Biocontrol Ability Research Articles

Isolation and characterization of Bacillus velezensis strain B19 for biocontrol of Panax notoginseng root rot

Medicine plants such as Panax notoginseng (Sanqi) frequently experience replant failure owing to the accumulation of soilborne pathogens and autotoxins in continuous cropping soil. Bacillus sp. is a commonly used biocontrol agent to combat soilborne pathogens, but further research is needed to understand its impact on controlling Sanqi root rot and the underlying mechanisms. Here, we isolated and screened a Bacillus strain, B19, from Sanqi rhizosphere soil that exhibited potential for inhibiting Sanqi root rot pathogens. We then tested the strain's effect on the incidence of Sanqi root rot in continuous cropping soil, along with its motility/chemotaxis and biofilm formation ability (i.e., potential for root colonization). We also analyzed the strain's genomic characteristics, including potential secondary metabolite synthesis gene clusters. Our results showed that the strain B19 exhibited high inhibitory activity against fungal pathogens (F. solani and F. oxysporum) and could metabolize saponins as a sole carbon source. The application of B19 to continuous cropping soil significantly reduced the incidence of root rot in Sanqi seedlings. B19 was identified as B. velezensis through morphological characteristics, 16S rRNA and gyrA gene sequence analysis, and genome-level annotation. Notably, B19′s genome encodes many genes associated with functions such as motility/chemotaxis and biofilm formation, as well as 13 biosynthetic gene clusters that could encode secondary metabolites, including surfactin, fengycin, and siderophore. Additionally, B19 demonstrated the capability to produce volatile organic compounds that inhibit pathogenic fungi. The motility/chemotaxis and biofilm-forming ability of B19 were enhanced by saponins. Collectively, these properties could enhance B19′s biocontrol ability, thereby reducing the incidence of root rot.

The presence of the plant pathogen Fusarium graminearum as a soil inoculum enhances the rhizosphere survival of bacterial biocontrol strains aimed at the pathogen

AbstractThe serious wheat pathogen Fusarium graminearum causes both root rot and head blight. Some classical biocontrol tests were first used to explore the biocontrol ability of 39 Pseudomonas fluorescens strains. The five most antifungal strains B4, P13, UTPf127, UTPf125 and UTPf105 were selected to screen known antifungal antibiotic genes and greenhouse experiments. The ability of bacteria to colonize wheat rhizosphere and their effect on plant growth in the presence and absence of soil F. graminearum inoculum was studied under greenhouse conditions. Overall, biocontrol bacteria populations were significantly higher in both wheat endo‐and ectorhizosphere of pathogen‐inoculated soil than in healthy soil. The population of all strains differently decreased with time. On day 28, endorhizosphere populations of strain B4 could be detected in inoculated but not healthy soil, while UTPf127 populations remained high in endorhizospheres at all tested times. Isolate B4 and UTPf105 showed the most substantial plant growth in pathogen‐inoculated soil compared to pathogen‐inoculated soil without added bacteria. UTPf127‐treated plants grew better in control soil than when the pathogen was present. In contrast, UTPf125 and P13 showed little effect on plant growth. These results point to complex interactions between pathogen and biocontrol bacteria and suggest that a fungal pathogen in the soil can affect the survival of potential bacterial biological control agents. Additionally, they highlight the importance of screening and evaluating potential biocontrol bacteria against soilborne fungal pathogens by in vivo tests rather than relying on plate screenings.

Cold adapted Pseudomonas: ecology to biotechnology.

The cold adapted microorganisms, psychrophiles/psychrotolerants, go through several modifications at cellular and biochemical levels to alleviate the influence of low temperature stress conditions. The low temperature environments depend on these cold adapted microorganisms for various ecological processes. The ability of the microorganisms to function in cold environments depends on the strategies directly associated with cell metabolism, physicochemical constrains, and stress factors. Pseudomonas is one among such group of microorganisms which is predominant in cold environments with a wide range of ecological and biotechnological applications. Bioformulations of Pseudomonas spp., possessing plant growth promotion and biocontrol abilities for application under low temperature environments, are well documented. Further, recent advances in high throughput sequencing provide essential information regarding the prevalence of Pseudomonas in rhizospheres and their role in plant health. Cold adapted species of Pseudomonas are also getting recognition for their potential in biodegradation and bioremediation of environmental contaminants. Production of enzymes and bioactive compounds (primarily as an adaptation mechanism) gives way to their applications in various industries. Exopolysaccharides and various biotechnologically important enzymes, produced by cold adapted species of Pseudomonas, are making their way in food, textiles, and pharmaceuticals. The present review, therefore, aims to summarize the functional versatility of Pseudomonas with particular reference to its peculiarities along with the ecological and biotechnological applications.

