Plant Pathogenic Microorganisms Research Articles

Antifungal activity of mangosteen pericarp and cashew leaf extract against Fusarium oxysporum in vitro

Polyphenols are secondary compounds that occur widely in plants and are highly effective in controlling plant pathogenic microorganisms. This study aimed to screen polyphenolic-rich plant extracts for their antifungal potential against Fusarium oxysporum. Several plant materials including cashew leaves, castor fruits, castor leaves, coffee husks, giant milkweed leaves, mangosteen pericarps and soapberry fruits were investigated for their total phenolic content. The results showed that cashew leaves and mangosteen pericarps contained high level of polyphenols at 108.23 and 124.14 mg GAE/g, respectively. The main phenolic compounds found in cashew leaves were gallic acid and protocatechuic acid at 377.29 mg/100 g and 56.44 mg/100 g, respectively. Mangosteen pericarps contained 16.22 mg/100 g protocatechuic acid and 55.75 mg/100 g of chlorogenic acid. The antifungal activity of cashew leaf and mangosteen pericarp extracts against F. oxysporum was 32.92 - 77.08% and 68.33 - 83.75%, respectively at the extract concentration from 2% to 10%. The combined use of cashew leaf and mangosteen pericarp extracts exhibited an additive inhibition against F. oxysporum. Cashew leaves and mangosteen pericarp are potential materials for producing bio-fungicides, which are not only effective but also safe for human and the environment.

LAMP Reaction in Plant Disease Surveillance: Applications, Challenges, and Future Perspectives.

Movements of plant pathogenic microorganisms in uncontaminated areas occur today at an alarming rate, driven mainly by global trade and climate change. These invaders can trigger new disease outbreaks able to impact the biodiversity and economies of vast territories and affect a variety of ecosystem services. National and supranational regulatory deficiencies, such as inadequate quarantine measures and ineffective early pathogen detection at ports of entry, exacerbate the issue. Thus, there is an urgent need for accurate and rapid diagnostic tools to intercept invasive and nonindigenous plant pathogens. The LAMP (Loop-mediated isothermal AMPlification) technique is a robust, flexible tool representing a significant advance in point-of-care (POC) diagnostics. Its user-friendliness and sensitivity offer a breakthrough in phytosanitary checks at points of entry (harbors and airports), for disease and pest surveillance at vulnerable sites (e.g., nurseries and wood-processing and storage facilities), and for territorial monitoring of new disease outbreaks. This review highlights the strengths and weaknesses of LAMP, emphasizing its potential to revolutionize modern plant disease diagnostics.

Phoma herbarum: A Potential Biocontrol Agent Against Weeds, that Promotes Wheat Growth

The usage of chemical weedicide adversely affects the soil fertility and environment. Hence, in order to reduce the use of chemical weedicide, current study was aimed to isolate plant pathogenic microorganisms from diseased weeds and evaluate their potential as a bioherbicide in wheat field. Twelve bacterial and thirty-one fungal isolates were screened to determine their bioherbicidal activity against prevalent weeds (Avena fatua, Phalaris minor, and Chenopodium album) by using detached leaf assay and in-vitro seed testing methods. Among the forty-three isolates, two potential isolates were selected for further studies. Potential fungal isolates DGL 8C and DGL 7A with significant bioherbicidal activity were molecularly (ITS sequencing) identified as Phoma herbarum R21 (GenBank ID- ON705696) and K_NESO2 (GenBank ID- ON705704). Phoma herbarum R21 was chosen for further research due to its superior herbicidal effect and positive influence on wheat growth. Effective herbicidal activity (up to 90%) of potential isolate was obtained in pre-germination testing, compared to control. Cell free culture filtrate (CFCF) treatment showed nonspecific inhibition in the germination of weeds and wheat. While, CFCF selectively deteriorated the target weeds in post-germination treatment. Phoma herbarum R21 enhanced the growth of Durum wheat varieties Poshan and Tejas, as it promoted the growth of shoot, root, and fresh weight up to 88% compared to control. Phoma herbarum R21 significantly inhibited the growth of phytopathogenic fungi up to 57%. In this study, Phoma herbarum R21 was identified as a potential bioherbicide against the weeds of wheat along with its growth promoting and antifungal activities.

