Fine mapping of the rice brown planthopper resistance gene BPH7 and characterization of its resistance in the 93-11 background

The brown planthopper (Nilaparvata lugens Stål; BPH) is a severe constraint to rice (Oryza sativa) production. A particularly important approach to controlling this insect pest is the identification and characterization of BPH resistance genes and the subsequent incorporation of the most effective ones into cultivars. Rice var. T12 has been reported to carry resistance gene BPH7 (previously designated bph7) that has not yet been assigned to a chromosome location and whose resistance mechanism is still unknown. In the study reported here we identified and mapped this gene using F2 and backcrossing populations and characterized its resistance in the rice var. 93-11 genetic background using near isogenic lines (NILs). Our analysis of the 93-11/T12 F2 population revealed that the BPH7 gene is located on the long arm of chromosome 12 between simple sequence repeat markers RM28295 and RM313. Subsequent fine mapping placed this gene more precisely in a region flanked by the markers RM3448 and RM313 which are 150 kb apart in the Nipponbare genome and 300 kb apart in the 93-11 genome. BPH7 explained 38.3 % of the phenotypic variance of BPH resistance in the F2 populations. Characterization of the BPH7-mediated resistance revealed that the settlement of the BPH on plants and the survival rate and population growth rate of the BPH were not different significantly between NIL-BPH7 and 93-11 plants. The NIL-BPH7 plants showed significant tolerance to the insects at the seedling and adult stages compared with the susceptible parent 93-11. Our results demonstrate that tolerance is the major component in the resistance conferred by BPH7. The gene mapping of BPH7 should be of great benefit for gene map-based cloning and in plant breeding programs for BPH-resistant rice lines.