Evaluation of Allelopathic Potential of Aqueous Extract of Russian Knapweed (Acroptilon repens L.) on Seed Germination and Early Seedling Growth of Wheat and Two Weed Species

Introduction and Objective: Weeds are among the major biological constraints limiting crop productivity, and their management in many agricultural systems relies heavily on chemical herbicides. However, repeated and intensive herbicide use can increase production costs, accelerate the evolution of herbicide resistance, and cause environmental concerns. Consequently, increasing attention has been directed toward naturally occurring plant compounds with allelopathic activity as potential components of sustainable and bio-based weed management. Acroptilon repens (Russian knapweed) is a plant known to contain biologically active secondary metabolites that may interfere with seed germination and early seedling development. Nevertheless, comparative information on the responses of weeds and crops to aqueous extracts of A. repens remains limited. Therefore, this study was conducted to evaluate the effects of different concentrations of aqueous A. repens extract on seed germination and early growth of wheat, wild mustard, and green foxtail and to quantify species sensitivity using dose–response analysis.
Materials and Methods: The experiment was conducted as a factorial experiment based on a completely randomized design in the laboratory of the Faculty of Agriculture, University of Mohaghegh Ardabili, in 2025. Seeds of wild mustard (Sinapis arvensis), green foxtail (Setaria viridis), and wheat (Triticum aestivum) were exposed to seven concentrations of aqueous A. repens extract: 0 (control), 5, 10, 20, 30, 40, and 50 g L⁻¹. Germination percentage, germination rate, mean germination time, seedling length, fresh weight, and dry weight were evaluated. Treatment means were statistically compared to determine differences among extract concentrations. In addition, three- and four-parameter log-logistic models were fitted to dose–response data to characterize concentration-dependent responses and estimate the effective concentration causing 50% inhibition (ED₅₀) for the studied traits.
Results: Increasing extract concentration significantly reduced germination percentage and germination rate in all three species, although the magnitude of inhibition differed among species. At 50 g L⁻¹, germination percentage decreased from 92%, 98%, and 99% in the controls to 33%, 20%, and 46% in wild mustard, green foxtail, and wheat, respectively, corresponding to reductions of 64.14%, 79.60%, and 53.53%. Germination rate was also strongly reduced, with decreases of 81.60% in wild mustard, 82.10% in green foxtail, and 56.00% in wheat relative to the control. Increasing extract concentration delayed germination. Mean germination time increased from 2.99 to 4.99 days in wild mustard, from 3.42 to 4.19 days in green foxtail, and from 2.04 to 2.21 days in wheat at 50 g L⁻¹, corresponding to increases of 2.00, 0.77, and 0.17 days, respectively. Seedling growth and biomass accumulation were also progressively inhibited as extract concentration increased. At 50 g L⁻¹, seedling length, fresh weight, and dry weight were reduced by approximately 60%, 62%, and 65%, respectively, compared with the control. Dose–response analysis further demonstrated differential sensitivity among species, with the weed species generally showing stronger responses than wheat. The findings demonstrate the allelopathic potential of A. repens and provide quantitative information on species responses to increasing extract concentrations. The results support further investigation of A. repens as a potential source of biologically active compounds for integrated and bio-based weed management. However, greenhouse and field experiments, together with chemical characterization of the active compounds and assessment of crop selectivity and environmental safety, are required before practical weed-management applications can be recommended.