Physiological Races of Phytophthora sojae in Iran and Race –Specific Reactions of Some Soybean Cultivars

Phytophthora root and crown rot of soybean is known as a destructive disease of soybean both through out the world and in Iran. Physiologic races of Phytophthora soja were determined in this research and also a fast, accurate and simple method for inoculation of soybean to test race specific resistance. During the years 2001-4, infected soybean plants at different growth stages were collected from different areas and 22 isolates of P. sojae were recovered using PARPH medium. Physiological races of the pathogen were determined on differential seedling lines by the hypocotyl inoculation method. Ten seedlings from each differential line grown in a 10-cm pot were inoculated under greenhouse conditions (25ºC) by a 10-14 days old fungus (LBA medium). The reaction of the seedlings was classified after 5-6 days as resistant (70% or more of seedlings alive) or susceptible (70% or more of the seedlings killed). Most isolates were identified as race one, six as race three, one as race four and one as a putative race 13. Race-specific resistance of the 60 cultivars towards race three was determined. Some of them such as ‘TMS’, ‘Maverick and ‘Williams 82’ were considered as resistant cultivars. All experiments were repeated three times