The rootstock effect on the tomato salinity response depends on the shoot genotype

With the aim of determining whether the rootstock effect depends on the shoot genotype, two distinctly different tomato (Lycopersicon esculentum Mill) genotypes, Moneymaker with excluder character and UC-82B with includer character, were grafted onto a commercial tomato hybrid (cv. Kyndia). Self-grafted plants were used as controls. The rootstock effect was first assessed by growing plants at different NaCl concentrations (0, 50 and 100 mM) under controlled conditions, and by determining the growth and physiological responses of the grafted plants after 35 days of salt treatment. The rootstock did not affect the shoot growth when Moneymaker was used as scion. However, when UC-82B was used as scion, the shoot biomass reduction induced by salinity was lower in plants with rootstock Kyndia than in the self-grafted plants. The effectiveness of the UC-82B grafted plants onto Kyndia was also showed on the basis of fruit yield. The rootstock also induced significant physiological changes in the leaves of these plants, with the most important changes being found in the ion saline accumulation and Na+/K+ ratio. The Na+ and Cl- accumulation induced by salinity in leaves of UC-82B was substantially lower when the root of this cultivar had been substituted by that of the cv. Kyndia, whereas the K+ concentration was less reduced by salinity, and consequently the leaf Na+/K+ ratio values were much lower. These results suggest that the saline ion accumulation in leaves was controlled predominantly by the genotype of the rootstock. In addition, the characteristics of the rootstock able to induce salt tolerance to the shoot depend on the salt tolerance mechanism of the shoot genotype. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.