6 Wood Discoloration

8.3 Tree Rots by Macrofungi 183
The degree of wood decay can be quantified by changes in wood strength
properties, modulus of rupture, work to maximal load in bending, maximal
crushing strength, compression perpendicular to the grain, impact bending,
tensile strength parallel to the grain, toughness, hardness, and shear strength
(Wilcox 1978; Zabel and Morrell 1992; Nicholas and Crawford 2003).
Isothermal microcalorimetry has been used to determine the activity of
fungi after exposure to high and low temperature, oxygen depletion, and drying
(Xie et al. 1997).
Different stainings detect fungal hyphae and spores in woody tissue (Erb
and Matheis 1983; Krahmer et al. 1986; Weiß et al. 2000). Treatment with
safranine and astra blue stains lignified wood areas red and lignin-free parts
blue, and thus differences between sound and decayed wood may become visible.
Light-microscopic degradation patterns have been summarized (Schwarze
et al. 1997). There is a key to identify wood decays based on light microscopic
features (Anagnost 1998).
Transmission (TEM) and raster electron microscopy (REM) result in detailed
views of the cell wall decay by the various groups of fungi (Liese 1970;
Daniel 1994). UV microspectrophotometry (UMSP) characterizes lignin and
phenolic compounds in situ, determines their content semiquantitatively in
the various layers of the wood cell wall (Koch and Kleist 2001), and has also
been applied to measure lignin content after microbial wood attack (Bauch
et al. 1976; Schmidt and Bauch 1980; Kleist and Seehann 1997; Kleist and
Schmitt 2001). General wood quality, microbial activity in wood, and composition
in fossil specimens may be quantified by chemical analyses of the wood
cell wall components, by UV and IR spectroscopy, and by gas chromatography/mass
spectrometry of lignin components (Faix et al. 1990, 1991; Nicholas
and Crawford 2003; Schwanninger et al. 2004; Uçar et al. 2005).
Biochemical methods to quantify microbial activity comprise assay of chitin
as component of the fungal cell wall (Braid and Line 1981; Vignon et al.
1986; Jones and Worrall 1995; Nilsson and Bjurman 1998) and ergosterol as
fungal membrane component (Nilsson and Bjurman 1990; Pasanen et al. 1999;
Dawson-Andoh 2002).
Molecular methods to detect and identify fungi, like protein gel electrophoresis,
immunology, and DNA-based techniques, are described in
Chap. 2.4.2.
8.3
Tree Rots by Macrofungi
There is a broad spectrum of macrofungi (macromycetes) affecting trees. Most
fungi belong to the Homobasidiomycetes (Table 2.12). About 20 species have
greater economic importance. Among them, the Agaricales are represented
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