Improvement of Guanghui 1002 resistance by polymerizing Pi2 and Xa23 genes through molecular marker-assisted selection

【Objective】The resistance to rice blast and bacterial blight of Guanghui 1002 was improved by polymerizing the Pi2 and Xa23 resistance genes, providing technical reference for maintaining elite restorer lines and further exploring the potential of strong dominant hybrid rice combinations. 【Method】Using Guanghui 1002—the most widely cultivated late-maturing,weak-photosensitive restorer line in southern China—as the recipient parent,simultaneously introduced the blast resistance gene Pi2 and bacterial blight resistance gene Xa23 via molecular marker-assisted selection（MAS） combined with conventional breeding. Five improved resistant lines were selected for disease resistance evaluation,agronomic trait assessment and grain quality analysis. These lines were then crossed with Jifeng A to analyze their heterosis performance. 【Result】Based on molecular marker detection and field agronomic performance of isolated populations,5 homozygous resistant improved lines（R1002-1, R1002-2, R1002-3, R1002-4 and R1002-5） were selected from the BC₄F₄ population. The 5 homozygous resistant improved lines exhibited over 97.62% genetic similarity with Guanghui 1002,with no significant difference（P＞0.05） in major agronomic traits（spike length,effective spike number, grain number per spike, seed setting rate, 1000-grain weight and yield）. However,their blast resistance frequency improved from 61.5% to 79.5%-94.9%,and bacterial blight resistance was greatly enhanced,showing high resistance to types Ⅲ,Ⅳ,Ⅴ and Ⅸ of Xanthomonas oryzae pv. oryzae. Notably,R1002-1 and R1002-3 demonstrated improved grain quality,reaching the “Ministry Standard Grade 2” level. When the 5 homozygous resistant improved lines crossed with Jifeng A,the F₁ hybrids showed no significant differences in agronomic traits（plant height,spike length,effective spike number, grain number per spike, seed setting rate and yield）, and the rice quality was ordinary. 【Conclusion】The genetic background recovery of 5 Guanghui 1002 improved lines resistant to rice blast and bacterial blight has met expectations. Without reducing production, the resistance of each improved line to rice blast and bacterial blight has greatly increased, and the rice quality of some improved lines has improved, achieving the improvement goal. Subsequently, these lines can replace the existing Guanghui 1002 to develop hybrid rice varieties with better resistance to rice blast and bacterial blight.