From waste to resilience: fish waste priming attenuates drought effects on cucumber seedlings via heightened osmoprotectants, antioxidant activity and metabolic stability

Global climate change is intensifying water scarcity, making drought stress a critical challenge for crop production. This study evaluated the potential of fish waste extract (FWE), a circular bioeconomy product, to enhance drought tolerance in cucumber seedlings. A 2 × 4 factorial design (FWE priming × polyethylene glycol at 0, 1, 2, and 3% to simulate drought) was applied to evaluate germination, growth, oxidative stress, antioxidant responses, and secondary metabolites. Qualitative phytochemical screening of FWE revealed the presence of phenolics, amino acids, flavonoids, alkaloids, reducing sugars and coumarins. Drought-stressed cucumber seedlings exhibited reduction in germination parameters and vigor indices, disruption in water homeostasis, decline in membrane stability alongside elevating malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) indicating oxidative damage. However, FWE priming significantly alleviated drought effects, enhancing germination, restoring water content and membrane stability, and reducing MDA and H₂O₂. Most obviously, under drought stress, FWE amplified proline accumulation and antioxidant enzyme activity, while boosting phenolics and flavonoids reflecting induction of secondary metabolism. Multivariate analyses, including hierarchical clustering and principal component analysis, revealed that FWE treatment significantly enhanced drought tolerance in cucumber seedlings under PEG-induced stress. These findings highlight FWE as a sustainable, low-cost biostimulant that converts agro-industrial byproducts into valuable inputs for drought-resilient cucumber cultivation.