Evaluation of Salt Tolerance in Commercial Cultivars Seedlings and Native Genotypes of Pistachio (Pistacia vera L.) under Controlled Conditions in Rafssanjan, Iran

Introduction: In Iran, main pistachio cultivation areas are located in the edge of desert. The major problem of these areas is the salinity of soil and irrigation water, which affects the growth and performance of plants and reduce yield. Material and methods: In the present study, the effects of salinity on growth characteristics and mineral contents of seedlings of seven pistachio cultivars and three genotypes (Akbari, Ahmad-Aghaei, Kaleh-Ghoochi, Fandoghi, Badami, Ebrahimi, Seyfadini and G1, G2 and G3 genotypes) were evaluated. The study was conducted in split plot based on randomized complete block design in three replications. The main plots were salinity levels of the irrigation water (0.6, 15 and 30 dS/m) by adding sodium chloride to tap water, and the sub plots were the pistachio cultivars. After germination of seeds in the lab, the seedlings were transplanted into new vases in the greenhouse. At 3rd leaf stage, the salinity treatments were imposed for a period of four months. At the end of the experiment, all samples were collected for growth and cation contents of shoots and roots and data were analyzed by analysis of variance and correlation method, using SAS statistical software and Duncan’s Multiple Range Test was employed at probability level of 5%. Results and discussions: The results showed that increasing salinity levels reduced stem, root and leaf dry weight as well as stem height and diameter. Salinity also caused a reduction in leaf number and leaf area. At the salinity level of 30 dS/m, dry weights of root and leaf decreased by more than 70%. The length and diameter of seedlings were decreased by 17.2 % and 37.9 % under the mentioned condition. According to the measured growth characteristics, Akbari and Kaleh-Ghoochi, considered as fast growing cultivars, while G3 genotype and Seyfoddini cultivar were considered as slow growing cultivars. By increasing salinity, sodium and calcium concentrations in root, stem and leaf increased significantly, and the ratio of potassium to sodium decreased in the mentioned parts of the plant. Fandoghi and Kaleh-Ghoochi cultivars accumulated the highest amounts of sodium in leaf, while G1 and G2 genotypes had the lowest sodium level. An important fact is that G3 variety had minimum stem and leaf sodium content and maximum root sodium content. In contrast, Kaleh-Ghoochi cultivar had maximum leaf sodium content and minimum root sodium content. This obviously indicates that G3 variety accumulates sodium in the root and avoids sodium transmission to stem and leaf, and Kaleh-Ghoochi variety acted conversely. G2 genotype and Kaleh-Ghoochi variety contain the highest (3%) and lowest (1.4%) levels of leaf potassium. At salinity levels of 15 and 30 dS/m, the index of potassium to sodium ratio decreased by 93% and 87%, respectively, in comparison to the control salinity level (0.6 dS/m2). Generally, local genotypes of pistachio (G1, G2 and G3) showed lower sodium absorption and transport to leaf, while G3 genotype had the highest sodium content in the root and the lowest concentration of sodium in stem and leaf. G2 genotype and Ahmad-Aghaei cultivar had the highest leaf potassium to sodium ratios of 7/8 and 6/3, respectively, while Kaleh-Ghoochi cultivar had the lowest leaf potassium to sodium ratio (3/95). It seems that Kaleh-Ghoochi, Fandoghi and Akbari cultivars are relatively sensitive and G1, G2 and G3 genotypes and Ahmad-Aghaei cultivar are relatively tolerant to salinity at seedling stage. Results of correlation analysis showed a significant negative correlation between the levels of salinity and growth characteristics of pistachio. Leaf sodium content has a significant negative correlation with leaf potassium content as well as the potassium to sodium ratio in root, stem and leaf. Reduced or stunted growth of the pistachio seedlings can be a result of water stress as well as sodium and chlorine toxicities. The impaired balance of nutrient uptake through the root in salt stress conditions leads to reduced growth characteristic of the pistachio seedlings. As the salinity of the irrigating water increases, concentrations of sodium and chlorine ions in soil solution increases, therefore, balance of nutrients is impaired and the root absorption of sodium and chlorine increases and potassium uptake decreases. Hence, the concentrations of sodium and chlorine ions increased in root, stem and leaf, andpotassium concentration decreased. Salinity tolerance in many plants is attributed to non-transmission or limited transmission of sodium to aerial parts of the plant. Various pistachio cultivars acted differently in absorption and accumulation of these elements in the parts of plant. The pistachio varieties with less sodium absorption and transmission to the leaf, but more potassium absorption and transmission, increased potassium to sodium ratio in the leaf and showed more tolerance to salinity. The mechanism is not clearly recognized, perhaps sodium is re-absorbed from the xylem sap and remained in the root and stem, without transmission to leaf. A similar mechanism probably occurs in local genotypes of pistachio (G1, G2, and G3) and results in improved tolerance to salinity