Cataloguing variability in Phytophthora infestans with respect to ploidy status and response of different polyploids to temperature

Abstract

Late blight, caused by the oomycete Phytophthora infestans, had been, and continues to be the most dreaded disease of potato and tomato world over. In the present study, P. infestans isolates collected from Indian hills, sub-tropical plains and plateau regions were analyzed for their ploidy status and results revealed that P. infestans population in the country are polyploid consisting of diploids, triploids and tetraploids. Diploids were predominant in all the locations while tetraploids were altogether missing from north-eastern and southern hills while in plateau only diploids were observed. Response of different polyploids to temperature was studied and results revealed that mycelial growth was observed in the range of 15–28 °C with the optimum temperatures being 15–20 °C. Indirect germination was highest at 4 °C, with germination decreasing drastically with increase in temperature while direct germination was fairly good in all polyploids in the range of 8–22 °C, though differed significantly, thereafter it declined drastically. Temperature differentially affected incubation period (IP), latent period (LP), lesion area (LA) and sporulation. In general, IP decreased with increase in temperature and shortest IP for all polyploids occurred at 24 °C. Lesion area increased with increase in temperature in all polyploids up to 20 °C and thereafter it decreased. At 28 °C, diploids and triploids could not establish infection while tetraploids could do after 72 h. No sporulation was observed for any of the polyploid at 10 and 28 °C while diploids and triploids did not sporulate at 24 °C. In general diploids had highest sporulation than tetraploids. Diploids were predominant at all locations and were more aggressive that could be one of the reasons for their dominance in the country.