RESULTS: The GY reductions in RS trials compared to NS trials ranged from 79 to 99 %. Plant height (PH) was reduced and days to flowering (DTF) was delayed under RS. Eleven BC1F5 MRQ74 PLs with yield advantages of 1009 to 3473 kg ha(-1) under RS and with yields equivalent to MRQ74 under NS trials were identified as promising drought tolerance PLs. Five best PLs, IR 98010-126-708-1-4, IR 98010-126-708-1-3, IR 98010-126-708-1-5, IR 99616-44-94-1-1, and IR 99616-44-94-1-2 with a yield advantage of more than 1000 kg ha(-1) under RS and with yield potential equivalent to that of MRQ74 under NS were selected. The effect of three drought grain yield QTLs under RS in MRQ74 was validated. Under NS, PLs with two qDTY combinations (qDTY 2.2 + qDTY 12.1 ) performed better than PLs with other qDTY combinations, indicating the presence of a positive interaction between qDTY 2.2 and qDTY 12.1 in the MRQ74 background.
CONCLUSION: Drought tolerant MRQ74 PLs with a yield advantage of more than 1000 kg ha(-1) under RS were developed. Differential yield advantages of different combinations of the qDTYs indicate a differential synergistic relationship among qDTYs.
RESULTS: Based on class analysis of the QTL combinations, the identified superior QTL classes in F3/BC1F3/BC2F3 generations with positive QTL x QTL and QTL x background interactions that were captured through phenotyping maintained its superiority in yield under non-stress (NS) and reproductive-stage drought stress (RS) across advanced generations in all five studies. The marker-assisted selection breeding strategy combining both genotyping and phenotyping in early generation significantly reduced the number of genotypes to be carried forward. The strategy presented in this study providing genotyping and phenotyping cost savings of 25-68% compared with the traditional marker-assisted selection approach. The QTL classes, Sub1 + qDTY 1.1 + qDTY 2.1 + qDTY 3.1 and Sub1 + qDTY 2.1 + qDTY 3.1 in Swarna-Sub1, Sub1 + qDTY 1.1 + qDTY 1.2 , Sub1 + qDTY 1.1 + qDTY 2.2 and Sub1 + qDTY 2.2 + qDTY 12.1 in IR64-Sub1, qDTY 2.2 + qDTY 4.1 in Samba Mahsuri, Sub1 + qDTY 3.1 + qDTY 6.1 + qDTY 6.2 and Sub1 + qDTY 6.1 + qDTY 6.2 in TDK1-Sub1 and qDTY 12.1 + qDTY 3.1 and qDTY 2.2 + qDTY 3.1 in MR219 had shown better and consistent performance under NS and RS across generations over other QTL classes.
CONCLUSION: "Deployment of this procedure will save time and resources and will allow breeders to focus and advance only germplasm with high probability of improved performance. The identification of superior QTL classes and capture of positive QTL x QTL and QTL x background interactions in early generation and their consistent performance in subsequent generations across five backgrounds supports the efficacy of a combined MAS breeding strategy".
RESULTS: The drought screening was successful in screening germplasm with a yield reduction of up to 60% and heritability for grain yield under drought was up to 78%. There was a wider phenotypic and molecular diversity within the panel, indicating the suitability of the population for quantitative trait loci (QTL) mapping. Structure analyses clearly grouped the accessions into three subgroups with admixtures. Linkage disequilibrium (LD) analysis revealed that LD decreased with an increase in distance between marker pairs and the LD decay varied from 5-20 cM. The Mixed Linear model-based structured association mapping identified 80 marker trait associations (MTA) for grain yield (GY), plant height (PH) and days to flowering (DTF). Seven MTA were identified for GY under drought stress, four of these MTA were consistently identified in at least two of the three analyses. Most of these MTA identified were on chromosomes 2, 5, 10, 11 and 12, and their phenotypic variance (PV) varied from 5% to 19%. The in silico analysis of drought QTL regions revealed the association of several drought-responsive genes conferring drought tolerance. The major-effect QTLs are useful in marker-assisted QTL pyramiding to improve drought tolerance.
CONCLUSION: The results have clearly shown that structured association mapping is one of the feasible options to identify major-effect QTLs for drought tolerance-related traits in rice.