A solution culture experiment was conducted to evaluate the salinity tolerance of 15 tomato genotypes in Hoagland’s nutrient solution with three levels of NaCl (0, 75, and 150 mM). The experiment was conducted in completely randomized design with three replicates. After 30 days of imposition of salt stress, gas exchange parameters including transpiration rate, stomatal conductance, CO₂ assimilation rate, and intercellular CO₂ concentration were recorded and the harvested plants were characterized for growth (shoot/ longest root lengths and fresh/dry weights) and ionic characteristics (Na⁺, K⁺ and K⁺/Na⁺ ratio) parameters. All growth and gas exchange parameters decreased with increasing NaCl concentrations. However, this decrease was less in salt-tolerant genotypes as compared to salt-sensitive genotypes. It was also observed that with the increasing NaCl concentration in the rooting medium, the amount of Na⁺ in the plant tissues increased while the amount of K⁺ ion decreased. Thus, it was concluded that the plants with more K⁺ absorbing ability, with high K⁺/Na⁺ ratio, and higher growth were more salt-tolerant. Also, the results showed that fresh and dry weights, gas exchange characteristics, and K⁺/Na⁺ ratio were very effective in determining salt tolerance of tomato. Considering the genotypes, Indent-1 and Nagina were characterized as salt tolerant and the Red Ball and Peto-86 as salt sensitive under saline conditions.

Keywords: Salinity tolerance, K+/Na+, Photosynthesis, Growth

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