Functional Roles of Arbuscular Mycorrhizal Fungi and Plant Growth-Promoting Rhizobacteria in Pistachio: Implications for Stress Tolerance, Nutrient Acquisition and Disease Suppression

Pistachio (Pistacia vera L.) is among the most economically important nut crops worldwide. They are increasingly exposed to the environmental constraints associated with climate change, including drought, salinity, nutritional imbalances, and heightened disease pressure. These stressors compromise plant growth, physiological performance, nutrient acquisition, and orchard productivity, highlighting the need for sustainable strategies to enhance crop resilience. This review critically examines the current knowledge on the functional roles of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) in pistachio production. Evidence indicates that AMF and PGPR contribute to plant performance through multiple complementary mechanisms, including improved nutrient mobilization and uptake, maintenance of ionic homeostasis, enhancement of water-use efficiency, stimulation of antioxidant defenses, modulation of stress-related signaling pathways, and suppression of phytopathogens. AMF primarily enhance phosphorus acquisition, water relations, and soil structural stability, whereas PGPR contribute to nutrient solubilization, biological control, and induction of plant defense responses. Despite promising experimental results, most studies have been conducted under controlled conditions, limiting the translation of microbial inoculation strategies to commercial orchards in the field. We identified the key knowledge gaps and research priorities required to improve the consistency, scalability, and field validation of microbiome-based approaches for sustainable pistachio production under increasingly challenging environmental conditions.