Physio-morphological and biochemical traits of dibutyldithiophosphate treated drought-stressed edamame

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Khoza, Minah Bongiwe
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University of the Free State
Edamame (Glycine max L. Merrill) has recently received attention in South Africa due to its high nutritional value. Production of edamame in South Africa is limited since the country consists of arid and semi-arid regions, with insufficient water available for irrigation. Dibutyldithiophosphate, a biodegradable chemical that slowly releases hydrogen sulfide, could be a solution based on recent studies that indicate H₂S acts as a signaling molecule for tolerance induction during various environmental stresses. This study investigated the impact of dibutyldithiophosphate on the physiological, biochemical and morphological characteristics of drought-stressed edamame cultivars (UVE14 and UVE17). Furthermore, the study established the relationships between the physiological, biochemical and the morphological characteristics [plant height, branches per plant, total seeds per plant, total seed mass per plant, and pods per plant] of drought-stressed edamame under different dibutyldithiophosphate concentrations. Dibutyldithiophosphate was directly applied around the seed during sowing before drought stress (30% water holding capacity) introduction at the third trifoliate leaf stage. Drought stress adversely affected the physiological, biochemical and morphological responses of the edamame cultivars. The efficacy of dibutyldithiophosphate differed according to the cultivars, growth stages (flowering and pod-filling), concentrations of dibutyldithiophosphate (0, 0.1, 1, and 2 mg/mL), as well as the water level (drought or optimal watering). The concentrations required to activate the physiological and biochemical responses were generally higher in drought-stressed UVE17 than UVE14 cultvar. To improve drought tolerance in edamame, dibutyldithiophosphate application upregulated the photosynthetic capacity (increased total chlorophyll content, chlorophyll-a, chlorophyll-b, and photochemical reflective index), which resulted in increased accumulation of sugars (total soluble sugars) and proline. The increase in total soluble sugars and proline indicate that dibutyldithiophosphate application increases the osmotic and antioxidative potential of drought-stressed edamame. Additionally, results of this study showed that dibutyldithiophosphate application decreased membrane damage by increasing the antioxidative capacity [superoxide dismutase, ascorbate peroxidase, flavonoid reflective index, and carotenoid reflective index] in drought-stressed edamame. Application of dibutyldithiophosphate also improved drought tolerance in a susceptible cultivar (UVE17) by increasing pods per plant (0.1 mg/mL), branches per plant (1 mg/mL), and total seed per plant (2 mg/mL). For drought-stressed UVE14, application of dibutyldithiophosphate increased branches per plant (all concentrations), pods per plant (0.1 and 1 mg/mL) and total seed per plant (2 mg/mL). Since there were more positive correlations between the physiological, biochemical and morphological characteristics under 0.1 and 1 mg/mL, these dibutyldithiophosphate concentrations could be recommended for drought tolerance stimulation in edamame. As a result, the hypothesis that application of dibutyldithiophosphate enhances the physiological, biochemical and morphological responses of drought-stressed edamame is accepted. In addition, it is acknowledged that application of dibutyldithiophosphate on drought-stressed edamame increases the relationships between physiological, biochemical and morphological responses.
Dissertation (M.Sc.(Botany))--University of the Free State, 2022