Identification of some drought resistance mechanisms in four pistachio seedling rootstocks under water stress

This research was conducted to identify the drought resistance mechanisms of four pistachio seedling rootstocks. Irrigation treatments were 100% ET_c (control), 65% ET_c (medium stress), and 30% ET_c (severe stress), which were applied on 4-month-old seedlings for 75 days. Evaluated rootstocks were Pistacia vera ‘Badami-e-Zarand’, ‘Ghazvini’, ‘Sarakhs’, and P. mutica. Physiological parameters such as gas exchanges, water relations, photochemical efficiency of photosystem ІІ (F_v/F_m ratio) and carbon isotope discrimination (Δ), biochemical parameters such as contents of proline, carbohydrate, and chlorophyll, and growth parameters were investigated. Generally, water stress decreased CO₂ assimilation (A), stomatal conductivity (g_s), leaf water potential (Ψ_w), relative water content (RWC), F_v/F_m ratio, carbon isotope discrimination, chlorophyll content, and biomass, while contents of proline and carbohydrate were increased. Based on the results, P. mutica and P. vera ‘Badami-e-Zarand’ had higher photosynthesis and higher RWC under water stress. The higher RWC of P. mutica, despite its lower leaf water potential, can be attributed to better osmotic regulation. The highest F_v/F_m ratio and chlorophyll content under water stress also were observed in P. mutica. A smaller reduction in growth parameters also was observed in P. mutica and P. vera ‘Badami-e-Zarand’ under water stress conditions. According to the mentioned reasons, it can be concluded that the rootstocks P. mutica and P. vera ‘Badami-e-Zarand were the most drought tolerant rootstocks. Carbon isotope discrimination and proline accumulation were not suitable indexes for the screening of drought-tolerant rootstocks.