Changes in mating types, resistance to metalaxyl, and Gpi-allozyme genotypes of Phytophthora infestans in Canadian provinces from 1996 to 1998

Variations within Phytophthora infestans populations in Canada, in terms of mating type, metalaxyl resistance, and glucose-6-phosphate isomerase alloz yme genotypes, are presented for the period 1996-1998. During 1996, only th e A2 mating type was found in most Canadian provinces. However, both A1 and A2 mating types were found in Ontario and British Columbia (BC). In 1997, samples of late blight-infected plants were received from five provinces on ly. The A2 mating type was isolated from samples from Prince Edward Island, New Brunswick, and Quebec (QC), while both A1 and A2 mating type isolates were found in BC and Manitoba. In 1998, late blight was confirmed in all pr ovinces, and all samples were of the A2, mating type, except those from BC and QC, which had both mating types. Changes in levels of metalaxyl-sensiti ve (MS), metalaxyl-intermediate (MI), and metalaxyl-resistant (MR) strains of P. infestans in Canada were also observed. Within the A2 mating type, th e frequency of MS isolates increased in most provinces, except in BC, where this rate is decreasing. For the Al mating type, there is an increase in M R individuals that have been displacing the MI strains from 1996 to 1998. A high variability was recorded either among Canadian provinces or from year to year inside each province in terms of mating types, Gpi-allozyme genoty pes, and especially metalaxyl response. In general, during 1996-1998, sampl es from four Canadian provinces have included both A1 and A2 mating types. In addition, beside US-8 and US-11, isolates with characteristics of US-7, US-10, and US-14 were found during 1998, with different levels of resistanc e to metalaxyl.