植物源除草剂是新农药研究和开发的热点之一。桥氧三尖杉碱是从我国特有植物中国粗榧中分离鉴定的除草活性化合物，本研究测定了其对反枝苋种子萌发、幼苗生长、形态结构及生理生化特性的影响，以期为深入研究其作用机制及进一步开发利用奠定基础。生物活性测定结果显示，桥氧三尖杉碱对反枝苋种子萌发和幼苗生长均具有显著的抑制作用，对其幼根的抑制中浓度（IC₅₀）为38.99 mg L⁻¹；盆栽试验显示，在4 g/L浓度下，对反枝苋的苗前鲜重抑制率在85%以上。桥氧三尖杉碱处理反枝苋后的α-淀粉酶活性和基因表达受剂量依赖性抑制，可溶性糖含量显著低于对照，总淀粉含量显著高于对照，说明抑制α-淀粉酶活性是桥氧三尖杉碱影响反枝苋种子萌发的主要机制之一。显微观察显示，经桥氧三尖杉碱处理后的反枝苋根毛数量明显减少，部分根冠脱落；超微结构观察显示，处理12 h后，根尖细胞排列紊乱，细胞结构受损，且随着处理时间的延长而加重。同时，桥氧三尖杉碱也增加了反枝苋幼苗的相对电导率，具有剂量和时间依赖性；丙二醛含量也随着处理浓度的增加而增加；过氧化物酶、过氧化氢酶和超氧化物歧化酶活性均显著高于对照。处理3 h后，桥氧三尖杉碱对反枝苋根尖过氧化物酶、过氧化氢酶和超氧化物歧化酶的活性显著升高，丙二醛含量在处理24 h后也发生改变。以上结果表明，桥氧三尖杉碱主要通过影响反枝苋防御酶系导致根尖结构受损，进而影响幼苗的生长发育。本研究首次报道了桥氧三尖杉碱对反枝苋生理生化指标及根尖形态结构的影响，可为该潜在新型植物源除草剂的进一步开发利用奠定基础。

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.