Thiophenes from Echinops grijsii as a Preliminary Approach To Control Disease Complex of Root-Knot Nematodes and Soil-Borne Fungi: Isolation, Activities, and Structure-Nonphototoxic Activity Relationship Analysis

The larvicidal efficacy and mechanism of action of 5-Ethenyl-2,2'-bithiophene extracted from Echinops ritro on Aedes aegypti larvae

Herein, we focused on the larvicidal effects and potential mechanisms of 5-ethenyl-2,2'-bithiophene (5 EB), a compound isolated from Echinops ritro L. on Aedes aegypti larvae. Our results show that 5 EB exhibits pronounced larvicidal activity against A. aegypti larvae, with an LC50 = 0.24 mg/L, considerably lesser than that of the traditional insecticide, rotenone. Observations using fluorescence microscopy, electron microscopy, and imaging flow cytometry demonstrated that 5 EB targets the hemocytes of larvae, leading to the disruption of their intracellular membrane systems. This disruption leads to considerable damage to the cellular structure and function, leading to the death of test subjects. Note that additional investigation into the molecular mechanism of 5 EB's action was conducted using transcriptomic analysis. Both GO and KEGG enrichment analyses reported that the differentially expressed genes were predominantly associated with membranes, lysosomes, and catalytic activities. To summarize, this study provides new options for developing new, environmentally friendly, plant-based larvicides for mosquito control.

A Review of the Phytochemistry and Biological Activities of Echinopsis Radix

The main varieties of Echinopsis Radix recorded in the Chinese Pharmacopoeia are the roots of Echinops latifolius Tausch or Echinops grijsii Hance. However, the chemical constituents and biological activities of this herb have not been reviewed. In order to clarify the chemical constituents of the main varieties of this herb and improve the quality of Chinese medicinal material resources, this paper systematically reviewed their chemical constituents and related biological activities. Phytochemical investigations reveal eighty-five compounds including fort y-nine thiophenes (1-49), eight flavonoids (50-57), seven caffeic acids and its derivatives (58-64), eight sesquiterpenoids (65-72), and thirteen triterpenoids and other compounds (73-85) were reported from Echinopsis Radix. The review of biological activities suggests that thiophenes are the main secondary metabolites of the medicinal material which exert antitumor, insecticidal and antifungal activities. In addition, caffeic acid and its derivatives and sesquiterpenes are potential active ingredients worthy of further study. This review provides an important scientific basis for the development of active ingredients and resource quality evaluation of Echinopsis Radix.

Discovery of Trifluorobutene Amide Derivatives as Potential Nematicides: Design, Synthesis, Nematicidal Activity Evaluation, SAR, and Mode of Action Study

Plant-parasitic nematodes are one of the major threats to crop protection. However, only limited nematicides are currently available and are confronted with a growing resistance problem, which necessitates the development of novel nematicides. In this study, a series of trifluorobutene amide derivatives was synthesized through the strategy of amide bond reversal, and their nematicidal activity against Meloidogyne incognita was evaluated. The bioassay showed that compounds C2, C10, and C18 and some analogues thereof exhibited good nematicidal activity. Among them, the derivatives of compound C2 containing a benzene ring [C26 (R = 2-CH3) and C33 (R = 2-Cl)] exhibited excellent bioactivity against M. incognita in vitro. The LC50/72h values reached 14.13 and 14.71 mg·L-1, respectively. Moreover, analogues of compounds C10 and C18 containing a thiophene ring [C43 (R = 5-CH3), C44 (R = 4-CH3), and C50 (R = 5-Cl)] exhibited significant bioactivity against M. incognita in vivo with inhibition rates of 68.8, 65.5, and 69.8% at 2.5 mg·L-1 in a matrix, respectively. Meanwhile, C44 and C50 also showed excellent control effects against M. incognita in both cups and microplots. The structure-activity relationship (SAR) of synthesized compounds was discussed in detail. Comparative molecular field analysis (CoMFA) was also conducted to develop the SAR profile. The preliminary mode of action investigation showed that compound C33 exhibited strong inhibition on egg hatching, motility, feeding behavior, and growth of Caenorhabditis elegans. At the same time, the impact of active compounds on biochemical indicators related to oxidative stress showed that compound C33 influenced the production of ROS (reactive oxygen species), and the accumulation of lipofuscin and lipids on C. elegans.

