Nematicidal Metabolites Research Articles

Multistress‐tolerant Pseudomonas aeruginosa SSVP3 uses multiple strategies to control Meloidogyne incognita in tomato

AbstractTomato is the most important horticultural crop, and India is its second largest producer; however, the plant‐pathogenic nematode Meloidogyne incognita is a serious pest of tomato, causing detrimental losses in its production. This study is focused on the use of multistress‐tolerant Pseudomonas aeruginosa SSVP3 to control this devastating nematode and attempts to decipher the roles of its metabolites and volatile organic compounds (VOCs) during this interaction. The supernatant of P. aeruginosa SSVP3 caused 58% mortality in M. incognita J2 juveniles. The major nematicidal metabolites, identified using liquid chromatography‐mass spectrometry, were pyocyanin, pyoluteorin, pyochelin, benthocyanin and phenazines. The VOCs secreted by P. aeruginosa SSVP3, which were identified via gas chromatography–mass spectrometry (HS‐SPME‐GC–MS) in a mixture, caused 98% mortality in M. incognita J2 juveniles. In a pot experiment, seedling root treatment with P. aeruginosa SSVP3 activated the induced systemic response in tomato plants to M. incognita by increasing the activity of defence and antioxidant enzymes as well as the proline and phenolic contents. The malondialdehyde content in P. aeruginosa SSVP3‐treated plants decreased as compared to those in the other treatment groups. The number of galls formed and the number of endoparasitic stages of M. incognita in the untreated nematode control plants were much greater (19 and 35) than those in the P. aeruginosa SSVP3‐treated (0.33 and 1) and chemically treated groups (0.67 and 1.33). These results indicate that P. aeruginosa and its secreted metabolites and VOCs have a high potential for controlling nematodes.

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

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. 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. 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. 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.

Biocontrol potential of endophytic fungi against phytopathogenic nematodes on potato (Solanum tuberosum L.)

Root-knot nematodes (RKNs) are a vital pest that causes significant yield losses and economic damage to potato plants. The use of chemical pesticides to control these nematodes has led to environmental concerns and the development of resistance in the nematode populations. Endophytic fungi offer an eco-friendly alternative to control these pests and produce secondary metabolites that have nematicidal activity against RKNs. The objective of this study is to assess the efficacy of Aspergillus flavus (ON146363), an entophyte fungus isolated from Trigonella foenum-graecum seeds, against Meloidogyne incognita in filtered culture broth using GC–MS analysis. Among them, various nematicidal secondary metabolites were produced: Gadoleic acid, Oleic acid di-ethanolamide, Oleic acid, and Palmitic acid. In addition, biochemical compounds such as Gallic acid, Catechin, Protocatechuic acid, Esculatin, Vanillic acid, Pyrocatechol, Coumarine, Cinnamic acid, 4, 3-indol butyl acetic acid and Naphthyl acetic acid by HPLC. The fungus was identified through morphological and molecular analysis, including ITS 1–4 regions of ribosomal DNA. In vitro experiments showed that culture filtrate of A. flavus had a variable effect on reducing the number of egg hatchings and larval mortality, with higher concentrations showing greater efficacy than Abamectin. The fungus inhibited the development and multiplication of M. incognita in potato plants, reducing the number of galls and eggs by 90% and 89%, respectively. A. flavus increased the activity of defense-related enzymes Chitinas, Catalyse, and Peroxidase after 15, 45, and 60 days. Leaching of the concentrated culture significantly reduced the second juveniles’ stage to 97% /250 g soil and decreased the penetration of nematodes into the roots. A. flavus cultural filtrates via soil spraying improved seedling growth and reduced nematode propagation, resulting in systemic resistance to nematode infection. Therefore, A. flavus can be an effective biological control agent for root-knot nematodes in potato plants. This approach provides a sustainable solution for farmers and minimizes the environmental impact.