Activity of East Siberian Trichoderma Isolates against Plant-pathogenic Microorganisms

The genus Trichoderma comprised important antagonists of pathogenic fungi and can be used in agriculture to combat various plant diseases. In the course of the present work, two micromycete strains were isolated from wood cuts in Eastern Siberia, which were identified by morphological and molecular genetic characteristics as Trichoderma atroviride and Trichoderma harzianum. These Trichoderma strains efficiently inhibited the development of the pathogenic fungi studied (by up to 80%). The data presented in the paper indicate that Trichoderma atroviride and Trichoderma harzianum may be promising for further study of the means of biocontrol of plant diseases.

Screening of reference genes for gene expression study in different tissues from the transcriptome data of the vector leafhopper Psammotettix striatus

Selecting appropriate reference genes is crucial for ensuring the accuracy and reliability of gene expression study using reverse transcription-quantitative PCR (RT-qPCR). To screen the optimal reference genes for analyzing gene expression in different tissues of the vector leafhopper Psammotettix striatus which causes extensive damage to a wide range of crops by vectoring multiple plant pathogenic microorganisms, the transcriptome data from Malpighian tubules (MTs) of P. striatus were mined. Twenty alternative candidate reference genes were initially selected for screening, among which seven genes with diverse Gene Ontology (GO) annotations were choosed as candidate reference genes, i.e., ribosomal protein L7A (RPL7A), ribosomal protein S28 (RPS28), ribosomal protein L22 (RPL22), ribosomal protein LP2 (RPLP2), H3 histone family 3A (H3F3A), elongation factor 1γ (EF-1γ), and elongation factor 1α (EF-1α). Gene expression levels in different tissues of P. striatus adults were examined using RT-qPCR, and their expression stability was analyzed using multiple reference gene screening software. This study revealed EF-1α as the most abundantly expressed gene, while RPL22 exhibited the lowest expression levels. EF-1α showed the most stable expression, whereas RPS28 showed the least stability. Various software tools confirmed EF-1α as the most stable single reference gene, and EF-1α and RPLP2 an optimal combination. This study provides a foundation for future investigation of the transmission of pathogenic microorganisms mediated by the vector leafhoppers, the function of the MTs, the biosynthesis of brochosomes, the coevolutionary processes and nutritional interactions of symbionts and host insects, and the gene expression study of other sap-sucking insects.

Isolation of anthraquinone derivatives from Rubia cordifolia (Rubiaceae) and their bioactivities against plant pathogenic microorganisms.

The discovery of antimicrobial ingredients from natural products could be an effective way to create novel fungicides. Rubia cordifolia L., a traditional Chinese herb, may have antimicrobial effects on plant pathogens according to our previous screening study. Rubia cordifolia L. extracts had moderate inhibitory effects on apple Valsa canker (Valsa mali) and tomato grey mould (Botrytis cinerea) at a concentration of 10 mg mL-1. With the use of bioguided isolation methods, eight compounds (1-8) were obtained, including the new compound 2,2,6-trimethyl-6-(4-methylphenyl)-tetrahydropyrano- 3-ol (7), and seven quinone derivatives. Two compounds, mollugin (1) and 1,3,6-trihydroxy-2-methylanthraquinone (6), were found to exhibit outstanding antifungal activities against V. mali and Phytophthora capsici Leon. The half maximal effective concentration (EC50) of compound 1 and compound 6 against V. mali were 79.08 and 81.78 μg mL-1, respectively, and the EC50 of compound 6 against P. capsici was 4.86 μg mL-1. Compound 1 also showed excellent activity against tobacco mosaic virus (TMV). The inactive, inductive, protective and curative activities against TMV were 84.29%, 83.38%, 86.81%, and 60.02%, respectively, at a concentration of 500 μg mL-1, which were all close to or greater than that of the positive control (100 μg mL-1 chitosan oligosaccharide, COS). Mollugin and 1,3,6-trihydroxy-2-methylanthraquinone are potentially valuable active compounds that lay a foundation for research on botanical fungicide products derived from R. cordifolia L. and provide lead structures for quinone derivative synthesis and structural modification. © 2024 Society of Chemical Industry.

