Bioactivity of allelochemicals isolated from the roots of Echinacea purpurea L. Moench on Amaranthus viridis L., Portulaca oleracea L. and Microcystis aeruginosa

Based on the bioassay-guided strategy, we isolated 6-six allelochemicals [cichoric acid (I), 1,3-dicaffeoylquinic acid (II), 4,5-dicaffeoylquinic acid (III), chlorogenic acid (IV), 1-hydroxy-2-phthoic acid (V), echinacoside (VI)] from the roots of Echinacea purpurea (L.) Moench. Their structures were identified by nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS) spectroscopic data. The bioassays studies included allelopathic and algicidal activities to test the effects of extracts and isolated fractions against the test weeds (Amaranthus viridis L., Portulaca oleracea L. and Microcystis aeruginosa Kutzing). At 100 µg/mL, compound (II) inhibited the shoot length and germination of A. viridis and P. oleracea weeds with the germination RI of -0.95±0.04 and -0.95±0.02, respectively. Furthermore, compound (III) showed the strongest inhibition of root length of P. oleracea L. We also found that compounds I-VI have algicidal activity. The compound (I) at low inoculum (5.0×102 cells mL-1) and high inoculum (1.0×104 cells mL-1), showed the highest algicidal activity of 78 % and 87.67 % 6 h after the treatment at 5 µg mL-1 respectively.