Interactive effects of salinity and air humidity on two tomato cultivars differing in salt tolerance

An environmentally controlled experiment was conducted in growth chambers to investigate the interactive effects of salinity and air humidity on two cultivars of tomato (Lycopersicon esculentum Mill.), Daniela (relatively salt tolerant) and Naomi (relatively salt sensitive). One month after germination, the plants were exposed for 15 days to factorial combinations of two salinity levels, 0 (control) and 80 mM sodium chloride (NaCl), and two relative humidity (RH) levels, 30% and 70%. The NaCl treatment decreased the growth of cv. Naomi by 34% and 21% at 30% and 70% RH, respectively, while there was no decrease in the growth of cv. Daniela at 30% RH and only a slight decrease at 70% RH. Under NaCl treatment, cv Daniela had significantly lower Na+ concentrations in leaves and stems and a higher root-to-shoot ratio than cv. Naomi at both relative humidities. Salt tolerance of cv. Daniela may be related to its high root-to-shoot ratio and its ability to exclude Na+ from the shoot. NaCl-treated plants of cv. Daniela had a lower biomass at 70% than at 30% RH. Conversely, NaCl-treated plants of cv. Naomi had a greater biomass at 70% compared with 30% RH. The ameliorating effects of high RH on NaCl-induced growth reductions in cv. Naomi could be attributed to an increase in leaf area, root growth, photosynthetic rate, and stomatal conductance and a decrease in Cl- concentration in leaves. The overall findings of this study suggest that the growth of salt-sensitive tomato cultivars under saline conditions could be improved by increasing air humidity.