healthywood,eveningrindedform,hasaverylowrumendigestibility.Thus,
the development of palo podrido by the action of fungi may be termed as
“biological wood pretreatment”. Due to the fungal delignification particularly
in the area of the middle lamella/primary walls, the woody tissue is loosened
and now edible by cattle. Figure 9.4b demonstrates that the Chilean cow prefers
the pineapple-like palo podrido (Fig. 9.4a) to the surrounding grass. Mainly
through the opening of the wood structure, now the anaerobic rumen bacteria
cangetaccesstothedigestiblewoodcarbohydrates.Thereductionofthelignin
content from 22% of healthyNothofagus wood to about 6%in the corresponding
palo podrido sample (Dill and Kraepelin 1986) may have promoted bacterial
activity, but is probably no premier factor, as it has also been stated for the
bacterial degradation of chemically pretreated wood (Chap. 5.2). The rumen
bacteria convert the wood carbohydrates in palo podrido to fatty acids like
acetic, propionic, and butyric acid. This fermentation is the “biotechnological”
part of palo podrido. Last, the cow uses the fatty acids and also the continually
dying bacteria to produce meat and milk.
Lignocelluloses which have been specifically treated with fungi to improve
the digestibility and protein content for use as ruminant feed have been termed
as “myco-fodder” (Heltay 1999; also Eriksson et al. 1990). For example, the
digestibility of straw that was treated with Lentinula edodes for 2 months
showed increased digestibility by 28% (Zadraˇzil 1985; Zadraˇzil and Brunnert
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