Worldwide, it has been recorded extensively that plants are subjected to severe abiotic and biotic stressors. The scientific research community has widely reported that multi-abiotic stressors cause horticultural crop losses, accounting for at least 50 to 70% of the crop yield and quality losses. Therefore, this review focused on the detrimental effects caused by abiotic stress factors occurring in single-, combined- and multi-cell stresses on horticultural plants worldwide, along with the best production systems practices for mitigation during and post-single and combined abiotic or multi-stress damages. A conclusion and recommendation could be reached using the pool of research material, which constituted research articles, reviews, book chapters, thesis, research short communications and industrial short communications from at least twenty-five years ago. Findings showed that some of the leading abiotic stresses are single- and combined abiotic stressors like water deficit, salinity, soil pH, phosphate deficiency, wounding, soil density and pot size. Established commercial and smallholder farmers are globally adapting to plant growth regulators and biostimulants as part of their production systems. However, as much as the effectiveness of biostimulants containing humic acids, algal extracts, plant growth-promoting microorganisms and phytohormones has been reported to promote plant development under multi-stress, only a few studies are focusing on organic phytohormone-based biostimulants on horticultural crops grown under adverse multi stress factoring. In conclusion, the review recommends alternative solutions for emerging South African farmers and growers who cannot afford agricultural insurance options and energy alternatives on the common single- and combined abiotic- or multi-stress-factors.

Maize (Zea mays L.) is the major produced crop in South Africa, but numerous abiotic/biotic stressors threaten its production. Herbicides are mainly in the agricultural sector to minimise crop yield losses caused by weed competition. However, with most weeds becoming resistant to glyphosate, South African farmers have used higher herbicide concentrations than typically recommended. This study was conducted to determine the effect of two biostimulants (brassinosteroids and KELPAK) and glyphosate on the morphophysiological parameters of maize seedlings. Experiments were carried out in the glasshouses of the Department of Soil, Crop, and Climate Sciences at the University of the Free State in Bloemfontein for eight weeks over two seasons, 2017/2018 and 2018/2019. The treatments did not significantly affect all maize morphological parameters except the plant dry mass. Compared to the control, plant dry mass was significantly (p < 0.05) increased by 15.72 g when glyphosate was applied in combination with brassinosteroids during the 2019 growing season. The application of glyphosate, brassinosteroids, and KELPAK differed significantly (p < 0.05) between weeks across the physiological parameters in the two seasons: an irrefutable significant increase was recorded in the rates of transpiration between the weeks. Although significant differences were recorded in the chlorophyll fluorescence, chlorophyll, and carotenoid content, these parameters were similar to the control, especially in the last week of data collection. During the early developmental stage of maize, farmers can administer biostimulants—brassinosteroid (5 g ai ha⁻¹) and KELPAK (5% ai ha⁻¹)—alone and in combination in glyphosate-resistant maize cultivars treated with glyphosate to aid maize seedlings.

The density and morphology of glandular trichomes in rose geranium (Pelargonium graveolens L’Her.) are often correlated to the essential oil biosynthesis. However, whether the different organs in the same rose geranium plant are affected by hail damage, or if they recover similarly following hail damage is still unknown concerning the essential oil biosynthesis. The objective of this study was to evaluate the effects of split-applying cytokinin (CK), gibberellic acid (GA) and defoliation on rose geranium trichome morphology and density, and essential oil biosynthesis. The experiment was carried out in a hail-net covered tunnel structure during 2017-2018 growing season. The experimental design was a complete randomized blocks with a 3x3 factorial arrangement of treatments: three defoliation levels (0, 50, and 100%), two levels of split-application of CK and GA (0.32 mg L-1 CK + 150 mg L-1 GA; and 0.64 mg L-1 CK + 300 mg L-1 GA), and a control. The attenuate, peltate, and capitate trichome groups were identified in the leaf. Morphologically, the attenuate trichome group was less dense on both recovered and new plant leaves, despite split-applied CK and GA treatment. With the peltate group, brevicollate trichome density declined in all plant leaves treated with 0.64 mg L-1 CK + 300 mg L-1 GA on both leaf surfaces. Application of 0.64 mg L-1 CK + 300 mg L-1 GA led to high density of the elongated-capitate type on leaves recovered from 50 and 100% defoliation. The essential oil yield was not affected by density and morphological changes of the trichomes. However, the application of 0.32 mg L-1 CK + 150 mg L-1 GA increased the citronellol content where plants endured 100% defoliation. Results demonstrated that the effects of hail damage stress and subsequent split-applied CK and GA could transform the morphology of trichomes, subsequently increasing the density.

Heavy metal pollution due to mining activities poses a significant threat to agricultural production, ecosystem health, and food security in South Africa. This review integrates current knowledge on the use of mustard spinach (Brassica juncea (L.) Czern.) for the bioremediation of polluted water and soil, focusing on enhancing phytoremediation efficiency through the use of silicon-based biostimulant treatments. Mustard spinach is known for its capacity to accumulate and tolerate high levels of toxic metals, such as Pb, Cd, and Hg, owing to its strong physiological and biochemical defense mechanisms, including metal chelation, antioxidant activity, and osmotic adjustment. However, phytoremediation potential is often constrained by the negative impact of heavy metal stress on plant growth. Recent studies have shown that silicon-based biostimulants can alleviate metal toxicity by reducing metal bioavailability, increasing metal immobilization, and improving the antioxidative capacity and growth of plants. Combining silicon amendments with mustard spinach cultivation is a promising, eco-friendly approach to the remediation of mining-impacted soils and waters, potentially restoring agricultural productivity and reducing health risks to the resident populations. This review elucidates the multifaceted mechanisms by which silicon-enhanced phytoremediation operates, including soil chemistry modification, metal sequestration, antioxidant defense, and physiological resilience, while highlighting the practical, field-applicable benefits of this combined approach. Furthermore, it identifies urgent research priorities, such as field validation and the optimization of silicon application methods.

In vitro and in vivo bio-stimulatory activity of a Lupinus albus cv. Bethuana white Seed Suspension (SS) was previously documented using vegetable crops. This was repeated for two grain crops, maize and wheat, in an attempt to provide a rationale forthe isolation and identification of the active compound(s) involved. In all cases, besides negative controls, the response to treatment with SS was compared to that of a commercial bio-stimulant, ComCat®. At an optimum concentration of 5 mg ℓ-1 SS significantly enhanced seedling growth and yield in both crops. Subsequently, activity directed liquid-liquid extraction of ground L. albus seed resulted in an ethyl acetate extract containing most of the bio-stimulatory activity. Two in vitro bio-assay procedures were employed to appraise the in vitro bio-stimulatory properties of semi-purified fractions as well as pure compounds contained in it. The highly active ethyl acetate extract was fractionated further by means of adsorption column chromatography resulting in eighty five fractions that were combined into twelve on the basis of similarities in thin layer chromatography profiles. Four of these fractions showed significant bio-stimulatory activity and were pooled. From this one compound was isolated, purified and identified as glyceryl trilinoleate by means of nuclear magnetic resonance spectroscopy. Key words: Lupinus albus, seed suspension, field trials, yield, NMR spectroscopy, glyceryl trilinoleate.