An oak ( Quercus robur L.) canker caused by Stereum rugosum (Pers.) Fr.

Abstract

A hitherto unreported destructive oak canker in Scotland and its causal organism, Stereum rugosum , have been studied and described from Dawyck, Peebleshire. The cankers, which have been found on trunks of trees about 50–60 years old growing in a damp and shady situation, are mostly open with a depressed to hollow centre which is surrounded by a prominent callus ridge and are often laterally extended. The fructifications of S. rugosum have been found at the edge or near the centre on the surface of the dead bark, usually around the stub of a dead branch. Microscopic characters of the rot are fully described and chemical changes in the wood during the process of decay have been examined. S. rugosum has been obtained in pure culture from areas of both advanced and incipient decay and also from spores. It can be easily identified in culture by its characteristic dense, white, cotton-woolly to felty mycelium, rapid growth and distinctive buff or pinkish buff colour of the mat with age. Inoculations, made on the wounded bark on the trunk of healthy oak tree employing mycelium as the inoculum, were positive. Laboratory studies showed S. rugosum to be able to attack sapwood much more readily than heartwood.