Biocontrol Strain Research Articles

Optimization of Fermentation and Biocontrol Efficacy of Bacillus atrophaeus XHG-1-3m2

Biological control plays an increasingly important role in various aspects of modern agriculture and forestry. Identifying biocontrol strains with commercial potential for effective disease management is currently a focal point in biological control research. In this study, Bacillus atrophaeus XHG-1-3m2, a strain with significant biocontrol potential against Wilsonomyces carpophilus causing shot hole disease in wild apricots, was developed. The study determined the antibacterial activity of the fermentation broth, the optimal fermentation medium composition and conditions, and explored its effectiveness in controlling Wilsonomyces carpophilus. The optimal fermentation medium for strain XHG-1-3m2 comprises 12.5 g/L yeast extract, 12.5 g/L soy peptone, 10.0 g/L sodium chloride, 1 g/L ammonium chloride, 1 g/L potassium dihydrogen phosphate, 1 g/L disodium hydrogen phosphate, and 0.5 g/L magnesium sulfate heptahydrate. With an initial pH of 7.0, a liquid volume of 40%, an inoculum volume of 3%, and shaking incubation at 28 °C for 24 h, the viable cell count reached 14 × 109 CFU/mL. In vitro and in vivo tests on leaves revealed that the fermentation broth and the biocontrol biofertilizer derived from this strain inhibited the leaf lesions caused by Wilsonomyces carpophilus on wild apricots, achieving inhibition rates of 94.62% and 82.46%, respectively.

Mitigating root rot in Panax notoginseng: The synergistic effects of biochar and Chaetomium globosum YIM PH30719

Root rot is the main soilborne disease that causes the replant failure of Panax notoginseng, a famous medicinal plant in Asia. Biochar and biocontrol agents have been shown to reduce replant failure separately; however, a knowledge gap still exists regarding the effectiveness and mechanisms of their combined application on the root rot incidence of P. notoginseng. In this study, we conducted a pot experiment using a randomized block design, biochar derived from tobacco stems was applied at 0, 1, 2, and 3 % (T0, T1, T2, T3) to the soil that cultivating P. notoginseng for 10 years continuously; moreover, Chaetomium globosum YIM PH30719, a newly screened biocontrol strain, was applied at 0, 1.0×107, and 1.0×1010 cfu·mL−1 (C0, C1, C2) to the soil. Six months post-transplantation of P. notoginseng seedlings, root rot incidence, soil physicochemical properties, fungal communities, and abundance of the primary pathogen Fusarium oxysporum were investigated. The results showed that, comparing with the single application of YIM PH30719, the combined application with biochar was more efficient in reducing the root rot incidence (P<0.05). P. notoginseng experienced a root rot incidence of 65.4 % under the T0+C0 treatment, however, under T3+C2 treatment, the root rot incidence was only 5.6 % (P<0.05). The reduction in root rot incidence might be linked to changes in soil pH, organic matter, and essential nutrient contents, as well as the increased soil fungal diversity and the relative abundance (RA) of beneficial Chaetomium and Trichoderma, and the decreased RA of pathogenic Fusarium and Alternaria. Consequently, the joint use of biochar and biocontrol agents (YIM PH30719) synergistically decreased the occurrence of root rot by modifying soil physicochemical characteristics and fungal communities. Since root rot is commonly found in agriculture, the results of this study may help in controlling root rot disease in other crops.

Employing Bacillus and Pseudomonas for phytonematode management in agricultural crops.

Phytonematodes are responsible for causing significant harm and reducing yields in various agricultural crops. To minimize losses caused by phytonematodes and meet the high demand for agricultural production, it is important to develop effective strategies with minimal environmental impact to manage this biotic stress. Due to the adverse environmental effects associated with synthetic pesticides, it is imperative to use beneficial bacteria, such as Bacillus and Pseudomonas spp., for biocontrol purposes to control phytonematode infestation in agricultural settings. This approach has gained considerable attraction, as there is a promising market for eco-friendly biopesticides based on bacteria that can effectively manage phytonematodes. Furthermore, biocontrol strains of Bacillus and Pseudomonas have the potential to enhance crop productivity by producing various substances that promote plant growth and development. This review aims to explore the role of Bacillus and Pseudomonas spp. in phytonematode management, elucidate different mechanisms by which these bacteria suppress nematode populations, and discuss the future prospects of utilizing these bacteria in agriculture.

