Mapping of a novel recessive brown planthopper resistance gene bph46 from wild rice (Oryza nivara)

Rice production is severely threatened by frequent outbreaks of Brown planthopper (BPH), Nilaparvata lugens (Stảl.) biotypes globally. On this account, host-plant resistance serves as an important strategy to reduce the damage caused by BPH. The wild species of rice Oryza nivara accession IRGC 93198 showed consistent resistance reaction against BPH biotype 4 for 5 consecutive years of screening under the greenhouse conditions. The mapping of the BPH resistance gene from Oryza nivara accession IRGC 93198 was conducted using BC2F2 and BC2F3 progenies. Out of 239 BC2F2 plants, 65 plants were resistant (1-3 score), and 174 plants (5, 7, and 9 score) were susceptible, thus fitting the segregation ratio of 3:1 (Susceptible: Resistant). The BC2F3 progenies segregated in 1:2:1 confirming that the resistance from O. nivara is governed by a single recessive gene. Bulked segregant analysis (BSA) identified genomic region on the short arm of chromosome 4 to be associated with BPH resistance. Molecular mapping performed on BC2F2 population identified a QTL on chromosome 4 within the marker interval RM16285 and RM6314 explaining phenotypic variance of 27% at LOD 22.34. The linked marker RM6659 was found efficient in demarcating the susceptible from resistant lines when applied on the panel of rice cultivars, hence can be used for marker assisted selection in crop breeding. The previously identified BPH-resistant genes located on chromosome 4 were found susceptible to the BPH biotype 4 screening test. This specifies bph46 to be a novel gene that can be deployed as a valuable donor in BPH resistance breeding programs.