SUMMARY
The aim of this work was to evaluate the allelophathic and antioxidant activity and the total phenolic contents of Hydrocotyle bonariensis. The bioactivity of the crude extract and fractions (hexane, ethyl acetate, ethanol-water) of aerial and underground parts and the alkaloid fraction from underground part of H. bonariensis were evaluated by germination and growth bioassays with lettuce, tomato, onion and wheat, in laboratory. The total phenolic contents were determined by the Folin-Ciocalteau method. Antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH). The results revealed that the extract and fractions inhibited the germination of lettuce, tomato, onion and wheat. The ethyl acetate fraction from the underground part inhibited lettuce germination by 68% and wheat germination by 60%. In the growth bioassays, the ethyl acetate fraction from underground and aerial parts showed strong inhibitory effect in the growth of root (> 40%), hypocotyl/coleoptiles (> 40%) and dry mass. The ethyl acetate fraction from underground parts presented higher total phenolic contents, better activity in the DPPH assay and the fraction with greater phototoxic effect by germination and growth of lettuce, tomato, onion and wheat.