Response of seedlings of three citrus-rootstock cultivars to salinity

Responses of seedlings of Trifoliata, Cleopatra mandarin and the Iranian mandarm Bakraie to concentrations of sodium ions over the range 2.6-152.6 mol m-3 were measured in sand culture. The major differences were in rates of leaf senescence; these and leaf expansion rates indicated that the cultivars increased in tolerance in the order: Trifoliata < Cleopatra < Bakraie. Although growth and net assimilation rates were related to the sodium ion concentration over the entire range explored, differences between cultivars could not be distinguished. Sodium concentrations in leaves were linearly related to concentrations in the external solution and increased with time; they, together with phosphorus, calcium and magnesium but not potassium, were higher in Bakraie than in Cleopatra. It is suggested that leaf abscission and leaf expansion rates provide useful indices for screening cultivar seedlings for salinity tolerance; leaf analyses may be less satisfactory.