Activity of East Siberian Trichoderma Isolates against Plant-Pathogenic Microorganisms

Activity of East Siberian Trichoderma Isolates against Plant-Pathogenic Microorganisms

Amelioration in nanobiosensors for the control of plant diseases: current status and future challenges

The increase in global population has had a tremendous impact on sustainable agri-food practices. With the growth in world population, various modern technologies are being utilized that more often result in the opening of tremendous opportunities in the agriculture and food sectors. Nanotechnology is used in agri-food sectors for a variety of purposes, including enhancing flavor, pest/pathogen diagnosis, production, processing, storage, packaging, and transportation of agricultural products. Plant pathogenic microorganisms including bacteria, viruses, fungi, and nematodes have a significant impact on the global economy. In particular, advances in nanotechnology, including nanobiosensors, have been used in the detection of plant diseases and pathogens, the evaluation and examination of infections caused by microorganisms, the management of diseases and, thus, the promotion of food security. Apart from the management of plant diseases, nanobiosensors offer better opportunities for sustainable agri-food production by controlling physical, chemical, and biological processes, thus improving food safety and the agricultural economy. This review outlines the application of nano-integrated nanobiosensors for better agricultural and food practices.

Unveiling the potential of Daldinia eschscholtzii MFLUCC 19-0629 through bioactivity and bioinformatics studies for enhanced sustainable agriculture production

Endophytic fungi constitute a rich source of secondary metabolites that can be manipulated to produce desirable novel analogs for combating current agricultural challenges for crop production, especially controlling plant disease. The endophytic fungus Daldinia eschscholtzii MFLUCC 19-0629, was newly isolated from tropical ancient plants, Oncosperma sp., and displays a broad-spectrum of antifungal and antibacterial activities against several plant pathogens including Ralstonia solanacearum, Fusarium oxysporum, Colletotrichum gloeosporioides, Colletotrichum acutatum, Stagonosporopsis cucurbitacearum, Corynespora cassiicola and Stemphylium spp. A high-quality genome sequence was obtained using Oxford nanopore technology, the accuracy and length of reads resulting in no need for Illumina or other sequencing techniques, for D. eschscholtzii MFLUCC 19-0629, resulting in a genome size of 37.56 Mb assembled over 11 contigs of significant size, likely to be at the chromosomal level. Bioinformatics analysis revealed that this strain is biosynthetically talented encoding 67 predicted biosynthetic gene clusters (BGCs). Only eight of the 67 BGCs matched or demonstrated high similarity to previously characterized BGCs linked to the production of known secondary metabolites. The high number of predicted unknown BGCs makes this strain a promising source of novel natural products. The discovery that D. eschscholtzii MFLUCC 19-0629 has a broad spectrum of antimicrobial activity against seven major plant pathogenic microorganisms relevant to crop production and its complete genome sequence carries immense importance in the advancement of novel microbial biocontrol agents (MBCAs). This also unveils the prospect of uncovering new compounds that could be utilized for sustainable agriculture and pharmaceutical purposes.

Identification of two phthalide derivatives and an oxindole compound isolated from the edible mushroom Pleurotus ostreatus and their inhibitory activities against plant pathogenic microorganisms

Identification of two phthalide derivatives and an oxindole compound isolated from the edible mushroom <i>Pleurotus ostreatus</i> and their inhibitory activities against plant pathogenic microorganisms

Biofabrication of novel silver and zinc oxide nanoparticles from Fusarium solani IOR 825 and their potential application in agriculture as biocontrol agents of phytopathogens, and seed germination and seedling growth promoters.

