Allelopathy in the Invasive Echinocystis lobata (Michx.) Torr. et A.Gray: Bioassays with Aqueous Extracts of Plant Organs and GC–MS Analysis

Prickly cucumber (Echinocystis lobata), originating from eastern North America, exhibits a range of adaptations that enable it to effectively colonize temperate and humid forest environments, among others in Europe. This study examined the allelopathic effects of E. lobata as a factor influencing its competitive interactions with other plant species. Laboratory bioassays were conducted to evaluate the effects of aqueous extracts (2.5%, 5%, and 7.5%) obtained from different organs of E. lobata on the germination of grains or seeds and the early growth of seedlings of Festuca arundinacea Schreb. (monocotyledon) and Raphanus sativus L. var. sativus ‘China Rose’ (dicotyledon). Germination percentage, as well as root and shoot growth parameters, were analyzed. In addition, biochemical analyses of E. lobata organs (leaves, stalks, fruits) used in the experiment were performed. Analysis using a combined chromatographic and mass spectrometric technique identified 21 compounds, including secondary metabolites potentially associated with allelopathic activity. Petri dish assays revealed significant inhibition of the germination of grains and seeds and the growth of seedlings of both tested species, depending on the E. lobata organ and extract concentration. The strongest inhibitory effects were generally observed at concentrations of 5% and 7.5%. In conclusion, the biochemical analyses confirmed the clear primary allelopathic potential of E. lobata, which presumably may enhance its competitive ability.