Mapping of quantitative trait loci conferring blast field resistance in the Japanese upland rice variety Kahei

Many upland rice cultivars show higher levels of blast field resistance than do lowland cultivars. In this study, we performed a linkage mapping of quantitative trait loci (QTLs) for blast field resistance using F-2 plants/F-3 progenies derived from a cross between the upland variety Kahei (high level of resistance) and the lowland variety Koshihikari (susceptible). We mapped two putative QTLs on chromosome 4. qBFR4-1 was mapped in the vicinity of restriction fragment length polymorphism (RFLP) marker G264 on chromosome 4. This QTL explained about 62% of the total phenotypic variation in F-3 lines. Another QTL, qBFR4-2, was also found near the RFLP marker G271 on chromosome 4. These two QTLs on chromosome 4 explained about 71% of total phenotypic variation based on the analysis of a multiple-QTL model. Alleles of Kahei increased the level of resistance in these two QTLs. The high level of resistance to blast in Kahei is mainly explained by these two QTLs. Applications of newly found QTL for breeding rice with blast field resistance is discussed.