Introduction: Plant pathogenic microorganisms adversely affect the growth and yield of crops, which consequently leads to losses in food production. Metal-based nanoparticles (MNPs) can be a remedy to solve this problem. Methods: Novel silver nanoparticles (AgNPs) and zinc oxide nanoparticles (ZnONPs) were biosynthesized from Fusarium solani IOR 825 and characterized using Dynamic Light Scattering (DLS), Fourier Transform Infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), X-ray diffraction (XRD) and measurement of Zeta potential. Antibacterial activity of NPs was evaluated against four plant pathogenic strains by determination of the minimum inhibitory (MIC) and biocidal concentrations (MBC). Micro-broth dilution method and poisoned food technique were used to assess antifungal activity of NPs against a set of plant pathogens. Effect of nanopriming with both types of MNPs on maize seed germination and seedlings growth was evaluated at a concentration range of 1-256μgmL-1. Results: Mycosynthesis of MNPs provided small (8.27nm), spherical and stable (zeta potential of -17.08mV) AgNPs with good crystallinity. Similarly, ZnONPs synthesized by using two different methods (ZnONPs(1) and ZnONPs(2)) were larger in size (117.79 and 175.12nm, respectively) with Zeta potential at -9.39 and -21.81 mV, respectively. The FTIR spectra showed the functional groups (hydroxyl, amino, and carboxyl) of the capping molecules on the surface of MNPs. The values of MIC and MBC of AgNPs against bacteria ranged from 8 to 256μgmL-1 and from 512 to 1024μgmL-1, respectively. Both types of ZnONPs displayed antibacterial activity at 256-1024μgmL-1 (MIC) and 512-2048μgmL-1 (MBC), but in the concentration range tested, they revealed no activity against Pectobacterium carotovorum. Moreover, AgNPs and ZnONPs inhibited the mycelial growth of Alternaria alternata, Fusarium culmorum, Fusarium oxysporum, Phoma lingam, and Sclerotinia sclerotiorum. MIC and MFC values of AgNPs ranged from 16-128 and 16-2048μgmL -1, respectively. ZnONPs showed antifungal activity with MIC and MFC values of 128-2048μgmL-1 and 256-2048μgmL-1, respectively. The AgNPs at a concentration of ≥32μgmL-1 revealed sterilization effect on maize seeds while ZnONPs demonstrated stimulatory effect on seedlings growth at concentrations of ≥16μgmL-1 by improving the fresh and dry biomass production by 24% and 18%-19%, respectively. Discussion: AgNPs and ZnONPs mycosynthesized from F. solani IOR 825 could be applied in agriculture to prevent the spread of pathogens. However, further toxicity assays should be performed before field evaluation. In view of the potential of ZnONPs to stimulate plant growth, they could be crucial in increasing crop production from the perspective of current food assurance problems.

Fabrication of supramolecular self-assembly of the Schiff base complex for improving bioavailability of aldehyde-containing plant essential oil

Plant essential oils have enormous potential in the management of crop disease for their easy availability, biocompatibility, biodegradability, and excellent antimicrobial activities. However, these substances usually show poor performance in practical applications due to the poor stability caused by their volatilization and oxidation. Herein, taking advantage of the biological characteristics that some plant pathogenic microorganisms can acidify microenvironment, a pH-responsive supramolecular self-assembly based on the Schiff base complex of cinnamaldehyde (Cin) and branched polyethylenimine (BPEI) was constructed through multiple covalent and noncovalent interactions. The results showed that the formation and physicochemical properties of the self-assembly were positively correlated with the molecular weight of BPEI. Combined with the stability, particle size, zeta potential, self-assembly rates, and morphological characteristics in different systems, BPEI with an average molecular weight of 10,000 (BPEI 10 k) was a preferable choice to push the formation of the self-assembly and the optimum mass ratio of Cin to BPEI 10 k was 3:4. The prepared spherical nanoparticles had low volatility, good surface activity, and high stability and could respond to acidic environments to release Cin by a Fickian diffusion or a non-Fickian behavior. The self-assembly exhibited superior activities against plant pathogenic fungi, desirable environmental compatibility, and convincing biosafety to the plants. These findings would provide guidance for achieving efficient utilization of aldehyde-containing plant essential oil and exploring a useful approach for sustainable plant disease management.

