Survival and infectivity of second-stage root-knot nematode Meloidogyne incognita juveniles depend on lysosome-mediated lipolysis

3-Furoic Acid from Sea-Derived Aspergillus luchuensis Hy-6 as a Valuable Lead Compound against Plant-Parasitic Nematodes in Cucumber

Root-knot nematodes pose a significant threat to crop growth and yield, thereby impacting global food security. Here, the sea-derived Aspergillus luchuensis hy-6 was identified as a producer of 3-furoic acid by liquid chromatography-mass spectrometry. Low doses of 3-furoic acid, an acidic compound with strong nematicidal activity, can reduce the motility, lifespan, and egg hatchability of nematodes in a dose-dependent manner. Additionally, 3-furoic acid was found to affect the chemotaxis of Meloidogyne incognita toward cucumber by decreasing the root's attractive activity to the nematodes. Metabolomic analyses indicated that the functional abnormalities in lipid metabolism may represent a critical molecular mechanism underlying severe metabolic dysfunction. Importantly, a significant enhancement in control efficacy was achieved through a simple structural modification, particularly with pent-4-en-1-yl furan-3-carboxylate (A1), which was superior to that of 3-furoic acid. These findings validated the potential of 3-furoic acid as a promising lead in the development of eco-friendly nematicides.

Bioactive Secondary Metabolites from Harposporium anguillulae Against Meloidogyne incognita

Root-knot nematodes (RKNs) are pathogens that endanger a wide range of crops and cause serious global agricultural losses. In this study, we investigated metabolites of the endoparasitic fungus Harposporium anguillulae YMF1.01751, with the expectation of discovering valuable Meloidogyne incognita biocontrol compounds. Based on results obtained by a liquid chromatograph coupled to a mass spectrometer (LC-MS) of crude extracts under five culture conditions and their nematicidal activity against M. incognita, corn meal agar (CMA) medium was determined as the scale-up fermentation medium. Twelve metabolites (1-12) were isolated from the fermentation products, and compound 1 was identified to be a new cyclic tetrapeptide. The activity assay results showed that phenylacetic acid (11) had good nematicidal activity at 400 μg/mL, and the mortalities of M. incognita were 89.76% and 96.05% at 12 and 24 h, respectively, while the mortality of canthin-6-one (2) against M. incognita was 44.26% at 72 h. In addition, the results of chemotaxis activity showed that 1-(1H-indol-3-yl)ethanone (10) possessed attraction activity towards M. incognita. At the tested concentrations, cyclo-(Arg-Pro) (4) and cyclo-(Val-Ile) (7) showed an avoidant response to M. incognita. This study provides insight into the nematode-active compounds of H. anguillulae origin and offers new opportunities for the development of RKN biocontrol products.

Cis-3-Indoleacrylic Acid: A Nematicidal Compound from Streptomyces youssoufiensis YMF3.862 as V-ATPase Inhibitor on Meloidogyne incognita

The application of the bionematicides derived from microorganisms and their secondary metabolites represents a promising strategy for managing root-knot nematodes. In this study, a nematicidal compound, cis-3-indoleacrylic acid, was isolated from Streptomyces youssoufiensis YMF3.862. This compound caused Meloidogyne incognita juveniles to have swollen bodies with apparent cracks on the cuticle surface. The LC50 value of cis-3-indoleacrylic acid against juveniles was 16.31 μg/mL 24 h of post-treatment. Cis-3-indoleacrylic acid at 20 μg/mL significantly inhibited V-ATPase expression and remarkably decreased enzyme activity by 84.41%. As an inhibitor of V-ATPase, cis-3-indoleacrylic acid caused significant H+ accumulation in nematode bodies, resulting in lower intracellular pH values and higher extracellular pH values of M. incognita. Application of 50 μg/mL cis-3-indoleacrylic acid generated a 71.06% control efficiency against M. incognita on tomatoes. The combination results of this study indicated that cis-3-indoleacrylic acid can be developed as a natural nematicide for controlling M. incognita.

