Genetic analysis of rice yield components under salinity stress

Genetic parameters and combining ability estimates of yield components in rice under salinity stress were investigated using seven-parent full diallel cross analysis. The parents involved were Pusa Basmati 1, Sadri (IRGC acc. 32329), IR64, FL478 (IR66946-3R-178-1-1), CSR28, IR4630-22-2-5-1-3 and IR70023-4B-4-12-3-1. The resulting F1 seeds of the 42 hybrids and seven parents were assessed in the field condition for salinity tolerance at reproductive stage. The experiment was conducted at IRRI in artificially salinized concrete blocks in a randomized complete-block design with three replications. Salinity stress was started at EC 3-4 d S/m by addition of saline water during transplanting and at seedling stage and increased to EC 6-8 d S/m after active tillering stage until maturity. The salinity level was monitored and adjusted when necessary to attain the desired level. Data obtained from diallel was analyzed using Jinks-Hayman's diallel analysis for genetic parameters and Griffing's method 1 model 1 for combining abilities. Significant variation for grain yield and yield components was observed among parents and F1s. Analysis of variance for the combining ability showed that GCA and SCA variance was significant (P less than or equal to 0.001) for all measured variables. Higher GCA-SCA ratio for days to flowering (1.99) and plant height supported the involvement of additive effects for these traits. The high estimate of narrow-sense heritability further supported the involvement of additive effects for days to flowering and plant height. Low GCA-SCA ratio for numbers of fertile tillers, straw yield, number of filled grains and grain yield (0.195) exhibited greater relevance of non-additive gene actions governing yield and its associated traits. Both additive and non-additive effects were found to control the expression of panicle length and spikelet fertility. Among the genotypes, Sadri ranked as the top general combiner for yield and yield components under salinity stress. FL 478 and IR64 were the top general combiner for spikelet fertility.