Assignment of a brown planthopper (Nilaparvata lugens Stål) resistance gene bph4 to the rice chromosome 6

Abstract

A Sri Lankan indica rice (Oryza sativa L.) cultivar Babawee harboring a brown planthopper (BPH) (Nilaparvata lugens Stål) resistance gene bph4 was crossed as a male parent with two susceptible cultivars, either indica IR24 or japonica Tsukushibare. Segregation of the BPH resistance in the two crosses was studied by directly assaying the F2 phenotypes and by determining the F2 genotypes based on the F3 phenotypes. In both cross combinations, the segregation of the BPH resistance significantly deviated from the ratio expected for the single recessive gene model. Using bulked DNAs of homozygous resistant and susceptible F2s and the parents, seven out of 214 RFLP markers were selected as linked markers, of which six on chromosome 6 were common in the two cross combinations. Two micro-satellite markers on chromosome 6 were also linked to bph4. Although the map position of bph4 could not be determined, the gene was assigned to the distal region of the short arm of rice chromosome 6 based on the bulked segregant analysis and linkage analysis.