Abstract
Drought is the major abiotic stress to rice grain yield under unpredictable changing climatic scenarios. The widely grown, high yielding but drought susceptible rice varieties need to be improved by unraveling the genomic regions controlling traits enhancing drought tolerance. The present study was conducted with the aim to identify quantitative trait loci (QTLs) for grain yield and root development traits under irrigated non-stress and reproductive-stage drought stress in both lowland and upland situations. A mapping population consisting of 480 lines derived from a cross between Dular (drought-tolerant) and IR64-21 (drought susceptible) was used. QTL analysis revealed three major consistent-effect QTLs for grain yield (qDTY1.1, qDTY1.3, and qDTY8.1) under non-stress and reproductive-stage drought stress conditions, and 2 QTLs for root traits (qRT9.1 for root-growth angle and qRT5.1 for multiple root traits, i.e., seedling-stage root length, root dry weight and crown root number). The genetic locus qDTY1.1 was identified as hotspot for grain yield and yield-related agronomic and root traits. The study identified significant positive correlations among numbers of crown roots and mesocotyl length at the seedling stage and root length and root dry weight at depth at later stages with grain yield and yield-related traits. Under reproductive stage drought stress, the grain yield advantage of the lines with QTLs ranged from 24.1 to 108.9% under upland and 3.0–22.7% under lowland conditions over the lines without QTLs. The lines with QTL combinations qDTY1.3+qDTY8.1 showed the highest mean grain yield advantage followed by lines having qDTY1.1+qDTY8.1 and qDTY1.1+qDTY8.1+qDTY1.3, across upland/lowland reproductive-stage drought stress. The identified QTLs for root traits, mesocotyl length, grain yield and yield-related traits can be immediately deployed in marker-assisted breeding to develop drought tolerant high yielding rice varieties.
Highlights
The development of rice cultivars with improved tolerance for drought stress is important to increase the production of rainfed rice ecosystems
The mean days to 50% flowering (DTF) and plant height at maturity of the population were intermediate to both parents
With the root and drought response traits measured in this study from a large population (>300 recombinant inbred lines (RILs)) at times ranging from seedling stage to harvest, we aimed to (1) integrate the relationships among traits at different growth stages in terms of their effects on yield and (2) identify the genetic loci controlling the traits that have an effect on yield under drought
Summary
The development of rice cultivars with improved tolerance for drought stress is important to increase the production of rainfed rice ecosystems. Several studies involving grain yield as the main selection criterion have identified stable, consistent and large-effect QTLs for grain yield under reproductive-stage drought stress (Bernier et al, 2007; Venuprasad et al, 2009; Vikram et al, 2011; Ghimire et al, 2012; Mishra et al, 2013; Swamy and Kumar, 2013; Yadaw et al, 2013; Dixit et al, 2014a,b). Some of these identified QTLs have been deployed to develop high-yielding reproductive-stage droughttolerant rice varieties (Kumar et al, 2014). Continued efforts are needed to identify QTLs and traits that confer improved rice yields under multiple types of drought stress
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