Genetic components and QTL analysis of salinity tolerance at reproductive stage in rice (Oryza sativa L.)

Genetic components and combining ability estimates of rice (Oryza sativa L.) at seedling and reproductive stage under salinity stress were investigated using a seven-parent full diallel cross analysis. The parental lines involved were IR4630-22-2-5-1-3, FL478 (IR66946-3R-178-1-1), Pusa, Basmati 1, CSR28, IR64,IR70023-4B-R-12-3-1 and Sadri. For the seedling stage experiment, the resulting 42 f sub 1's and seven parents were exposed to salinity stress 4 days after germination at EC 12 dS/m in IRRI [International Rice Research Institute] phytotron. Data recording was done 14 days after salinization, when the susceptible parents were severely affected. The general combining ability estimates revealed that among the parents, FL478 was the best general combiner for salinity score, shoot dry weight, K sup + uptake and a good combiner for Na sup + exclusion and K-Na ratio. Estimates of genetic parameters revealed that both additive and dominance effects were significant for salinity score, shoot height, root dry weight, Na sup +, K sup + and K-Na ratio. For root length and shoot dry weight, only dominance effects were significant. For the reproductive stage experiment, the seven parents and 42 F sub 1's were exposed to salinity stress in the field condition after active tillering stage to maturity at EC 6 to 8 dS/m. The general combining ability estimates at reproductive stage revealed that among the parents, Sadri was the best general combiner for grain yield and good to average combiner for the most of the yield components. In the F sub 1 hybrids, Sadri x CSR28 and Sadri x FLA478 had the highest grain yield with 55.68 and 54.29 g., respectively. Estimate of genetic parameters of the 14 characters at productive stage revealed that both additive and dominance effects were significant for days to flowering, plant height, panicle length, number of sterile spikelets fertility, 1000-grain weight, Na sup +, K sup + and K-N ratio. For number of panicles, straw dry weight, number of fertile spikelets, number of total spikelets and grain yield, only dominance effects were significant. The environmental effects were significant for all traits except days to flowering, plant height, straw dry weight and number of total spikelets. The 232 F sub 2 progenies produced from the cross between Sadri and FL478, were used for phenotyping under salinity stress at reproductive stage and identification of associated QTL regions. The phenotyping experiment was conducted in the artificially salinized field condition using salt stress of 6-8 dS/m. The performance of F sub 2 population showed transgressive segregation in the yield components under salinity stress. A genetic linkage map was constructed using 123 microsatellite markers on 232 F sub 2 progenies. The total size of the linkage map was 1855 cM and distance between markers raised from 0.9 to 60.6 cm with an average of 15 cm. QTL identification was done through composite interval mapping using QGENE software. In total, 36 QTLs were detected, 35 QTLs for yield components under salinity stress and one major QTL for pericarp color. These QTLs were distributed on all rice chromosomes except chromosomes 11 and 12. Of all 36 QTLs, eight QTLs accounted for more than 10% of the phenotypic variation. The QTLs detected in this study may be useful for molecular breeding for 12 identifying useful genes for salinity tolerance.