QTL analysis for rice stripe resistance in the Japanese Upland Rice Kanto72

Many Japanese upland rice varieties show a high level of resistance to rice stripe virus (RSV). This resistance is thought to be controlled by a pair of complementary dominant genes, Stva and Stvb. Quantitative trait locus (QTL) analysis for the rice stripe virus resistance was performed using 120 F-2 plants/ F-3 lines derived from a cross between the susceptible variety Nipponbare, and the resistant line Upland Rice Kanto72 (URK72), As a result, two QTLs were detected on chromosomes 2 and 11. The chromosomal regions of the two QTLs were introgressed into two resistant paddy lines Chugoku40 and Chugoku41, which were developed by introducing resistance genes from URK72. In order to verify the two QTLs, we selected two informative plants NR8 (heterozygous at the QTL on chromosome 11) and NR23 (heterozygous at the QTL on chromosome 2), from F2 plants and we used the self-pollinated progenies of NR23 (99 plants) and NR8 (96 plants) for further QTL analyses. In these secondary analyses, one QTL was mapped near the RFLP marker G257 on chromosome 11 and the other QTL was mapped near SSR marker MS-11 on chromosome 2. Since the Stvb gene is allelic with the other RSV resistance gene Stvb-i, mapped on chromosome 11, the QTL detected on chromosome 11 was thought to correspond to the Stvb gene. However, this QTL seemed to have a larger effect on RSV resistance than previously reported and was found to contribute to the suppression of RSV infection. On the other hand, since the QTL detected on chromosome 2 did not suppress the RSV infection, it probably enhanced the QTL on chromosome 11 and suppressed the symptoms after infection by RSV.