Marker-assisted breeding of the elite Rice Restorer Line R202 for resistance to rice bacterial blight and blast diseases, brown plant hopper pest and inhibiting herbicides

Background Hybrid rice plays a pivotal role in ensuring global food security, yet the weak multiple resistance of restorer lines remains a major bottleneck limiting the stability and environmental sustainability of hybrid varieties. The elite restorer line R202 possesses desirable combining ability and good grain quality, but it is chronically susceptible to bacterial blight, blast, brown planthopper (BPH), and herbicides. Single-trait improvements have proven insufficient to meet the demands of modern intensive rice production. Results In this study, we employed backcross breeding combined with marker-assisted selection to introgress the broad-spectrum bacterial blight resistance gene Xa23 , the blast resistance gene Pigm , the brown plant hopper resistance (BPH) gene Bph6 , and the acetolactate synthase (ALS) inhibiting herbicide resistance gene ALS ^W548M into the R202 genetic background. After BC ₄ F ₂ generations coupled with stringent foreground selection, we successfully developed the novel restorer line R4202. The hybrid combination 1892S/R4202, derived from R4202, was evaluated under artificial inoculation and (or) natural field infection conditions. Results demonstrated that R4202 and its hybrid exhibited high resistance to both bacterial blight and blast, moderate-to-high resistance to BPH, and good tolerance to ALS-inhibiting herbicides. Multi-location field yield trials showed that R4202 and its hybrid achieved synergistic stacking of these multiple resistances without incurring any significant yield and grain quality penalty; grain yields remained comparable to those of the recurrent parent R202 and its hybrid (with no statistically significant difference, 0.214 <  P value < 0.910). Conclusion Collectively, R4202 is a novel restorer line that integrates resistances to bacterial blight, blast, BPH, and ALS-inhibiting herbicides, while simultaneously retaining good eating quality and high yield potential. This germplasm provides valuable genetic resources for breeding green, low-input, high-quality hybrid rice varieties