Hypotheses for the inter-regional movement of new genotypes of Phytophthora infestans in Canada

During late blight surveys conducted from 1994 to 1996, hypotheses were dev eloped to explain the migration of novel genotypes of Phytophthora infestan s between regions or provinces via infected potato and tomato tissues and v ia winds of tropical storm systems. The appearance of isolates of the US-7 genotype in Alberta (a province affected predominantly by US-I) in 1994, wa s believed to be due to infected seed tubers from British Columbia. Similar ly, the initial isolation of the US-8 genotype in Nova Scotia in 1995 and i n Newfoundland in 1996 could be explained by the importation of infected po tato seed tubers from other regions. The discovery of Al, metalaxyl-insensi tive (glucose phosphate isomerase banding pattern = 100/100/111; g11 or US- 11) isolates of P. infestans in a tomato field in Ontario in 1996 (a provin ce affected predominantly by US-8), suggested the introduction of this new strain had occurred via infected or infested tomato tissue. Circumstantial evidence was also obtained for the introduction of the US-8 genotype to Pri nce Edward Island via sporangia carried in winds of tropical storm systems moving along the eastern seaboard.