Vegetable-type soybean, also known as edamame, was recently introduced to South Africa. However, there is lack of information on its responses to drought. The aim of this study was to investigate the photosynthetic efficiency and carbohydrates responses of six edamame cultivars under drought stress. Photosynthetic efficiency parameters, including chlorophyll fluorescence and stomatal conductance, were determined using non-invasive methods, while pigments were quantified spectrophotometrically. Non-structural carbohydrates were quantified using Megazyme kits. Structural carbohydrates were determined using Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Drought stress significantly increased the Fv/Fm and PIabs of AGS429 and UVE17 at pod filling stage. Chlorophyll-a, which was most sensitive to drought, was significantly reduced in AGS429 and UVE17, but chlorophyll-b was relatively stable in all cultivars, except UVE17, which showed a significant decline at flowering stage. AGS354 and AGS429 also showed reduced chlorophyll-b at pod filling. UVE17 showed a significant reduction in carotenoid content and a substantial reduction in stomatal conductance during pod filling. Drought stress during pod filling resulted in a significant increase in the contents of trehalose, sucrose and starch, but glucose was decreased. Chlorophyll-a positively correlated with starch. The FTIR and XRD results suggest that the cell wall of UVE14, followed by UVE8 and AGS429, was the most intact during drought stress. It was concluded that carotenoids, stomatal conductance, starch and hemicellulose could be used as physiological/biochemical indicators of drought tolerance in edamame. This information expands our knowledge of the drought defense responses in edamame, and it is essential for the physiological and biochemical screening of drought tolerance.

Severe drought stress affects the production of vegetable-type soybean (Glycine max L. Merrill), which is in infancy for Africa despite its huge nutritional benefits. This study was conducted under controlled environmental conditions to establish the effects of severe drought stress on ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and glutathione reductase (GR) activities as well as proline, total soluble sugars (TSS), and hydrogen peroxide (H₂O₂) contents of five vegetable-type soybean cultivars (UVE8, UVE14, UVE17, AGS354, AGS429) at flowering and pod-filling stages. Drought induced significant increases in the contents of proline (selectively at pod filling for AGS429), TSS (at both stages for AGS429, and only at pod filling for UVE14), and malondialdehyde (AGS354 at flowering; UVE17 at pod filling). UVE8 and AGS354 had the highest H₂O₂ levels at flowering under drought stress, while AGS429 had the lowest. However, AGS429 was the only cultivar with significantly increased H₂O₂ under drought stress. Furthermore, drought stress induced significant increases in APX, GPX, and GR activities at flowering for AGS429. AGS354 recorded the highest decline for all antioxidative enzymes, while UVE17 decreased for GPX only. All biochemical parameters, except H₂O₂, were significantly higher at pod filling than at the flowering stage. The relationship between H₂O₂ and total seed mass (TSMP) or total seed per plant (TSP) was significantly positive for both stages, while that of TSS (at flowering) and proline (at pod filling) were significantly related to total pods per plant (TPP). The study suggests that during drought, the tolerance responses of vegetable-type soybean, APX, GPX, and GR (especially at the flowering stage), function in concert to minimize H₂O₂ production and lipid peroxidation, thereby allowing H₂O₂ to function in the signaling events leading to the induction of drought tolerance. The induction of TSS at flowering and proline at pod filling is important in the drought tolerance response of this crop.

Spinach (Spinacia oleracea L.) is a highly nutritious, desirable green leafy vegetable, which is less tolerant to drought. This study was conducted to establish the impact of a natural bio-stimulant consisting of a mixture of fish protein hydrolysates and kelp extract (trade name, Xcell Boost) on the physiological and biochemical responses as well as vegetative growth of spinach (Spinacia oleracea L.) under different water levels (100% (full irrigation), 50% (mild drought stress) and 30% (severe drought stress) water holding capacity). Bio-stimulant application at any strength (single, BX1 or double, BX2) had no effect on the photochemical reactions. The application of bio-stimulant at double strength concentration (BX2) increased the chlorophyll and carotenoid contents, as well as the activities of antioxidative enzymes, ascorbate peroxidase (APX) and guaiacol peroxidase (GPX), under drought stress. Application at single strength (BX1) increased the normalised difference vegetation index (NDVI), stomatal conductance, accumulation of osmoprotectants (proline and total soluble sugars) and reduced electrolyte leakage under drought stress. Furthermore, bio-stimulant applications at either concentration induced remarkable increases in plant height, leaf area, stem dry weight, root length and root moisture. Under BX2, APX and stomatal conductance positively correlated with stem dry weight, while root length positively correlated with total chlorophyll content. These results show that Xcell Boost is a highly advantageous bio-stimulant for increasing the tolerance of spinach to drought stress, which can most likely benefit other crops grown in semi-arid and arid areas.

Drought and heat stress often co‐occur in nature, and their combined effects are a major driver of crop losses, causing more severe damage to plant metabolism than when they occur individually. This study investigates the responses of three edamame cultivars (AGS429, UVE14, and UVE17) to combined drought and heat (DH) stress, with emphasis on the reactive oxygen species (ROS), antioxidative mechanisms and cell wall modifications. Malondialdehyde (MDA), electrolyte leakage (EL), and hydrogen peroxide (H ₂ O ₂ ) were used to measure oxidative stress and membrane damage. The non‐enzymatic (ascorbic acid, AsA) and enzymatic (superoxide dismutase, ascorbate peroxidase (APX), guaiacol peroxidase, and glutathione reductase) antioxidant responses were determined spectrophotometrically. Cell wall biomass composition (cellulose, hemicellulose, lignin, and phenols) was determined using Fourier transform Infrared Spectroscopy and spectrophotometry. Ascorbate peroxidase activity and AsA content in DH‐stressed AGS429 at flowering strongly correlated to reduced lipid peroxidation (r ² = −0.97 and − 0.98). Cultivar UVE14 accumulated high AsA under DH stress at both growth stages, which, in turn, was positively associated with total phenolic content (r ² = 0.97), APX activity, and holocellulose, suggesting enhanced ROS‐dependent oxidative polymerisation. On the contrary, poor ROS quenching in UVE17 led to MDA accumulation ( p ≤ 0.05), leading to high EL and poor cellulose synthesis at pod‐filling (r ² = −0.88). Therefore, at the physio‐biochemical level, AGS429 and UVE14 showed DH stress tolerance through enhanced antioxidative responses and cell wall modifications, while UVE17 was susceptible. Identifying the key biochemical traits linked to DH stress tolerance in edamame offers novel insights for breeding more resilient edamame cultivars.