Effects of NaCl salinity on growth, ion content and CO2 assimilation rate of six olive cultivars

The effects of NaCl salinity on the growth, ion content and gas exchange of six olive (Olea europaea L.) cultivars (Koroneiki, Mastoidis, Kalamata, Amphissis, Kothreiki and Megaritiki) were studied. The plants were grown in 8.51 pots containing sand-perlite mixture (1:3) for 5 months and were irrigated with half-strength Hoagland solution containing 0, 25, 50, 100 and 200 mM NaCl. Shoot length was reduced significantly above 25 mM for cvs Koroneiki, Kalamata and Megaritiki and above 50 mM NaCl for the others. Total plant leaf area was reduced significantly above 25 mM NaCl, reaching 85% at 200 mM NaCl for the cvs Mastoidis and Amphissis, due to defoliation. At high salinity the aerial part of the plants was more depressed than the root. The concentration of Na and Cl (% d.w.) was higher in roots than in other parts of the plant (shoots and leaves), and increased with the increase of salinity. In Kalamata, leaf Na and Cl concentration was very low for all salinity treatments. Salt injury symptoms (leaf tip burning) appeared in Koroneiki, Amphissis and Mastoidis at 100 mM NaCl, becoming more severe at 200 mM due to defoliation. The cultivars Kothreiki and Megaritiki at 200 mM NaCl exhibited only a few symptoms, while in Kalamata no any injury was observed. Assimilation rate of CO, and stomatal conductance were significantly reduced at high salinity levels in all cultivars. Gas exchange in the leaves was not highly correlated with chloride and sodium contents in all cultivars. Kalamata showed higher resistance to salinity, followed by Megaritiki and Kothreiki. Inferences on the mechanisms of action of salt on olive trees are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.