In vitro salinity tolerance of two pistachio rootstocks: Pistacia vera L. and P. atlantica Desf

Seedlings of Pistacia vera L. and Pistacia atlantica Desf. were cultured on hormone-free DKW medium supplemented with NaCl. The plants were subjected to low NaCl concentrations ranging from 0 to 80mM for 45 days or to high salt concentrations (0, 131, and 158.5mM for P. vera and 0, 131, and 240mM for P. atlantica) for 25 days. Toxicity symptoms were recorded for seedlings exposed to low NaCl treatments. Plant growth, survival rates, mineral content, as well as proline and soluble sugar contents were determined and evaluated at the end of the culture period. The results indicated that low NaCl treatments yielded no instances of plant death in both species. At high salt conditions, however, significant mortality rates were noted for both species, being 22.86% at 240mM NaCl for P. atlantica and 25.8% at 158.5mM NaCl for P. vera. With regards to salinity effects, levels of 60 and 80mM NaCl induced significant decreases of stem elongation and leaf number in the P. vera species. Salinities between 40 and 80mM NaCl, however, induced a decrease in the root number of both species. The fresh weights of P. vera and P. atlantica also decreased significantly after 45 days of culture at NaCl concentrations between 40 and 80mM and after 25 days of culture at 158.5 and 240mM NaCl, respectively. The sodium and chloride uptake in plant organs seemed to be controlled more efficiently in P. atlantica than in P. vera. In both species, the K⁺ content was noted to undergo a significant decrease when salinity increased. While the K⁺/Na⁺ ratio was maintained above 2 at low NaCl treatments, it was sharply decreased at high NaCl conditions, suggesting a failure of K-Na selectivity mechanism. The Ca²⁺/Na⁺ ratio decreased significantly at 60 and 80mM NaCl in P. vera and at 60mM NaCl for P. atlantica. In both Pistacia species, high NaCl treatments (131-240mM NaCl) induced a significant increase in proline content.