Synthesis, antimicrobial activity, molecular docking and pharmacophore analysis of new propionyl mannopyranosides

Carbohydrates are considered as biomolecules playing numerous biological roles and can act as receptors part for several microbial pathogens as well as a barrier to microbial infection. Here we synthesize five novel methyl α-D-mannopyranoside (1) analogues following regioselective acylation, where, methyl 6-O-propionyl-α-D-mannopyranoside was converted into 2,3,4-tri-O-propionyl analogues with excellent percentage of yields. Structural configurations of the synthesized methyl α-D-mannopyranoside analogues were confirmed by spectroscopic, physicochemical, and elemental study. Prediction of activity spectra for substances (PASS) and in vitro antimicrobial experiment of the methyl α-D-mannopyranoside analogues against seven human and plant pathogenic microorganisms transpired solid antibacterial and antifungal activities are studied. Most of the compounds exhibited salient antibacterial potentiality with minimum inhibitory concentration (MIC) values ranging from 0.25 µg/mL to 2.00 µg/mL and minimum bactericidal concentration (MBC) values ranging from 8.00 µg/mL to 16.00 µg/mL. The above observations were rationalized by molecular docking against Escherichia coli and Bacillus cereus (4V7S and 1KZN), Aspergillus flavus (6K3H) and Aspergillus niger (3K4Q) specific targets to search the binding affinities and different interactions of methyl α-D-mannopyranoside analogues. Compounds 3 and 6 were discovered to be the most promising for binding with the target due to their high affinity energy and the stability of the docked complexes were confirmed by molecular dynamics. Combination of in silico ADMET prediction and drug-likeness had shown assuring results for compounds 3 and 6 due to their improved kinetic parameters in terms of biological activity. Overall, the findings are encouraging for the development of novel drugs for the treatment of human and plant pathogens.

Characterization of a Bacillus velezensis with Antibacterial Activity and Its Inhibitory Effect on Gray Mold Germ

The present study provides a comprehensive overview of the Bacillus velezensis strain Htq6, and its potential applications in plant disease control. Htq6 is an endophytic bacterium derived from walnut, which was found to possess a strong inhibitory effect on a wide range of plant pathogenic microorganisms and was identified as a good plant disease control agent. The entire genome of the Bacillus velezensis Htq6 was sequenced, and a comparative genomic analysis was conducted with various Bacillus species in order to better understand the mechanism of the strain’s biological control. At the same time, a new classification result was presented. Additionally, transcriptome analysis was performed to explore the response mechanism of tomato gray mold fungus after treatment with the fermentation liquid of Bacillus velezensis Htq6. The study analyzed the distribution of various secondary metabolite gene clusters in the Bacillus model strains and employed RNA-Seq technology to obtain transcriptome expression profiles. Furthermore, the cell wall, cell membrane, and antioxidant-related genes of Botrytis cinerea were analyzed, providing insight into the antibacterial mechanism of biocontrol bacteria and the stress response mechanism of Botrytis cinerea. The results of the research are promising, and could potentially lead to the development of an effective biocontrol agent for the prevention and control of various plant diseases.

Effect of Trichoderma viride on rhizosphere microbial communities and biocontrol of soybean root rot.

Biological seed dressing is a cost-effective means to protect plant roots from pathogens. Trichoderma is generally considered as one of the most common biological seed dressings. However, there is still a dearth of information on the effects of Trichoderma on microbial community of rhizosphere soil. High-throughput sequencing was used to analyze the effects of Trichoderma viride and a chemical fungicide on microbial community of soybean rhizosphere soil. The results showed that both T. viride and chemical fungicide could significantly reduce the disease index of soybean (15.11% for Trichoderma and 17.33% for Chemical), while no significant difference was observed between them. Both T. viride and chemical fungicide could affect the structure of rhizosphere microbial community, they increased the β-diversity of microbial community and significantly reduce the relative abundance of Saprotroph-Symbiotroph. Chemical fungicide could reduce the complexity and stability of co-occurrence network. However, T. viride is beneficial for maintaining network stability and increasing network complexity. There were 31 bacterial genera and 21 fungal genera significantly correlated with the disease index. Furthermore, several potential plant pathogenic microorganisms were also positively correlated with disease index, such as Fusarium, Aspergillus, Conocybe, Naganishia, and Monocillium. From this work, T. viride may be used as a substitute for chemical fungicide to control soybean root rot and be more friendly to soil microecology.

