Alcohol Dehydrogenase Activity and Electrical Conductivity of Seed Exudates as Potential Indicators of Flooding Tolerance in Soybean Groups During the Germination Stage

Flooding stress is one of the abiotic stresses that limit soybean growth and development, particularly in seed germination. Excess water in soil depletes oxygen, leading to germination failure and uneven plant populations and establishment. Previous studies have evaluated the effects of flooding stress on germination in the field and across multiple growth stages. However, the response of soybean germination under flooding stress between tolerance levels is not well understood. In this study, seed soaking was performed in the laboratory to simulate flooding stress. Fifteen soybean varieties, grouped by seed soaking tolerance (tolerant, moderate, and susceptible), were investigated. Each soybean group was exposed to seed soaking for 12, 24, 36, and 48 h. Imbibition curve, electrical conductivity (EC), alcohol dehydrogenase activity (ADH), and ethanol content were analyzed. The results showed that ADH activity in cotyledon tissues and EC differed between groups. ADH in cotyledon tissues of the moderate and susceptible groups was induced at 12 h, whereas under stress, it was induced at 48 h in the tolerant group. Interval EC measurements from seed exudates indicated that tolerant varieties had lower conductivity than the moderate and susceptible groups. In summary, ADH activity in cotyledon tissues at 48 h and EC can serve as indirect physiological traits for discriminating flooding-tolerant groups during germination. KKU–SB052 is recommended as a natural genetic resource for soybean breeding programs, as indicated by high ADH activity after prolonged flooding and maintenance of cell membrane integrity under flooding stress.