Foliar Spray Application of an Extract from Klebsormidium sp. K39 Retrieved by Phycoremediation Process: Biochemical Response to Drought Stress on Tomato Plants

One of the main objectives of agriculture is to improve crop production and mitigate oxidative damage caused by climate change, such as water stress. This study evaluated the potential use of Klebsormidium sp. K39 extract (Kleb), obtained by phycoremediation treatment, to address these agricultural challenges. The experimental trials involved the application of Kleb at 1 mg Corg L−1 through foliar spray, under standard or water stress (WS) conditions. The effect of Kleb was evaluated by monitoring growth parameters, antioxidant activities, and lipid peroxidation. The quality parameters of the tomato fruits were also evaluated. The results demonstrated that the application of Klebsormidium extract enhanced tomato growth while maintaining root development and canopy cover under water stress conditions. These findings suggest that Kleb may act as a biostimulant to improve crop resilience. Moreover, treated plants under water stress conditions had an increase in yield of around 35% with respect to untreated stressed plants. Although fruit quality parameters were not significantly affected, in Kleb-treated plants lycopene content increased only under standard conditions, while polyphenol content significantly increased under both WS and standard conditions. In treated plants, lipid peroxidation decreased by 58% in the leaves and 19% in the fruits under WS conditions, suggesting a significant reduction in oxidative damage. In the fruits, correlation analysis revealed positive relationships among key stress markers. These findings suggest that Kleb extract enhances resilience to water stress in tomato plants by modulating antioxidant responses and secondary metabolite production, making it an eco-friendly approach to sustainable crop management under climate-related stressors.