Current and emerging trends in techniques for plant pathogen detection.

Plant pathogenic microorganisms cause substantial yield losses in several economically important crops, resulting in economic and social adversity. The spread of such plant pathogens and the emergence of new diseases is facilitated by human practices such as monoculture farming and global trade. Therefore, the early detection and identification of pathogens is of utmost importance to reduce the associated agricultural losses. In this review, techniques that are currently available to detect plant pathogens are discussed, including culture-based, PCR-based, sequencing-based, and immunology-based techniques. Their working principles are explained, followed by an overview of the main advantages and disadvantages, and examples of their use in plant pathogen detection. In addition to the more conventional and commonly used techniques, we also point to some recent evolutions in the field of plant pathogen detection. The potential use of point-of-care devices, including biosensors, have gained in popularity. These devices can provide fast analysis, are easy to use, and most importantly can be used for on-site diagnosis, allowing the farmers to take rapid disease management decisions.

Plant Growth-promoting Ability and Pathogen Inhibitory Effect of Actinomycetes Isolated from Fecal Pellets of the Giant Millipede Thyropygus resimus (Diplopoda)

The microbial properties of millipede fecal pellets have been studied mainly in Glomerida (pill millipedes), and much less in the significant majority of other millipede groups. Therefore, the present study examined actinomycetes isolated from the fecal pellets of the non-glomerid giant millipede Thyropygus resimus Attems, 1938 (Spirostreptida) to (1) test their plant growth-promoting ability, and (2) evaluate their potential to control and inhibit plant pathogenic microorganisms. Millipedes were collected from Phu Kum Khao, Kalasin Province, Thailand. A total of 59 actinomycete isolates were obtained and identified as belonging to the genus Streptomyces using 16S rRNA sequencing. The plant growth-promoting properties of the isolates were tested by screening four characteristics: nitrogen fixation, phosphate solubility, siderophore production, and indole-3-acetic acid (IAA) production. A nitrogen-fixation test on nitrogen-free solid malate media (NFM) showed that 54 isolates were capable of fixing nitrogen. Phosphate solubility was tested on double-layered glucose yeast extract agar (GYA) medium containing tricalcium phosphate. This showed that 42 isolates formed a clear zone around the colonies due to phosphate dissolution. Siderophore production was tested on chrome azurol sulfate (CAS) agar. This showed that 55 isolates could grow on this medium and form clear yellow to orange zones around their colonies. IAA production tests revealed that 41 isolates could produce IAA. Based on the combined results of these four tests, eight of the 59 isolates were the most effective in promoting plant growth: KLS-AC04, KLD-AC01, KLD-AC02-1, KLD-AC08, KLD-AC09, KLD-AC16, KLD-AC29-1, and KLD-AC30. Seventeen isolates inhibited the growth of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight disease in rice, more effectively than rifampicin (100 ppm), with isolate KLS-AC02-1-1 being the most effective (inhibition zone, 58.25 mm in diameter). Therefore, these isolates can be used for growth promotion and rice disease control in the future.

Nano Fertilizer in Crop Production: The Changing Scenario

While the world's population is growing exponentially, there is an alarming increase in the need for food, which might reach a record nine billion people by 2050. In order to address the issue of rising food demand, a number of initiatives are being put into place to boost crop output and safeguard them against agricultural pests. The growing population pressures agricultural civilization to develop fresh strategies for boosting crop output. For nations all across the world, the issue of poverty and malnutrition has grown to be of great concern. Progress in the agricultural sector, which provides the raw materials for the food and feed industries, is crucial for both economic development and population expansion. With economic development, the soil nutrient balances are differed. Soil fertility is important in developing countries for assisting the economy and agriculture. There is a high demand in the twenty-first century for efficient, reliable, and cost-effective systems for detecting, supplying, monitoring, and diagnosing biological host molecules and nutrients. Traditional farming methods are incapable of keeping up with the rate at which food needs are increasing, so we must rely on and incorporate nanotechnology in agriculture and related sectors. In modern agriculture, increasing agricultural productivity is impossible without the use of chemical fertilizers and pesticides; however, the majority of agrochemicals are not eco-friendly and are thus harmful to human health. Nanotechnology is a novel technique for improved and sustainable agricultural production and also harbours a good capacity to bring novel alterations in the agricultural systems. Nanotechnology introduces new technologies and materials for use in molecular biology for the identification of plant pathogenic microorganisms. By bringing novel methods for distributing nutrients through nano fertilizers, specialized pathogen-targeted treatment, and boosting plant pest-resistance, nanotechnology has the potential to change the agricultural industry. Moreover, it can increase plants' ability to absorb nutrients and to endure environmental stresses. The fertility of the soil is a key factor in helping the economy and agriculture in developing nations. The benefits of strategies using nanotechnology for sustainable agriculture are covered here.

