Influence of different selenium application methods on the physiology and morphology of drought-stressed edamame

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Sekhurwane, Masego
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University of the Free State
Drought is one of the common stress factors accelerated by anthropogenic climate change contributing to crop losses across the globe. Since South Africa is classified as semi-arid, production of drought sensitive crops such as edamame (Glycine max L. Merrill) is a challenge. Over the recent years, selenium application gained attention of biologists due to its ability to reduce the adverse impacts of drought stress on crops. However, the effective method of selenium application for inducing tolerance to drought stress in edamame is not recorded. Therefore, the aim of this research was to determine the influence of different selenium application methods (seed dressing, foliar spray and soil drench) on the physiological, biochemical and morphological responses of two edamame cultivars (tolerant UVE14 and susceptible UVE17) under drought stress. The study also established relationships between the physiological, biochemical, and morphological characteristics under drought stress in edamame. The research was conducted under controlled conditions in a greenhouse. Before drought stress induction (30% water holding capacity, WHC) at the third trifoliate leaf stage (vegetative stage 4, V4), selenium was applied using different application methods [i.e., seed dressing (before sowing), foliar spray and soil drench (at first trifoliate stage)]. Optimally watered (100% WHC) plants treated with different selenium application methods served as positive controls. Physiological and biochemical data collection took place at flowering stage (reproductive stage 2, R2) and pod filling stage (R4), whereas morphological data was collected at maturity (R8) stage. The physiological responses included different chlorophyll a fluorescence parameters, stomatal conductance (gs), chloroplast pigments, electrolyte leakage (EL) and relative water content RWC). The biochemical parameters included superoxide dismutase (SOD), hydrogen peroxide (H₂O₂), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and protein content. Results showed that the physiological and biochemical parameters were significantly different for selenium application methods at flowering and pod filling stages under drought stress. Water levels in the soil affected the physio-biochemical responses of edamame cultivars under different selenium application methods. Also, cultivars responded differently under different selenium application methods. The soil drench method was more efficient because it increased total performance index (PItotal),total chlorophyll content, stomatal conductance, RWC, H₂O₂, carotenoid, APX, GPX and SOD. Morphological data further agreed with the physio-biochemical data, showing that selenium application through soil drenching and seed dressing increased the number of seeds per plant (SPP) for drought-stressed UVE17 cultivar. The soil drenching treatment on drought-stressed edamame resulted in a high significant mean difference in the number of pods per plant (PPP), SPP and seed mass per plant (SMP), compared to the foliar and seed application methods. Correlation analysis provided evidence that increased PPP under selenium soil drench application was positively associated with high RWC, PIabs, PItotal. In addition, SOD and GPX were positively correlated to plant height (PH) and PPP for drought-stressed edamame under selenium soil drench application. Furthermore, carotenoid content positively correlated with PPP, SMPP and SPP for drought-stressed edamame under selenium seed dressing application. This study shows that under drought stress, application of selenium as a soil drench treatment is the most effective method for improving tolerance of edamame to drought stress, followed by the seed dressing method. Therefore, this work provides essential information for combating the negative effects of drought stress, which can positively contribute to food security in South Africa.
Dissertation (M.Sc.(Botany))--University of the Free State, 2022