Exploring the nematicidal mechanisms and control efficiencies of oxalic acid producing Aspergillus tubingensis WF01 against root-knot nematodes

Background and aims

Root-knot nematodes (RKN; Meloidogyne spp.) are among the highly prevalent and significantly detrimental pathogens that cause severe economic and yield losses in crops. Currently, control of RKN primarily relies on the application of chemical nematicides but it has environmental and public health concerns, which open new doors for alternative methods in the form of biological control.

Methods

In this study, we investigated the nematicidal and attractive activities of an endophytic strain WF01 against Meloidogyne incognita in concentration-dependent experiments. The active nematicidal metabolite was extracted in the WF01 crude extract through the Sephadex column, and its structure was identified by nuclear magnetic resonance and mass spectrometry data.

Results

The strain WF01 was identified as Aspergillus tubingensis based on morphological and molecular characteristics. The nematicidal and attractive metabolite of A. tubingensis WF01 was identified as oxalic acid (OA), which showed solid nematicidal activity against M. incognita, having LC50 of 27.48 μg ml-1. The Nsy-1 of AWC and Odr-7 of AWA were the primary neuron genes for Caenorhabditis elegans to detect OA. Under greenhouse, WF01 broth and 200 μg ml-1 OA could effectively suppress the disease caused by M. incognita on tomatoes respectively with control efficiency (CE) of 62.5% and 70.83%, and promote plant growth. In the field, WF01-WP and 8% OA-WP formulations showed moderate CEs of 51.25%-61.47% against RKN in tomato and tobacco. The combined application of WF01 and OA resulted in excellent CEs of 66.83% and 69.34% toward RKN in tomato and tobacco, respectively. Furthermore, the application of WF01 broth or OA significantly suppressed the infection of J2s in tomatoes by upregulating the expression levels of the genes (PAL, C4H, HCT, and F5H) related to lignin synthesis, and strengthened root lignification.

Conclusion

Altogether, our results demonstrated that A. tubingensis WF01 exhibited multiple weapons to control RKN mediated by producing OA to lure and kill RKN in a concentration-dependent manner and strengthen root lignification. This fungus could serve as an environmental bio-nematicide for managing the diseases caused by RKN.

Sulfonamide modified chitosan oligosaccharide with high nematicidal activity against Meloidogyne incognita

Chitosan oligosaccharide (COS) modification is a feasible way to develop novel green nematicides. This study involved the synthesis of various COS sulfonamide derivatives via hydroxylated protection and deprotection, which were then characterized using NMR, FTIR, MS, elemental analysis, XRD, and TG/DTG. In vitro experiments found that COS-alkyl sulfonamide derivatives (S6 and S11-S13) exhibited high mortality (>98 % at 1 mg/mL) against Meloidogyne incognita second-instar larvaes (J2s) among the derivatives. S6 can cause vacuole-like structures in the middle and tail regions of the nematode body and effectively inhibit egg hatching. In vivo tests have found that S6 has well control effects and low plant toxicity. Additionally, the structure-activity studies revealed that S6 with a high degree of substitution, a low molecular weight, and a sulfonyl bond on the amino group of the COS backbone exhibited increased nematicidal activity. The sulfonamide group is a potential active group for developing COS-based nematicides.

Biological Control of a Root-Knot Nematode Meloidogyne incognita Infection of Tomato (Solanum lycopersicum L.) by the Oomycete Biocontrol Agent Pythium oligandrum

