Mitigation of Salt Stress in Soybean (Glycine max (L.) Merrill) Using Exogenous Application of Onion Extract

Plant extracts have been shown to improve plant growth and development under salt stress. The current study focuses on how the exogenous application of onion extract stimulates morpho-physiological traits and enzymatic antioxidant activities, while mitigating salt stress in soybean. In this study, salt-stressed (150 mM NaCl) soybean plants were treated with 25% onion extract at different time intervals (T3, four times at 3 days interval; T4, 2 times at 6 days interval; T5, 2 times at 9-day interval and T6, one time on the 10th day after sowing) and compared with T1 (control plants irrigated with water) and T2 (150 mM NaCl-treated soybean) using the soil drenching method. There was a drastic improvement in growth (number of leaves, shoot length, shoot biomass, root length, root numbers and root biomass) in T4 plants compared to T2. Moreover, T4 plants showed enhanced physiological changes such as photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids) and leaf relative water content compared to T2 (salt-stressed plants). In addition, onion extract treatment reduced membrane damage and hydrogen peroxide content, and improved antioxidant enzyme activities as well as total polyphenolic content. Our findings indicated that onion extract possesses a growth-stimulatory role, anti-osmotic properties and enhanced salt tolerance in soybean. Onion extract usage will be eco-friendly and cost-effective for large-scale field applications. In the future, onion extract might be one of the commercially important products to eradicate abiotic stress in crops.