Exogenous glutathione enhances antioxidant defense, physiological performance and fruit quality of strawberry under deficit fertigation

Strawberry ( Fragaria × ananassa ) is high-value horticultural crop rich in bioactive compounds with significant nutritional and economic importance. However, deficit fertigation imposes oxidative stress that constrains plant productivity and fruit quality, especially under controlled greenhouse systems. The role of redox-active compounds, including L-glutathione (GSH) in mitigating these constraints remains insufficiently understood. This study aimed to characterize the physiological and biochemical responses of strawberry (cv. Sabrina) to exogenous GSH under deficit fertigation. Plants were treated with GSH at 0, 500, and 1000 µM under two fertigation regimes (160 and 200 mL plant⁻¹ applied every other day) using a factorial completely randomized design. Deficit fertigation significantly impaired plant performance, inducing oxidative damage and reducing yield-related attributes. In contrast, GSH application effectively alleviated stress-induced damage by improving antioxidant defense systems and maintaining cellular redox balance. While GSH had no significant effect on total phenolic (TP), total flavonoid (TF), and FRAP values, it significantly increased DPPH scavenging activity, total anthocyanin content (TAC), and ascorbic acid (AsA). Moreover, GSH treatment enhanced the activities of key antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (POD), while reducing malondialdehyde (MDA) accumulation and polyphenol oxidase (PPO) activity, suggesting decreased lipid peroxidation and oxidative damage. The effects of GSH varied among the measured traits: yield and MDA showed the most favorable responses at 500 µM GSH under full fertigation (200 mL), DPPH scavenging activity was highest at 500 µM GSH under deficit fertigation (160 mL), TAC was highest at 1000 µM GSH under deficit fertigation, and AsA content was highest at 1000 µM GSH under full fertigation. These findings demonstrate that exogenous glutathione mitigates the adverse effects of deficit fertigation by enhancing antioxidant defenses and sustaining physiological performance. The results further indicate that GSH responses were trait-specific and varied with both GSH concentration and fertigation regime, with no single treatment combination consistently producing the most favorable response across all measured traits. The observed responses therefore indicate concentration-dependent and non-linear effects of GSH within the tested concentration range.