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 developed to explain the migration of novel genotypes of Phytophthora infestans between regions or provinces via infected potato and tomato tissues and via winds of tropical storm systems. The appearance of isolates of the US-7 genotype in Alberta (a province affected predominantly by US-l) in 1994, was believed to be due to infected seed tubers from British Columbia. Similarly, the initial isolation of the US-8 genotype in Nova Scotia in 1995 and in Newfoundland in 1996 could be explained by the importation of infected potato seed tubers from other regions. The discovery of Al, metalaxyl-insensitive (glucose phosphate isomerase banding pattern = 100/]00/111; gll or US-ll) isolates of P. infestans in a tomato field in Ontario in 1996 (a province 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 introducti...