Multiple factor analysis of genetic and metabolite profiles as an improved strategy for potential Bacillus biocontrol agent selection to control crown gall and fire blight diseases

We aimed to improve the screening method for the selection of Bacillus biocontrol agents against crown gall and fire blight diseases caused by Agrobacterium tumefaciens and Erwinia amylovora, respectively. The relationship between the strain biocontrol ability and the secondary metabolites biosynthetic gene profile, the production of antibacterial compounds, the thin layer chromatography, and Rep-PCR profiles was investigated. The Bacillus strains showed variability in their antibacterial activity as well as their lipopeptide, polyketide, and bacilysin biosynthetic gene profiles. The thin layer chromatography of the methanolic extracts and the Rep-PCR banding patterns showed relatively low heterogeneity. The study of the relationship between variables was performed using the multiple-factor analysis differentiating strains according to their biocontrol ability. Interestingly, the most efficient biocontrol strains against both phytopathogens could be identified by the use of specific profiles. New screening procedures of Bacillus biocontrol agents against both diseases relying on the use of the antibacterial compound gene profile, the thin layer chromatography profile, or the Rep-PCR profile could be proposed. These markers are specific for Bacillus biocontrol agents, which may prove useful for the isolation and identification of new and effective biocontrol strains.

Biocontrol efficacy of Wickerhamomyces anomalus on tomato field diseases and study of the relevant mechanisms via microbiome analysis

Tomatoes (Solanum lycopersicum L.) are vulnerable to infections by pathogens found in a complex environment. Most of these infections are triggered by an imbalance between plant microorganisms and pathogens, leading to various tomato rots and high economic losses. This study aims to test the biocontrol ability of an antagonistic yeast, Wickerhamomyces anomalus, towards gray mold disease in tomatoes in the field and explore the relevant mechanisms through microbiome analysis of the microbial community on the surface of tomatoes. The results showed that W. anomalus decreased the tomato disease severity index during plant growth period, along with some changes in the microorganism community composition, including the increase of the abundance of some plant growth promotion bacteria such as Pantoea sp. and Pseudomonas sp. and biocontrol agents such as Golubevia sp. and Papiliotrema sp., and abundance decrease in some potential pathogens such as species of Alternaria. All these results suggest that W. anomalus could control tomato diseases in the field and the regulation in microorganism composition might be a possible mechanism.

Characterization of a Novel Bacillus glycinifermentans Strain MGMM1 Based on Full Genome Analysis and Phenotypic Properties for Biotechnological Applications.

Bacillus species have gained much attention based on their phenotypic characteristics and their genetic architecture as biological control agents and plant growth-promotor with bioremediation potential. In this study, we analyzed the whole genome of a novel strain, Bacillus glycinifermentans MGMM1, isolated from the rhizosphere of a weed plant (Senna occidentalis) and assayed its phenotypic characteristics, as well as antifungal and biocontrol ability. The whole genome analysis of MGMM1 identified 4259 putative coding sequences, with an encoding density of 95.75% attributed to biological functions, including genes involved in stimulating plant growth, such as acetolactate synthase, alsS, and genes involved in the resistance to heavy metal antimony (arsB and arsC). AntiSMASH revealed the presence of biosynthetic gene clusters plipastatin, fengycin, laterocidine, geobacillin II, lichenysin, butirosin A and schizokinen. Tests in vitro confirmed that MGMM1 exhibited antifungal activity against Fusarium oxysporum f.sp. radicis-lycopersici (Forl) ZUM2407, Alternaria alternata, F. graminearum and F. spp. and produce protease, lipase amylase and cellulase. Bacillus glycinifermentans MGMM1 demonstrated proteolytic (4.82 ± 1.04 U/mL), amylolytic (0.84 ± 0.05 U/mL) and cellulosic (0.35 ± 0.02 U/mL) enzymatic activities, as well as indole-3-acetic acid production (48.96 ± 1.43 μg/mL). Moreover, the probiotic strain MGMM1 demonstrated a high biocontrol potential of inhibiting (up to 51.45 ± 8.08%) the development of tomato disease caused by Forl ZUM2407. These results suggest that B. glycinifermentans MGMM1 has significant potential as a biocontrol, plant growth-promoting agent in agriculture.

