Effects of lemon balm (Melissa officinalis L.) extract on germination and seedling growth of six plants.
The n-hexane-, acetone- and water-soluble fractions obtained from an aqueous acetone extract of lemon balm (Melissa officinalis) shoots inhibited the germination and growth of roots and shoots of cockscomb (Amaranthus caudatus), cress (Lepidium sativum), crabgrass (Digitaria sanguinalis), timothy (Phleum pratense), lettuce (Lactuca sativa) and ryegrass (Lolium multiflorum). The inhibitory activity of the water-soluble fraction was greatest, followed by that of acetone- and n-hexane-soluble fractions in all bioassays. The effectiveness of these fractions on the roots was greater than on the shoots of the test plants. Significant reductions in the germination and growth of the roots and shoots were observed as the extract concentration increased. Such rate-dependent responses of the test plants to the fractions suggest that each fraction might contain allelochemical(s).