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 microsatellite 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.