Evaluating herbicidal potential of aqueous-ethanol extracts of local plant species against Echinochloa crus-galli and Raphanus sativus

Abstract

Crude aqueous-ethanol leaf extracts of local plant species can be used as natural herbicides. To test this hypothesis, crude aqueous-ethanol leaf extracts of 19 local species were tested for major secondary metabolites (total phenolic and flavonoid contents) and their herbicidal activity, at concentrations of 2.5 and 5 g L -1 , based on germination bioassays against radish (Raphanus sativas L.) and barnyardgrass (Echinochloa crus-galli (L.) Beauv.) and distilled water was used as control. Mitrephora wangii, E. scaber and Magnolia cathcarii observed the highest crude yield of metabolites while Cinnamomum porrectum and Zingiber zerumbet had the minimum metabolites. Goniothalamus calvicarpa and Agapetes lobbii extract had highest total phenolic contents (143.7 and 145.86 mg GAE g -1 crude extract, respectively). Moreover, Ficus microcarpa extrct had the highest phenolic contents (7,639.70 μg quercetin equivalent g -1 crude extract), followed by Orophea polycarpa while Z. zerumbet extrct had the least total flavonoid contents (607.97 μg quercetin equivalent g -1 crude extract). Aqueous-ethanol extracts derived from leaves of Elephantopus scaber and A. lobbii observed over 50% inhibition on the root growth of barnyardgrass and extracts derived from Pachyptera hymenaea, Magnolia citrates, Anomianthus dulcis and F. microcarpa observed over 50% inhibition in root length of radish. In conclusion, extracts of P. hymenaea, F. microcarpa, A. dulcis, E. scaber and A. lobbii observed strong inhibitort effects on germination and early seedling growth of radish and barnyardgrass due to higher phenolic and flavonoid contents. Results of this study might be considered for further studies to develop natural herbicides based on plant extracts.