Effect of Zinc Nutrition on Growth Traits, Sodium and Potassium Concentrations and Calcium Molarity Ratio of Roots and Leaves in Two Olive Cultivars under Different Salinity Levels

In order to study the effect of zinc (Zn) nutrition on relative tolerance of olive (Olea europea L.) seedlings to salinity, a factorial pot experiment was conducted, based on completely randomized design with three replications, during fall 2013. One-year seedlings of two olive cultivars (‘Frontoio’ and ‘Conservolea’) were planted in 10-litre plastic pots containing sand and perlite (1:1 ratio) and treated with nutrient solutions having different levels of sodium chloride (0, 40, 80 and 120 mM) and Zn (0, 1 and 5 µM zinc sulfate). Results showed that salinity reduced root and leaf dry weight, seedling height, number of leaves, potassium/sodium (K/Na) ratio of roots and leaves, and calcium (Ca) molarity ratio in roots and leaves of both cultivars. With increasing Zn content to 5 µM, all the growth traits of the two cultivars were increased significantly. This trend was observed in the leaf K content and K/Na ratio of roots and leaves as well. Interaction of Zn×cultivar and salinity×cultivar was significant only on root dry weight. The Frontoio cultivar had maximum root dry weight at all salinity levels. The Zn had a positive and significant effect on root and leaf dry weight. Interactions of Zn×salinity and Zn×cultivar were not significant on leaf dry weight. Frontoio cultivar was more tolerant cultivar to salinity according to the maximum root and leaf dry weight, as well as other studied traits. Application of Zn not only raised growth indices, but also increased K absorption, K/Na ratio, and Ca molarity ratio. This role led to improved nutrition conditions and finally increased dry leaf and root weights. In general, Ca molarity ratio is more proper index in comparison with K/Na ratio to determine tolerance to salinity in the olive seedlings