Natural nematicidal metabolites and advances in their biocontrol capacity on plant parasitic nematodes

Covering: 2010 to 2021Natural nematicidal metabolites are important sources of nematode control. This review covers the isolation and structural determination of nematicidal metabolites from 2010 to 2021. We summarise chemical structures, bioactivity, metabolic regulation and biosynthesis of potential nematocides, and structure-activity relationship and application potentiality of natural metabolites in plant parasitic nematodes' biocontrol. In doing so, we aim to provide a comprehensive overview of the potential roles that natural metabolites can play in anti-nematode strategies.

Biocontrol Activity of Aromatic and Medicinal Plants and Their Bioactive Components against Soil-Borne Pathogens

Soil-borne phytopathogens can have detrimental effects on both cereal and horticultural crops resulting in serious losses worldwide. Due to their high efficiency and easy applicability, synthetic pesticides are still the primary choice in modern plant disease control systems, but stringent regulations and increasing environmental concerns make the search for sustainable alternatives more pressing than ever. In addition to the incorporation of botanicals into agricultural practices, the diversification of cropping systems with aromatic and medicinal plants is also an effective tool to control plant diseases through providing nutrients and shaping soil microbial communities. However, these techniques are not universally accepted and may negatively affect soil fertility if their application is not thoroughly controlled. Because the biocontrol potential of aromatic and medicinal plants has been extensively examined over the past decades, the present study aims to overview the recent literature concerning the biopesticide effect of secondary metabolites derived from aromatic and medicinal plants on important soil-borne plant pathogens including bacteria, fungi, and nematodes. Most of the investigated herbs belong to the family of Lamiaceae (e.g., Origanum spp., Salvia spp., Thymus spp., Mentha spp., etc.) and have been associated with potent antimicrobial activity, primarily due to their chemical constituents. The most frequently tested organisms include fungi, such as Rhizoctonia spp., Fusarium spp., and Phytophthora spp., which may be highly persistent in soil. Despite the intense research efforts dedicated to the development of plant-based pesticides, only a few species of aromatic herbs are utilized for the production of commercial formulations due to inconsistent efficiency, lack of field verification, costs, and prolonged authorization requirements. However, recycling the wastes from aromatic and medicinal plant-utilizing industries may offer an economically feasible way to improve soil health and reduce environmental burdens at the same time. Overall, this review provides comprehensive knowledge on the efficiency of aromatic herb-based plant protection techniques, and it also highlights the importance of exploiting the residues generated by aromatic plant-utilizing sectors as part of agro-industrial processes.

Synthesis and Biological Evaluation of Dipeptide-Based Stilbene Derivatives Bearing a Biheterocyclic Moiety as Potential Fungicides

The escalating demand for crop production, environmental protection, and food safety warrants the development of new fungicides with greater efficiency, environmental friendliness, and innocuous metabolites to fight against destructive phytopathogens. Herein, we report on the synthesis and antifungal activity of dipeptide-based stilbene derivatives bearing a thiophene-substituted 1,3,4-oxadiazole fragment for the first time. In vitro bioassay indicated that the target compounds had remarkable antifungal potency superior to previously reported counterparts without a dipeptidyl group, of which compound 3c exhibited the highest activity against Botrytis cinerea with EC₅₀ values of 106.1 μg/mL. Moreover, the in vivo protective effect of compound 3c (59.1%) against tomato gray mold was more potent than that of carboxin (42.0%). Preliminary investigations on the mode of action showed that compound 3c induced marked hyphal malformations and increased the membrane permeability of B. cinerea as well as inhibiting mycelial respiration. These promising results suggest that this novel type of molecular framework has great potential to be further developed as alternative fungicides.

