Functional traits of okra cultivars (Chinese green and Chinese red) under salt stress

Two okra cultivars (Chinese green and Chinese red) were subjected to salt stress for 12 weeks. Salt stress treatments T1 (20.8 mM), T2 (103.3 mM), T3 (180.0 mM) and T4 (257.0 mM) were applied with equal proportions of NaCl and CaCl₂ in Hoagland nutrient solution. Salt stress significantly affects photosynthesis, transpiration, stomatal conductance, water use efficiency, water potential, plant height, root length, fresh weight and dry weight of both okra cultivars in every salt stress treatment. At T2, T3 and T4, Chinese red plants maintained their physiological and growth traits up to Weeks 9, 6 and 3, respectively; beyond these salt-stress durations, growth reductions were found. Similarly, Chinese green plants maintained their growth up to Weeks 9, 5 and 3, respectively, at T2, T3 and T4 treatments. In comparison, Chinese red showed more tolerance than Chinese green. According to the results, the third and ninth weeks are the tolerance threshold limits for both cultivars to sustain their physiological traits and growth under T4 and T2 salinity treatments. Similarly, Chinese red has the threshold limit to bear T3 treatment up to the eighth week and Chinese green, up to the fifth week. Thus, this study provides a new method to determine the threshold value of crops with respect to duration under salt stress. This finding would be useful in the field of water saving and utilisation of saline water resources.