6 Wood Discoloration

6.3 Red Streaking 129
6.3
Red Streaking
Red-streaking discoloration (known as “Rotstreifigkeit” in Germany) is one of
the most common and important damage in seasoning logs and sawn lumber,
occurring only in conifers (spruce, pine, fir) and recognized as a distinct condition
in continental Europe. The stripe-shaped to spotted yellow to reddishbrowndiscolorationextendsinlogsfromboththeirbark-coveredfacesand
from their cut ends (Butin 1995; Baum and Bariska 2002) (Fig. 6.4). Stems that
are not debarked show a rather flat discoloration and debarked stems exhibit
a streakier staining (v. Pechmann et al. 1967).
Causal agents are several white-rot Basidiomycetes, in spruce particularly
Stereum sanguinolentum (Kleist and Seehann 1997) and Amylostereum areolatum.InsouthGermany,Amylostereum
chailettii is common (Zycha and Knopf
1963; v. Pechmann et al. 1967). In pine, red streaking is mainly due to Trichaptum
abietinum (Butin 1995). According to Kreisel (1961), S. sanguinolentum
and T. abietinum occur often together in stored logs.
Red streaking develops if the wood remains in a semi-moist state over
a long period, especially in the warmer season (v. Pechmann et al. 1967). The
fungi gain access to the wood through the exposed cut ends and bark fissures.
The mycelium reaches its greatest density in the medullary rays, where the
fungus uses the primary storage compounds in the ray parenchyma cells.
From there, the discoloration spreads axially deeply in the wood, penetrating
the bordered pits and also by thin bore hyphae that perforate the tracheids
cell wall (Kleist and Seehann 1997; Kleist 2001). Logs may be stained during
overseas shipment, and red streaks producing fungi become again active in
rewetted boards due to their ability to dryness resistance. The staining is mainly
an oxidative process (Butin 1995). Kleist (2001) stated that the fungi involved
excrete the pigments.
The moisture optimum of most species lies between 50 and 120% u. Redstreaking
fungi are slowly growing white-rot fungi, so that initially no serious
strength loss is connected with turning red. During longer colonization however
an intensive white rot develops with substantial mass and strength loss, so
that red streaking damage represents a transition from discoloration to decay
(v. Pechmann et al. 1967; Peredo and Inzunza 1990).
Secondary infections by brown-rot fungi may occur. Red-streaked wood
samples were degraded in the lab test more strongly by brown-rot fungi than
controls without pre-infection. From reddish discolored fir wood, 26 Basidiomycetes
(white and brown rot) and numerous blue-stain and mold fungi
were isolated (v. Pechmann et al. 1967). From Pinus radiata wood, different
molds, blue-stain fungi, Stereum sp. and the white-rot fungi Ganoderma sp.,
Schizophyllum commune and Trametes versicolor were isolated (Peredo and
Inzunza 1990). Spruce wood samples from forest dieback sites contained more
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