1Central Potato Research Institute, Shimla-171 001, (Himachal Pradesh).
2Central Potato Research Institute Campus, Modipuram, Meerut-250 110, (Uttar Pradesh).
3Depmtment of Plant Protection, Faculty of Agricultural Sciences, Aligarh Muslim University, Aligarh-202 002, (Uttar Pradesh).
Aggressiveness of A1 and A2 mating types of Phytophthora infesfans was compared at three temperature regimes viz., 15, 18 and 21°C and two levels of relative humidity viz., 85% and 100% using potato cultivars Kufri Chandramukhi and Kufri Jyoti. Data revealed that A2 mating type isolates were more aggressive at all the three temperature regimes but the differences were non-significant. Interaction between temperature regimes × cultivars was also non-significant. Zoosporangial germination in A2 mating type isolates was significantly higher than A1 mating type isolates at 10, 18, 20 and 23°C. A2 mating type isolates also showed higher aggressiveness both at 85 and 100% RH but the differences were more pronounced at 100% RH.