Dual RNA-Seq Profiling Unveils Mycoparasitic Activities of Trichoderma atroviride against Haploid Armillaria ostoyae in Antagonistic Interaction Assays.

Armillaria ostoyae, a species among the destructive forest pathogens from the genus Armillaria, causes root rot disease on woody plants worldwide. Efficient control measures to limit the growth and impact of this severe underground pathogen are under investigation. In a previous study, a new soilborne fungal isolate, Trichoderma atroviride SZMC 24276 (TA), exhibited high antagonistic efficacy, which suggested that it could be utilized as a biocontrol agent. The dual culture assay results indicated that the haploid A. ostoyae-derivative SZMC 23085 (AO) (C18/9) is highly susceptible to the mycelial invasion of TA. In the present study, we analyzed the transcriptome of AO and that of TA in in vitro dual culture assays to test the molecular arsenal of Trichoderma antagonism and the defense mechanisms of Armillaria. We conducted time-course analysis and functional annotation and analyzed enriched pathways and differentially expressed genes including biocontrol-related candidate genes from TA and defense-related candidate genes from AO. The results indicated that TA deployed several biocontrol mechanisms when confronted with AO. In response, AO initiated multiple defense mechanisms to protect against the fungal attack. To our knowledge, the present study offers the first transcriptome analysis of a biocontrol fungus attacking AO. Overall, this study provides insights that aid the further exploration of plant pathogen-biocontrol agent interaction mechanisms. IMPORTANCE Armillaria species can survive for decades in the soil on dead woody debris, develop rapidly under favorable conditions, and harmfully infect newly planted forests. Our previous study found Trichoderma atroviride to be highly effective in controlling Armillaria growth; therefore, our current work explored the molecular mechanisms that might play a key role in Trichoderma-Armillaria interactions. Direct confrontation assays combined with time course-based dual transcriptome analysis provided a reliable system for uncovering the interactive molecular dynamics between the fungal plant pathogen and its mycoparasitic partner. Furthermore, using a haploid Armillaria isolate allowed us to survey the deadly prey-invading activities of the mycoparasite and the ultimate defensive strategies of its prey. Our current study provides detailed insights into the essential genes and mechanisms involved in Armillaria defense against Trichoderma and the genes potentially involved in the efficiency of Trichoderma to control Armillaria. In addition, using a sensitive haploid Armillaria strain (C18/9), with its complete genome data already available, also offers the opportunity to test possible variable molecular responses of Armillaria ostoyae toward diverse Trichoderma isolates with various biocontrol abilities. Initial molecular tests of the dual interactions may soon help to develop a targeted biocontrol intervention with mycoparasites against plant pathogens.

Biocontrol activity of endophytic bacteria from cocoa against Phytophthora sp. and Colletotrichum sp.

