EFFECT OF SALT STRESS ON WATER RELATIONS AND ANTIOXIDANT ACTIVITY IN TOMATO

We investigated the effects of saline irrigation on water status, antioxidant content and mineral composition of tomato (Lycopersicon esculentum Mill.) fruits. Increasing the electrical conductivity of the irrigation water from 0.5 dS m^-1 (non-salinized control) to 15.7 dS m^-1, caused a reduction of both leaf and root water potentials. Leaf osmotic adjustment was linearly related to the salinity of the irrigation water. Total carotenoids and lycopene concentrations gradually increased until 4.4-dS m^-1 and decreased at higher salinity levels. The increase in plant carotenoids and lycopene contents obtained upon mild saline irrigation was comparable to that obtained via genetic engineering. A moderate salt stress also improved the levels of other desirable components for the processed tomatoes industry (i.e. TSS, nitrates content, acidity). Overall these data indicate that it is possible to improve carotenoids and ascorbic acid contents and antioxidant activity of tomato, with an acceptable yield reduction (10%), by irrigating with saline water containing sea salt up to 4.4-dS m^-1 (0.25% w/v). Adopting targeted agronomic techniques to enhance the nutritional value of tomato fruits is an environment-compatible strategy that may be considered alternative and/or complementary to other approaches. However, an appropriate irrigation scheduling is needed to contain potential hazards of soil salinization associated to long-term irrigation with saline water.