Abstract:
Studies on salt tolerance of 8 indica rice cultivars; RD25, RD23, RD8, Khao Dawk Mali 105, Nahng Mon S-4, Niaw San-pah-tawng, Leuang Pra-tew 123, and Khao Tah Haeng 17 obtained from the research project "New Varieties of Rice for Saline and Acid Soil Through Tissue Culture", which used tissue culture in combination with NaCl 0%, 1% and 2% as a mean of inducing somaclonal variation. R0 refers to the regenerants obtained through tissue culture and R1 refers to the progenies of R0. These studies were made on R2 through R5 by mainly selecting of somaclonal variants using 0.5% NaCl in nutrient solution giving electrical conductivity 9-10 mmho/cm at 25ํC. The selection began when the R2 seedlings attained 5-leaf stage using hydroponic culture method for four weeks, the survivors were planted in ordinary soil for seed production and the procedures were repeated to R5. The selection in the seedling stage of 322 lines of R2, 172 lines (53.4%) survived through R5. Of these, three lines were found to be high tolerance; Leuang Pra-tew 123 (89.7% survival), Khao Dawk Mali 105 (54.0%) and RD23 (53.4%), which the survivors exceeded 50%. The other less tolerant lines were Khao Tah Haeng 17, RD25, Nahng San-pah-tawng and RD8, which the survival rates in the R5 were 18.0%, 17.8%, 17.4%, 17.1% and 3.1%. It is interesting to note that, most of the salt tolerant lines selected are from tissue culture which has 1% and 2% NaCl added to the medium during callus stage, however, Nahng Mon S-4 and Niaw Sun-pah-tawng are from NaCl-free medium. The analysis of ions in the roots and leaves of plant grown in nutrient solution which 0.5% NaCl added, showed distinctly high level of accumulation of Na and Cl in all plants studied. However, the plants from the most tolerant line accumulated less ions than the moderately tolerant lines and controls. Accumulation of K+ and Ca++ was slightly reduced in all lines tested, as a result of high concentration of NaCl. The F1 of the most tolerant line, Leaung Pra-tew 123 (R5-LPT123 TC-171) and the plants raised from breeder seeds gave 65.7% survival (when plants from breeder seed were male) and 57.1% (a reciprocal cross) respectively. This indicates that genes controlling salt tolerant character of this cultivar are in nucleus, and are of incomplete dominant types. Gene expression in such heterozygous state could be the result of a gene in one locus (which may be single gene or possibly multiple allele) or genes in more than one loci (polygene). Chromosome counts from roots of the most tolerant lines of each cultivar and the plants raising from breeder seeds showed 2n=24 in all plants. so, the change in factors responsible for salt tolerance is likely to be in the gene level