In this paper, a number of strategies to overcome the deleterious effects of salinity on plants will be reviewed; these strategies include using molecular markers and genetic transformation as tools to develop salinity-tolerant genotypes, and some cultural techniques. For more than 12 years, QTL analysis has been attempted in order to understand the genetics of salt tolerance and to deal with component traits in breeding programmes. Despite innovations like better marker systems and improved genetic mapping strategies, the success of marker-assisted selection has been very limited because, in part, of inadequate experimental design. Since salinity is variable in time and space, experimental design must allow the study of genotype×environment interaction. Genetic transformation could become a powerful tool in plant breeding, but the growing knowledge from plant physiology must be integrated with molecular breeding techniques. It has been shown that the expression of several transgenes promotes a higher level of salt tolerance in some species. Despite this promising result, the development of a salt-tolerant cultivar by way of transgenesis has still not been achieved. Future directions in order to overcome the present limitations are proposed. Three cultural techniques have proved useful in tomato to overcome, in part, the effects of salinity: treatment of seedlings with drought or NaCl ameliorates the adaptation of adult plants to salinity; mist applied to tomato plants grown in Mediterranean conditions improves vegetative growth and yield in saline conditions; and grafting tomato cultivars onto appropriate rootstocks could reduce the effects of salinity.

Tomato crop productivity under salinity can be improved by grafting cultivars onto salt‐tolerant wild relatives, thus mediating the supply of root‐derived ionic and hormonal factors that regulate leaf area and senescence. A tomato cultivar was grafted onto rootstocks from a population of recombinant inbred lines (RILs) derived from a Solanum lycopersicum × Solanum cheesmaniae cross and cultivated under moderate salinity (75 mm NaCl). Concentrations of Na⁺, K⁺ and several phytohormones [abscisic acid (ABA); the cytokinins (CKs) zeatin, Z; zeatin riboside, ZR; and the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid (ACC)] were analysed in leaf xylem sap in graft combinations of contrasting vigour. Scion leaf area correlated with photosystem II (PSII) efficiency (F_v/F_m) and determined fruit productivity. Xylem K⁺ (but not Na⁺), K⁺/Na⁺, the active CK Z, the ratio with its storage form Z/ZR and especially the ratio between CKs and ACC (Z/ACC and Z + ZR/ACC) were positively loaded into the first principal component (PC) determining both leaf growth and PSII efficiency. In contrast, the ratio ACC/ABA was negatively correlated with leaf biomass. Although the underlying physiological mechanisms by which rootstocks mediate leaf area or chlorophyll fluorescence (and thus influence tomato salt tolerance) seem complex, a putative potassium–CK interaction involved in regulating both processes merits further attention.

Control of intracellular Na⁺ and K⁺ concentrations in plant tissues under saline conditions is crucial for salt tolerance. In this study, two Na⁺ ‐selective class I‐HKT transporters, HKT1;1 and HKT1;2, from tomato were found to be closely linked in proximity to the position with the maximum LOD score for major QTLs in chromosome 7 (at a distance of 35 kb), thus contributing to stem and leaf Na⁺ and K⁺ in two populations of tomato RILs derived from two salt‐tolerant lines from wild tomato species S. pimpinellifolium and S. cheesmaniae. This result, together with their patterns of expression and phenotypic effects on a pair of near isogenic lines (NILs) differing in terms of HKT1‐like alleles, support the hypothesis that HKT1;1 and/or HKT1;2 genes underlies a major tomato QTL for shoot Na⁺ / K⁺ .