Allelopathic activity of aqueous extracts of Richardia brasiliensis Gomes on germination and initial growth of common bean and soybean

Abstract

ABSTRACT: Weeds are major constraints on crop productivity not only because of competition for resources but also because they release allelopathic compounds. Richardia brasiliensis Gomes (Rubiaceae) is widely distributed in agricultural systems and may affect neighboring crops by producing bioactive secondary metabolites. This study evaluated the effects of aqueous extracts of R. brasiliensis at different concentrations on the germination and early development of soybean and common bean, and identified the main phytochemical constituents of the extracts. Bioassays were conducted under laboratory and greenhouse conditions to assess germination, emergence, seedling growth, and biomass accumulation. Phytochemical characterization was performed using high-performance liquid chromatography with diode-array detection (HPLC-DAD). The extracts reduced soybean germination under greenhouse conditions and altered biomass accumulation, leading to increased fresh mass and root dry mass at intermediate concentrations. In the common bean, germination and biomass were not significantly affected, although shoot and root length decreased at higher extract concentrations. Chromatographic analysis identified caffeic, ferulic, and vanillic acids as the major phenolic compounds. The results demonstrate species-specific and concentration-dependent allelopathic effects, suggesting the involvement of hormetic responses and synergistic interactions among secondary metabolites.