Variability for some physiological characters affecting salt tolerance in tomato

Salt tolerance in Lycopersicon has been found in wild species, but these are of limited use in breeding because of the transfer of undesirable characters. We demonstrate here the existence of variability for some physiological characters related to salt tolerance in modern tomato cultivars. This variability could be the basis for breeding programmes aiming at introducing, in one genotype, some of these physiological characters. Nine tomato cultivars were grown in hydroponic culture with half strength Hoagland solution, with and without NaCl (50 mm). We estimated transpiration from loss of solution volume, Na+ contents in leaves 2, 5 and 10, the area of the 5(th) leaf, and fresh and dry shoot weight. The total Na+ content in the plant expressed as a proportion of the Na+ in the nutrient solution absorbed by the plant (root Na+ selectivity) varied widely - between just 2.8 % for Moneymaker to 7.0 % for Energy. There was less variability for leaf tissue tolerance, estimated as the relation between salt-induced reduction in the area of the 5(th) leaf and Na+ concentration of this leaf: Energy showed the highest leaf tissue tolerance and Moneymaker the lowest. The ratio of Na+ concentration of 10(th) leaf / Na+ of 2(nd) leaf (leaf-to-leaf tolerance), estimates the capacity for accumulating Na+ in old (10(th)) relative to young (2(nd)) leaves. This character varied from 3.4 (Pera) to 1.3 (Daniela). The highest K+/ Na+ ratio was shown by Atletico (3.4) while the lowest by Edkawy (1.6). A salt tolerant tomato cultivar should be one with the root Na+ selectivity of Moneymaker, the leaf tissue tolerance of Energy, the leaf-to-leaf tolerance of Pera and the K+/Na+ ratio of Atletico.