Thiophenes-Naturally Occurring Plant Metabolites: Biological Activities and In Silico Evaluation of Their Potential as Cathepsin D Inhibitors

Naturally, thiophenes represent a small family of natural metabolites featured by one to five thiophene rings. Numerous plant species belonging to the family Asteraceae commonly produce thiophenes. These metabolites possessed remarkable bioactivities, including antimicrobial, antiviral, anti-inflammatory, larvicidal, antioxidant, insecticidal, cytotoxic, and nematicidal properties. The current review provides an update over the past seven years for the reported natural thiophene derivatives, including their sources, biosynthesis, spectral data, and bioactivities since the last review published in 2015. Additionally, with the help of the SuperPred webserver, an AI (artificial intelligence) tool, the potential drug target for the compounds was predicted. In silico studies were conducted for Cathepsin D with thiophene derivatives, including ADMET (drug absorption/distribution/metabolism/excretion/and toxicity) properties prediction, molecular docking for the binding interaction, and molecular dynamics to evaluate the ligand-target interaction stability under simulated physiological conditions.

Secondary Metabolites with Agricultural Antagonistic Potentials from Beauveria felina, a Marine-Derived Entomopathogenic Fungus

Soil-borne pathogens and weeds could synergistically affect vegetable growth and result in serious losses. The investigation of antagonistic metabolites from a marine-derived entomopathogenic fungus, Beauveria felina, obtained polyhydroxy steroid (1), tricyclic diterpenoid (2), isaridin (3), and destruxin cyclodepsipeptides (4-6). The structures and absolute configurations of new 1-3 were elucidated by extensive spectroscopic and X-ray crystallographic analyses, as well as electronic circular dichroism (ECD) calculations. Compounds 1 and 2 showed antifungal activities against carbendazim-resistant strains of Botrytis cinerea, with the minimum inhibitory concentration (MIC) values ranging from 16 to 32 μg/mL, which were significantly better than those of carbendazim (MIC = 256 μg/mL). Compound 5 exhibited significant antagonistic activity against the radicle growth of Amaranthus retroflexus seedlings, which was almost identical to that of the positive control (2,4-dichlorophenoxyacetic acid). The structure-activity differences of 4-6 suggested that the Cl atom in HMPA¹ and β-Me in Pro² should be the key factors to their herbicidal activities. Besides, compounds 3-6 showed moderate nematicidal activities against Meloidogyne incognita. These antagonistic effects of 1-6 were first reported and further revealed the synergistically antagonistic potential of B. felina to be developed into the biopesticide.

Chemical Nematicides: Recent Research Progress and Outlook

Plant-parasitic nematodes have caused huge economic losses to agriculture worldwide and seriously threaten the sustainable development of modern agriculture. Chemical nematicides are still the most effective means to manage nematodes. However, the long-term use of organophosphorus and carbamate nematicides has led to a lack of field control efficacy and increased nematode resistance. To meet the huge market demand and slow the growth of resistance, new nematicides are needed to enter the market. The rational design and synthesis of new chemical scaffolds to screen for new nematicides is still a difficult task. We reviewed the latest research progress of nematicidal compounds in the past decade, discussed the structure-activity relationship and mechanism of action, and recommended some nematicidal active fragments. It is hoped that this review can update the recent progress on nematicide discoveries and provide new ideas for the design and mechanism of action studies of nematicides.

Novel Bithiophene Dimers from Echinops latifolius as Potential Antifungal and Nematicidal Agents

Three novel dimeric bithiophenes, echinbithiophenedimers A-C (1-3), along with two known thiophenes, 4 and 5, were obtained from Echinops latifolius, and their structures were identified through extensive spectroscopic analysis and electronic circular dichroism calculations. Compounds 1-3 possessed new carbon skeletons; they are dimeric bithiophenes with 1 and 2 featuring an unprecedented 1,3-dioxolane ring system and 3 featuring an unusual 1,4-dioxane ring. These compounds are the first examples of bithiophene dimers furnished by different cyclic diethers. Dimeric bithiophenes 1-3 had good antifungal activities against five phytopathogenic fungi, and compound 3 showed excellent activity against Alternaria alternate and Pyricularia oryzae, with a minimal inhibitory concentration value of 8 μg/mL, which was close to or higher than that of carbendazim. Moreover, its effect on the mycelial morphology was observed by scanning electron microscopy. Compounds 1-3, which were demonstrated to be nonphototoxic thiophenes, exhibited better nematicidal activity than the commercial nematicide ethoprophos against Meloidogyne incognita. This study revealed that dimeric bithiophenes containing 1,3-dioxolane or 1,4-dioxane rings could be used as novel antifungal and nematicidal agents for controlling plant fungal and nematode pathogens.

