Variability and genetics of salt tolerance in japonica rice (Oryza sativa L.)

Salinity tolerance among japonicas studied in depth, showed that the reductions in seedling height, dry shoot weight, and dry root weight were directly related to the tolerance level. The tolerant varieties absorbed less Na+ and maintained a low Na-K ratio in shoot. Shoot K+ did not show any relationship with tolerance. Correlation among the tolerance criteria showed that shoot Na+ concentration and Na-K ratio were highly correlated with salt tolerance. Comparison between indica checks and japonicas showed that the tolerance of Pokkali (indica) was superior to the best tolerant japonica. Study on the genetics of salt tolerance by diallel analysis revealed the presence of both additive and dominance gene effects for shoot Na+ concentration was significant. Covariance-variance graphical analysis showed that tolerant varieties possesed most dominant alleles whereas susceptible varieties had most recessive alleles for Na+ uptake. The graphical analysis further indicated the partial dominance of salinity tolerance. Four gene groups governed the shoot Na+ concentration. The narrow-sense heritability was 0.49. The preponderance of additive gene effects of shoot K+ concentration were detected. Covariance-variance graphical analysis showed that tolerant varieties possessed most dominant alleles whereas susceptible varieties has most recessive alleles. Partial dominance of K+ uptake was indicated in the analysis. Two gene groups governed the shoot K+ concentration. The narrow-sense heritability was 0.53 and broad-sense heritability was 0.72, indicating both additive and dominance gene action for shoot K+ concentration. Both additive and dominance gene effects were present for shoot Na-K ratio. Covariance-variance graphical analysis showed that tolerant varieites possessed most dominant alleles whereas susceptible varieties had most recessive alleles. The graphical analysis indicated partial dominance of Na-K ratio. Five gene groups controlled the shoot Na-K ratio. The narrow-sense heritability was 0.51. Salt tolerance in japonica rice as determined by shoot Na+, K+, and Na-K ratio appeared to be determined by several genes. Narrow-sense heritability of all the three traits was low (around 0.50). Data suggested that in breeding for salt tolerance, selection should be delayed to later generations