Vegetative growth and salt accumulation of six olive cultivars under salt stress

Olive is one of the most cultivated fruit trees in Croatia, particularly in its Mediterranean part-Dalmatia. The average yield is less than 10 kg/tree, a value considered very low, and attributed mostly to summer drought. The coastal areas and especially the islands are scarce with water of good quality. On the other hand, somewhat saline ground water is available in many areas, but has not yet been used for irrigation. Olive is considered moderately tolerant to salinity, and is more tolerant than many other fruit trees. The aim of this work was to identify autochthonous olive cultivars that exhibit the greatest tolerance to salinity. Five self-rooted Croatian autochthonous cultivars (Buza, Drobnica, Istarska bjelica, Lastovka and Oblica) and an Italian cultivar (Leccino) were grown in 1:1 quartz sand : perlite substrate in the greenhouse. The plants were irrigated twice a day with 1/4-strength Hoagland nutrient solution and subjected to 0, 33, 66 and 100 mM NaCl for seventy days. The effect of salinity appeared on some cultivars as early as 10 days after salinization began. During the following 50 days of salinity exposure, all the cultivars showed reduced shoot growth at high saline concentrations, particularly at the 100 mM level. At the end of the experiment the shoot growth of Buza, Leccino, and Lastovka, treated at the 100 mM level decreased the most, (i.e. 21, 36 and 37%, respectively) relative to growth obtained under control conditions. Under the same treatment, cultivar Oblica performed significantly better, obtaining 54% of the control-plants growth. In addition, Oblica accumulated the lowest amount of sodium in the leaves. Most of the cultivars differed significantly in terms of the number of nodes and leaves at the highest NaCl concentration.