6 Wood Discoloration

120 6 Wood Discoloration
The wood-discoloring molds and staining fungi live on nutrients in the
parenchyma cells of the sapwood. Conifers and hardwoods, round wood, lumber,
finished wood and wood products can be colonized. Discoloring fungi
do not cause any or only very little cell wall attack. Prioritization of the color
damage depends on subsequent wood use.
Several Deuteromycetes and Ascomycetes stain woody substrates. Phialophora
fastigiata (Hyphomycetes) causes a grey stain of poplar wood. Arthrographis
cuboides (Hyphomycetes) produces a pink stain in several hardwoods
and softwoods, and a naphthalenedione has been isolated from such wood
(Golinski et al. 1995). Red alder wood used in the USA for furniture is stained
reddish purple by Ophiostoma piceae if not rapidly processed after harvesting
(Morrell 1987). Black streaking of beech logs occurs by Bispora monilioides.
Red spotting of beech wood is effected by Melanomma sanguinarum (Dothideales).
Paecilomyces variotii produces a yellow discoloration of oak wood
during drying through its pH-change, which causes chemical reactions of the
hydrolyzable gallotannins (Bauch et al. 1991).
So-called green rot is caused by species of the ascomycete Chlorociboria
(Helotiales). Chlorociboria aeruginascens and C. aeruginosa discolor rotten
and moist hardwood (and conifer) branches and other woody debris in the
forest (Jahn 1990). The green wood has often been employed in marquetry
and veneering and is a feature of the famous Tunbridge ware (Ellis 1976).
The naphthoquinone pigment, xylindein, produced by the fungus is mainly
deposited in the ray parenchyma cells as well as in vessels and fibers adjacent
to the rays. The pigment is now since more than 500 years durable
(Blanchette et al. 1992a; Michaelsen et al. 1992). In a recent reproduction of
a violin from the 17th century, green stained wood was used for the ornaments
(Fig. 6.1).
Fig.6.1. “Green rot” caused by Chlorociboria species. a Green-rotten poplar wood. The
missing section was used for the green intarsia b of the replica c, d by T. Schmitt in 1998 of
a violin by J. Meyer from 1670 (photos b–d:T.Schmitt)
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