Nematicidal Effect of Eupatorium odoratum Linn. Aqueous Extract on Burrowing Nematodes (Radopholus similis) and its Application to Control Toppling Disease on Cavendish Banana (Musa acuminata)

Abstract Radopholus similis (Cobb 1893) (Rhabditida, Pratylenchidae) is a common and destructive pest that causes significant yield losses in Cavendish bananas. The repeated use of synthetic pesticides to control this nematode has raised concerns about toxicity to users and the environment. An alternative approach to managing this harmful species involves the use of nontoxic plant-derived extracts that enhance protection against various biological constraints. In this study, aqueous extract from the leaves and stems of Eupatorium odoratum Linn. (EAEO) was used to control R. similis in banana roots under in vitro and on-plant conditions. Through direct contact and penetration experiments on roots, as well as on-plant trials, concentrations of 12500, 6250, 3120, 1560, and 780 mg DW·L−1 EAEO were used to evaluate nematode mortality rates, infection levels in root segments (in vitro experiment), root infection, root necrosis index, shoot and root fresh weight, and growth parameters such as stem length, diameter, leaf number, and leaf surface area (on-plant experiment). The results showed that the nematode mortality rate due to EAEO ranged from 35.3% to 90.1%, which is statistically significant compared to the mortality rate in the control treatment (16%). Significant nematode inhibition was observed in banana roots infected with R. similis and exposed to EAEO for 48 h. There were no statistically significant differences in root infection, root necrosis, and plant fresh weight between plants treated with fenamiphos and EAEO. Maximum effectiveness was observed at the 12500 mg DW·L−1 EAEO concentration. These findings provide valuable insights into the nematicidal metabolites of EAEO against R. similis. Thus, the potential of EAEO as a biocontrol agent against R. similis has been demonstrated. For future research, investigations will be extended to elucidate the mechanisms of action of the essential compounds in EAEO against nematodes, determine the optimal EAEO dosage for nematode control without harm to banana plants and the environment, assess the long-term effects of EAEO on banana plants and the environment, explore the ecological impact of EAEO use in agricultural ecosystems, study the effectiveness of EAEO on various plant species, and consider the development of commercial products or formulations based on EAEO.

Photorhabdus-Derived Secondary Metabolites Reduce Root Infection by Meloidogyne incognita in Cowpea.

Root-knot nematodes (RKNs) cause significant economic damage to crop plants, spurring demand for safe, affordable, and sustainable nematicides. A previous study by our research team showed that the combination of two nematicidal secondary metabolites (SMs) derived from Photorhabdus bacteria, trans-cinnamic acid (t-CA), and (4E)-5-phenylpent-4-enoic acid (PPA) have a synergistic effect against RKNs in vitro. In this study, we considered in planta assays to assess the effects of this SM mixture on the virulence and reproductive fitness of the RKN Meloidogyne incognita in a cowpea. Factorial combinations of five t-CA + PPA concentrations (0, 9.0, 22.9, 57.8, and 91.0 μg/ml) and two nematode inoculation conditions (presence or absence) were evaluated in 6-week growth chamber experiments. Results from this study showed that a single root application of the t-CA + PPA mixture significantly reduced the penetration of M. incognita infective juveniles (J2s) into the cowpea roots. The potential toxicity of t-CA + PPA on RKN-susceptible cowpea seedlings was also investigated. The effect of t-CA + PPA × nematode inoculation interactions and the t-CA + PPA mixture did not show significant phytotoxic effects, nor did it adversely affect plant growth parameters or alter leaf chlorophyll content. Total leaf chlorophyll and chlorophyll b content were significantly reduced (by 15 and 22%, respectively) only by the nematode inoculum and not by any of the SM treatments. Our results suggest that a single root application of a mixture of t-CA and PPA reduces M. incognita J2's ability to infect the roots without impairing plant growth or chlorophyll content.