Plant Pathogenic Microorganisms: State-of-the-Art Research in Spain

Pathogenic microorganisms, including fungi, oomycetes, bacteria, viruses, and viroids, constitute a serious threat to agriculture worldwide [...].

Antagonistic Activity of Volatile Organic Compounds Produced by Acid-Tolerant Pseudomonas protegens CLP-6 as Biological Fumigants To Control Tobacco Bacterial Wilt Caused by Ralstonia solanacearum.

Tobacco bacterial wilt, which is caused by Ralstonia solanacearum, is a devastating soilborne disease of tobacco worldwide and is widespread in the continuously acidic fields of southern China. Here, the fumigation activity under different pH conditions, component identification, and bioactivity of the volatile organic compounds (VOCs) produced by an acid-tolerant strain, Pseudomonas protegens CLP-6, were investigated. There was a wide antimicrobial spectrum of the VOCs against phytopathogens, including four bacteria, eight fungi, and two oomycetes. The antagonistic activity of the VOCs against R. solanacearum was proportionally correlated with the concentration of the inoculum, amount, culture time, and culture pH for CLP-6. The number of gene copies of R. solanacearum was significantly inhibited by VOCs produced at pH 5.5 in vivo. The control effect of VOCs emitted at pH 5.5 was 78.91% for tobacco bacterial wilt, which was >3-fold greater than that at pH 7.0. Finally, the main volatile compounds were identified by solid-phase microextraction (SPME)-gas chromatography-mass spectroscopy (GC-MS) as S-methyl thioacetate, methyl thiocyanate, methyl disulfide, 1-decene, 2-ethylhexanol, 1,4-undecadiene, 1-undecene, 1,3-benzothiazole, and 2,5-dimethylpyrazine, and the inhibition rates of 1,3-benzothiazole, 2-ethylhexanolmethyl thiocyanate, dimethyl disulfide, and S-methyl thioacetate were 100%, 100%, 88.91%, 67.64%, and 53.29%, respectively. S-Methyl thioacetate was detected only at pH 5.5. In summary, VOCs produced by P. protegens CLP-6 had strong antagonistic activities against phytopathogens, especially R. solanacearum, under acidic conditions and could be used to develop a safe and additive fumigant against R. solanacearum on tobacco and even other Solanaceae crop bacterial wilt diseases in acidic fields. IMPORTANCE VOCs produced by beneficial bacteria penetrate the rhizosphere to inhibit the growth of plant-pathogenic microorganisms; thus, they have the potential to be used as biological agents in controlling plant diseases. Tobacco bacterial wilt, which is caused by the acidophilic pathogen R. solanacearum, is a major bacterial disease in southern China and is prevalent in acidic soil. In this study, we discovered that the VOCs produced by P. protegens CLP-6 had excellent inhibitory effects on important plant pathogens. Moreover, two of the VOCs, namely, 1,3-benzothiazole and 2-ethylhexanol, had excellent inhibitory effect on R. solanacearum, and another VOC substance, methyl thiocyanate, was produced only at pH 5.5. The VOCs produced by the acid-tolerant strain P. protegens CLP-6 may have potential as environment-friendly microbial fumigant agents for bacterial wilt of tobacco or even other Solanaceae crops in acidic soils in China.