Cocoa (Theobroma cacao L.) and chili pepper (Capsicum annuum L.) are commonly cultivated by farmers, and in some cases, both crops are grown together in intercropping systems. The main pathogen infected cocoa is the Phytophthora sp. fungus, which causes fruit rot, stem cancer, and leaf blight, while Colletotrichum sp. causes anthracnose in chili pepper plants. The ability of endophytic bacteria to inhibit the growth of fungi and bacterial pathogens is well known. In this study, the biocontrol ability of endophytic bacteria against fungal pathogens was tested, and a biocontrol preliminary test was also observed by examining their potential inhibition on Chromobacterium violaceum called antiquorum sensing test. Endophytic bacteria were isolated from cocoa plants, while Phytophthora and Colletotrichum were isolated from cocoa and chili pepper plants that showed symptoms of fruit rot and anthracnose. A total of 34 endophytic bacterial isolates were successfully obtained, with 10 isolates from leaves (DK), 12 isolates from branches (RK), and 12 isolates from roots (KA) of cocoa plant ICCRI 4. Sixteen isolates showed quorum sensing ability, which AHL degradation index ranging from 0.44 – 1.56. Antagonistic tests showed that 11 out of 16 isolates had strong antibiosis against Phytophthora sp., with inhibition zones ranging from 0.6-1.35 cm. Meanwhile, 10 out of 16 isolates had strong antibiotics against Colletotrichum sp., with clear zones ranging from 0.6 – 1.1 cm. The three best endophytic bacterial isolates that had a combination of antiquorum sensing ability on C. violaceum and biocontrol against Phytophthora sp. and Colletotrichum sp. were RK 11, KA 1, and KA 8. [Keywords: antagonist, ahl lactonase, plant beneficial microorganism]

AlgU controls environmental stress adaptation, biofilm formation, motility, pyochelin synthesis and antagonism potential in Pseudomonas protegens SN15-2

Pseudomonas protegens is a typical plant-growth-promoting rhizobacterium that can serve as an agricultural biocontrol agent. The extracytoplasmic function (ECF) sigma factor AlgU is a global transcription regulator controlling stress adaption and virulence in Pseudomonas aeruginosa and Pseudomonas syringae. Meanwhile, the regulatory role of AlgU in the biocontrol ability of P.protegens has been poorly studied. In this study, deletion mutations of algU and its antagonist coding gene mucA were constructed to investigate the function of AlgU in P.protegens SN15–2 via phenotypic experiment and transcriptome sequencing analysis. On the basis of phenotypic analyses, it was concluded that the AlgU whose transcription was induced by osmotic stress and oxidative stress positively regulated biofilm formation and tolerance towards osmotic, heat, and oxidation stresses, while it negatively regulated motility, pyochelin synthesis, and the ability to inhibit pathogens. On the basis of the RNA-seq analysis, compared to the wild-type strain, 12 genes were significantly upregulated and 77 genes were significantly downregulated in ΔalgU, while 407 genes were significantly upregulated and 279 genes were significantly downregulated in ΔmucA, indicating the involvement of AlgU in several cellular processes, mainly related to resistance, carbohydrate metabolism, membrane formation, alginate production, the type VI secretion system, flagella motility and pyochelin production. Our findings provide insights into the important role of AlgU of P.protegens in biocontrol, which is of value in improving the biocontrol ability of P.protegens.

Metabolomic profiling and its association with the bio-efficacy of Aspergillus niger strain against Fusarium wilt of guava.

Bio-control agents are the best alternative to chemicals for the successful management of plant diseases. The fungus Aspergillus niger is known to produce diverse metabolites with antifungal activity, attracting researchers to exploit it as a bio-control agent for plant disease control. In the present study, 11 A. niger strains were isolated and screened for their antagonism against the guava wilt pathogen under in vitro and in planta conditions. Strains were identified morphologically and molecularly by sequencing the internal transcribed spacer (ITS), β-tubulin, and calmodulin genes. The strains were evaluated through dual culture, volatile, and non-volatile methods under an in vitro study. AN-11, AN-6, and AN-2 inhibited the test pathogen Fusarium oxysporum f. sp. psidii (FOP) at 67.16%, 64.01%, and 60.48%, respectively. An in planta study was conducted under greenhouse conditions with 6 months old air-layered guava plants (var. Allahabad Safeda) by pre- and post-inoculation of FOP. The AN-11 strain was found to be effective under both pre- and post-inoculation trials. Furthermore, gas chromatography-mass spectrometry (GC-MS) analysis was carried out to characterize the volatile compounds of the most potential strain, A. niger. The hexane soluble fraction showed the appearance of characteristic peaks of hexadecenoic acid methyl ester (4.41%), 10-octadecanoic acid methyl ester (3.79%), dodecane (3.21%), undecane (3.19%), gibepyrone A (0.15%), 3-methylundecane (0.36%), and citroflex A (0.38%). The ethyl acetate fraction of the bio-control fungi revealed the occurrence of major antifungal compounds, such as acetic acid ethyl ester (17.32%), benzopyron-4-ol (12.17%), 1,2,6-hexanetriol (7.16%), 2-propenoic acid ethanediyl ester (2.95%), 1-(3-ethyloxiranyl)-ethenone (0.98%), 6-acetyl-8-methoxy dimethyl chromene (0.96%), 4-hexyl-2,5-dihydro dioxo furan acetic acid (0.19%), and octadecanoic acid (1.11%). Furthermore, bio-control abilities could be due to hyper-parasitism, the production of secondary metabolites, and competition for sites and nutrients. Indeed, the results will enrich the existing knowledge of metabolomic information and support perspectives on the bio-control mechanism of A. niger.

