Screening for Plant Volatile Emissions with Allelopathic Activity and the Identification of L-Fenchone and 1,8-Cineole from Star Anise (Illicium verum) Leaves

One hundred and thirty-nine medicinal plant species were screened for their allelopathic activity through volatile emissions using <i>Lactuca sativa</i> as a test plant. Volatile emissions from the leaves of star anise (<i>Illicium verum</i>) showed the highest inhibition (100%) on the radicle and hypocotyl growth. Using headspace gas collection and gas chromatography-mass spectrometry (GC-MS), seven major volatile compounds from the leaves of star anise, including α-pinene, β-pinene, camphene, 1,8-cineole, D-limonene, camphor, and L-fenchone were detected. To determine volatile compounds that may contribute to the inhibitory activity of star anise, the allelopathic potential of individual volatiles from star anise was evaluated using the cotton swab bioassay. The EC₅₀ was calculated for each of the seven identified compounds. L-fenchone showed the strongest growth inhibitory activity (EC₅₀ is 1.0 ng/cm³ for radicle and hypocotyl growth of lettuce), followed by 1,8-cineole, and camphene. This is the first report that L-fenchone could be an important volatile allelochemical from the leaves of star anise. From the actual concentration of each volatile compound in headspace and EC₅₀ value, we concluded that the four volatile compounds, including L-fenchone, 1,8-cineole, β-pinene, and camphene are the most important contributors to the volatile allelopathy of star anise.