Selection of donors for salt-tolerance in tomato using physiological traits

Attempts to enhance the salt-tolerance of the cultivated tomato using the tolerance of related wild species of Lycopersicon Mill. have been unsuccessful commercially. An alternative approach is to attempt to accumulate physiological characters that contribute to tolerance within a genotype. We have investigated the relationships between tolerance and certain physiological characteristics in accessions of L. esculentum Mill., L. cheesmanii (Hook) C. H. Mull., L. pennellii (Correll) D'Arcy, L. peruvianum (L.) Mill. and L. pimpinellifolium Mill, with this aim in view. At a salinity equivalent to 40 % of that in an artificial seawater, the growth of young plants was ranked both in absolute terms (fresh weight, dry weight or the growth in area of a leaf that developed during the salt treatment) and relative to growth in a salinity 2 % of that of seawater. In absolute terms, two cultivars of L. esculentum ('Moneymaker' and 'Edkawy') performed about as well as L. pimpinellifolium and better than L. pennellii and L. cheesmanii: L. peruvianum showed the poorest tolerance. In relative terms, L. pimpinellifolium remained the most tolerant of the species, and L. peruvianum the most sensitive. L. cheesmanii was little more tolerant than L. peruvianum. The five species differed in their succulence and the Na: K ratio in leaves that developed during the treatment with salinity. Succulence was higher at low salinity in L. pennellii and L. cheesmanii than in the other species, but increased less on salinization. L. pimpinellifolium showed the greatest increase in succulence on salinization, a consequence of its low water content in 2 % seawater. Sodium concentrations increased dramatically in all five species on salinization: L. pimpinellifolium had the highest and L. esculentum the lowest values. L. peruvianum was notable for maintaining a Na:K ratio of less than 3 throughout the period of the experiment.