Aqueous extracts of Ailanthus altissima bark and foliage were previously shown to be toxic to other plants. Using bioassay-directed fractionation, I isolated the phytotoxic compound from A. altissima root bark and identified it to be ailanthone, a quassinoid compound having molecular mass of 376. Ailanthone was highly phytotoxic, with concentrations of 0.7 ml/L causing 50% inhibition of radicle elongation in a standardized bioassay with garden cress (Lepidium sativum) seeds. Ailanthone exhibited potent pre- and postemergence herbicidal activity in greenhouse trials. Postemergence activity was especially striking; even the lowest application rate (0.5 kg/ha) caused complete mortality of five of the seven plant species tested within 5 d of treatment. In contrast, the highest application rate (8 kg/ha) did not cause any detectable injury to A. altissima seedlings, indicating the presence of a protective mechanism in the producer species to prevent autotoxicity. Ailanthone was rapidly detoxified in field soil as a result of microbial activity. Applications of ailanthone equivalent to 0.5 and 4.0 kg/ha completely lost their phytotoxicity within ≤5 d when incubated in the presence of nonsterile soil. When incubated with sterile soil under identical conditions, however, ailanthone remained highly phytotoxic throughout the 21-d duration of the investigation. The high level of postemergence herbicidal activity in conjunction with its rapid biodegradation in soil suggest ailanthone may have potential for development as a natural-product herbicide.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics
- Plant Science