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6 Wood Discoloration

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8.1 Fungal Damage to Living Trees 165<br />

Fig.8.1. Beech bark disease. a tarry spots on the bark, b occluded bark lesions, c determination<br />

of extent of necrosis by scoring the bark with a timber scribe, d early stage of necrosis,<br />

e late stage with incipient white rot (from Butin 1995, by permission of Oxford University<br />

Press)<br />

develop dark regions with dead cambium to over 1 m in extension. Small<br />

necroses with exposed wood may be closed by callus formation, which leads<br />

to a T-shaped fault in the xylem. Tylosis formation causes wilting. Massive<br />

invasions can result in tree dieback. Larger necroses form infestation gates for<br />

white-rot fungi (Bjerkandera adusta, Fomes fomentarius, Fomitopsis pinicola,<br />

Hypoxylon species, Stereum hirsutum) (Eisenbarth et al. 2001).<br />

8.1.1.2<br />

Chestnut Blight<br />

The Chestnut blight (chestnut bark canker) (Fig. 8.2) is caused by the ascomycete<br />

Cryphonectria parasitica (Halmschlager 1966; Heiniger 1999). The<br />

pathogen was imported on Asian rootstock to New York in 1904 and caused<br />

lethal cankers on more than 3.5 billion susceptible American chestnut trees,<br />

Castanea dentata, across 9 million acres of the eastern US, being there at that<br />

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