Evaluation of botanicals for the management of Meloidogyne incognita infecting carrot and volatile nematicidal metabolite profiling

Plant-parasitic nematodes infect and cause substantial yield losses in numerous crops. Growing concern over chemical nematicides has attracted attention to safe alternatives. Meloidogyne incognita is one of the plant parasitic nematode species in the tropics and subtropics, which have a drastic economic effect on crops. This nematode is polyphagous, attacking both monocotyledons and dicotyledons crops. This study aimed to investigate the management of M. incognita using six botanical viz., Commelina benghalensis, Evolvulus nummularius, Gomphrena celosioides, Lindenbergia indica, Scoparia dulcis, and Vernonia cinerea under the pots condition. It was found that the pots treated with the amendment of fresh leaves (60 g) of selected botanicals with dried powder 10 g of L. indica efficiently reduced the infestation caused by M. incognita on carrots along with significantly increased growth and biochemical attributes. Out of the six botanicals, GC–MS analysis was performed with the two most effective plants, namely, L. indica and S. dulcis. Results from GC–MS analysis showed various volatile compounds in leaves extract of both plants, out of which phytol was a major compound. Our study concluded that various compounds, along with phytol shown by GC–MS analysis, suppress the infestation of M. incognita and increase the yield of carrots.

Nematicidal and antioxidant activities of the methanolic extract from Tithonia diversifolia grown in Vietnam

Summary This study aimed to evaluate the nematicidal activity of the Tithonia diversifolia leaf extract (TDE) against Meloidogyne incognita under in vitro and pot conditions. In addition, the antioxidant activity of TDE was evaluated using the 2,2-Diphenyl-2-picrylhydrazyl hydrate (DPPH) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. The results revealed that TDE possesses antioxidant potential. Nematicidal activity bioassays revealed that the TDE treatment resulted in 3.0, 16.3, 36.6, 52.4 and 64.2% second-stage juvenile (J2) hatch inhibition at MeOH control, 0.125, 0.25, 0.5 and 1.0 mg ml−1, respectively, for a 5-day treatment. The corresponding values for a 10-day treatment were 3.3, 16.0, 30.7, 56.0 and 69.3%, respectively. The TDE treatment resulted in 64.6, 86.4, 95.3 and 100% J2 movement inhibition at 0.125, 0.25, 0.5 and 1.0 mg ml−1, respectively, for a 48 h treatment. In pot experiments, at 60 days after treatment (DAT), the J2 populations in non-treated, 0.25, 0.5, 1.0 mg TDE (g soil)−1, and Tervigo 020SC 1.0 mg (g soil)−1 were 477.1, 277.3, 142.7, 23.9 and 19.7 per 5 g of root, respectively. The corresponding values in 100 g of soil were 33.2, 5.5, 3.6, 1.1 and 4.0, respectively. The relative galling formation on the Robusta coffee plants was 100, 55.3, 39.1, 33.5 and 80.8% in the non-treated, 0.25, 0.5, 1.0 mg TDE (g soil)−1, and Tervigo-treated plants, respectively. These results may provide crucial information for exploring the nematicidal metabolites of TDE against M. incognita. Therefore, the purified active compounds of TDE should be identified in future studies before the commercialisation of TDE for the biocontrol of M. incognita.

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.

Nematicidal Potential of Sulla (Hedysarum coronarium L.) against the Root-Knot Nematode Meloidogyne incognita.

The content of nematicidal metabolites such as saponins, flavonoids and tannins in sulla (Hedysarum coronarium L.) suggests its potential nematicidal activity. In this study, the biocidal activity of 62.5–1000 μg mL−1 concentrations of flavonoid and tannin fractions from sulla was assessed in in vitro assays on the infective juveniles (J2) of the root-knot nematode (RKN) Meloidogyne incognita, while the suppressive effects of soil amendments with 10–40 g kg−1 soil rates of sulla biomass were investigated on potted tomato infested by M. incognita. The content of total nitrogen, carbon, flavonoids, tannins and saponins of sulla experimental material was also determined. After a 96-h exposure, more than 80% of the M. incognita J2 were killed even by a 125 µg mL−1 concentration of the flavonoid extract, while mortality peaked at 89% only at the 1000 µg mL−1 concentration of the tannin solution. Soil incorporation with sulla biomass significantly reduced the M. incognita densities both on tomato roots and in the soil, compared to either the non-treated control and chemical treatment with Fluopyram. The data confirmed the nematicidal potential of sulla, mainly due to its content of flavonoids and tannins, suggesting its suitability as green manure or a soil amendment for sustainable RKN management.

