Genetic components of salinity tolerance in rice (Oryza sativa L.).

Graphical analysis of variance and covariance showed that P1(IR28) and P2(IR29) had excess recessible alleles in all traits. P6(IR10206-29-2-1) was consistent in showing excess dominant alleles. All traits indicated overdominance. Estimates of genetic components showed the important role of additive (D), dominance (H), and environmental (E) effects in the heritability of salinity tolerance. Gene asymmetry was present and predominance dominant genes are exhibited among the parents. Na+ uptake showed overdominance, while both K+ and Na/K ratio exhibited incomplete to complete dominance. One group of genes controlling Na+ and K+ exhibit dominance while two groups were detected in Na/K ratio. Both the general combining ability (GCA) and specific combining ability (SCA) effects were significant in both Na+ and K+ uptake, suggesting the important contribution of additive and dominance gene action. SCA of Na/K ratio appeared not significant, suggesting that the performance of a single cross progeny can be predicted on the basis of its high negative GCA effect. Reciprocal effects were also present in all traits studied. Among the traits studied P4(IR4595-4-1-13) and P5(IR9884-54-3-IE-P1) were the best general combiners. The best combining parent for Na+ appeared to be P4 crossed with P2 or P5 and for K+, P3 crossed to either P4 or P6. All best combinations have susceptible parents either crossed to moderate on tolerant parents. The presence of reciprocal effects suggested that all susceptible must be used as a male parent. For Na/K ratio the best combination was the cross between P4 and P5, due to maternal effects P4 must be used as female and P5 as male. Low heritability of all traits confirmed the large influence of environmental and non-additive effects to salinity tolerance in rice. The significant dominance effect of genes among the parents studied suggests the potential use of hybrid rice in saline areas. Selection for salinity tolerance must be done at later generation where dominance effects will be dissipated.