Leaf ion concentrations and salt tolerance in barley
Breeding and selection for salt tolerance has been limited because of the large heterogeneity of natural saline soils and the lack of efficient criteria for measuring salt tolerance. Regulation of salt balances in leaves is an important aspect of salt tolerance. This work analyses the relationship between leaf ion concentrations and salt tolerance with the aim of using these traits as indicators of salt tolerance. This is done both in solution culture (hydroponics) and field trials (sprinkler irrigation with saline water). Varieties were found to differ in the amounts of ions accumulated in their leaves. However, these differences did not relate directly with their level of salt tolerance. The lack of correlation was partly due to difficulties in estimating salt tolerance in the field. Also, the Triple Line Sprinkler system (TLS) used in the field experiments posed several problems, the most important ones being related to direct ion absorption by the leaves. The high concentrations of CaC12 (in addition to NaCl) used in the irrigation water added a further complication. In hydroponic experiments, a minimum of 2 mol in-' Ce' was enough to prevent an indiscriminate entry of Na' and to ameliorate the growth inhibition of plants growing at 200 mol in-' NaCl. Higher Caý' concentrations (50 mol in-' CaCl2) reduced even more the concentrations of Na' in leaves without significantly affecting growth. At these high levels of CaCl2 any toxic effect was probably caused by high Clconcentrations.