Comparative Morphology of Two Varieties of Glycine Max Under Drought Ameliorated by Plant Growth Regulators

This research investigated how soybean (Glycine max L.) varieties (TGX 1440-1E and TGX 1448-2E) responds physiologically to drought stress and how plant growth regulators (PGRs) can help alleviate its impacts. The study was carried out in the screen house of the Department of Plant Biology and Biotechnology at the University of Benin over a period of 12 weeks, focusing on growth, photosynthetic efficiency, and yield. Three experimental conditions/treatments were implemented: a control group (well-watered), a drought-stressed group, and a drought-stressed group treated with PGRs (2,4-Dichlorophenoxyacetic acid and Salicylic acid) at concentrations of 5 ppm, 10 ppm, and 30 ppm. The plants were provided with 5%, 10%, or 30% of the normal water requirements. The main physiological parameters analyzed included chlorophyll, carotenoid, lycopene, the activity of enzymes (superoxide dismutase and catalase), protein levels, ascorbic acid, and proline content. Drought conditions notably decreased the levels of chlorophyll, carotenoids, and lycopene, as well as the activity of antioxidant enzymes, while resulting in increased accumulation of protein, ascorbic acid, and proline. The weekly application of plant growth regulators (PGRs) enhanced drought tolerance by enhancing biomass and seed yield. However, excessive concentrations of PGRs had a detrimental impact on chlorophyll, lycopene, and antioxidant enzyme activity, indicating potential oxidative harm. Overall, the findings suggest that a moderate application of PGRs (Salicylic acid and 2,4-D) is effective in alleviating drought stress, thereby improving both physiological and agronomic characteristics of both varieties of soybean under limited water conditions.