β-Glucan Enhances the Biocontrol Efficacy of Marine Yeast Scheffersomyeces spartinae W9 against Botrytis cinerea in Strawberries.

The marine yeast Scheffersomyeces spartinae W9 is a promising biocontrol agent for gray mold caused by Botrytis cinerea in strawberries. Improving the biocontrol efficacy of S. spartinae W9 is necessary for its commercial application. In this study, different concentrations of β-glucan were added to the culture medium to evaluate its effect on the biocontrol efficacy of S. spartinae W9. The results showed that 0.1% β-glucan could increase the biocontrol effect of S. spartinae W9 against B. cinerea in strawberries and in vitro. We found that adding 0.1% β-glucan to the culture medium promoted the growth of S. spartinae W9 in wounds of strawberries, enhanced biofilm formation ability, and secreted more β-1,3-glucanase. In addition, 0.1% β-glucan increased the survival rate of S. spartinae W9 under oxidative, thermal, osmotic, and plasma membrane stressors. Transcriptome analysis revealed 188 differential expressed genes in S. spartinae W9 cultured with or without 0.1% β-glucan, including 120 upregulated and 68 downregulated genes. The upregulated genes were associated with stress response, cell wall formation, energy production, growth, and reproduction. Thus, culturing with 0.1% β-glucan is an effective way to improve the biocontrol ability of S. spartinae W9 against gray mold in strawberries.

Strain improvement of Trichoderma harzianum for enhanced biocontrol capacity: Strategies and prospects.

In the control of plant diseases, biocontrol has the advantages of being efficient and safe for human health and the environment. The filamentous fungus Trichoderma harzianum and its closely related species can inhibit the growth of many phytopathogenic fungi, and have been developed as commercial biocontrol agents for decades. In this review, we summarize studies on T. harzianum species complex from the perspective of strain improvement. To elevate the biocontrol ability, the production of extracellular proteins and compounds with antimicrobial or plant immunity-eliciting activities need to be enhanced. In addition, resistance to various environmental stressors should be strengthened. Engineering the gene regulatory system has the potential to modulate a variety of biological processes related to biocontrol. With the rapidly developing technologies for fungal genetic engineering, T. harzianum strains with increased biocontrol activities are expected to be constructed to promote the sustainable development of agriculture.

Biocontrol ability and action mechanism of Bacillus amyloliquefaciens Baf1 against Fusarium incarnatum causing fruit rot in postharvest muskmelon (cv. Yugu) fruit

Muskmelon (Cucumis melo L. cv. Yugu) is favoured by consumers for its high quality, attractive appearance, and good palatability. However, fruit rot is a prominent threat during postharvest storage, resulting in potentially substantial serious losses. In this study, we investigated the biocontrol efficacy of Bacillus amyloliquefaciens Baf1 against fruit rot caused by Fusarium incarnatum in post-harvest Yugu muskmelon, and examined the underlying antagonistic mechanisms. Baf1 had more than 75% control effect on F. incarnatum in vitro and in vivo. In addition, Baf1 treatment effectively improved the fruit defense enzyme activities (PAL, POD, and PPO) and maintained the quality (weight loss, respiration rate, ascorbic acid and total soluble solid) of muskmelon during storage. A 5 mL/L lipopeptide extracted from Baf1 inhibited the hypha growth and conidia germination and production of F. incarnatum by 55%, 63.2%, and 65%, respectively, and caused hyphal malformation. The active antifungal substances of Baf1 were preliminarily identified as C13–C15 surfactins and C17 bacillomycin L based on matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Thus, the biocontrol agent Baf1 showed great potential for inhibiting postharvest grey mould in muskmelons and could be a useful approach for enhancing the quality and storability of muskmelons.

