Inhibitory mechanism of 6-Pentyl-2H-pyran-2-one secreted by Trichoderma atroviride T2 against Cylindrocarpon destructans

Antifungal efficacy of Bacillus amyloliquefaciens ZK-9 against Fusarium graminearum and analysis of the potential mechanism of its lipopeptides

Fusarium graminearum is a destructive fungal pathogen that seriously threatens wheat production and quality. In the management of fungal infections, biological control is an environmentally friendly and sustainable approach. Here, the antagonistic strain ZK-9 with a broad antifungal activity was identified as Bacillus amyloliquefaciens. ZK-9 could produce extracellular enzymes such as pectinase, protease, cellulase, and amylase, as well as plant growth-promoting substances including IAA and siderophore. Lipopeptides extracted from strain ZK-9 had the high inhibitory effects on the mycelia of F. graminearum with the minimum inhibitory concentration (MIC) of 0.8 mg/mL. Investigation on the action mechanism of lipopeptides showed they could change the morphology of mycelia, damage the cell membrane, lower the content of ergosterol and increase the relative conductivity of membrane, cause nucleic acid and proteins leaking out from the cells, and disrupt the cell membrane permeability. Furthermore, metabolomic analysis of F. graminearum revealed the significant differences in the expression of 100 metabolites between the lipopeptides treatment group and the control group, which were associated with various metabolic pathways, mainly including amino acid biosynthesis, pentose, glucuronate and glycerophospholipid metabolism. In addition, strain ZK-9 inhibited Fusarium crown rot (FCR) with a biocontrol efficacy of 82.14 % and increased the plant height and root length by 24.23 % and 93.25 %, respectively. Moreover, the field control efficacy of strain ZK-9 on Fusarium head blight (FHB) was 71.76 %, and the DON content in wheat grains was significantly reduced by 69.9 %. This study puts valuable insights into the antifungal mechanism of lipopeptides against F. graminearum, and provides a promising biocontrol agent for controlling F. graminearum.

Uncovering the multifaceted properties of 6-pentyl-alpha-pyrone for control of plant pathogens

Some volatile organic compounds (VOCs) produced by microorganisms have the ability to inhibit the growth and development of plant pathogens, induce the activation of plant defenses, and promote plant growth. Among them, 6-pentyl-alpha-pyrone (6-PP), a ketone produced by Trichoderma fungi, has emerged as a focal point of interest. 6-PP has been isolated and characterized from thirteen Trichoderma species and is the main VOC produced, often accounting for >50% of the total VOCs emitted. This review examines abiotic and biotic interactions regulating the production of 6-PP by Trichoderma, and the known effects of 6-PP on plant pathogens through direct and indirect mechanisms including induced systemic resistance. While there are many reports of 6-PP activity against plant pathogens, the vast majority have been from laboratory studies involving only 6-PP and the pathogen, rather than glasshouse or field studies including a host plant in the system. Biopesticides based on 6-PP may well provide an eco-friendly, sustainable management tool for future agricultural production. However, before this can happen, challenges including demonstrating disease control efficacy in the field, developing efficient delivery systems, and determining cost-effective application rates must be overcome before 6-PP's potential for pathogen control can be turned into reality.

2-Heptanol inhibits Botrytis cinerea by accelerating amino acid metabolism and retarding membrane transport

During the postharvest storage of tomatoes, they are susceptible to infection by Botrytis cinerea, leading to significant economic losses. This study evaluated the antifungal potential of 2-heptanol (2-HE), a volatile biogenic compound, against B. cinerea and explored the underlying antifungal mechanism. The results indicated that 2-HE effectively suppressed the growth of B. cinerea mycelia both in vivo and in vitro and stimulated the activities of antioxidative enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in tomatoes. Furthermore, 2-HE reduced spore viability, compromised membrane integrity, and resulted in increased levels of extracellular nucleic acids, protein content, and membrane lipid peroxidation. Transcriptomic analysis revealed that 2-HE disrupted the membrane transport system and enhanced amino acid metabolism, which led to intracellular nutrient depletion and subsequent B. cinerea cell death. Additionally, the 2-HE treatment did not negatively impact the appearance or quality of the tomatoes. In conclusion, the findings of this study offer insights into the use of 2-HE as a biocontrol agent in food and agricultural applications.

