The quantitative blast resistance gene, pi21 has only been used to improve the resistance of temperate japonica rice cultivars against Japanese blast isolates. To determine the applicability of pi21 in breeding for leaf blast resistance across rice growing regions outside of Japan, the expression of the gene when transferred to different genetic backgrounds against isolates from geographically diverse sources needs to be established. In this study, pi21 was introgressed from Sensho to the indica background of the breeding line IR63307-4B-13-2 and the pyramiding line IRBB4/5/13/21, as well as to the tropical japonica background of 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 three genetic backgrounds, demonstrated resistance against leaf blast composites in the field and a broader spectrum of 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 were 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.
|State||Published - Jan 2019|