Nematicidal activity of volatile organic compounds produced by Bacillus altitudinis AMCC 1040 against Meloidogyne incognita

The application of nematicidal microorganisms and their virulence factors provides more opportunities to control root-knot nematodes. Bacillus altitudinis AMCC 1040, previously isolated from suppressive soils, showed significant nematicidal activity, and in this study, nematicidal substances produced by Bacillus altitudinis AMCC 1040 were investigated. The results of the basic properties of active substances showed that these compounds have good thermal stability and passage, are resistant to acidic environment and sensitive to alkaline conditions. Further analysis showed that it is a volatile component. Using HS-SPME-GC/MS, the volatile compounds produced by Bacillus altitudinis AMCC 1040 were identified and grouped into four major categories: ethers, alcohols, ketone, and organic acids, comprising a total of eight molecules. Six of them possess nematicidal activities, including 2,3-butanedione, acetic acid, 2-isopropoxy ethylamine, 3-methylbutyric acid, 2-methylbutyric acid and octanoic acid. Our results further our understanding of the effects of Bacillus altitudinis and its nematicidal metabolites on the management of Meloidogyne incognita and may help in finding less toxic nematicides to control root knot nematodes.

Soluble macromolecules from two Streptomyces strains with potent nematicidal activity against Meloidogyne incognita

Actinobacteria, which produce nematicidal metabolites, have been reported wildly. However, macromolecules were rarely described. The culture filtrates of Streptomyces albogriseolus ND41 and S. fimicarius D153 presented 82.13% and 86.96% nematicidal activity against Meloidogyne incognita after 12 h, respectively. A pot experiment highlighted that the biocontrol efficiency of strain ND41 reached 68.89% and that of strain D153 74.44% after 30 days at a dose of 100 mL per pot. The active metabolites produced by the two strains were hydrosoluble, with molecular weights above 8000 Da for ND41 and of 1000–8000 Da for D153. A chemical characteristic test indicated that these active metabolites were polar polymers that contained a large amount of sugar and phenolic hydroxyl compounds. The insoluble property of most nematicidal pesticide limits dosage form and range of application. Nematicidal metabolites from S. albogriseolus ND41 and S. fimicarius D153 would be preferred candidates for the control of root-knot nematodes, as hydrosoluble macromolecules have good compatibility to soil and root, and are convenient for practical application.

Identification of the Genes of the Plant Pathogen Pseudomonas syringae MB03 Required for the Nematicidal Activity Against Caenorhabditis elegans Through an Integrated Approach.

Nematicidal potential of the common plant pathogen Pseudomonas syringae has been recently identified against Caenorhabditis elegans. The current study was designed to investigate the detailed genetic mechanism of the bacterial pathogenicity by applying comparative genomics, transcriptomics, mutant library screening, and protein expression. Results showed that P. syringae strain MB03 could kill C. elegans in the liquid assay by gut colonization. The genome of P. syringae MB03 was sequenced and comparative analysis including multi locus sequence typing, and genome-to-genome distance placed MB03 in phylogroup II of P. syringae. Furthermore, comparative genomics of MB03 with nematicidal strains of Pseudomonas aeruginosa (PAO1 and PA14) predicted 115 potential virulence factors in MB03. However, genes for previously reported nematicidal metabolites, such as phenazine, pyochelin, and pyrrolnitrin, were found absent in the MB03 genome. Transcriptomics analysis showed that the growth phase of the pathogen considerably affected the expression of virulence factors, as genes for the flagellum, glutamate ABC transporter, phoP/phoQ, fleS/fleR, type VI secretion system, and serralysin were highly up-regulated when stationary phase MB03 cells interacted with C. elegans. Additionally, screening of a transposon insertion mutant library led to the identification of other nematicidal genes such as acnA, gltP, oprD, and zapE. Finally, the nematicidal activity of selected proteins was confirmed by heterologous expression in Escherichia coli.

