Directional upgrading of brown planthopper resistance in an elite rice cultivar by precise introgression of two resistance genes using genomics-based breeding.

Brown planthopper (BPH) is a devastating pest that threatens the food security of rice-producing countries. At present, most cultivars planted in farmers' paddies lack effective BPH resistance, which constitutes a potential threat to rice yield. Moreover, developing BPH-resistant rice varieties using traditional breeding approaches is time-consuming, labor-intensive, and unpredictable. In this study, we successfully enhanced BPH resistance of the elite rice cultivar Wushansimiao by introgressing the resistance genes BPH14 and BPH15 through positive selection, negative selection, and whole genome background selection. Through backcrossing, the introgression fragments were reduced to 428.3 kb for BPH14 and 413.1 kb for BPH15. Except for these two fragments, the residual genetic background of the selected near-isogenic lines (NILs) was nearly identical to that of the recurrent parent, with a genetic background recovery rate of 99.78%. As a result, the selected NILs exhibited much stronger BPH resistance at the seedling and adult stages compared to the recurrent parent. Moreover, field tests showed that grain yield, major agronomic traits, and grain quality of the five selected NILs were statistically indistinguishable from those of the recurrent parent. Our results provide an effective approach for directionally upgrading the target traits and will inform and facilitate rice breeding.