Chemical Characterization and Allelopathic Effects of Ambrosia psilostachya (Asteraceae)

Ambrosia spp. have been introduced and distributed across different continents as an invasive alien plant species. The present study aimed to identify the chemical components of essential oil isolated from different parts of Ambrosia psilostachya and evaluate the phytotoxic effect of its aqueous extracts on the growth parameters of Phaseolus vulgaris L. (bean) and Arachis hypogaea L. (peanut) under greenhouse conditions. The chemical components of the essential oil of A. psilostachya were analyzed by gas chromatography-mass spectrometry. Total 44 compounds, including isoaromadendrene epoxide (17.38 %), citral (15.13 %), caryophyllene (7.23 %), borneol (8.76%), (+)-2-bornanone (6.45 %), eucalyptol (4.61 %), and 22 compounds including endo-borneol (22.76%), (+)-2-bornanone (8.08%), caryophyllene oxide (7.77%), citral (14.65%), cis-verbenol (4.43%), and eucalyptol (4.72%) as the major components were identified and isolated in the shoots and roots, respectively. To evaluate the allelopathic effect of A. psilostachya on bean and peanut seedlings, the aqueous extracts were prepared at four concentrations (25%, 50%, 75%, and 100%). The extracts at the concentrations of 50% or higher had a significant inhibitory effect on yield, dry weight, height, and LAI in both species. The inhibitory activity of A. psilostachya may be attributed to its high content of isoaromadendrene epoxide, citral, caryophyllene, and caryophyllene oxide. This study highlights that the allelopathy effects of A. psilostachya are due to the action of its compounds, which should be analyzed in future studies, and an accurate evaluation of the allelopathy effects of this invasive plant requires comprehensive, long-term studies in the environment.