Analysis of Phytophthora cactorum using Random Amplified Microsatellites (RAMS) revealed considerable variation among isolates, most of which correlated with the original host plants. The lack of variation among isolates originating from strawberry suggests that crown rot of strawberry is caused by a single clone within the geographical area studied. It was also shown that P. cactorum isolates form a unique group different from other Phytophthora spp. from Group I.

P. cactorum isolates from necrotic stem lesions on Betula pendula seedlings or Fragaria × ananassa plants suffering from crown rot were highly pathogenic to their original host plants. P. cactorum isolates from strawberry inoculated via wounds also caused necrotic lesions on B. pendula. On the other hand isolates from B. pendula did not cause disease symptoms on strawberry plants. On Alnus glutinosa the percentage of successful inoculations with a birch isolate was 40.