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Abstract
Lycopersicon esculentum Mill. cv. New Yorker, Solanum pennellii Corr. PI 246502, and 16 stable breeding lines of horticultural type derived from this cross were evaluated under saline (0.1 m NaCl) and control conditions. The breeding line population exhibited a much wider range of salt tolerance than that found in the cultivated species. Relative ability to regulate sodium accumulation in the leaves was significantly correlated with growth under saline irrigation. Absolute levels of foliar sodium or chloride accumulated under saline irrigation were not significantly correlated with plant growth. Regulation of ion accumulation was assessed as the ratio of foliar ionic content in saltgrown plants to foliar content in control plants, a value which we define as ion regulation index (IRI). A low index indicated regulation of accumulation of a particular ion. Regulation of ion uptake is interpreted as reflecting an effective homeostatic system. The homeostasis was attributed to tomato, and salt tolerance improvement occurred only if the requisite homeostasis was combined with other factors conferred by S. pennelli. Information regarding occurrence and possible mechanisms of this type of salt tolerance is reviewed.