In vitro screening for NaCl tolerance of some soybean genotypes

A protocol was standardized for in vitro screening against for salinity tolerance in soybean genotypes, viz., JS 335, Pusa 9712, Pusa 9814, Pusa 24 and Line 3. The cotyledonary segments were cultured on (Murashige and Skoog, Plant Physiology 15:473–497, 1962 ) medium supplemented with 20 mg l −1 2,4- d , 30 g l −1 sucrose and solidified with 8 % agar with pH adjusted to 5.8. Thereafter, the callus was multiplied and sub-divided into 50 ± 5 mg clumps, which were subjected to NaCl stress by sub-culturing on MS medium supplemented with 20 mg l −1 2,4- d along with different concentrations of NaCl, viz. 0, 20, 40, 60, 80, 100, 120, 140 mM. Data suggested that NaCl salinity had a profound effect on callus growth and contents of free proline, total phenols and antioxidative enzyme activities. Callusing was highest (86.7 %) in JS 335 and lowest (31.2 %) in Pusa 24. In vitro screening of callus for salinity tolerance revealed that callus survival was lowest at 120 mM NaCl with only two genotypes, i.e. JS 335 and Pusa 9814 showing 10.2 and 5.8 % survival. The genotypes were ranked based on their salinity stress tolerance ability; JS 335 > Pusa 9814 > Pusa 9712 > Pusa 24 > Line 3. There was a gradual decline in both the fresh as well as dry weights of calli with the increasing salinity. The genotypes differed significantly for endogenous proline content, which was highest in genotype JS 335 followed by Pusa 9814 and Pusa 9712, while Pusa 24 and Line 3 had low proline levels. Similarly, the levels of total phenols increased due to rising salinity levels. The enzymatic studies also revealed the similar pattern with the rising salinity up to 120 mM NaCl. Activities of antioxidative enzymes (superoxide dismutase, catalase and peroxidase) showed differential genotypic pattern due to salt stress. It was noted that the enzyme activities were much higher in the tolerant (JS 335, Pusa 9814 and Pusa 9712) genotypes compared to susceptible (Line 3 and Pusa 24) genotypes.