PATHOGENICITY AND GENETIC-VARIATION OF PHYTOPHTHORA-CACTORUM FROM SILVER BIRCH AND STRAWBERRY

Phytophthora cactorum strains isolated from necrotic stem lesions on B etula pendula seedlings or from Fragaria x ananassa plants suffering f rom crown rot were pathogenic to their host plants. Only isolates from birch caused clear lesions on non-wounded bark of birch. P. cactorum isolates from birch were not detrimental to strawberry. Random Amplifi ed Polymorphic DNA (RAPD) analysis revealed variation within P. cactor um, isolates from silver birch having different banding patterns than those from strawberry. UPGMA analysis clustered isolates from silver b irch and strawberry plants into separate groups. The data show that th e recent outbreak in Finland of P. cactorum in birch could not be caus ed by the import of strawberry plants affected by crown rot.