Isolation and identification of a phytotoxic substance from the emergent macrophyte Centrostachys aquatica

Background: Centrostachys aquatica is a perennial emergent macrophyte in marshy places and in rivers. The species was recorded in Senegal and Nigeria, but widespread in tropical Africa, and South and East Asia. Aqueous methanol extracts C. aquatica was found to be toxic to several plant species. However, no phytotoxic substance has been reported in this species. Therefore, we investigated phytotoxic activity and searched for phytotoxic substances with allelopathic activity in C. aquatica. Results: An aqueous methanol extract of C. aquatica inhibited the growth of roots and hypocotyls of cress (Lepidium sativum). The extract was then purified by several chromatographic runs and a phytotoxic substance with allelopathic activity was isolated and identified by spectral analysis as loliolide. Loliolide inhibited cress root and hypocotyl growth at concentrations greater than 0.03 mu M. The concentrations required for 50% growth inhibition of cress roots and hypocotyls was 0.18 and 0.15 mu M, respectively. Conclusion: These results suggest that loliolide is a phytotoxic substance and may contribute to the allelopathic effect caused by C. aquatica.