Pyramiding Xa21, Bph14, and Bph15 genes into the elite restorer line Yuehui9113 increases resistance to bacterial blight and the brown planthopper in rice

Utilization of resistant varieties is the most economical and effective strategy to control bacterial blight (BB) and brown planthopper (BPH) in rice. Yuehui9113 is a widely used elite restorer line with high combining ability, and one of its hybrids, C815S/Yuehui9113, has been designated as a check variety for late season single-cropping rice; however, both of the parental lines are susceptible to BB and BPH. To simultaneously improve resistance to both BB and BPH in Yuehui9113 and F1 hybrids derived from it, one BB resistance gene (Xa21) and two BPH resistance genes (Bph14 and Bph15) were pyramided in Yuehui9113 using a marker-assisted backcrossing (MABC) strategy coupled with phenotypic selection in this study. Evaluation of BB and BPH resistance showed that all improved restorer lines that were homozygous for the resistance genes, and their derived F1 hybrids crossed with C815S, were at least moderately resistant to fourteen Xanthomonas oryzae pv. oryzae (Xoo) strains except for strain FuJ. They were also resistant or highly resistant to BPH, except for the improved line BX9113-06 and its hybrid C815S/BX9113-06, suggesting that BB and BPH resistances were significantly improved compared with the parent Yuehui9113 and the original hybrid C815S/Yuehui9113. Evaluation of agronomic traits and plot yields in 2014 and 2016 suggested that the improved lines BX9113-01 and BX9113-12 and their hybrids with C815S are superior or similar to the original parental line Yuehui9113 and the original hybrid C815S/Yuehui9113 with respect to important agronomic traits, and the two hybrids showed higher yield potential than the control hybrid C815S/Yuehui9113. The results of this study show that introgression of the Xa21, Bph14, and Bph15 genes can significantly improve resistance to BB and BPH in Yuehui9113 and its hybrids. Thus, the improved restorer lines BX9113-01 and BX9113-12 will play an important role in breeding hybrid rice with high levels of resistance to BB and BPH in the Yangtze River valley of China.