Since several years, extensive oak decline is observed in European parts of the Soviet Union and other regions of eastern Europe. Quercus species of the subgenus Lepidobalanus are predominantly concerned. Oak twigs were collected in August, 1989, from diseased trees near Wolgograd, and histological symptoms of the decline were studied. External signs of the damage such as rhombic bark wounds, scale infestation and sooty moulds following aphid attack are features pointing towards a dieback due to trought and/or frost. Bark lesions associated with cambial reactions seem to be the major cause of xylem anomalies like the formation of thick-walled wound tyloses in vessels and the deposition of coloured wound substances in the adjacent tissue, already macroscopically visible on transverse and longitudinal sections. Pronounced necroses usually led to fungal infections in the xylem by varous Ascomycetes and imperfect fungi. Other histological features of decline were seen in fracture-like zones in the xylem, traumatic parenchyma and changes of the frequency and arrangement of vessels within annual rings.
443.3 (Krankheiten in späteren Wachstumsstadien) 416.16 (Welken, Absterben) 176.1 (Dicotyledoneae [Siehe Anhang D]) [47] (Europäischer Teil der Sowjetunion (UdSSR) (1917-1990) Gemeinschaft Unabhängiger Staaten (GUS))
