PHYTOPHTHORA ROOT-ROT IN DECLINING FOREST TREES

Studies by light and scanning-electron microscopy in combination with specific isolation techniques revealed the presence of soil-borne Phyt ophthora - species in declining oak, beech and other forest trees. The sequence of histopathological reactions in infected roots and distinc t fungal structures found in necrotic tissues are documented. Specific laboratory procedures used for the detection and identification of Ph ytophthora are presented. Pathogenicity of the isolated Phytophthora - species is shown by common tests of soil infestation and stem inocula tion. The possible role of predisposing and contributing factors leadi ng to this type of decline is discussed with emphasis on climate chang e and excess nitrogen.