The biocontrol agent Pythium oligandrum, which is a member of the phylum Oomycota, can control diseases caused by a taxonomically wide range of plant pathogens, including fungi, bacteria, and oomycetes. However, whether P. oligandrum could control diseases caused by plant root-knot nematodes (RKNs) was unknown. We investigated a recently isolated P. oligandrum strain GAQ1, and the P. oligandrum strain CBS530.74, for the control of an RKN Meloidogyne incognita infection of tomato (Solanum lycopersicum L.). Initially, P. oligandrum culture filtrates were found to be lethal to M. incognita second-stage juveniles (J2s) with up to 84% mortality 24 h after treatment compared to 14% in the control group. Consistent with the lethality to M. incognita J2s, tomato roots treated with P. oligandrum culture filtrates reduced their attraction of nematodes, and the number of nematodes penetrating the roots was reduced by up to 78%. In a greenhouse pot trial, the P. oligandrum GAQ1 inoculation of tomato plants significantly reduced the gall number by 58% in plants infected with M. incognita. Notably, the P. oligandrum GAQ1 mycelial treatment significantly increased tomato plant height (by 36%), weight (by 27%), and root weight (by 48%). A transcriptome analysis of tomato seedling roots inoculated with the P. oligandrum GAQ1 strain identified ~2500 differentially expressed genes. The enriched GO terms and annotations in the up-regulated genes suggested a modulation of the plant hormone-signaling and defense-related pathways in response to P. oligandrum. In conclusion, our results support that P. oligandrum GAQ1 can serve as a potential biocontrol agent for M. incognita control in tomato. Multiple mechanisms appear to contribute to the biocontrol effect, including the direct inhibition of M. incognita, the potential priming of tomato plant defenses, and plant growth promotion.

Transcriptomic and physiological analysis of the effect of octanoic acid on Meloidogyne incognita

Root knot nematodes are the most devastating root pathogens, causing severe damage and serious economic losses to agriculture worldwide. Octanoic acid has been reported as one of the nematicides, and its mode of action is not fully understood. The main objective of this study was to elucidate the effect of octanoic acid on Meloidogyne incognita by transcriptomic analysis combined with physiological and biochemical assays. In the toxicity assays with octanoic acid, the threshold concentration with nematicidal activity and the maximum concentration to which nematodes could respond were 0.03 μL/mL and 0.08 μL/mL respectively. Microscopic observation combined with protein and carbohydrates assays confirmed that the structure of the second-stage juveniles (J2s) was severely disrupted after 72 h of immersion in octanoic acid. Transcriptome analysis has shown that octanoic acid can interfere with the nematode energy metabolism, lifespan and signaling. Although the effects are multifaceted, the findings strongly point to the cuticle, lysosomes, and extracellular regions and spaces as the primary targets for octanoic acid. In addition, nematodes can withstand the negative effects of low concentration of octanoic acid to some extent by up-regulating the defense enzyme system and heterologous metabolic pathways. These findings will help us to explore the nematicidal mechanism of octanoic acid and provide important target genes for the development of new nematicides in the future.

Molecular Defense Response of Bursaphelenchus xylophilus to the Nematophagous Fungus Arthrobotrys robusta

Bursaphelenchus xylophilus causes pine wilt disease, which poses a serious threat to forestry ecology around the world. Microorganisms are environmentally friendly alternatives to the use of chemical nematicides to control B. xylophilus in a sustainable way. In this study, we isolated a nematophagous fungus-Arthrobotrys robusta-from the xylem of diseased Pinus massoniana. The nematophagous activity of A. robusta against the PWNs was observed after just 6 h. We found that B. xylophilus entered the trap of A. robusta at 24 h, and the nervous system and immunological response of B. xylophilus were stimulated by metabolites that A. robusta produced. At 30 h of exposure to A. robusta, B. xylophilus exhibited significant constriction, and we were able to identify xenobiotics. Bursaphelenchus xylophilus activated xenobiotic metabolism, which expelled the xenobiotics from their bodies, by providing energy through lipid metabolism. When PWNs were exposed to A. robusta for 36 h, lysosomal and autophagy-related genes were activated, and the bodies of the nematodes underwent disintegration. Moreover, a gene co-expression pattern network was constructed by WGCNA and Cytoscape. The gene co-expression pattern network suggested that metabolic processes, developmental processes, detoxification, biological regulation, and signaling were influential when the B. xylophilus specimens were exposed to A. robusta. Additionally, bZIP transcription factors, ankyrin, ATPases, innexin, major facilitator, and cytochrome P450 played critical roles in the network. This study proposes a model in which mobility improved whenever B. xylophilus entered the traps of A. robusta. The model will provide a solid foundation with which to understand the molecular and evolutionary mechanisms underlying interactions between nematodes and nematophagous fungi. Taken together, these findings contribute in several ways to our understanding of B. xylophilus exposed to microorganisms and provide a basis for establishing an environmentally friendly prevention and control strategy.