Identification of QTLs for Salt Tolerance at the Germination and Seedling Stages in Rice

Rice is highly sensitive to salinity stress during the seedling establishment phase. Salt stress is widely occurring in cultivated areas and severely affects seed germination ability and seedling establishment, which may result in a complete crop failure. The objective of the present study is to identify quantitative trait loci (QTLs) related to salt tolerance of the germination and seedling stages in a rice backcross inbred line (BIL) population that was derived from a backcross of an Africa rice ACC9 as donor and indica cultivar Zhenshan97 (ZS97) as the recurrent parent. Under salt stress, ACC9 exhibited a higher germination percentage, but more repressed seedling growth than ZS97. Using the BIL population, 23 loci for germination parameters were detected at the germination stage and 46 loci were identified for several morphological and physiological parameters at the seedling stage. Among them, nine and 33 loci with the ACC9 alleles increased salt tolerance at the germination and seedling stages, respectively. Moreover, several major QTLs were found to be co-localized in the same or overlapping regions of previously reported genes for salt stress. These major loci will facilitate improving salt-tolerance rice in genome-breeding programs.

Genetic gain and morpho-physiological characterisation of BILs (Backcross inbred lines) under different moisture regimes in wheat (Triticum aestivum. L)

Drought stress is one of the major yield limiting factors in realising the full genetic potential of wheat. In the present study, backcross inbred line population derived from GW322*2/ HI1500 was characterized for different morpho-physiological traits and grain yield under rainfed and irrigated conditions. Principal component analysis revealed that first five components explained over 66.35 per cent of variation. Grain yield showed significant correlation with biomass and physiological traits viz., NDVI2, NDVI3, NDVI5, CT2, CT3 and CT4. The analysis of variance on grain yield data showed that mean squares of environments, genotypes and GEI were highly significant (p 0.01). To determine effects of GEI on grain yield, data were subjected to AMMI and GGE biplot analysis, which identified BILs G20, G2, G254, G214, G44 and G64 as the most stable and high yielding. Based on Smith selection index expected genetic gain for grain yield at 5% was 131.01gm/plot. Hence, selecting genotypes based on morpho-physiological traits will be rewarding under moisture depleting environment.

Mapping QTLs for cold tolerance at seedling stage using an Oryza sativa × O. rufipogon backcross inbred line population

Tolerance to low temperature is an important factor affecting the growth and development of rice (Oryza sativa L.) at an early growing season in the temperate region, and at high altitudes of tropical regions. In this study, a backcross inbred line (BIL) population derived from an interspecific cross between Xieqingzao B (O. sativa L.) and an accession of Dongxiang wild rice (O. rufipogon Griff.) was used to identify quantitative trait loci (QTLs) associated with cold tolerance at the seedling stage. Seedlings were treated with a temperature of 6°C for 2 days and seedling mortality was measured for QTL mapping. QTL analysis was performed on the whole BIL population and on one subpopulation that showed Xieqingzao B homozygous at QTL detected in the whole population. One major QTL, qSCT8, and one QTL, qSCT4.3, with smaller effect was found in the whole population. The QTLs qSCT8 and qSCT4.3 were mapped on chromosome 8 and 4, explaining 60.96% and 8.83% of the phenotypic variance, respectively. In the subpopulation, three QTLs, qSCT4.1, qSCT4.2 and qSCT12, accounting for 56.22%, 57.62% and 53.09% of the phenotypic variance, respectively, were detected on chromosome 4 and 12. At all five loci, the alleles introduced from the Dongxiang wild rice were effective in decreasing seedling mortality. Our results provide a basis for fine mapping and cloning of QTLs associated with cold tolerance, and the markers linked with QTLs could be used to improve the cold tolerance of rice varieties by marker-assisted selection.