HOST RESISTANCE AND AGGRESSIVENESS OF A1 AND A2 MATING TYPES OF PHYTOPHTHORA INFESTANS IN POTATOES

Abstract

Studies on the effect of host resistance on P. infeslans aggressiveness revealed that mostly A₂ mating type was more aggressive than A₁ mating type. However, in some cases aggressiveness varied with host background. The aggressiveness of A₂ was more on seedlings of 10 crosses, whereas that of A₁ was more on seedlings of 6 crosses. The performance of mixture of A₁ and A₂ mating types also varied with host background. The aggressiveness of the mixture was, in general, higher than A ₁ or A₂ alone on potato cultivars but its effect on seedlings of different crosses was not similar. No statistical differences were observed in aggressiveness of the two mating types when tested on germplasm accessions using detached leaves and tuber slice tests. It is concluded that aggressiveness of the two mating types varies with host background and the germplasm accessions need to be evaluated using both the mating types to select parents with durable host resistance for use in resistance breeding programme.