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To improve the grain yield of the lowland-adapted popular rice variety Samba Mahsuri under reproductive-stage drought (RS) and to understand the interactions between drought QTLs, two mapping populations were developed using marker-assisted selection (MAS) and marker-assisted recurrent selection (MARS). The mean grain yield of pyramided lines (PLs) with q DTY 2.2 + q DTY 4.1 in MAS is significantly higher under RS and irrigated control than lines with single QTLs. Among MARS PLs, lines with four qDTYs (qDTY 1.1 + qDTY 2.1 + qDTY 3.1 + qDTY 11.1 ) and two QTLs (qDTY 1.1 + qDTY 11.1 ) yielded higher than PLs with other qDTY combinations. The selected PLs showed a yield advantage of 0.3-2.0 t ha-1 under RS. An allelic profile of MAS PLs having same qDTY combination but with different yields under drought was studied. Hierarchical clustering grouped together the selected lines with high yield under drought. Epistasis test showed the interaction of qDTY 4.1 and qDTY 9.1 loci with qDTY 7.1 significantly increased yield under drought and all the lines with higher yield under drought possessed the conserved region of qDTY 7.1 on chromosome 7. The positive interactions among QTLs, effectiveness of QTLs in different backgrounds, introgression of DTY QTLs together with resistance to biotic stresses shall help enhance grain yield under RS.

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