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Browsing Plant Sciences by Subject "A. cruentus"
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Item Open Access Influence of abiotic stress on allelopathic properties of Amaranthus cruentus L.(University of the Free State, 2016-06) Allemann, Ingrid; Cawood, M. E.; Allemann, J.English: Allelopathic plants disrupt germination and growth of agricultural crops which will lead to a lower yield production. However, allelopathy is also important in an environmentally friendly approach to control weeds and reduce chemical herbicide usage. Allelochemicals are secondary metabolites, released into the environment through leaching, volatile emissions, root exudation and the decaying of plant residues. The isolation and identification of allelochemical compounds involved in the plant-plant interactions are of great importance. Amaranthus cruentus is used for both its grain and leaves for consumption. This plant is now being considered at as a new agricultural crop; therefore it is important to understand how this plant will interact within a changing environment and how this will influence other plants. It is known that amaranth plants have the ability to synthesize allelochemicals in order to protect itself from different types of stress. In this study, the leaf litter as well as the polar and non-polar extracts of the leaves of A. cruentus from three different temperature regimes were investigated for their in vitro allelopathic properties towards tomato, pepper, cucumber and lettuce. The chemical compounds induced during each temperature treatment were also compared. Methanol-water and dichloromethane (DCM) crude extracts were prepared from each of the temperature treated amaranth plants using dried ground leaf litter. The identification of compounds present in the different treated plants was done through thin layer chromatography (TLC), high pressure liquid chromatography (HPLC) and gas chromatography coupled to mass spectrometry (GC-MS). TLC indicated the presence of phenolics, terpenes and flavonoids in all A. cruentus extracts. Differences were seen in the number and type of compounds between the temperature treated plant extracts. Methanol-water extracts of the three plant treatments were analysed using HPLC with specific consideration to phenolic compounds. The optimal treatment showed the most peaks followed by the cold and lastly the heat treatment that showed the least amount of peaks. Compounds identified in the optimal and cold treatments included catechin and rutin, while the cold treatment also contained quercetin. The heat treatment contained none of the compounds that were used as standards. Dichloromethane (DCM) extracts of the three plant treatments were analysed using GC-MS. In the optimal treatment, the compound found in the highest abundance was phosphine imide, P, P, P-triphenyl (38.59%), the cold treatment contained neophytadiene (27.35%) and α-linolenic acid (24.41%). Dichloroacetic acid (29.68%) was identified as the major compound in the DCM extract of A. cruentus heat treated plant litter. Laboratory bioassays were carried out to evaluate the in vitro allelopathic activity of different concentrations of the stressed amaranth plant litter or methanol-water and DCM crude extracts, against four vegetables (tomato, lettuce, cucumber and pepper) by means of the Sandwich Method. Germination, hypocotyl and radicle length were adversely influenced by the plant litter for all the temperature treatments. The inhibition caused by the litter was dependant on concentration and each vegetable species showed different levels of sensitivity. The extracts indicated that both types of extracts and all temperature treatments had a negative influence on the germination of all the vegetables. The methanol-water and DCM extracts adversely affected organ length for all the vegetables at the highest concentration for each of the treatments. The severity of inhibition was dependent on both the concentration and temperature treatment. Each vegetable species showed different levels of sensitivity against the different extract treatments. The results obtained in this study, demonstrated that cold, hot and optimal temperature treatments induced the expression of different chemical compounds in the leaves of A. cruentus plants. All temperature treatments however affected germination and growth of some vegetables, exhibiting allelopathic properties. Therefore, plant litter and both polar and non-polar extracts of all the treated amaranth plants, contained compounds responsible for allelopathy. Furthermore, the results indicated that vegetables reacted differently towards the treatments of the leaf litter and extracts, showing variation in sensitivity against various compounds. Thus, abiotic stress does have an influence on both the chemical composition and allelopathy of A. cruentus, but it was likewise proven that plants grown under optimal growth conditions also produced both polar and non-polar compounds with allelopathic properties which may have a negative impact in crop rotation systems.