Excessive soil salinity diminishes crop yield and quality. In a previous study in tomato, we identified two closely linked genes encoding HKT1-like transporters, HKT1; 1 and HKT1; 2, as candidate genes for a major quantitative trait locus ( kc7. 1) related to shoot Na+/K+ homeostasis - a major salt tolerance trait - using two populations of recombinant inbred lines (RILs). Here, we determine the effectiveness of these genes in conferring improved salt tolerance by using two near-isogenic lines (NILs) that were homozygous for either the Solanum lycopersicum allele (NIL17) or for the Solanum cheesmaniae allele (NIL14) at both HKT1 loci; transgenic lines derived from these NILs in which each HKT1; 1 and HKT1; 2 had been silenced by stable transformation were also used. Silencing of ScHKT1; 2 and SlHKT1; 2 altered the leaf Na+/K+ ratio and caused hypersensitivity to salinity in plants cultivated under transpiring conditions, whereas silencing SlHKT1; 1/ ScHKT1; 1 had a lesser effect. These results indicate that HKT1; 2 has the more significant role in Na+ homeostasis and salinity tolerance in tomato. [ABSTRACT FROM AUTHOR]