Marker‐assisted improvement of a stable restorer line, KMR‐3R and its derived hybrid KRH2 for bacterial blight resistance and grain quality

KMR-3R is a stable restorer line with medium-bold grain type and is the male parent of the popular public-bred Indian rice hybrid, KRH2. As both KMR-3R and KRH2 are highly susceptible to bacterial blight (BB) and possess undesirable bold-grain type, we crossed KMR-3R with a high-yielding, BB resistant, fine-grain-type variety, Improved Samba Mahsuri, possessing the major BB resistant gene, Xa21. The F(1)s were backcrossed to KMR-3R, and the BC1F1 plants were subjected to marker-assisted selection (MAS) for Xa21 and two major fertility restorer genes, Rf3 and Rf4. 'Triple' positive BC1F1 plants were selfed and their progeny were subjected to MAS for Xa21 coupled with phenotype-based visual selection for agromorphological and grain-quality traits. At BC1F5 generation, three backcross derived lines (BK9, BK49 and BK61) possessing higher yield than KMR-3R, tall plant stature along with fine-grain type were identified and crossed with IR598025A, the female parent of KRH2. The hybrids were completely fertile, possessed long-slender grain type, exhibited resistance to BB and displayed a yield advantage of 24% over KRH2 under BB infection.