Diallyl Trisulfide Acts as a Soil Disinfestation Against the Ilyonectria destructans through Inducing the Burst of Reactive Oxygen Species

Soil-borne diseases represent an impediment to the sustainable development of agriculture. A soil-borne disease caused by Ilyonectria destructans severely impacts Panax species, and soil disinfestation has proven to be an effective management approach. Here, diallyl trisulfide (DATS), derived from garlic, exhibited pronounced inhibitory effects on the growth of I. destructans in vitro tests and contributed to the alleviation of soil-borne diseases in the field. A comprehensive analysis demonstrated that DATS inhibits the growth of I. destructans by activating detoxifying enzymes, such as GSTs, disrupting the equilibrium of redox reactions. A series of antioxidant amino acids were suppressed by DATS. Particularly noteworthy is the substantial depletion of glutathione by DATS, resulting in the accumulation of ROS, ultimately culminating in the inhibition of I. destructans growth. Briefly, DATS could effectively suppress soil-borne diseases by inhibiting pathogen growth through the activation of ROS, and it holds promise as a potential environmentally friendly soil disinfestation.

Systematic assessment of the antifungal mechanism of soil fumigant methyl isothiocyanate against Fusarium oxysporum

Fusarium oxysporum is an important phytopathogenic fungus, it can be controlled by the soil fumigant methyl isothiocyanate (MITC). However, the antimicrobial mechanism of MITC against F. oxysporum, especially at the transcriptional level, is still unclear. In this experiment, the antimicrobial mechanism of MITC against F. oxysporum was investigated. Our results indicated that when F. oxysporum was exposed to 6 mg/L MITC for 12 h, the inhibitory rate of MITC on F. oxysporum was 80%. Transmission electron microscopes showed that the cell wall and membrane of F. oxysporum had shrunk and folded, vacuoles increased, and mitochondria swelled and deformed. In addition, the enzyme activity of F. oxysporum treated with MITC showed a decrease of 32.50%, 8.28% and 74.04% in catalase, peroxidase and superoxide dismutase, respectively. Transcriptome sequencing of F. oxysporum was performed and the results showed that 1478 differentially expressed genes (DEGs) were produced in response to MITC exposure. GO and KEGG analysis showed that the DEGs identified were involved in substance and energy metabolism, signal transduction, transport and catalysis. MITC disrupted cell homeostasis by influencing the expression of some key genes involved in chitin synthase and detoxification enzymes production, but F. oxysporum also protected itself by up-regulating genes involved in energy synthesis (such as upregulating acnA, CS and LSC2 in TCA). qRT-PCR data validated the reliability of transcriptome data. Our research used biochemical and genetic techniques to identify molecular lesions in the mycelia of F. oxysporum exposed to MITC, and provide valuable insights into the toxic mechanism of pathogenic fungi mediated by MITC. These techniques are also likely to be useful for rapidly screening and identifying new, environmentally-friendly soil fumigants that are efficacious against fungal pathogens.

6-Pentyl-2H-pyran-2-one from Trichoderma erinaceum Is Fungicidal against Litchi Downy Blight Pathogen Peronophythora litchii and Preservation of Litchi

The postharvest losses of litchi caused by litchi downy blight are considerably high. We identified a natural antifungal volatile pyrone, 6-pentyl-2H-pyran-2-one (6PP), synthesized by Trichoderma erinaceum LS019-2 and investigated as biocontrol for litchi downy blight and preservation. 6PP significantly inhibited the growth and sporangial germination of Peronophythora litchii, the causal agent of litchi downy blight, and caused severe cellular and intracellular destructions, as evidenced by electron microscopic analysis. Furthermore, in the treatment, the fruit kept better color, higher weight, and antioxidant activity, so it can maintain freshness and prolong shelf life. Metabolome analysis confirmed the decline of lipids and the accumulation of organic acids in litchi fruits in response to 6PP treatment. These effects from 6PP could alleviate disease effects and prolong the shelf life of litchi fruits. These findings suggested that 6PP could be a useful natural product to control downy blight disease and a new preservative of litchi fruits.

A New Insight into 6-Pentyl-2H-pyran-2-one against Peronophythora litchii via TOR Pathway

