Sulfur reduces the adverse effects of common pistachio psylla on pistachio nut (Pistacia vera L.): physiological, biochemical, and molecular responses

Abstract

The common pistachio psylla (CPP) is a major pest of pistachio (Pistacia vera L.) orchards in Iran. Although sulfur is widely used as an insecticide, its potential role in modulating internal plant defense mechanisms in this valuable nut crop remains largely unexplored. This study investigated how foliar sulfur application (4%) affects enzymatic and non-enzymatic defenses in two pistachio genotypes, cultivated (Ghazvini) and wild (Sarakhs), under CPP infestation. Sulfur treatment triggered a genotype-dependent response in pistachio, significantly enhancing the activities of key antioxidant enzymes, including SOD, POX, CAT, and PPO, and increasing the accumulation of secondary metabolites such as anthocyanins, phenolics, and flavonoids. It also maintained higher chlorophyll (a and b) and carotenoid contents, thereby mitigating the CPP‑induced decline in photosynthetic pigments. Under combined sulfur treatment and CPP infestation, Ghazvini exhibited stronger enzymatic defenses, whereas Sarakhs relied more on phenolic and anthocyanin compounds. In addition, sulfur reduced oxidative stress markers (MDA, H₂O₂) and upregulated key defense genes (CHS, PAL) in pistachio under CPP infestation, collectively alleviating the effects of this biotic stress. These findings indicate that sulfur, beyond its traditional pesticidal role, acts as a modulator of genotype-dependent defense responses in pistachio. The results provide insight into the physiological and molecular mechanisms underlying genotype-specific responses and contribute to the development of genotype-based and sustainable pest management strategies.