Phytotoxic Effects of Ethanolic Extracts of Magonia pubescens A.St.-Hil. (Sapindaceae) on the Germination of Emilia sonchifolia (L.) DC. Seeds.

Emilia sonchifolia (L.) DC. is a weed characterized by seed production and efficient wind dispersal. This study evaluated the allelopathic potential of extracts from the leaves, stem bark, and fruit pericarp (EECFMp) of Magonia pubescens on E. sonchifolia seed germination. HPLC-DAD analysis identified caffeic acid in all extracts, while p-coumaric and ferulic acids were detected in the stem bark and fruit pericarp extracts. The extracts exhibited concentration-dependent activity. The leaf extract was the most phytotoxic, reducing germination to 33% at the highest concentration and outperforming glyphosate under the same conditions. Higher concentrations delayed germination (T50), reduced the germination speed index, and inhibited radicle and shoot growth. Lower concentrations stimulated germination, with the 50% stem bark extract achieving the highest germination rate (82%), indicating hormesis. These effects are likely associated with phenolic compounds, particularly caffeic acid. Overall, M. pubescens is a promising source of allelochemicals with potential application as a bioherbicide for weed management and as a seed germination biostimulant. Further investigations could elucidate the mechanisms of action and identify the specific compounds responsible for the phytotoxic and stimulatory effects.