Nematicidal Activity of Cyclopiazonic Acid Derived From Penicillium commune Against Root-Knot Nematodes and Optimization of the Culture Fermentation Process.

Among 200 fungal strains isolated from the soil, only one culture filtrate of Aspergillus flavus JCK-4087 showed strong nematicidal activity against Meloidogyne incognita. The nematicidal metabolite isolated from the culture filtrate of JCK-4087 was identified as cyclopiazonic acid (CPA). Because JCK-4087 also produced aflatoxins, six strains of Penicillium commune, which have been reported to be CPA producers, were obtained from the bank and then tested for their CPA productivity. CPA was isolated from the culture filtrate of P. commune KACC 45973. CPA killed the second-stage juveniles of M. incognita, M. hapla, and M. arearia with EC50–3 days 4.50, 18.82, and 60.51 μg mL–1, respectively. CPA also significantly inhibited egg hatch of M. incognita and M. hapla after a total of 28 days of treatment with the concentrations > 25 μg mL–1. The enhancement of CPA production by P. commune KACC 45973 was explored using an optimized medium based on Plackett–Burman design (PBD) and central composite design (CCD). The highest CPA production (381.48 μg mL–1) was obtained from the optimized medium, exhibiting an increase of 7.88 times when compared with that from potato dextrose broth culture. Application of the wettable power-type formulation of the ethyl acetate extract of the culture filtrate of KACC 45973 reduced gall formation and nematode populations in tomato roots and soils under greenhouse conditions. These results suggest that CPA produced by P. commune KACC 45973 can be used as either a biochemical nematicide or a lead molecule for developing chemical nematicides to control root-knot nematodes.

Pathogenicity and Volatile Nematicidal Metabolites from Duddingtonia flagrans against Meloidogyne incognita.

Plant parasitic nematodes, especially parasitic root-knot nematodes, are one of the most destructive plant pathogens worldwide. The control of plant root-knot nematodes is extremely challenging. Duddingtonia flagrans is a type of nematode-trapping fungi (NTF), which produces three-dimensional adhesive networks to trap nematodes. In this study, the pathogenicity and volatile organic compounds (VOCs) of the NTF D. flagrans against the plant root-knot nematode, Meloidogyne incognita, were investigated. The predatory process of D. flagrans trapping M. incognita was observed using scanning electron microscopy. Gas chromatography-mass spectrometry analysis of the VOCs from D. flagrans led to the identification of 52 metabolites, of which 11 main compounds were tested individually for their activity against M. incognita. Three compounds, cyclohexanamine, cyclohexanone, and cyclohexanol, were toxic to M. incognita. Furthermore, these three VOCs inhibited egg hatching of M. incognita. Cyclohexanamine showed the highest nematicidal activity, which can cause 97.93% mortality of M. incognita at 8.71 µM within 12 h. The number of hatched juveniles per egg mass after 3 days was just 8.44 when treated with 26.14 µM cyclohexanamine. This study is the first to demonstrate the nematicidal activity of VOCs produced by D. flagrans against M. incognita, which indicates that D. flagrans has the potential to biocontrol plant root-knot nematodes.

Discovery of novel biologically active secondary metabolites from Thai mycodiversity with anti-infective potential

