(22)Na influx is significantly lower in salt tolerant groundnut (Arachis hypogaea) varieties

Distinct varieties differing in salt tolerance were initially identified from two separate green house experiments using two systems; solution as well as soil culture. The first screening involved a diverse group of 27 cultivars. Several physiological traits; Chlorophyll Stability Index (CSI), Salt Tolerance Index (STI) and ion content were determined to screen the cultivars for differences in salt tolerance using solution culture in the first experiment. A set of six varieties (three tolerant and three susceptible) were selected from this experiment and then subjected again to salt stress adopting a natural soil system in the second experiment which involved a screening approach essentially similar to that of the first experiment. In the third experiment using two distinct cultivars differing in salt tolerance selected from experiment II, (22)Na influx rate was determined in the root and shoot at the end of a 24 h salt imposition in Hoagland's nutrient system containing 180 KBq of (22)Na. The results suggested that there were distinct differences in (22)Na influx rate into root and concurrently in the shoot. The salt tolerant Spanish improved and one of the moderately tolerant Trombay variety TAG 24, showed good regulation of (22)Na influx resulting in low (22)Na concentration. The salt susceptible variety JSP39 had nearly 7-8 fold higher root (22)Na content as compared to the tolerant and moderately tolerant cultivars. The results have highlighted the importance of Na exclusion as an important determinant of salt tolerance in groundnut.