Responses of a salt-tolerant and a salt-sensitive line of sunflower to varying sodium/calcium ratios in saline sand culture

The effects on two-week-old plants of a salt-tolerant line (Euroflor) and a salt-sensitive (SMH-24) line of sunflower, of varying sodium/calcium (Na/Ca) ratios in a saline growth medium were assessed after three weeks growth in sand culture under greenhouse conditions. The different Na/Ca ratios of the salt treatment were 36.5, 74.0, and 149, at a constant concentration of 150 mol m(-3) NaCl. Euroflor was superior to SMH-24 in fresh and dry matters of shoots and roots at varying external Na/Ca ratios. The leaf Na+ concentration in SMH-24 increased consistently with increase in external Na/Ca ratio, whereas that in Euroflor remained almost unaffected. Although leaf chlorine (Cl-) was significantly greater in SMH-24 than Euroflor, there was no effect of decreasing Ca2+ concentration of the saline growth medium on the leaf Cl- concentrations of both lines. The lines did not differ in K+, Ca2+ or Mg2+ concentrations of both shoots and roots. The leaf K/Na and Ca/Na ratios, K versus Na selectivity were considerably higher in Euroflor than in SMH-24. The lines also did not differ in leaf water potential and gas exchange and these variables were not affected due to decreasing Ca2+ concentration of the saline growth medium. Stomatal conductance and transpiration remained unchanged in Euroflor, whereas those in SMH-24 decreased significantly at the highest external Na/Ca ratio. Euroflor had significantly greater stomatal conductance and transpiration than those of SMH-24 at almost all external Na/Ca ratios, whereas the reverse was true for water use efficiency. It was established that Euroflor was tolerant to low Ca2+ concentrations of the saline growth medium as compared with SMH-24. This was mainly attributable to accumulation of relatively low Na+ and Cl- in the leaves, and maintenance of high leaf K/Na and Ca/Na ratios and K versus Na selectivity in Euroflor.