Effect of drought stress on growth, water relations, and gas exchange of two lines of sunflower differing in degree of salt tolerance

Responses of a salt-tolerant line (Euroflor) and st salt-sensitive line (SMH-24) of sunflower to water deficit were assessed when 2-wk-old plants were subjected for 16 d to 0 or -0.6 MPa polyethylene glycol (8000) in aerated nutrient solution. The salt-tolerant line was superior to the salt-sensitive one in growth performance under simulated drought conditions. The two lines did not differ in leaf water, osmotic, and turgor potentials under water deficit. A decrease in leaf water and osmotic potentials as well as an increase in turgor potential were observed uniformly in both lines at -0.6 MPa polyethylene glycol. Stomatal conductance, transpiration, and gas exchange in Euroflor were not affected by water deficit, whereas all were in SMH-24. Euroflor had significantly greater values for all these variables than SMH-24. The lines did not differ in water-use efficiency. From this study it is clear that salt tolerance and drought tolerance of the two lines examined share osmotic effect. The differing degree of drought tolerance of the lines can be related to stomatal conductance, transpiration, and gas exchange but is independent of any of the water relation parameters measured.