Mapping of a brown planthopper (Nilaparvata lugens Stål) resistance gene Bph9 on the long arm of rice chromosome 12

A dominant gene Bph9 of rice (Oryza sativa L.) confers resistance against a serious insect pest, brown planthopper (BPH; Nilaparvata lugens Stål). To map the Bph9 locus, a susceptible japonica breeding line ‘Norin-PL9’ was crossed as a seed parent with an indica cultivar ‘Pokkali’, which is a Bph9-carrier. Due to high sterility in the F1 and F2 progenies, genotypes for BPH response of F2 individuals were estimated indirectly by the phenotypes of F3:4 families in BPH bioassay. Segregation of BPH resistance in 62 F2 individuals did not deviate from the single dominant gene ratio. Seven RFLP and two RAPD markers were selected in the bulked segregant analysis, all of which showed normal segregation in the mapping population. Bph9 was mapped on the long arm of rice chromosome 12.