Growth, biomass allocation and leaf ion concentration of seven olive (Olea europaea L.) cultivars under increased salinity

Olive (Olea europaea L.) is the major fruit tree in the Mediterranean region, often grown in locations where plants are exposed to increased salinity. To determine the effect of NaCl on shoot and root growth, dry matter allocation, leaf Na+ and K+ concentration, electrolyte (EL) and K+ leakage (KL), seven olive cultivars of different origins were grown in nutrient solution containing 0, 33, 66, 100 or 166 mM NaCl for three months. The general effect of salinity was linear and quadratic decrease of observed plant growth parameters. Different responses of tested cultivars to applied levels of salinity were found for stem dry weight, shoot length and number of leaves. As salinity increased, growth of ‘Manzanillo’ declined sharply, whereas ‘Frantoio’ was the most tolerant to growth reduction in most of the observed growth parameters. Allometric analysis showed that biomass allocation under salinity stress was similar in all cultivars, but the slope between shoot weight and total plant weight decreased as salinity increased. Since the higher allocation in roots was not found, it seems that salinity only slowed the above ground plant canopy growth. Sodium concentration in leaves of all cultivars increased as salinity increased with the highest increment reached when the salinity of nutrient solution was raised from 100 to 166 mM NaCl. Significant differences among genotypes were found in leaf Na+ and K+ concentration and K+:Na+ ratio, but they were not related to the growth rate. Generally, ‘Frantoio’ and ‘Oblica’ accumulated less Na+ and were able to maintain higher K+:Na+ ratios as compared to other genotypes. Electrolyte leakage and KL linearly increased with increasing salinity and the magnitude of the response depended upon the olive cultivar.