A Fungitoxic Phenolic Compound in Hydrilla verticillata

Leaves and internode sections of the submersed aquatic weed Hydrilla verticillata grown in culture were collected during development over a 17-day period of growth and analyzed for phenolic content by high-pressure liquid chromatography and thin-layer chromatography. Phenols present in trace amounts included ferulic, cblorogenic, and caffeic acids. Phenols were not esterified to the cell wall as in other monocotyledonous species. Flavonoid anthocyanins accumulated in internodes as the tissues matured. During the 17-day period of development, the major compound in both leaves and internodes was a caffeic acid ester. The ester inhibited germination and germ tube elongation of conidia of the fungal pathogen Fusarium culmorum. Mass spectrometry and nuclear magnetic resonance analyses of the ester indicated the presence of a carbohydrate component and that the molecule has a composition of 2:1 caffeic:carbohydrate moieties. Substantially more of the ester accumulated in leaves than in internodes, and in leaves it represented up to 0.273% of the leaf fresh weight. The unusually high content of the caffeic acid ester in hydrilla tissues and its fungitoxicity suggest that the compound may be an allelopathic factor that could inhibit fungal pathogens selected as potential mycoherbicides. (C) 1992 Academic Press, Inc.