Molecular mapping of gene Gm-6(t) which confers resistance against four biotypes of Asian rice gall midge in China

The Chinese rice cultivar Duokang #1 carries a single dominant gene Gm-6(t) that confers resistance to the four biotypes of Asian rice gall midge (Ors eolia oryzae Wood-Mason) known in China. Bulked segregant analysis was perf ormed on progeny of a cross between Duokang #1 and the gall midge-susceptib le cultivar Feng Yin Zhan using the RAPD method. The RAPD marker OPM06((140 0)) amplified a locus linked to Gm-6(t). The locus was subsequently mapped to rice chromosome 4 in a region flanked by cloned RFLP markers RG214 and R G163. Fine mapping of Gm-6(t) revealed that markers RG214 and RG476 flanked the gene at distances of LO and 2.3 cM, respectively. Another gall midge r esistance gene, Gm-2, mapped previously to chromosome 4. is located about 1 6 cM from Gm-6(t). to judge by data from a segregating population derived f rom a cross between Duokang #1 and the Indian cultivar Phalguna that carrie s Gm-2. We developed a PCR-based marker-assisted selection kit for transfer of the Gm-6(t) gene into Ming Hui 63 and IR50404, two parental lines commo nly used in hybrid rice production in China. The kit contains PCR primer pa irs based on the terminal sequences of the RG214 and RG476 clones. Polymorp hism between Duokang #1 and the hybrid parental lines was found at these ma rkers after digestion of the PCR products with specific restriction endonuc leases. The kit will accelerate introduction of gall midge resistance into hybrid rice in China.