Mapping of quantitative genes controlling Na+ and K+ content in Rice under salinity

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.