The litchi downy blight disease of litchi caused by Peronophythora litchii accounts for severe losses in the field and during storage. While ample quantitative studies have shown that 6-pentyl-2H-pyran-2-one (6PP) possesses antifungal activities against multiple plant pathogenic fungi, the regulatory mechanisms of 6PP-mediated inhibition of fungal pathogenesis and growth are still unknown. Here, we investigated the potential molecular targets of 6PP in the phytopathogenic oomycetes P. litchii through integrated deployment of RNA-sequencing, functional genetics, and biochemical techniques to investigate the regulatory effects of 6PP against P. litchii. Previously we demonstrated that 6PP exerted significant oomyticidal activities. Also, comparative transcriptomic evaluation of P. litchii strains treated with 6PP Revealed significant up-regulations in the expression profile of TOR pathway-related genes, including PlCytochrome C and the transcription factors PlYY1. We also noticed that 6PP treatment down-regulated putative negative regulatory genes of the TOR pathway, including PlSpm1 and PlrhoH12 in P. litchii. Protein-ligand binding analyses revealed stable affinities between PlYY1, PlCytochrome C, PlSpm1, PlrhoH12 proteins, and the 6PP ligand. Phenotypic characterization of PlYY1 targeted gene deletion strains generated in this study using CRISPR/Cas9 and homologous recombination strategies significantly reduced the vegetative growth, sporangium, encystment, zoospore release, and pathogenicity of P. litchii. These findings suggest that 6PP-mediated activation of PlYY1 expression positively regulates TOR-related responses and significantly influences vegetative growth and the virulence of P. litchii. The current investigations revealed novel targets for 6PP and underscored the potential of deploying 6PP in developing management strategies for controlling the litchi downy blight pathogen.

Trichoderma as a biological control agent: mechanisms of action, benefits for crops and development of formulations

Currently, the food and economic losses generated by the attack of phytopathogens on the agricultural sector constitute a severe problem. Conventional crop protection techniques based on the application of synthetic pesticides to combat these undesirable microorganisms have also begun to represent an inconvenience since the excessive use of these substances is associated with contamination problems and severe damage to the health of farmers, consumers, and communities surrounding the fields, as well as the generation of resistance by the phytopathogens to be combated. Using biocontrol agents such as Trichoderma to mitigate the attack of phytopathogens represents an alternative to synthetic pesticides, safe for health and the environment. This work explains the mechanisms of action through which Trichoderma exerts biological control, some of the beneficial aspects that it confers to the development of crops through its symbiotic interaction with plants, and the bioremedial effects that it presents in fields contaminated by synthetic pesticides. Also, detail the production of spore-based biopesticides through fermentation processes and formulation development.

Comparative physiological and transcriptome analysis provide insights into the inhibitory effect of 6-pentyl-2H-pyran-2-one on Clarireedia jacksonii

Clarireedia spp. is a destructive phytopathogenic fungus that causes turf dollar spot of bent-grass, leading to widespread lawn death. In this study, we explored the antifungal capability of 6-pentyl-2H-pyran-2-one (6PP), a natural metabolite volatilized by microorganisms, which plays an important role in the biological control of turfgrass dollar spot. However, the mechanisms by which 6PP inhibits Clarireedia jacksonii remain unknown. In the present study, C. jacksonii mycelial growth was inhibited by the 6PP treatment and the 6PP treatment damaged cell membrane integrity, causing an increase in relative conduc-tivity. Furthermore, physiological and biochemistry assay showed that 6PP treatment can enhance reactive oxygen species (ROS) levels, malondialdehyde (MDA) content obviously increased with 6PP exposure, increased alchohol dehydrogenase (ADH) and depleted acetalde-hyde dehydrogenase (ALDH), and activated the activities of many antioxidant enzymes in C. jacksonii. Gen Ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that some genes in C. jacksonii after 6PP treatment related to integrity of the cell wall and membrane, and oxidative stress were significantly downregulated. It is worth mentioning that the fatty acid degradation pathway is significantly upregulated, with an increase in ATP content and ATP synthase activity, which may promote fungal cell apoptosis. Moreover, we found that the expression of ABC transporters, and glutathione metabolism encoding genes were increased to respond to external stimuli. Taken together, these findings revealed the potential antifungal mechanism of 6PP against Clarireedia spp., which also provides a theoretical basis for the commercial utilization of 6PP as a green pesticide in the future.

Trichoderma Species: Our Best Fungal Allies in the Biocontrol of Plant Diseases-A Review

Biocontrol agents (BCA) have been an important tool in agriculture to prevent crop losses due to plant pathogens infections and to increase plant food production globally, diminishing the necessity for chemical pesticides and fertilizers and offering a more sustainable and environmentally friendly option. Fungi from the genus Trichoderma are among the most used and studied microorganisms as BCA due to the variety of biocontrol traits, such as parasitism, antibiosis, secondary metabolites (SM) production, and plant defense system induction. Several Trichoderma species are well-known mycoparasites. However, some of those species can antagonize other organisms such as nematodes and plant pests, making this fungus a very versatile BCA. Trichoderma has been used in agriculture as part of innovative bioformulations, either just Trichoderma species or in combination with other plant-beneficial microbes, such as plant growth-promoting bacteria (PGPB). Here, we review the most recent literature regarding the biocontrol studies about six of the most used Trichoderma species, T. atroviride, T. harzianum, T. asperellum, T. virens, T. longibrachiatum, and T. viride, highlighting their biocontrol traits and the use of these fungal genera in Trichoderma-based formulations to control or prevent plant diseases, and their importance as a substitute for chemical pesticides and fertilizers.

