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

Genetic analysis of salinity tolerance in rice was investigated in five experiments concerning identification of varietal difference for salt tolerance, suitable testing method for salinity screening, discriminating level of salinity for selection and the parameters of measuring salinity tolerance, and to study the genetic behavior of these traits by 8 x 8 diallel cross and generation mean analysis of six crosses including parental, F1, F2, B1 and B2 generations. Varieties differed in their reaction from tolerant to moderately tolerant and moderately tolerant to susceptible but not from tolerant to susceptible or vice versa. Among the four methods cup method was advantageously utilized for varietal evaluation as well as salinity screening. The better discriminating level for selection was observed around 9 ds/m. Low Na+ concentration, low Na/K ratio and lower visual score resulted in better salinity tolerance. Salinity tolerance was partially dominant over susceptibility. Much higher GCA effects than SCA effects in all the traits indicated preponderance of additive gene action for salinity tolerance. Gene asymmetry over all loci showing dominance and this was in favor of recessive alleles. One group of recessive genes that shows dominance was involved in controlling the traits. An excess of recessive genes for Na concentration whereas an equal proportion of dominant and recessive genes for Na/K ratio and visual score in the parents were shown. Tolerant and moderately tolerant parents were genetically similar. + Pokkali, NonaBokra and Binnatoa were the good general combiners. Most of the best crosses were obtained from susceptible parents crossed with tolerant parents. Transfer of salinity tolerant traits from these varieties to modern varieties may offer potential for increasing the level of salinity tolerance in rice. High heterotic effect found in some crosses and significant dominance effect of genes in NonaBokra/BR29 suggests the use of hybrid rice where production of hybrid rice seed is feasible. Analysis of generation means corroborated diallel analysis showing more importance of additive gene action although significant amount of epistasis were observed in four crosses having moderately tolerant and susceptible parents.