• A project funded via the EU-H2020 MSCA-RISE was carried out from 2014 to 2018. • Partners from Germany, the Netherlands and Thailand were involved. • Numerous new fungal species and secondary metabolites were discovered. • Some important studies on Ascomycota phylogeny were also published. • The early stage researchers involved in the staff exchange benefitted very much. This mini-review is dedicated to the summary of results of the EU-funded Project “Golden Mycological Triangle” (acronym GoMyTri), which was carried out in collaboration of three research infrastructures in Germany, the Netherlands and Thailand during the years 2014–2018. The cooperation explored the mycological and microbiological biodiversity of Europe and Southeast Asia with regard to the search for the badly needed new antibiotics and other biologically active secondary metabolites. The project was conducted to foster international collaboration networks, know-how exchange and interdisciplinary training of young scientists. The first two years of the project were mainly dedicated to field work, and several hundreds of fungal cultures have been isolated from material mostly collected in Thailand. These fungal strains were characterized by morphological and molecular phylogenetic methods and several new taxa were discovered. The cultures underwent screening for antimicrobial and nematicidal metabolites and a number of bioactive metabolites have already been found, isolated and characterized. Several large phylogenetic studies have already been published that resulted from the project work. The results were also brought to the attention of the scientific community as well as the general public through various dissemination events. Based on the tremendous success of this project, a follow-up project application including additional partners from Africa and further European countries has recently been filed and approved, and the international, interdisciplinary collaboration will now continue in the new RISE-MSCA-Project (acronym “Mycobiomics” 2 2 https://cordis.europa.eu/project/id/101008129 ).

Linking Organic Metabolites as Produced by Purpureocillium Lilacinum 6029 Cultured on Karanja Deoiled Cake Medium for the Sustainable Management of Root-Knot Nematodes

Root-knot nematodes pose a serious threat to agriculture and forest systems, causing significant losses of the crop worldwide. A wide range of chemical nematicides has traditionally been used to manage phyto-nematodes. However, due to their ill effects on the environment, biological control agents (BCAs) like Purpureocillium lilacinum that exhibit antagonistic effects on root-knot nematodes are preferred. The current study focused on identifying nematicidal metabolites produced by the fungus Purpureocillium lilacinum cultivated on akaranja deoiled cake-based liquid medium through bioactivity-guided fractionation against Meloidogyne incognita. Column chromatography of the ethyl acetate extract of fungal filtrate exhibited the most potent fraction (fraction 14–15), giving 94.6% egg mass hatching inhibition on the 5th day and a maximum nematicidal activity of 62% against second-stage juveniles after 48 h at 5000 mg/L. Gas chromatography coupled with mass spectrometry (GC-MS) analysis of this fraction revealed five major compounds, viz., 2-ethyl butyric acid, phenyl ethyl alcohol, benzoic acid, benzene acetic acid, and 3,5-Di-t-butylphenol. These biocompounds have potential biocontrol applications in agriculture, but further in vivo studies are warranted.

Screening, isolation and evaluation of a nematicidal compound from actinomycetes against the pine wood nematode, Bursaphelenchus xylophilus.

Bursaphelenchus xylophilus is a migratory endoparasitic nematode known to cause severe environmental damage and economic losses in pine forest ecosystems. This present study investigated the nematicidal metabolites of actinomycetes in vitro and evaluated the disease control efficacy of the active compound and metabolites under greenhouse and field conditions. Five thousand types of actinobacteria from Korean forest soil samples were screened to identify novel nematicidal agents against the pine wood nematode. Streptomyces sp. AN091965 showed the strongest nematicidal activity. One active compound, spectinabilin, was obtained by nematicidal asssy-directed fractionation, and it showed significant nematicidal activity against B. xylophilus, with an LC50 value of 0.84 µg mL-1 . Spectinabilin effectively suppressed the development of pine wilt disease in 5-year-old Pinus densiflora trees, even at 0.9mg per tree under greenhouse conditions. Moreover, the acetone extract of the active strain's mycelia efficiently suppressed the development of pine wilt disease under field conditions. To the best of our knowledge, this the first report to describe the nematicidal activity of spectinabilin against B. xylophilus. The cell extracts described herein merit further field studies as potential nematicides against the pine wood nematode. © 2018 Society of Chemical Industry.

Nematodes avoid and are killed by Bacillus mycoides-produced styrene.

