Allelopathic potential and soil persistence of bergamot (Citrus bergamia Risso & Poit.) and pomegranate (Punica granatum L.) peel powders, as sustainable plant-derived products for the management of resistant weeds associated with durum wheat

Introduction: Chemical pesticides negatively affect humans and environment, and increase weed resistance, forcing modern agriculture to shift to natural means. Plant derived products offer a sustainable and eco-friendly alternative for weed control. This study aimed to evaluate the allelopathic potential of bergamot (Citrus × bergamia (Risso) Risso & Poit.) and pomegranate (Punica granatum L.) fruit peel powders, alongside the potential weed-suppressive efficacy of EP5 commercial powder, under in vitro and in vivo conditions. Methods: Powder water extracts were preliminarily tested under laboratory conditions against Alopecurus myosuroides, and Lolium multiflorum seeds, as well as durum wheat kernels. Subsequently, two greenhouse pot-experiments were carried out to evaluate the powder herbicidal activity, phytotoxicity on durum wheat, and persistence over time within the soil. A set of germination-related parameters, including the final germination percentage, mean germination time, germination index and seed vigor index, and a set of growth-related parameters, such as root, shoot and total seedling lengths and dry matter content, plant inhibition index and biomass accumulation inhibition were detected on both weeds and wheat. Results: The in vitro experiment revealed a strong inhibitory effect on weeds without affecting wheat. In the first in vivo experiment, EP5 reduced wheat germination and seed vigor by approximately 50%, while pomegranate reduced wheat dry matter; on weeds, EP5 was the strongest germination inhibitor, all powders reduced root length, and pomegranate maximized overall plant and biomass inhibition. The second in vivo experiment revealed a biostimulatory trend: bergamot and pomegranate accelerated wheat germination, EP5 promoted seedling elongation, and pomegranate enhanced dry matter. Furthermore, seed vigor of weeds increased under all treatments, with bergamot promoting plant length, while pomegranate and EP5 minimized growth inhibition. Discussion: The tested powders are promising natural alternatives to chemical herbicides; however, their short-term soil persistence and slight phytotoxicity to wheat suggest that they may be particularly suitable for preemergence applications.