How Do the Extracts From the Invasive Plant <i>Acmella radicans</i> Inhibit Germination and Growth of <i>Brassica rapa</i> (Field Mustard) and <i>Chrysanthemum coronarium</i> (Garland Daisy)?

The allelopathic effects have not previously been studied for Acmella radicans (Jacquin) R. K. Jansen, a new invasive species recorded for Yunnan Province, China. In the current study, the allelopathic potential of root, stem, leaf, flower, and fruit head aqueous extracts from A. radicans on two important vegetable crops, Brassica rapa (field mustard) and Chrysanthemum coronarium (garland daisy), was explored in the laboratory. All four plant part aqueous extracts had some inhibitory effects on B. rapa and C. coronarium in terms of seed germination and seedling growth. Increasing concentrations of aqueous extracts of A. radicans reduced many indicators significantly, including germination rate, the seed germination index, root length, stem length, and biomass of B. rapa and C. coronarium . Generally, the most inhibited parameter was root length, followed by shoot length and biomass, with the lowest being seed germination. In terms of allelopathic response index, flowers and fruit heads yielded the strongest inhibition, followed by leaves and stems, with the lowest impact from root extracts. Root extracts had positive effects at 0.0125–0.025 g·mL −1 . The inhibition rates for A. radicans extracts on B. rapa were generally higher than those of C . coronarium . It is concluded that A. radicans has allelopathic potential on vegetable crops with the overall inhibition rates ranked in the order flower and fruit head &gt; leaf &gt; stem &gt; root. This was the first study to show that the allelopathic potential of A. radicans against crops may be strongly linked to its invasion and expansion.