Responses of lettuce to salinity. I. Effects of NaCl and Na2SO4on growth

Two lettuce cultivars (Lactuca sativa L., cv. Calmar and cv. Climax) were selected to compare their tolerance to salt stress. The plants were grown in a hydroponic system using a 0.5 modified Hoagland solution. Treatments of 0, 40, 80, and 120 mol m–3 NaCl or 0 and 20 mol m–3 Na2SO4 were started when the second leaf above the cotyledons appeared. The plants were harvested 20 days later. Climax showed a greater tolerance to salinity at the 40 mol m–3 NaCl concentration; the % decrease in both shoot and root fresh weight was significantly less than Calmar. No differences between the cultivars were found in the Na2SO4 experiments. Differences in root Cl– content at the 40 mol m–3 concentration corresponded to an enhanced water content of the roots. A mechanism for the observed differences in salt tolerance between the two cultivars is discussed.