Characterization of Pi13, a blast resistance gene that maps to chromosome 6 in indica rice (Oryza sativa L. variety, Kasalath)

Characterization of resistance genes is essential for the development of a new variety resistant to blast (Magnaporthe grisea) in rice (Oryza sativa L.). In this study, we found that an indica variety, Kasalath, harbored a resistance gene that showed a broad spectrum of resistance reactions against standard differential blast isolates from the Philippines and Japan. Quantitative trait locus (QTL) analysis was conducted using backcross inbred lines derived from crosses between Kasalath and the japonica cultivar, Koshihikari, to detect the QTL for blast resistance. QTLs were detected on chromosomes 6 and 8. Further, QTL analysis of chromosome segment substitution lines of Kasalath in the Koshihikari genetic background revealed that the Kasalath allele at the QTL on chromosome 6 strongly contributed to blast resistance. These results suggested that the gene locus might be identical to Pi13(t) that had already been reported. By marker-assisted breeding, a near-isogenic line, Koshihikari Toyama BL7, with a Kasalath chromosome segment containing Pi13(t) introduced into Koshihikari genetic background, was developed. The reaction of Koshihikari Toyama BL7 to the differential blast isolates indicated that Pi13(t) was a broad-spectrum and moderate resistance gene. Since Pi13(t) showed single-gene segregation and was characterized, the gene was re-designated as Pi13.