Objective  Allelopathic effect of Ambrosia trifida on vegetables was studied by an in vitro experimentation.

  Method  Genotoxicity and effects of the aqueous extracts of A. trifida stems and leaves on the seed germination and seedling growth of cabbage (Brassica chinensis L.) and rape (Brassica napus L.) were determined. Seed germination and seedling growth were conducted using the box filter paper method under the mass concentrations of A. trifida extracts at 0.025, 0.050, 0.075, and 0.100 g·mL⁻¹, along with distilled water as control. Genotoxicity of the extracts was compared according to the root tip micronucleus assay on broad beans.

  Result  The germination of the cabbage and rape seeds were inhibited by the presence of the extract which was mainly displayed by the alternation in allelopathy. The length of main cabbage and rape seedling roots was promoted by the extract at low concentrations and inhibited at high concentrations. The strongest enhancing effect was shown at 0.025 g·mL⁻¹, while the greatest inhibition occurred at 0.100 g·mL⁻¹. On the other hand, the plant height and fresh weight of the cabbage and rape seedlings increased with the increasing extract concentration. The photosynthetic pigment in the cabbage and rape seedling leaves increased with increasing extract as well. The micronucleus experiments on broad beans showed a variety of chromosomal aberrations, such as micronuclei, chromosomal bridges, and chromosomal lagging, on the bean root tip cells after treatment.

  Conclusion  The aqueous extract of A. trifida tissues exhibited allelopathic effects on the growth and development of cabbage and rape seedlings with the cabbage responded more strongly than the rape. The micronucleus of broad bean root tips under the extract treatments showed a significant damaging effect on the genetic materials.