Constituents Leached by Tomato Seeds Regulate the Behavior of Root-Knot Nematodes and Their Antifungal Effects against Seed-Borne Fungi

Germinating seeds can release diverse phytochemicals that repel, inhibit, or kill pathogens such as root-knot nematodes and seed-borne fungi. However, little is known about the composition of these phytochemicals and their effects on pathogens. In this study, we demonstrated that tomato seed exudates can attract the nematode Meloidogyne incognita using a dual-choice assay. Eighteen compounds were then isolated and identified from the exudates. Of these, esters (1-3), fatty acids (4-6), and phenolic acids (10-12) were proven to be the signaling molecules that facilitated the host-seeking process of second-stage juveniles (J2s) of nematodes, while alkaloids (17 and 18) disrupted J2s in locating their host. Furthermore, some phenolic acids and alkaloids showed antifungal effects against seed-borne fungi. In particular, ferulic acid (12) showed obvious activity against Aspergillus flavus (minimum inhibitory concentration (MIC), 32 μg/mL), while dihydrocapsaicin (17) showed noticeable activity against Fusarium oxysporum (MIC, 16 μg/mL). Overall, this study presents the first evidence that M. incognita can be attracted to or deterred by various compounds in seed exudates through identification of the structures of the compounds in the exudates and analysis of their effects on nematodes. Furthermore, some antifungal compounds were also found. The findings of this work suggest that seed exudates are new source for finding insights into the development of plant protective substances with nematocidal and antifungal effects.

Chitosan Oligosaccharide Fluorinated Derivative Control Root-Knot Nematode (Meloidogyne incognita) Disease Based on the Multi-Efficacy Strategy

Plant root-knot nematode disease is a great agricultural problem and commercially available nematicides have the disadvantages of high toxicity and limited usage; thus, it is urgent to develop new nematicides derived from nature substances. In this study, a novel fluorinated derivative was synthesized by modifying chitosan oligosaccharide (COS) using the strategy of multiple functions. The derivatives were characterized by FTIR, NMR, elemental analysis, and TG/DTG. The activity assays show that the derivatives can effectively kill the second instar larvae of Meloidogyne incognita in vitro, among them, chitosan-thiadiazole-trifluorobutene (COSSZFB) perform high eggs hatching inhibitory activity. The derivatives can regulate plant growth (photosynthetic pigment), improve immunity (chitinase and β-1,3-glucanase), and show low cytotoxicity and phytotoxicity. According to the multi-functional activity, the derivatives exhibit a good control effect on plant root-knot nematode disease in vivo. The results demonstrate that the COS derivatives (especially fluorinated derivative) perform multiple activities and show the potential to be further evaluated as nematicides.

Sesquiterpenes and Cyclodepsipeptides from Marine-Derived Fungus Trichoderma longibrachiatum and Their Antagonistic Activities against Soil-borne Pathogens

Soil-borne pathogens, including phytopathogenic fungi and root-knot nematodes, could synergistically invade vegetable roots and result in serious economic losses. The genus of Trichoderma has been proven to be a promising reservoir of biocontrol agents in agriculture. In this study, the search for antagonistic metabolites from a marine-derived fungus, Trichoderma longibrachiatum, obtained two structural series of sesquiterpenes 1-6 and cyclodepsipeptides 7-9. Notably, the novel 1 was a rare norsesquiterpene characterized by an unprecedented tricyclic-6/5/5-[4.3.1.0^1,6]-decane skeleton. Their structures were elucidated by extensive spectroscopic analyses, while the absolute configuration of novel 1 was determined by the comparison of experimental and calculated ECD spectra. The novel 1 and known 2 and 3 showed significant antifungal activities against Colletotrichum lagrnarium with MIC values of 8, 16, and 16 μg/mL respectively, even better than those of the commonly used synthetic fungicide carbendazim with 32 μg/mL. They also exhibited antifungal potential against carbendazim-resistant Botrytis cinerea. Cyclodepsipeptides 7-9 showed moderate nematicidal activities against the southern root-knot nematode (Meloidogyne incognita). This study constitutes the first report on the antagonistic effects of metabolites from T. Longibrachiatum against soil-borne pathogens, also highlighting the integrated antagonistic potential of marine-derived T. Longibrachiatum as a biocontrol agent.