PLANT GROWTH INHIBITORY ACTIVITY OF MEDICINAL PLANT HYPTIS SUAVEOLENS: COULD ALLELOPATHY BE A CAUSE?

Abstract

The present study was conducted to explore the allelopathy of Hyptis suaveolens Poit, an important medicinal plant of Lamiaceae family. The aqueous methanol extracts of this plant at four different concentrations (3, 10, 30 and 100 mg dry weight [DW] equivalent extract/mL), were examined on the seedling growth of eight test plant species, cress (Lepidum sativum L.), lettuce (Lactuca sativa L.), alfalfa (Medicago sativa L.), rapeseed (Brassica napus L.), timothy (Phleum pratense L.), crabgrass (Digitaria sanguinalis L. scop.), barnyardgrass (Echinochloa crus-galli L.) and Italian ryegrass (Lolium multiflorum Lam.), and on the germination of cress and Italian ryegrass. The germination of cress, Italian ryegrass and the growth of all eight test species were significantly inhibited by the H. suaveolens plant extracts at a concentration greater than 3, 30 and 10 mg DW equivalent extract/mL, respectively. The inhibitory activity of the extracts was concentration dependent. The root growth of all the test plants was more sensitive to the extracts than the hypocotyl/coleoptile growth of those. The concentrations required for 50% inhibition (defined as I50) of the hypocotyl/coleoptile and root growth of the eight test plant species range from 9.3–79.3 and 4.9–29.5 mg DW equivalent extract/mL, respectively. The hypocotyl growth of lettuce and the root growth of crabgrass were most sensitive to the extract, whereas coleoptile growth of barnyardgrass and the root growth of alfalfa were the least sensitive. The inhibitory activities of the H. suaveolens on the germination and growth of the test plant species suggest that the plant has allelopathic potentiality and may possess allelochemicals. These allelochemicals might be responsible for the restricted growth of other plant species near their colony in natural ecosystems. However, isolation and identification of these allelochemicals from H. suaveolens plant extracts could serve as the lead for new natural herbicides development for sustainable weed management strategies.