CHARACTERIZATION OF CHANGES IN PHENOTYPE AND GENOTYPE OF PHYTOPHTHORA INFESTANS ISOLATES FROM INDIA
V.P. Chimote, M. Kumar, P.K. Sharma, P.H. Singh, B.P. Singh
The present study was undertaken to evaluate the diversity of Phytophthora infestans isolates collected between 1996 and 2006 from potato-growing regions of India. Thirty-two genotypes were distinguished among 70 isolates characterized using mating type, metalaxyl resistance, mitochondrial DNA (mtDNA) haplotypes and microsatellite markers. The mating type analysis revealed that the A1 mating type prevailed (90%) in the subtropical Indo-Gangetic plains, whereas the A2 mating type was dominant (93%) in temperate highland regions. All 11 isolates collected before 2000 were metalaxyl sensitive, whereas all 28 isolates from after 2004 were metalaxyl tolerant. Before 2002, the Ib mtDNA haplotype was seen in all 26 isolates, but a shift was observed from 2004 to 2006 after which the Ia mtDNA haplotype was found to have replaced the Ib haplotype everywhere except in the north eastern hills of India. Microsatellite analysis revealed that isolates from the north Himalayan hills after 2000 were distinct from the all the others. Little divergence was observed among earlier isolates from the same region along with earlier isolates from the north Indian plains and the 2005 isolates from the north-eastern hills. The highest variability was observed in regions with high pathogen build-up and where frequency of exchange of planting materials was relatively high. The results of this study indicate a drift in the pathogen population in the first half of the present decade throughout India.