Phytoinhibitory activities and extraction optimization of potent invasive plants as eco-friendly weed suppressant against Echinochloa colona (L.) Link

Parasitic Echinochloa colona (L.) Link has globally invaded paddy fields that could devote to severe grain yield loss. Prolonged extensive application of commercial synthetic herbicides could pose the weed evolved resistance, bioaccumulation and environmental deterioration. Hence, this paper pertains to the aim of investigating potent natural products which have shown considerable phytotoxic activities, subsequent phytotoxin studies and extraction optimization for pre-emergent control of E. colona. In the phytotoxicity study, a suite of invasive plants was procured and the leaf, stem and root extracts were evaluated by in vitro germination and seedling growth assays. The invasive plant extracts exhibited multiple magnitudes of inhibition against E. colona in the plant species-, plant part- and concentration-dependent manners. Along with the dose-response study, the leaf extracts of Mikania micrantha Kunth ex H.B.K., Clidemia hirta (L.) D. Don , Dicranopteris linearis (Burm.f.) Underw. and Ageratum conyzoides L. showed the attainable half maximal effective doses (ED50) below the concentration 100 g biomass dry weight equivalent (BDWE)/L, indicating the top-ranked inhibition of E. colona among the investigated plant extracts. The top-ranked phytotoxic leaf extracts were subjected to qualitative and quantitative characterizations including extraction yield, total phenolic content, phytochemical screening and spectroscopic analysis of the phytochemicals with possible inhibitory effect. Joint putative allelochemicals consisting of 16 phenolics and 5 aromatics were detected concurrently by liquid chromatography-mass spectrometry (LC-MS), were found contributed to the appreciable germination inhibition. Amongst the abundant phenolic acids were protocatechuic acid, gallic acid, p-hydroxyphenylacetic acid and chlorogenic acid. To suit the industrial desire in product development, the phytotoxic leaves were processed through extraction optimization using response surface methodology (RSM). A multivariate face-centered cube design (FCCD) was established to seek the functional relationship between the process variables (extraction time, agitation speed and solvent consumption) and the response (germination inhibition). Quadratic response surface models were obtained with the models significance and significant effect of the process factors at 95% confidence interval were examined by various statistical analyses. Verification experiments at the optimal conditions were well matched with the predicted values, along with absolute errors in the range 3.63% to 6.70%, indicating the proposed quadratic models were valid and useful prediction of the extraction conditions. These outcomes provide the valuable findings on the possible use of potent invasive plants as bioeffective, economical and eco-friendly herbicide alternative towards fostering the sustainable weed management.