راکش کومار سینگ

Rice is one of the most important cereal with great variation, which is a major food for more than half of the world’s population. Mapping quantitative traits loci is one of the applied and momentous approaches to study yield-related traits. In present study 188 F4 rice lines derived from CSR28 and Sadri cross along with the parents were used for genotyping and phenotyping. The objective of this study was to construct high saturation linkage map using SNPs markers (Infinium Illumina 6K SNP chip) and QTL identification of yield-related traits in 188 F4 population. Mapping of quantitative traits loci led to identify 21 QTLs for studied traits on chromosomes 1, 2, 3, 5, 7, 8 and 10. One QTL (qFG_N-3-1) was identified for filled grain number per plant on chromosome 3. For spikelet fertility, three QTLs (qSpkF_N-2-1, qSpkF_N-3-1 and qSpkF_N-5-1) were mapped on chromosomes 2, 3 and 5, which explained 29.28 percentage of phenotypic variation. One QTL (qGY_N-8-1) was detected for grain yield on chromosome 8, which was flanked by 9037125 and 9049928 markers. In conclusion, besides the QTLs which is reported for first time, the QTLs were consistent as reported previously, could be introduced as reliable QTLs that is suitable for marker assisted breeding programs.

This research was conducted to validate and fine map the region attributed to salinity tolerance on chromosome1 in rice (Saltol) at International Rice Research Institute (IRRI) during 2005 to 2007. A major effect QTL (Saltol) which is responsible for Na+ and K+ uptake and their ratio was identified using F8 recombinant inbred lines (RILs) of Pokkali/ IR29 cross on chromosome 1. This QTL explained around 64.3 to 80.2% of the phenotypic variation for the mentioned traits. Fine mapping was done using 10 SSR and EST-SSR markers and near isogenic lines (BC3F4), derived from IR29 × Pokkali that were produced for this trait. Random BC3F4 individuals were genotyped and phenotyped under two different electrical conductivities at seedling stage. QTL responsible for salinity tolerance at both ECs, were found in the same place in Saltol region, which explained 18 and 24% of the phenotypic variation for SES scores, respectively. According to the present results, possible location of Saltol was found in the interval around 1.2 cM on chromosome 1 that could physical map. It was around 350Kb. This QTL was mapped at the intervals of RM8094, RM3412 and CP6224. Therefore, molecular breeding for salinity tolerance in Iranian genotypes could be done using the mentioned markers.

To identify the QTLs responsible for salinity tolerance in tolerant line (FL478), 2350 BC3F4lines derived from IR29×FL478 were used at IRRI during 2005-2007. Significant differences among back cross families were found for salinity tolerance scoring, sodium and potassium concentration and their ratio. The results showed that the low ratio for Na+/K+ in FL478 is mainly through lower amount of Na+ uptake rather than high amount of K+. Selective Genotyping with 500 extreme individuals indicated that the highest and lowest number of QTLs for Na+ and K+, respectively. The result of QTL mapping by SSRmarkers using 500 extremes individuals showed the highest and lowest number of QTLs for Na+ and K+ respectively. Composite interval mapping analysis revealed that in addition to chromosome 1, there are major QTLs on chromosomes 6, 8, 10 and 12 for salinity tolerance at seedling stage in rice. In the Saltol region, one QTL was found for Na+ concentration while for the other traits the QTLs were found in the upper part of Saltol region. Major QTLs responsible for salinity tolerance scoring were located on hromosomes 1, 3 and 6. For Na+ concentration and Na+/K+ ratio, chromosomes 1, 3, 6, 10 and 12 contained the major QTLs which mainly originated tolerant parent. The epistatic effects were not found for any of detected major QTLs. Based on the present results, breeding methods for QTLs pyramiding using marker-assisted selection could be very useful for the development of new varieties with a high level of salt tolerance by targeting several major QTLs for salt-tolerance using FL478.