Effect of Zinc on the Growth of Two Pistachio (Pistacia vera L.) Rootstocks under Drought Stress

In this research, the effect of two irrigation treatments (90 and 40% of available water) and four different levels of zinc (control, 5, 10, and 20 mg kg^-1 soil) was investigated on pistachio rootstock seedlings including ‘Akbari’ and ‘Badami’ in a completely randomized design with four replications during 90 days. At the end of the experiment, plant growth characteristics including shoot height, stem diameter, number of leaves, leaf area, and dry matter accumulation in root, stem, and leaf were evaluated. Additionally, the relative water content, membrane stability index, photosynthetic pigment concentrations, and content of organic osmolytes were appraised as well. The results showed that drought stress reduced plant height, number of leaves, leaf area, and biomass of plants, and increased root dry weight. The zinc application increased plant growth under irrigation treatments. In addition, under drought stress, the application of 5 mg kg^-1 zinc increased the membrane stability by16.76%, maintained chlorophyll a by 20.69%, b by 31.96%, and total chlorophyll of the leaf by 27.74%. However, the application of 20 mg kg^-1 Zn in soil caused toxicity and exacerbated the effects of drought stress which led to the accumulation of proline and soluble carbohydrates in the pistachio rootstocks with more proline in ‘Akbari’ than ‘Badami’ rootstock, while Zinc could reduce the accumulation of soluble carbohydrates and proline. In general, ‘Badami’ was introduced as a tolerant rootstock for use underwater stress, as well as using 5 mg kg^-1 Zn to improve the growth and efficiency of both rootstocks under drought stress or without stress.