Botanical herbicide has been a hot topic in the research and development of novel pesticides.  The herbicidal activity and biochemical characteristics of the botanical compound drupacine were studied by evaluating its effects on seed germination, seedling growth, morphological and physiological characteristics of Amaranthus retroflexus.  Drupacine inhibited seed germination and seedling growth, and had a median inhibition concentration (IC₅₀) value of 38.99 mg L⁻¹ against A. retroflexus root.  The α-amylase activity and soluble sugar content in treated plants were significantly lower than that of the control.  The expression of α-amylase gene was dosage-dependently inhibited compared to the untreated control.  This suggested that inhibition of α-amylase activity was a mode of action on seed germination.  The root hairs were significantly decreased and part of the root cap fell off after treatment with drupacine.  The ultrastructure observation showed that cell damage of root tips increased with the treatment time.  Drupacine also increased the relative conductivity and malondialdehyde (MDA) content.  Peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD) activities were significantly enhanced in the treatment compared to the control.  These findings indicated that the physiological and biochemical reaction changes leading to morphological and membrane injuries were the main effects of drupacine on the inhibition of seedling growth.  Drupacine can be developed as a botanical herbicide. 

A total of 479 bacterial strains were isolated from brine (Bohai, Qinhuangdao City, Hebei Province, China). Bioassay results indicated that 4 strains named Ha1, Ha17, Ha38, and Ha384 had herbicidal activity. And strain Ha1 had the highest effective herbicidal activity. As a result, this study aims to identify strain Ha1, characterize its physiological and biological activities, evaluate the herbicidal activity of its metabolites, and develop a ‘pesta’ formulation and assess its effectiveness on Digitaria sanguinalis. Ha1 was identified as Serratia marcescens based on 16S rDNA sequencing. This strain has a flagellum, a diameter of 0.5 to 0.8 μm, and a length of 0.9 to 2.0 μm. The indole test shows positive results, and the catalase enzyme exhibits strong positive reactions. Results further showed that the inhibitory concentration (IC50) of the crude extracts to D. sanguinalis radicula and coleoptile were 3.332 and 2.828 mg mL–1, respectively. Both the suppression of D. sanguinalis and the cell viability of the Ha1 formulation in ‘pesta’ were higher when stored at 4°C than at (25±2)°C. These results indicated that S. marcescens Ha1 can potentially be used as a biocontrol agent against D. sanguinalis.

CB-4, a bacterial strain with highly effective herbicidal activity, was isolated from infected corn leaves. Through morphology, physiological and biochemical tests, and 16S ribosomal DNA gene sequencing methods, CB-4 was identified as Pseudomonas aeruginosa. We conducted activity-evaluation experiments in the laboratory to assess the herbicidal potential of metabolites produced by strain CB-4. Crude extracts of strain CB-4 have high inhibition activity on Digitaria sanguinalis. In general, the root and shoot growth parameters of D. sanguinalis were significantly reduced by metabolites of strain CB-4. The IC50 of the culture filtrate extracts for the radicula and coleoptile of D. sanguinalis were 0.299 and 0.210 mg mL-1, respectively. Component 2 of the herbicidal activity of the crude toxin from strain CB-4 was successfully purified for the first time by using high-speed counter current chromatography with a two-phase solvent system composed of petroleum ether-ethyl acetate-methanol-water (4:5:4:5, v/v) and high-performance liquid chromatography. We concluded that the metabolites of strain CB-4 have the potential to be developed as a microbe-based herbicide.

In order to understand the composition and structure of herbicidal active substance from the root of Flaveria bidentis (L.) Kuntze, the isolation and structural identification were researched in this paper. The crude extract from the root of F. bidentis (L.) Kuntze was extracted by petroleum ether, ethyl acetate, and water saturation of n-butyl alcohol, respectively, and the extraction fluid was separated by using the method of TLC, then the main fraction was separated by HPLC, and the structure of the herbicidal active substance was analyzed by LC-MS, elemental analysis and 1H-NMR. The results showed that the petroleum extraction had the strongest herbicidal activity, and the purple blue stripe separated by TLC had the strongest effect on Digitaria sanguinalis. The herbicidal active substance was identified as α-terthienyl according to the data of LC-MS, elemental analysis and 1H-NMR.

Large amounts of Flaveria bidentis’s root culturing solution were obtained by using DFT (deep flow technique) equipment and these solution which was vacuum concentrated (10, 20 mg mL-1) can have a certain inhibition on Triticum aestivum, Cucumis sativus, Raphanus sativus, Amaranthus retroflexus, Setaria viridis, Chenopodium album, Echinochloa crusgalli and Chloris virgata. This outcome suggested some active compounds in the root exudates of Flaveria bidentis can inhibit the germination, seedling elongation and root length. The dichloromethane extract of root exudates was identificated by GC-MS, and 29 kinds of compounds, including esters, hydrocarbons, ketones, thiazole, amines, etc. were obtained and the phthalate n-octyl ester, phthalate 2-ethylhexyl ester were proved to be allelochemicals. The culturing solution of root exudates was separated through the resin column and silica gel column and a component inhibiting seedling height, root length and fresh weight of wheat was got. There were 6 kinds of organic compounds in this component including dioctyl phthalate, 1,2-phthalate, mono(2-ethylhexyl) ester by GC-MS.

Natural herbicides, or environment-friendly bioherbicides have been attracted more and more attentions. Isolation and structural identification of natural herbicide-active compounds from plant pathogens has been proved to be an effective approach for novel lead discovery of the pesticide development. In this study, the metabolites of the mutant strain PAM1, which obtained from PA1 of Pythium aphanidermatum (Eds.) Fitzp by ultraviolet radiation were separated and identified by HPLC, NMR, and IR. The results revealed that three active compounds including 4-hydroxy-3-methoxycinnamic acid and two indole derivatives, exhibited inhibition activity on the elongation of radical and coleoptile of Digtaria sanguinalis (L.) Scop.