Genetic and physical mapping of the avirulence gene Avr-Pik m in Magnaporthe oryzae

The interaction between rice and the rice blast fungus Magnaporthe oryzae follows a gene-for-gene model. The pathotype of a strain is determined by its avirulence gene content. In this study, we crossed avirulent strain S1522 and virulent strain S159 to generate 108 progenies. We subsequently isolated the avirulence gene Avr-Pik (m) through classical genetic analysis. The segregation ratio in F1 population was 1:1 and confirmed the presence of a single locus in the genome of S1522. Two SCAR and five SSR markers linked to the avirulence gene were identified from the segregated population, and Avr-Pik (m) was mapped on the chromosome of M. oryzae. A genomic library of avirulence parental strain S1522 was then constructed; the library was screened using the markers SCE12(1406) and SSR47A18, which were linked to the AVR gene as probes. Using these procedures, a fine physical map was assembled to include five TAC clones. TAC clone 35C5 is 32 kb in length and contains the two above-mentioned SCE12(1406) and SSR47A18 probes, suggesting that the Avr-Pik (m) gene spans across the two markers located on the clone. These results provide support towards Avr-Pik (m) map-based cloning.