Random amplified polymorphic DNA (RAPD) analysis of Phytophthora infestansisolates collected in Canada during 1994 to 1996

Mating type, glucose-6-phosphate isomerase (Gpi) allozyme banding patterns, response to the fungicide metalaxyl and random amplified polymorphic DNA ( RAPD) markers were used to characterize genetic variability among 141 Canad ian isolates of Phytophthora infestans collected between 1994 and 1996. Mul tiple correspondence analysis of RAPD profiles separated isolates into 21 g roups that were not correlated to groups defined by mating type, Gpi allozy me banding patterns or response to metalaxyl. Population subdivision analys is showed that 97% of the total genetic variation was found among individua ls within populations, compared with 3% among populations. The average simi larity coefficient among isolates was 80%. No significant differences in ha plotypic diversity were observed among the years under study, but levels of genetic diversity among local populations of P. infestans were high (0.76) . All classes of response to the fungicide metalaxyl were observed, with 55 % of isolates displaying moderate levels of insensitivity. The high level o f genetic diversity detected within populations indicates that migration an d sexual recombination probably play important roles in the population biol ogy of P. infestans in Canada.