Ailanthone from Ailanthus altissima (Mill.) Swingle as potential natural herbicide.
Ailanthone (Ail) is the most phytotoxic quassinoid in plant extracts of Ailanthus altissima (Mill.) Swingle, an invasive tree of Simaroubaceae with allelopathic activity. Ail has raised attention as a potential biological herbicide in weed management to reduce the impact on the environment and human health. However, high costs for its extraction and purification, and low persistence in the soil have been considered so far limits for its development as herbicide for open field applications. In this study we explored its phytotoxic activity and persistence, through five experiments, to evaluate its potential for the weed management in the horticulture sector and in urban green areas, where lower herbicide amounts are needed. Ail inhibition activity on germination and growth was evaluated on two model species (garden cress - Lepidium sativum L. - and radish - Raphanus sativus L.). Firstly, the dose-response curve between Ail concentration and index of germination was calculated in filter paper and Ail persistence along 30 days was also assessed. Afterwards, Ail bioactivity and persistence were evaluated in a non-sterile urban soil and a horticultural substrate. Ail inhibited by 80 to 90% the plant growth already at low doses (7.5 mg L-1) in paper and soil, while higher concentrations (≥ 30 mg L-1) were necessary in the cultivation substrate to obtain similar results. Regarding the phytotoxic persistence, the two species were similarly inhibited at the first evaluation (10 days after treatment) both in paper and cultivation substrate, whereas on the longer period (20 and 30 days after treatment), radish was more affected, with growth inhibition higher than 45% until 30 days. Results of these experiments implement the knowledge on Ail phytotoxic activity, envisioning its potential use as a biological solution for weed management in urban areas and protected cultivation environments.