Antifungal Activity and Alleviation of Salt Stress by Volatile Organic Compounds of Native Pseudomonas Obtained from Mentha piperita.

As salt stress has a negative impact on plant growth and crop yield, it is very important to identify and develop any available biotechnology which can improve the salt tolerance of plants. Inoculation with plant-growth-promoting rhizobacteria (PGPR) is a proven environmentally friendly biotechnological resource for increasing the salt stress tolerance of plants and has a potential in-field application. In addition, bacterial volatile organic compounds (mVOCs) are signal molecules that may have beneficial roles in the soil-plant-microbiome ecosystem. We investigated the effects of mVOCs emitted by Pseudomona putida SJ46 and SJ04 on Mentha piperita grown under different levels of NaCl stress by evaluating their growth-promoting potential and capacity to increase salt tolerance effects. Furthermore, we evaluated under control and salt stress conditions the biocontrol ability of VOCs emitted by both these strains to inhibit the growth of Alternaria alternata and Sclerotium rolfsii. The VOCs emitted by both strains under control conditions did not lead to an significant improvement in peppermint growth. However, under salt stress conditions (75 or 100 mM NaCl), an amelioration of its physiological status was observed, with this effect being greater at 100 mM NaCl. This led to an enhancement of the number of leaves and nodes and, increased the shoot fresh and root dry weight by approximately twice in relation to control stressed plants. Moreover, the VOCs released by the two bacteria grown in control or saline media showed a significant reduction in the mycelial growth of A. alternata. In contrast, S. rolfsii growth was reduced 40% by the mVOCs released only under control conditions, with no effects being observed under salt stress. We also explored the composition of the bacterial volatile profiles by means of a solid-phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS) analysis. From the headspace of SJ46, three VOCs were identified: n-octanol, decane and tetradecane. The emission of SJ04 had the same chromatographic profile, with the addition of two more compounds: 1-(N-phenyl carbamyl)-2-morpholino cyclohexene and tridecane. Only compounds that were not present in the headspace of the control groups were recorded. The salt stress conditions where the bacteria were grown did not qualitatively modify the mVOC emissions. Taken together, our results suggest that plant-associated rhizobacterial VOCs play a potentially important role in modulating plant salt tolerance and reducing fungal growth. Thus, biological resources represent novel tools for counteracting the deleterious effects of salt stress and have the potential to be exploited in sustainable agriculture. Nevertheless, future studies are necessary to investigate technological improvements for bacterial VOC application under greenhouse and open field conditions.

Exposure to flupyradifurone affect health of biocontrol parasitoid Binodoxys communis (Hymenoptera: Braconidae) via disrupting detoxification metabolism and lipid synthesis

Assessing the potential effects of insecticides on beneficial biological control agents is key to facilitating the success of integrated pest management (IPM) approaches. Flupyradifurone (FPF) is a novel neonicotinoid insecticide that is replacing traditional neonicotinoids over a large geographical range to control pests. Binodoxys communis, is the dominant parasitic natural enemy of aphids. To date, no reports have addressed sublethal effects of FPF on B. communis. In this study, the lethal and sublethal effects of FPF on B. communis were investigated by indirect exposure to larvae and direct exposure to adults. Results showed that the sublethal LC10 and LC25 of FPF had negative effects on the biological parameters of B. communis, including significantly reducing survival rate, adult longevity, parasitism rate, and emergence rate, and significantly prolonging the developmental stages from egg to cocoons. In addition, we observed a transgenerational effect of FPF on the next generation (F1). RNA-Seq transcriptomic analysis identified a total of 1429 differentially expressed genes (DEGs) that were significantly changed between FPF-treated and control groups. These DEGs are mainly enriched in metabolic pathways such as peroxisomes, glutamate metabolism, carbon metabolism, fatty acid metabolism, and amino acid metabolism. This report is the first comprehensive evaluation of how FPF effects B. communis, which adds to the methods of assessing pesticide exposure in parasitic natural enemies. We speculate that the significant changes in pathways, especially those related to lipid synthesis, may be the reason for weakened parasitoid biocontrol ability. The present study provides new evidence for the toxic effects and environmental residue risk of FPF.

