Mating Type, Virulence, Aggressiveness and Metalaxyl Resistance of Isolates of Phytophthora Infestans in Poland

A total of 93 single-lesion isolates of Phytophthora infestans were collected from late blight diseased potatoes grown in several locations in Poland, in the years 2002–2004. They were tested for mating type, virulence, aggressiveness and metalaxyl resistance. Sixty one percent of the isolates was of the A1 and 39% of the A2 mating type. Regarding virulence, complex races predominated. Most of the isolates were highly and moderately aggressive. Among isolates, tested together with 38 previously collected (1995–2001) ones, 14.5% was metalaxyl resistant, 3.5% intermediately resistant and 82.0% of the isolates was sensitive to metalaxyl. In addition, 14 isolates tested with three simple sequence repeat markers showed high genetic diversity. These data indicate that Polish population of P. infestans is diverse and aggressive, with potential for sexual recombination and spreading of fungicide insensitivity.