MICROSCOPIC AND MYCOLOGICAL INVESTIGATIONS ON WOOD OF PENDUNCULATE OAK (QUERCUS-ROBUR L) RELATIVE TO THE OCCURRENCE OF OAK DECLINE

Microscopical studies exhibited great differences between healthy and damaged pendunculate oak trees (Quercus robur L.) relative to the stat e of sapwood Vessels and the degree of fungal infection. In the sapwoo d of damaged trees deposits, discolorations and early tylosis formatio ns were found which frequently occurred in combination with fungal inf ections. These results lead to the assumption that the defence reactio n of the trees probably induced by fungal infection changes the struct ure of the tree vessels to such an extent that their water transfer fu nction is disturbed. Some fungal genera playing an important role in t he discussion of the causes of oak decline could be isolated. Fungal h yphae in the vessels and tylosis formation in the vessels cause the br eakdown of the water economy in the trees. These observations, however , are not evidence for causal predisposition of tree damage by fungal infections.