Implications of Euphorbia peplus and Euphorbia geniculata Allelopathy on Some Plant Species and Phytopathogenic Fungi

Invasive species of Euphorbia peplus and Euphorbia geniculata weeds compete with the crops and act as hosts for other pests, consequently interfering with the livestock. Therefore, a comprehensive allelopathic screening of Euphorbia spp. was implemented via aqueous extracts and decayed residues against Triticum aestivum and their associated weeds. Aqueous and ethyl acetate extracts of E. peplus and E. geniculata were suppressed by the target weeds. The effects were influenced by plant types and concentrations. The Brassica nigra weeds were very susceptible, while T. aestivum was slightly sensitive. The phytotoxicity of Euphorbia spp. decayed residues correlated with the used concentrations and soil properties. Euphorbia spp. extracts were tested against Sclerotina sclerotiorum, Alternaria alternata, and Fusarium oxysporum fungi. E. peplus at 2000 µg/mL decreased fungal growth by 57.1% (S. sclerotiorum), 63.1% (A. alternata), and 63.0% (F. oxysporum), while E. geniculata at 2000 µg/mL decreased fungal growth by 73.0% (S. sclerotiorum), 64.8% (A. alternata), and 72.7% (F. oxysporum). Euphorbia spp. allelochemicals were analysed by HPLC, which indicated the differential in secondary metabolite concentrations between the two species. These substances have a positive potential as natural pesticides that are used in the management of these species.