Molecular-Marker-Based Design for Breeding Indica-Japonica Hybrid Rice with Bacterial Blight Resistance.

Background/Objectives: To overcome the limitations imposed by bacterial blight on widely adopted indica-japonica hybrid rice, this study employed molecular design breeding strategies to develop a resistant germplasm. Methods: Through conventional backcross breeding combined with molecular-marker-assisted selection, the Xa23-carrying material XR39 was hybridized with the wide-compatibility restorer line R5315 harboring the S5n gene. Progeny selection integrated evaluations of agronomic traits, disease resistance identification, and test-crossing with sterile lines. Results: Five wide-compatibility restorer lines simultaneously incorporating the Xa23 and S5n genes were successfully developed, demonstrating outstanding bacterial blight resistance and restoration ability. The selected hybrid combinations, A3/RP1, A1/RP4, and A4/RP4, exhibited yield increases of 2.6-8.6% compared to the control. Conclusions: This study not only established a novel germplasm for developing bacterial blight-resistant indica-japonica hybrid rice varieties, but also established a model for gene design breeding for rice improvement.