Drought stress and recovery: Coordinated physiological and molecular responses in interspecific hybrids of Pistacia

Drought is a major limitation in pistachio ( Pistacia vera L.) production. This study aimed to identify elite drought-tolerant rootstocks and characterize their integrated physiological, biochemical, and molecular defense mechanisms in seven Pistacia hybrids. The hybrids were assessed under a 30-day water withholding followed by a 30-day recovery period. Results revealed that tolerant hybrids (‘C9–4′, ‘C1’, ‘C2’) exhibited minimal MSI reductions (14–19%), whereas sensitive hybrids (‘C8–3′, ‘C4–2′) showed severe declines (78–85%). Tolerant clones displayed significantly lower oxidative damage with H 2 O 2 increases of 50–67%, compared to 178–179% in sensitive ones, supported by a 52–116% increase in catalase activity. Furthermore, drought stress significantly increased root-zone redox potential (ORP) at deeper layers (35 cm) in sensitive hybrids. At the molecular level, the tolerant clone ‘C9–4′ showed strong induction of CAT1 (∼4-fold), NCED3 (∼2-fold), and PP2CA (∼4.5-fold), revealing coordinated ROS detoxification and ABA-signaling, which was negligible in the sensitive clone. Based on these responses, cluster analysis categorized the hybrids into resistant (‘C9–4′, ‘C1’, ‘C2’), moderate (‘UCB1’), and sensitive (‘C4–2′, ‘C8–3′, ‘C16–1′) groups. Following re-watering, a distinct "strong-recovery" cluster including ‘C4–2′ and tolerant hybrids re-established homeostasis, while ‘C8–3′ and ‘C16–1’ showed limited recovery. These integrated indicators provide a robust framework for selecting superior pistachio rootstocks.