Isolation of allelopathic substance from Piper sarmentosum Roxb

Allelopathic activity of Piper sarmentosum Roxb. was determined and a potent growth inhibitory substance was isolated. The aqueous methanol extracts of P. sarmentosum inhibited the growth of 6-test plant species [cress (Lepidium sativum L.), lettuce (Lactuca sativa L.), alfalfa (Medicago sativa L.), timothy (Phleum pretense L.), Italian ryegrass (Lolium multiflorum Lam.) and crabgrass (Digitaria sanguinalis L.)] to various degrees in a dose-dependent manner. The active substance 3-phenylpropionic acid was purified from the aqueous methanol extract of P. sarmentosum and identified by ¹H-, ¹³C-NMR and MS. The threshold of 3-phenylpropionic acid for growth inhibition was 1 μM. The concentrations required for 50% growth inhibition of cress and lettuce were 1.2-9.3 μM and the concentrations required for 50% growth inhibition of timothy and Italian ryegrass were 4.7-51.8 μM. The endogenous concentration of 3-phenylpropionic acid in P. sarmentosum was 121 μmol/kg. Considering the endogenous level and the inhibitory activity, 3-phenylpropionic acid may work as allelopathic substance in P. sarmentosum through growth inhibition of neighbouring plant species.