A novel protein elicitor (PeSy1) from Saccharothrix yanglingensis induces plant resistance and interacts with areceptor-like cytoplasmic kinase in Nicotiana benthamiana.

Previously, we reported a rare actinomycete Saccharothrix yanglingensis Hhs.015 with strong biocontrol ability, which can colonize plant tissues and induce resistance, but the key elicitor and immune mechanisms were unclear. In this study, a novel protein elicitor screened from the genome of Hhs.015, PeSy1 (protein elicitor of S.yanglingensis 1), could induce a strong hypersensitive response (HR) and resistance in plants. The PeSy1 geneencodes an 11 kDa protein with 109 amino acids that is conserved in Saccharothrix species. PeSy1-His recombinant protein induced early defence events such as acellular reactive oxygen species burst, callose deposition, and the activation of defence hormone signalling pathways, which enhanced Nicotiana benthamiana resistance to Sclerotinia sclerotiorum and Phytophthora capsici,and Solanum lycopersicum resistance to Pseudomonas syringae pv. tomato DC3000. Through pull-down and mass spectrometry, candidate proteinsthat interacted with PeSy1 were obtainedfrom N.benthamiana. We confirmed theinteraction between receptor-like cytoplasmic kinase RSy1 (Response to PeSy1) and PeSy1 using co-immunoprecipitation, bimolecular fluorescence complementation, and microscale thermophoresis. PeSy1 treatment promoted up-regulation of marker genes in pattern-triggered immunity. The cell death it elicited was dependent on the co-receptors NbBAK1 and NbSOBIR1, suggesting that PeSy1 acts as a microbe-associated molecular pattern from Hhs.015. Additionally, RSy1 positively regulated PeSy1-induced plants resistant to S.sclerotiorum. In conclusion, our results demonstrated a novel receptor-like cytoplasmic kinase in the plant perception of microbe-associated molecular patterns, and the potential of PeSy1 in induced resistance provided a new strategy for biological control of actinomycetes in agricultural diseases.

Biological control efficacy of Bacillus licheniformis HG03 against soft rot disease of postharvest peach

This study aimed to investigate the biocontrol ability of Bacillus licheniformis HG03 against Rhizopus stolonifer causing agent of peach fruit rot and explore its mechanism. The biocontrol strain B. licheniformis HG03 was applied on inhibition of the pathogen Rhizopus stolonifer, which is expected to improve the preservation of peach fruit. The results revealed that the peach treated with B. licheniformis HG03 were significantly more resistant to postharvest soft rot when stored at 20 °C and high humidity. Comparison to the control, treatment with HG03 improved the activity of related enzymes and balanced the metabolism of reactive oxygen species. Such treatment reduced the accumulation of lipid peroxidation products and enhanced free radical scavenging ability of peaches. Furthermore, the transcriptome analysis revealed that the HG03 treatment activated MAPK signaling pathway, induced the expression of antioxidant activity-related genes and different WRKY transcription factors in plant pathogen interaction metabolic pathway. Hence, the results revealed that HG03 treatment is an effective biological control method to improve peach fruit disease resistance and prolong the storage time of peaches.

