Pathogenicity, morphology and genetic variation of Phytophthara cactorum from strawberry, apple, rhododendron, and silver birch

The analysis of random amplified microsatellite (RAMS) markers of Phytophth ora cactorum from strawberry showed that leather rot of strawberry fruits a nd crown rot are not caused by genetically different strains of this specie s. UPGMA-analysis showed that the populations of P. cactorum on strawberry differ between North America and Europe and that no clear genetic separatio n between isolates from different plants can be made among these population s. Slight morphological variation exists in the diameters of oogonia and oo spores among the isolates but is insufficient for the identification of gen etic groups or host specificity of P, cactorum isolates. Pathogenicity expe riments proved that strains show a tendency towards host specialization.