The quantitative resistance gene pi21 from Sensho was introgressed to an indica breeding line IR63307-4B-13-2, a pyramiding line IRBB4/5/13/21, and a tropical japonica line Kinandang Patong by marker-assisted backcrossing. A total of 192 improved lines at the BC₄F₃ and BC₄F₄ generations were developed and confirmed to have the gene introgression via genotyping using a pi21-specific InDel marker. Thirteen randomly selected improved lines, representing all the three genetic backgrounds, demonstrated resistance against leaf blast composites in the field and a broader spectrum resistance against individual isolates compared to the recurrent parents in the glasshouse. Specifically, the tested lines exhibited pi21-acquired resistance against 11 leaf blast isolates that elicited susceptible reactions from the recurrent parents. All the tested lines maintained a comparative heading date, and similar or improved panicle length, number of primary branches per panicle and number of total grains per panicle relative to the recurrent parents. The physical grain characteristics of the recurrent parents were also maintained in the 13 lines tested, although variability in the amylose content and chalkiness degree was observed. The successful marker-assisted introgression of pi21 in diverse genetic backgrounds and the resulting broader spectrum resistance of improved lines against leaf blast indicate the potential of pi21 for deployment in cultivars grown across other rice growing regions in Asia.

定量抗性基因pi21从Sensho被渗入到籼稻育种线IR63307-4B-13-2，一个金字塔线IRBB4 / 5/13/21，和热带粳稻线Kinandang巴东通过标记辅助回交。在BC ₄ F ₃和BC ₄ F ₄世代共开发了192条改良品系，并通过使用pi21进行的基因分型证实具有基因渗入专用的InDel标记。与温室中的轮回亲本相比，代表所有三个遗传背景的13条随机选择的改良品系表现出了对田间叶瘟复合物的抗性和对单个菌株的更广谱抗性。具体而言，测试线显示pi21获得的抗11种叶胚分离株的抗性，这些分离株引起了轮回亲本的易感反应。所有测试的品系都保持了比较的抽穗期，穗的长度，相对穗的亲本相近或改善，穗的初级分支数和穗的总粒数。尽管观察到直链淀粉含量和白垩度存在变化，但在13个试验品系中也保持了轮回亲本的物理谷物特性。pi21在不同遗传背景下成功的标记辅助基因渗入以及改良品系对叶瘟的更广谱抗性表明pi21在亚洲其他水稻种植区栽培的栽培品种中具有潜在的应用潜力。