We assessed the allelopathic effects of the aqueous extract of Sonchus oleraceus dry shoots on the germination and seedling growth of Trifolium alexandrinum, three weed species (Brassica nigra, Chenopodium murale and Melilotus indicus) and S. oleraceus itself. We assayed four different concentrations of the aqueous extract (w v −1 ): 1%, 2%, 3% and 4%. To determine whether the effects of the extract were attributable to the presence of allelopathic compounds, its osmotic potential or both, we prepared concentrations of polyethylene glycol (PEG) with osmotic potentials equivalent to those of the aqueous extract. All concentrations of the plant extract completely inhibited the germination and seedling growth of C. murale. The lowest concentration of the plant extract partially inhibited germination and seedling growth of B. nigra, M. indicus and S. oleraceus, whereas the higher concentrations inhibited those parameters completely. The germination of T. alexandrinum was not affected by the aqueous extract at 1% or 2%. In general, the aqueous extracts were more effective in inhibiting seed germination and seedling growth than were the PEG solutions. Phytochemical analyses revealed that phenols and alkaloids were the most abundant compounds in S. oleraceus dry matter. Our results suggest that the aqueous extract of S. oleraceus has an allelopathic effect on some weeds, and its usefulness as a bioherbicide therefore merits further study.

-Laboratory and greenhouse experiments were conducted to evaluate the phytotoxic effect of black mustard extracts and root exudates on two crops: Trifolium alexandrinum and Triticum aestivum, and two weeds: Phalaris paradoxa and Sisymbrium irio. The seeds were treated with aqueous and ethanolic extracts and chloroform for eight days, or subjected to root exudates of just harvested mustard in a greenhouse for five weeks. High-performance liquid chromatography (HPLC) was used to quantify phytotoxins from plant tissues. Seed germination of P. paradoxa was reduced with the lowest concentration of the different extracts. However, the aqueous extract at 4% completely curtailed the germination of all the target species. In general, plant extracts had a concentration-dependent reduction of seedling growth of the target species. However, the ethanolic extract, at the lowest concentration, has stimulated the shoot length of both T. alexandrinum and T. aestivum, and the root length of the former. Mustard root exudates inhibited emergence and growth of the target species throughout the experiment. Ferulic and syringic acids were the dominant allelochemicals found when HPLC was used.Keywords: allelopathy, Brassica nigra, plant extracts, isothiocyanates (ITCs), phenolic acids.RESUMO -Experimentos de laboratório e estufa foram realizados para avaliar o efeito fitotóxico dos extratos de mostarda-preta e exsudatos de raiz de duas culturas: Trifolium alexandrinum e Triticum aestivum, bem como de duas plantas daninhas: Phalaris paradoxa e Sisymbrium irio. As sementes foram tratadas com extratos aquosos, etanólicos e clorofórmio por oito dias, ou submetidas a exsudatos de raiz de mostarda recém-colhidaem estufa durante cinco semanas. A cromatografia líquida de alto desempenho (HPLC) foi usada para a quantificação de fitotoxinas a partir de tecidos de plantas. Sementes de P. paradoxa apresentam germinação reduzida com a menor concentração dos diferentes extratos. No entanto, o extrato aquoso a 4% restringiu completamente a germinação de todas as espécies-alvo. Em geral, os extratos de plantas tiveram uma redução, dependendo da concentração do crescimento de mudas das espécies-alvo. No entanto, o extrato etanólico, na concentração mais baixa, tem estimulado o comprimento dos ramos de T. alexandrinum e T. aestivum e o comprimento da raiz da primeira. Exsudatos de raiz de mostarda inibiram o surgimento e crescimento das espécies-alvo durante todo o experimento. Os ácidos ferúlico e siringico foram os aleloquímicos dominantes encontrados utilizando HPLC.Palavras-chave: alelopatia, Brassica nigra, extratos vegetais, isotiocianatos (ITCs), ácidos fenólicos.