Root-knot nematodes are obligate parasites that feed on plant roots and cause serious crop losses worldwide. Bacillus species (Bacilliaceae) can produce nematicidal metabolites and have shown good potential for biological control of nematodes. In this study, Bacillus mycoides strain R2 isolated from rhizosphere soil of tomato plants exhibited high nematicidal activity against the free-living nematode Caenorhabditis elegans and the root-knot nematode Meloidogyne incognita. In a pot experiment, control efficiency of B. mycoides R2 on M. incognita was as high as 90.94%. The nematicidal compound was isolated and identified as styrene. The median lethal concentration of styrene against M. incognita was 4.55 μg/ml (m/v). The volatile styrene caused avoidance and killed nematodes primarily by the olfactory neuron and G protein signal pathway. C. elegans detected styrene with the AWB neuron; the signal was then transmitted to the downstream G protein coupled receptors CHE-3, DOP-3, and STR-2. Then signal activated G protein GPA-3 and GPA-7. The signal was then transmitted to ion channels (CNGs channel and TRPV channel), causing calcium ion internal flow and a stress response towards the increased concentration of intracellular calcium. Styrene should be registered as a nematode repellent and biocontrol agent for protection of crops against root-knot nematode attack.

Transcriptomic and metabolomic analyses reveal that bacteria promote plant defense during infection of soybean cyst nematode in soybean

BackgroundSoybean cyst nematode (SCN) is the most devastating pathogen of soybean. Our previous study showed that the plant growth-promoting rhizobacterium Bacillus simplex strain Sneb545 promotes soybean resistance to SCN. Here, we conducted a combined metabolomic and transcriptomic analysis to gain information regarding the biological mechanism of defence enhancement against SCN in Sneb545-treated soybean. To this end, we compared the transcriptome and metabolome of Sneb545-treated and non-treated soybeans under SCN infection.ResultsTranscriptomic analysis showed that 6792 gene transcripts were common in Sneb545-treated and non-treated soybeans. However, Sneb545-treated soybeans showed a higher concentration of various nematicidal metabolites, including 4-vinylphenol, methionine, piperine, and palmitic acid, than non-treated soybeans under SCN infection.ConclusionsOverall, our results validated and expanded the existing models regarding the co-regulation of gene expression and metabolites in plants, indicating the advantage of integrated system-oriented analysis.

New nematicidal and antimicrobial secondary metabolites from a new species in the new genus, Pseudobambusicola thailandica.

During the course of a study on the functional biodiversity of the mycobiota inhabiting rainforests in Thailand, a fungal strain was isolated from a plant sample and shown to represent an undescribed species, as inferred from a combination of morphological and molecular phylogenetic methods. Molecular phylogenetic analyses, based on four DNA loci, revealed a phylogenetic tree with the newly generated sequences clustering in a separate branch, together with members of the Sulcatisporaceae (Pleosporales, Ascomycota). The Thai specimen morphologically resembled Neobambusicola strelitziae in having pycnidial conidiomata with phialidic conidiogenous cells that produce both fusoid-ellipsoid macroconidia and subcylindrical microconidia. However, the new fungus, for which the name Pseudobambusicola thailandica is proposed, differs from N. strelitziae in having conidiomata with well-defined necks, the presence of globose to subglobose thick-walled cells adjacent to conidiomata and the production of chlamydospores in culture. When cultures of P. thailandica, growing on water agar, were confronted with Caenorhabditis elegans nematodes, worms approaching the fungal mycelia were killed. This observation gave rise to a study of its secondary metabolites and six novel and two known compounds were isolated from submerged cultures of P. thailandica. The structures of metabolites 1–6, for which the trivial names thailanones A–F are proposed, were elucidated using a combination of spectral methods, including extensive 1 and 2D NMR analysis and high resolution mass spectrometry. Compounds 4 and 8 showed strong nematicidal and weak antifungal activity, whereas all other tested compounds showed moderate to weak nematicidal activity but no significant effects in the serial dilution assay against various fungi and bacteria. Compounds 1 and 8 also inhibited growth of the pathogenic basidiomycete Phellinus tremulae in a plate diffusion assay.