Population structure of Magnaporthe grisea from north-western Himalayas and its implications for blast resistance breeding of rice

Neutral and pathogenicity markers were used to analyse the population structure of Magnaporthe grisea rice isolates from the north-western Himalayan region of India. Random amplified polymorphic DNA (RAPD)-based DNA fingerprinting of 48 rice isolates of M. grisea with five primers (OPA-04, OPA-10, OPA-13, OPJ-06 and OPJ-19) showed a total of 65 RAPD bands, of which 54 were polymorphic. Cluster analysis of 48 rice isolates of M. grisea on the basis of these 65 RAPD bands revealed the presence of high genotypic diversity and continuous DNA fingerprint variation in the pathogen population. No correlation was observed between RAPD patterns and virulence characteristics of the pathogen. The observed population structure contrasted with presumed clonal reproductive behaviour of the pathogen and indicated the possibility of ongoing genetic recombination in the pathogen population. Analysis of the virulence organization of five RAPD groups (RG1-RG5) using 20 rice genotypes comprising at least 15 resistance genes revealed that no combination of resistance genes would confer resistance against all RAPD fingerprint groups present in the M. grisea rice population. The possible implications of the observed population structure of M. grisea for blast resistance breeding have been discussed.