A New Recessive Gene Conferring Resistance Against Rice Blast

Rice blast (causative pathogen Magnaporthe oryzae) represents a major biotic constraint over rice production. While numerous genes for resistance have been found in both japonica and indica germplasm, as yet the diversity harbored by aus germplasm has not been widely exploited. The blast resistance present in the aus type cultivar AS20-1 was shown, via an analysis of segregation in the F-2 generation bred from a cross with the highly blast susceptible cultivar Aichi Asahi, to be due to the action of a single recessive gene, denoted pi66(t). The presence of pi66(t) gave an intermediate level control to plants infected with the blast pathogen isolate EHL0635. A bulked segregant analysis indicated that four microsatellite loci (SSRs) mapping to chromosome 3 were probably linked to pi66(t). Localized mapping using chromosome 3-based SSRs and Indels defined a genetic window for pi66(t), flanked by the markers F04-j2 and M19-i12, which physically equals to 27.7 and 49.0 kb, respectively, in the reference genomes of cultivars Nipponbare and 93-11. This physical interval does not harbor any major gene currently associated with disease resistance. pi66(t) is one of just three recessive genes controlling rice blast, and is the first major gene for resistance to be mapped to chromosome 3.