Foliar Pathogen Infection Manipulates Soil Health through Root Exudate-Modified Rhizosphere Microbiome

Negative plant-soil feedback (NPSF) due to the buildup of soilborne pathogens in soil is a major obstacle in sustainable agricultural systems. Beneficial rhizosphere microfloras are recruited by plants, and mediating this has become a strategic priority to manipulate plant health. Here, we found that foliar infection of Panax notoginseng by Alternaria panax changed plant-soil feedback from negative to positive. Foliar infection modified the rhizosphere soil microbial community and reversed the direction of the buildup of the soilborne pathogen Ilyonectria destructans and beneficial microbes, including Trichoderma, Bacillus, and Streptomyces, in rhizosphere soil. These beneficial microbes not only showed antagonistic ability against the pathogen I. destructans but also enhanced the resistance of plants to A. panax. Foliar infection enhanced the exudation of short- and long-chain organic acids, sugars, and amino acids from roots. In vitro and in vivo experiments validated that short- and long-chain organic acids and sugars play dual roles in simultaneously suppressing pathogens but enriching beneficial microbes. In summary, foliar infection could change root secretion to drive shifts in the rhizosphere microbial community to enhance soil health, providing a new strategy to alleviate belowground disease in plants through aboveground inducement. IMPORTANCE Belowground soilborne disease is the main factor limiting sustainable agricultural production and is difficult to manage due to the complexity of the soil environment. Here, we found that aboveground parts of plants infected by foliar pathogens could enhance the secretion of organic acids, sugars, and amino acids in root exudates to suppress soilborne pathogens and enrich beneficial microbes, eventually changing the plant and soil feedback from negative to positive and alleviating belowground soilborne disease. This is an exciting strategy by which to achieve belowground soilborne disease management by manipulating the aboveground state through aboveground stimulation.

Metabolites derived from fungi and bacteria suppress in vitro growth of Gnomoniopsis smithogilvyi, a major threat to the global chestnut industry

INTRODUCTION

Chestnut rot caused by the fungus Gnomoniopsis smithogilvyi is a disease present in the world's major chestnut growing regions. The disease is considered a significant threat to the global production of nuts from the sweet chestnut (Castanea sativa). Conventional fungicides provide some control, but little is known about the potential of biological control agents (BCAs) as alternatives to manage the disease.

OBJECTIVE

Evaluate whether formulated BCAs and their secreted metabolites inhibit the in vitro growth of G. smithogilvyi.

METHODS

The antifungal potential of BCAs was assessed against the pathogen through an inverted plate assay for volatile compounds (VOCs), a diffusion assay for non-volatile compounds (nVOCs) and in dual culture. Methanolic extracts of nVOCs from the solid medium were further evaluated for their effect on conidia germination and were screened through an LC-MS-based approach for antifungal metabolites.

RESULTS

Isolates of Trichoderma spp., derived from the BCAs, significantly suppressed the pathogen through the production of VOCs and nVOCs. The BCA from which Bacillus subtilis was isolated was more effective in growth inhibition through the production of nVOCs. The LC-MS based metabolomics on the nVOCs derived from the BCAs showed the presence of several antifungal compounds.

CONCLUSION

The results show that G. smithogilvyi can be effectively controlled by the BCAs tested and that their use may provide a more ecological alternative for managing chestnut rot. The in vitro analysis should now be expanded to the field to assess the effectiveness of these alternatives for chestnut rot management.

2E,4E-Decadienoic Acid, a Novel Anti-Oomycete Agent from Coculture of Bacillus subtilis and Trichoderma asperellum

