Exploring drought adaptation strategies in pistachios through morpho-physiological analysis under deficit irrigation

Water scarcity, intensified by climate change, poses a major challenge to pistachio production in arid and semi-arid regions of the world. Water stress in these areas drastically reduces yield and endangers the long-term sustainability of orchards. Deficit irrigation (DI) is widely recognized as a water-saving strategy to optimize crop production under limited water resources. This study investigated and compared the key components of drought adaptation strategies in four pistachio varieties-'Badami', 'Akbari', 'Ahmad-Aghaei' and 'Kale-Ghochi'-under DI in controlled conditions. A factorial experiment was conducted using a completely randomized design (CRD) to assess the effects of three DI levels: full irrigation (control), mild (DI30%) and severe (DI60%), on two-month-old pistachio seedlings over 10 weeks. We comprehensively assessed morphological and physiological characteristics, including root and shoot growth and stomatal traits. Photosynthetic pigment concentrations and relative water content were also measured. Based on the results, distinct varietal adaptation mechanisms emerged: 'Badami' exhibited a well-developed root system and enhanced osmotic adjustment, facilitating drought avoidance; 'Akbari' demonstrated robust aerial resistance through efficient stomatal regulation and sustained pigment retention, indicative of dehydration tolerance; 'Ahmad-Aghaei' showed a balanced root-shoot coordination, especially under mild DI, suggesting moderate adaptability; whereas 'Kale-Ghochi' displayed the least drought resistance, characterized by restricted root growth and impaired water status. Multivariate analyses integrating these traits effectively discriminated the varieties based on their drought response profiles. These results indicate the potential of drought-tolerant varieties, particularly 'Badami' to achieve up to 30% water savings under DI, a practical approach to sustaining pistachio production in regions facing water scarcity.