Relationships between pathotypes and RAPDs, Gpi-allozyme patterns, mating types, and resistance to metalaxyl of Phytophthora infestans in Canada in 1997

Relationships between pathotypes and other markers such as mating types, me talaxyl resistance, Gpi-allozyme and random amplified polymorphic DNA (RAPD ) patterns, were investigated among 33 isolates of Phytophthora infestans o btained from both potato and tomato across Canada in 1997. Pathogenicity te stings, based on virulence against potato differentials carrying single-res istance genes and the size of lesions on leaves, revealed higher pathogenic diversity in 1997 than in the few past years, with more pathotypes and mor e race-complex isolates. A higher pathogenic diversity was observed within A2 (US-8) than within Al (US-11) isolates. There was no correlation between the level of resistance to metalaxyl of an isolate and its pathogenicity. Nevertheless, when grouped into metalaxyl-sensitive (MS), -intermediate (MI ), and -resistant (MR) classes, both average pathotype complexity and avera ge lesion size were lowest for MS group. RAPD data revealed a good distinct ion between A1 (US-11) and A2 (US-8) mating type groups, and between isolat es from British Columbia and those from other provinces. The detection in t he last few years of both A1 and A2 mating types in Canada and the occurren ce in 1997 of some isolates sharing different characteristics of both of th ese two groups suggest that sexual reproduction may have occurred locally.