Phytophthora nicotianae is an oomycete pathogen of global significance threatening many important crops. It is mainly controlled by chemosynthetic fungicides, which endangers ecosystem and human health; thus, there is an urgent need to explore alternatives for these fungicides. In this study, a new anti-oomycete aliphatic compound, 2E,4E-decadienoic acid (DDA), was obtained through coculture of Bacillus subtilis Tpb55 and Trichoderma asperellum HG1. Both in vitro and in vivo tests showed that DDA had a strong inhibitory effect against P. nicotianae. In addition, rhizosphere microbiome analysis showed that DDA reduced the relative abundance of Oomycota in rhizosphere soil. Transcriptome sequencing (RNA-Seq) analysis revealed that treatment of P. nicotianae with DDA resulted in significant downregulation of antioxidant activity and energy metabolism, including antioxidant enzymes and ATP generation, and upregulation of membrane-destabilizing activity, such as phospholipid synthesis and degradation. The metabolomic analysis results implied that the pathways influenced by DDA were mainly related to carbohydrate metabolism, energy metabolism, and the cell membrane. The biophysical tests further indicated that DDA produced oxidative stress on P. nicotianae, inhibited antioxidant enzyme and ATPase activity, and increased cell membrane permeability. Overall, DDA exerts inhibitory activity by acting on multiple targets in P. nicotianae, especially on the cell membrane and mitochondria, and can therefore serve as a novel environment-friendly agent for controlling crop oomycete disease. IMPORTANCE P. nicotianae is an oomycete pathogen that is destructive to crops. Although some oomycete inhibitors have been used during crop production, most are harmful to the ecology and lead to pathogen resistance. Alternatively, medium-chain fatty acids have been reported to exhibit antimicrobial activity in the medical field in previous studies; however, their potential as biocontrol agents has rarely been evaluated. Our in vivo and in vitro analyses revealed that the medium-chain fatty acid 2E,4E-decadienoic acid (DDA) displayed specific inhibitory activity against oomycetes. Further analysis indicated that DDA may acted on multiple targets in P. nicotianae, especially on the cell membrane and mitochondria. Our findings highlight the potential of DDA in controlling oomycete diseases. In conclusion, these results provide insights regarding the future use of green and environment-friendly anti-oomycete natural products for the prevention and control of crop oomycete diseases.

RNA-Seq Provides Insights into the Mechanisms Underlying Ilyonectria robusta Responding to Secondary Metabolites of Bacillus methylotrophicus NJ13

(1) Background: Ilyonectria robusta can cause ginseng to suffer from rusty root rot. Secondary metabolites (SMs) produced by Bacillus methylotrophicus NJ13 can inhibit the mycelial growth of I. robusta. However, the molecular mechanism of the inhibition and response remains unclear. (2) Methods: Through an in vitro trial, the effect of B. methylotrophicus NJ13’s SMs on the hyphae and conidia of I. robusta was determined. The change in the physiological function of I. robusta was evaluated in response to NJ13’s SMs by measuring the electrical conductivity, malondialdehyde (MDA) content, and glucose content. The molecular interaction mechanism of I. robusta’s response to NJ13’s SMs was analyzed by using transcriptome sequencing. (3) Results: NJ13’s SMs exhibited antifungal activity against I. robusta: namely, the hyphae swelled and branched abnormally, and their inclusions leaked out due to changes in the cell membrane permeability and the peroxidation level; the EC50 value was 1.21% (v/v). In transcripts at 4 dpi and 7 dpi, the number of differentially expressed genes (DEGs) (|log2(fold change)| > 1, p adj ≤ 0.05) was 1960 and 354, respectively. NJ13’s SMs affected the glucose metabolism pathway, and the sugar-transporter-related genes were downregulated, which are utilized by I. robusta for energy production. The cell wall structure of I. robusta was disrupted, and chitin-synthase-related genes were downregulated. (4) Conclusions: A new dataset of functional responses of the ginseng pathogenic fungus I. robusta was obtained. The results will benefit the development of targeted biological fungicides for I. robusta and the study of the molecular mechanisms of interaction between biocontrol bacteria and phytopathogenic fungi.

Allyl Isothiocyanate in the Volatiles of Brassica juncea Inhibits the Growth of Root Rot Pathogens of Panax notoginseng by Inducing the Accumulation of ROS

The cultivation of Panax notoginseng is often seriously hindered by root rot disease caused by the accumulation of soil-borne pathogens. Here, the inhibitory activity of Brassica juncea volatiles on P. notoginseng root rot pathogens was assessed and compounds in volatiles were identified. Furthermore, the antimicrobial activity and mechanism of allyl isothiocyanate (AITC) were deciphered by integrated transcriptome and metabolome analyses. The volatiles of B. juncea showed dose-dependent antimicrobial activity against root rot pathogens. AITC, identified as the main volatile compound, not only significantly inhibited pathogen growth in vitro but also suppressed root rot disease in the field. Integrated transcriptomic and metabolomics analysis revealed that AITC inhibited Fusarium solani by interfering with energy production and induced the accumulation of ROS by decreasing the content of glutathione (GSH). In summary, B. juncea releases AITC to inhibit soil-borne pathogens and could be used as a rotation crop or soil fumigant to alleviate root rot disease.