Tree pathogens Armillaria solidipes influence the biocontrol activity of Bacillus velezensis BY6

This is the first-time work to integrate transcriptome and metabolome sequencing data, providing a comprehensive knowledge of how the pathogen Armillaria solidipes affects the spore development, biofilm creation, and antifungal activity of Bacillus velezensis BY6. The dynamic growth of BY6 indicated that A. solidipes had a significant growth-inhibiting effect on BY6. Using scanning electron microscopy (SEM), it was discovered that the cell wall and cell membrane was compromised, resulting in the leakage of intracellular components. On the basis of gene and metabolite network analysis, several genes and metabolites are predominantly involved in the “ Phosphotransferase system (PTS)”, “Two-component system”, and “Ubiquinone and other terpenoid-quinone biosynthesis” pathway. The mechanism by which A. solidipes inhibits the biological control ability of BY6 is influenced by numerous factors, including cell membrane damage (Folding, disintegration, disappearance), nutrient limitation (Pyruvic acid, Menadione concentration down-regulated), and spore and biofilm formation inhibition (Spo0 A, Spo0 B and Kin B ∼ D genes down-regulated). We conclude that interference of A. solidipes with the growth and development of BY6 results in a decrease in BY6 biocontrol levels. This result contributes to a complete and thorough understanding of the mechanism by which A. solidipes inhibits BY6′s biocontrol ability and identifies additional potential molecular targets. To further genetically modify the BY6 strains for tackle the problem of drug resistance.

Testing the Biocontrol Ability of a Trichoderma-Streptomycetes Consortium against Pyrrhoderma noxium (Corner) L.W. Zhou and Y.C. Dai in Soil.

The Brown root rot pathogen Pyrrhoderma noxium (Corner) L.W. Zhou and Y.C. Dai is known to infect a large number of culturally and economically important plant species across the world. Although chemical control measures have been effective in managing this pathogen, their adverse effects on the ecosystem have limited their use. The use of biological control agents (BCAs) thus is generally accepted as an environmentally friendly way of managing various pathogens. Testing various consortia of the BCAs with different antagonistic mechanisms may even provide better disease protection than the use of a single BCA against aggressive plant pathogens such as the P. noxium. In the presented study, the wood decay experiment and the pot trial confirmed that the consortium of Trichoderma strains (#5029 and 5001) and streptomycetes (#USC-6914 and #USC-595-B) used was effective in protecting wood decay and plant disease caused by P. noxium. Among the treatments, complete elimination of the pathogen was observed when the BCAs were applied as a consortium. In addition, the BCAs used in this study promoted the plant growth. Therefore, Trichoderma and streptomycetes consortium could be used as a potential biocontrol measure to manage P. noxium infections in the field over the application of hazardous chemical control measures.

Persistence as a Constituent of a Biocontrol Mechanism (Competition for Nutrients and Niches) in Pseudomonas putida PCL1760.

Competition for nutrients and niches (CNN) is known to be one of the mechanisms for biocontrol mostly exhibited by Pseudomonas strains. Phenotypic and full genome analysis revealed Pseudomonas putida PCL1760 controlling tomato foot and root rot (TFRR) solely through CNN mechanism. Although the availability of nutrients and motility are the known conditions for CNN, persistence of bacteria through dormancy by ribosomal hibernation is a key phenomenon to evade both biotic and abiotic stress. To confirm this hypothesis, rsfS gene knockout mutant of PCL1760 (SB9) was first obtained through genetic constructions and compared with the wild type PCL1760. Primarily, relative expression of rsfS in PCL1760 was conducted on tomato seedlings which showed a higher expression at the apical part (1.02 ± 0.18) of the plant roots than the basal (0.41 ± 0.13). The growth curve and persistence in ceftriaxone after the induction of starvation with rifampicin were performed on both strains. Colonization on the tomato root by CFU and qPCR, including biocontrol ability against Fusarium, was also tested. The growth dynamics of both PCL1760 and SB9 in basal and rich medium statistically did not differ (p ≤ 0.05). There was a significant difference observed in persistence showing PCL1760 to be more persistent than its mutant SB9, while SB9 (pJeM2:rsfS) was 221.07 folds more than PCL1760. In colonization and biocontrol ability tests, PCL1760 was dominant over SB9 colonizing and controlling TFRR (in total, 3.044 × 104 to 6.95 × 103 fg/µL and 55.28% to 30.24%, respectively). The deletion of the rsfS gene in PCL1760 reduced the persistence and effectiveness of the strain, suggesting persistence as one important characteristic of the CNN.