Interactive effects of Ca2+ and NaCl salinity on the growth of two tomato genotypes differing in Ca2+ use efficiency

Two tomato (Lycopersicon esculentum Mill.) lines differing in Ca²⁺ use efficiency (Ca²⁺ use efficient line 113 and Ca²⁺ use inefficient line 67) were subjected to salinity treatments in two separate experiments to determine whether they differed in salt tolerance. In experiment I, three NaCl and two CaCl₂ treatments were imposed. The Na⁺ concentrations were 1.1, 100 and 150 mM and the Ca²⁺ concentrations were either 1.51 or 10 mM. In experiment II, one NaCl and three Ca²⁺ treatments (as CaCl₂ or CaSO₄) were imposed. The treatments consisted of 150 mM NaCl at either 1.51 mM CaCl₂, 10 mM CaCl₂, or 10 mM CaSO₄. Response to treatments was determined by analysis of growth parameters (shoot and root dry weights, plant height, and root length). Shoot and root dry weight, and root length were depressed as salinity increased in plants lacking additional Ca²⁺. No significant differences in salt tolerance were detected between the two tomato lines after 24 d of salinity treatment. An important finding of this study was that root growth and length appeared to be more sensitive to the effect of CaCI₂ treatment alone and to the effects of CaCl₂ × NaCl treatments. This suggests that over the long term, both root growth and root length may be more sensitive indicators of salinity effects than shoots. Supplemental CaCl₂ had no ameliorative effect on NaCl stress in shoot growth. The inability of Ca²⁺ to counter Cl⁻ entry or toxicity may account for the lack of amelioration. Additional Ca²⁺ as CaSO₄ improved shoot growth of plants exposed to 150 mM NaCl. In contrast, root growth and length were improved by 10 mM Ca²⁺ as either CaCl₂ or CaSO₄.