The effect of increasing NaCl levels on the potassium utilization efficiency of tomatoes grown under low-K stress

Tomato strains were grown under low-K stress (71 µM K) over a wide range of external Na levels (from 0.014 to 27.8 mM Na) to measure strain response in Na substitution capacity in relation to Na concentration. Relative differences among strains for Na substitution capacity were similar at all Na levels except for the minus Na control treatment. Successive doubling of external Na concentration over the range of Na levels tested resulted in a positive linear response in plant dry weight, under low-K stress, with a similar slope for all five strains. The five strains also were grown at a toxic Na level (87 mM Na) under low and adequate conditions. Plant dry weight was not reduced at the toxic Na level relative to the minus Na control when the strains were grown under low-K stress; however, plant dry weight was reduced an average of fifty-five percent at the toxic Na level relative to the control when the strains were grown under adequate conditions. There was no relationship between Na substitution capacity of strains grown under low-K stress and tolerance to toxic Na levels under adequate conditions.