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Annual sowthistle (Sonchus oleraceus) has been reported to produce allelopathic effects. Two greenhouse experiments were conducted to estimate the allelopathic potential of both plant residue and root exudates of S. oleraceus on flavonoid composition and nodulation in a leguminous crop, Trifolium alexandrinum, and in two leguminous weeds, Melilotus indicus and T. resupinatum. The results of high performance liquid chromatography-mass spectrometry (HPLC--MS/MS) showed that all three legumes contained six flavonoid aglycones: apigenin, daidzein, kaempferol, luteolin, myricetin and quercetin; and seven flavonoid glycosides: daidzin, genistin, hesperidin, hyperoside, kaempferol-7-O--glucoside, naringin and rutin. In general, both plant residue and root exudates had inhibitory effects on the flavonoid composition and nodulation of the target species. However, residue of S. oleraceus caused a significant increase in both individual and total detected flavonoids in T. alexandrinum. The results suggest that the phytotoxins released from S. oleraceus may restrain the biosynthesis of flavonoids in the target species, whereas the accumulated flavonoids in T. alexandrinum are allelopathic-induced metabolites and suggest a resistance mode in this crop.

This study was conducted to evaluate the use of the phenolic-rich Sonchus oleraceus residue as an environmentally safe approach to induce the nutritive and health-promoting values of common bean ( Phaseolus vulgaris L. cv. Bronco). S. oleraceus shoot residue, at rates of 150 and 300 g m, has improved soil fertility via accumulation of soil macronutrients, organic matter, organic carbon, and total phenolics. The growth and yield of bean were significantly increased. Moreover, chemical composition of the treated seeds was significantly altered, whereas higher levels of total antioxidant capacity, proteins, carbohydrates, and most of the individual phenolic acids, flavonoids, vitamins, essential amino acids, and unsaturated fatty acids were recorded. Interestingly, a concentration dependent effect was also observed, for instance, a lower saturated-to-unsaturated fatty acid ratio was only observed in the case of the lower residue rate. These findings recommend the use of S. oleraceus in organic farming of bean to enhance the health benefits of the produced seeds.

Interference of Sonchus oleraceus was studied by evaluating its competitive and allelopathic potential on three weed species: Brassica nigra, Chenopodium murale and Melilotus indicus. The allelopathic potential of S. oleraceus was assessed using the S. oleraceus-infested soil collected from its dominating communities and its root exudates trapped using living S. oleraceus, while its competitive ability was assessed in greenhouse in an additive design with ratio 1:1 at different densities. The rhizosphere soil of S. oleraceus inhibited germination and growth of B. nigra and M. indicus. Chlorophyll content of the target weeds was not affected in this test. Soils containing living S. oleraceus inhibited germination and growth of all weeds except germination of C. murale. Interspecific competition reduced germination of C. murale and M. indicus, and increased mortality of the former at all densities. HPLC analyses for soil samples indicated the presence of several phenolic compounds among which caffeic acid and catechol were abundant in the S. oleraceus-infested soil while caffeic and ferulic acids were abundant in its root exudates. The data suggest that both allelopathic and competitive potential of S. oleraceus function, and its interference plays at least a partial role in the community organization of weeds in agroecosystem. ª 2014 Production and hosting by Elsevier B.V. on behalf of Faculty of Agriculture, Ain Shams

Human impact in newly urbanized deserts creates new environments that may favor the establishment/dominance of certain plant species. In this study, we showed how the human activities during desert urbanization do affect distribution, composition and diversity of plant species in a new urban ecosystem. In a field study during 2015–2016 and 2017–2018 growing seasons, we investigated these vegetation criteria in three new habitats created recently due to human manipulations in addition to the old habitat of such area (i.e. the desert). We also compared vegetation criteria comprising the floristic cover, composition and diversity between the desert locations inside and on the outskirts of the city. The detrended correspondence analysis (DCA) successfully separated the different habitats studied. Besides, the floristic composition and diversity were significantly varied amongst these habitats. The canonical correspondence analysis (CCA) revealed an apparent correlation between floristic composition and soil criteria across the study area. For the desert vegetation, the cover values of both Tamarix nilotica and Zygophyllum coccineum , in addition to the whole diversity indices, were significantly suppressed in the desert fragments inside the newly constructed city in comparison with their cover in the desert adjacent to it. Moreover, the cover of both species was significantly declined in 2018 compared with their cover in 2015. On converse, the covering areas of Phragmites australis and Bassia indica were increased after intensive constructions in 2018. These results suggest that the human activities and, consequently, urbanization may influence plant life in newly urbanized desert ecosystems, leading to dispersal of new species and destruction of plant cover in some parts of the desert. Efforts and conservation strategies should be devoted to save the desert species that are vulnerable to elimination due to expansion of urbanization.