Selective Degradation of Lignin and Condensed Tannins of Douglas-Fir Bark Sclereids by Fungi

William D. Ross, Malcolm E. Corden


Chemical analysis of decayed bark confirms visual observations that colored materials rich in tannins and cell-wall lignin are removed separately from bark of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) by different species of fungi colonizing the bark. Ball-milled sclereid lignin is similar in many ways to lignin from Douglas-fir sapwood. In one instance, lignin is removed from sclereid walls by fungal action that leads to wall "bleaching," and tannins are only darkened, but not removed. In a second instance, tannins are removed from primary walls and lumina of sclereids, but wall lignin is not removed. Two fungi suspected as causal agents for the two white rots, Bispora betulina (Cda.) Hughes and a fungus resembling Isaria, failed to produce typical white rots in axenic culture, but evidence strongly suggests that they are involved in the "bleaching" process.


Pseudotsuga menziesii;decay;extractives

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