Novel biostimulants-mediate tolerance to drought stress in Phaseolus vulgaris plants by optimizing osmoprotectants and antioxidant defense systems

Abstract

Background: Drought stress is a major constraint to the growth and productivity of Phaseolus vulgaris, particularly in dry regions. Utilizing natural biostimulants offers an eco-friendly approach to enhancing drought tolerance by modulating plant physio-biochemical responses. This study investigates the effectiveness of diluted lemon fruit juice (DLFJ) and diluted bee honey (DBH) as foliar biostimulants to mitigate drought-induced stress in P. vulgaris under two irrigation regimes: full (100% ETc) and deficit irrigation (60% ETc). Results: Both DLFJ and DBH treatments significantly enhanced photosynthetic efficiency, relative water content (RWC), membrane stability index (MSI), osmoprotectant levels, antioxidant activity, and nutrient accumulation under drought conditions. Among all treatments (4% and 8% DBH, and 3% and 6% DLFJ), DBH-4% was the most effective. It significantly increased chlorophyll and carotenoid contents, photosynthetic efficiency, leaf integrity (RWC and MSI), osmoprotectant levels, antioxidant activities, and green pod yield under 60% ETc compared to untreated controls. It also markedly reduced oxidative stress markers (e.g., malondialdehyde and hydrogen peroxide) and further boosted enzyme activities, including superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase. Conclusions: These findings demonstrate that DBH-4% is a promising and sustainable biostimulant for improving drought resilience in P. vulgaris. Its rich content of antioxidants and osmoprotectants confers significant physiological and agronomic gains under water-limited conditions.