NaCl inhibits Geotrichum citri-aurantii growth by inducing lipid droplets accumulation and enhances the biocontrol efficacy of Kloeckera apiculata 34-9

Decays resulting from infections by Geotrichum citri-aurantii cause a significant reduction in citrus postharvest quality and marketable yield. In the present work, 0.8 mol · L-1 NaCl of Generally Recognized as Safe (GRAS) salts were identified to have complete inhibition activity to G. citri-aurantii in vitro and in vivo. An inhibitory mechanism study showed that 0.1 mol · L-1 NaCl changed the expression of six genes (Gci002087, Gci003354, Gci000013, Gci000394, Gci003505 and Gci004433) in target of rapamycin (TOR) pathway, thus inducing a large number of lipid droplets (LDs) accumulation with TEM observations and staining. In vivo, 0.1 mol · L-1 NaCl could raise up the activities of CAT, PAL, PPO and cellulase which hence to strengthen the ability of resistance tolerance of citrus. In addition, NaCl not only accelerated the growth of the biocontrol yeast Kloeckera apiculata strain 34-9, but also increased the expression level of adhesin-encoding genes and biofilm-formation encoding gene (34-9 - 3691). Finally, the storage experiments in 3 months demonstrated that the combination of NaCl and the yeast 34-9 could keep fresh, reduce decay and prolong its shelf-life, thus implying that the combination of biocontrol strain and GRAS salts has been explored as a promising alternative to synthetic fungicides.

Effect of pH on the growth and competition of Trichoderma spp. and Fusarium spp.

Collar rot caused by Fusarium spp. is a serious threat to the production of Passiflora edulis. However, biocontrol methods are lacking. Trichoderma spp., as the most widely applied biocontrol fungus, can be effective in managing crop diseases. The effectiveness is significantly influenced by environmental factors, such as soil pH. To screen potential biocontrol strains against collar rot of P. edulis, and to explore the effect of pH on the inhibition rate of Trichoderma spp., we selected four Trichoderma species and four Fusarium species isolated from P. edulis planting area in Xishuangbanna. The growth dynamics of different strains under different pH conditions were determined using the mycelial growth rate method. The effect of pH on the growth inhibition of Fusarium spp. by Trichoderma spp. was investigated using the plate confrontation assay. The results showed that the optimal growth pH range was 4-6 for Trichoderma spp. and 7-9 for Fusarium spp. All four Trichoderma strains exhibited significant inhibitory effects on the growth of the four Fusarium strains. T. harzianum showed the most notable inhibition, reaching up to a 72% inhibitory rate. Moreover, pH significantly influenced the inhibitory effect of Trichoderma spp., with variations observed depending on the specific species of Trichoderma spp. and Fusarium spp. Therefore, it is essential to consider the environmental pH impact on the efficacy of biocontrol agents when applying biological control measures in the field, tailored to the specific pathogen and biocontrol agent involved.

Antifungal metabolites of biocontrol stain LB-1 and their inhibition mechanism against Botrytis cinerea.

Chaetomium subaffine LB-1 is a novel biocontrol strain that produces non-volatile metabolites that inhibit the growth of Botrytis cinerea. However, the specific metabolites and antimicrobial mechanism of the strain LB-1 remains unclear. In this study, the antifungal substances produced by strain LB-1, as well as the underlying mechanism of its inhibitory effect against B. cinerea, were explored using metabolomic and transcriptomic analysis. The results found that 45 metabolites might be the key antifungal substances, such as ouabain, ferulic acid, chlorogenic acid, spermidine, stachydrine, and stearic acid. The transcriptomic analysis indicated that the inhibition effect of LB-1 on B. cinerea resulted in the upregulation of genes related to adenosine triphosphate (ATP)-binding cassette (ABC) transporters, peroxisome, ER stress, and multiple metabolic pathways, and in downregulation of many genes associated with the synthesis of cell walls/membranes, carbohydrate metabolism, cell cycle, meiosis, and DNA replication. These results suggested that the inhibitory effect of strain LB-1 against B. cinerea might be due to the destroyed cell wall and membrane integrity exerted by antimicrobial substances, which affect cell metabolism and inhibit cell proliferation.

Reappraisal of Didymella macrostoma causing white tip disease of Canada thistle as a new species, Didymella baileyae, sp. nov., and bioactivity of its major metabolites

ABSTRACT Bioherbicides are expected to be a supplement to integrated pest management, assisting in the control of problematic weed species. For instance, bioherbicides (Phoma and BioPhoma) were recently registered in Canada and the USA for the control of some perennial dicotyledonous weeds in lawns. These products are based on strains of the fungus Didymella macrostoma (syn. Phoma macrostoma) that causes white tip disease (WTD) in Canada thistle (Cirsium arvense). In this study, WTD was reported for the first time in the Russian Federation. Analysis of the internal transcribed spacer (ITS) region of nuc rDNA and secondary metabolite profiling confirmed the identity of Russian WTD isolates to Canadian biocontrol strains identified as D. macrostoma. Multilocus phylogenetic analysis based on sequencing of the ITS region, partial large subunit nuc rDNA region (28S), RNA polymerase II second largest subunit gene (rpb2), and partial β-tubulin gene (tub2) has differentiated the WTD isolates from C. arvense and D. macrostoma isolates from other plant hosts. Based on phylogenetic, morphological, and chemotaxonomic features, these WTD isolates were described as a new species named Didymella baileyae, sp. nov. This study also demonstrated the low pathogenicity of the ex-type D. baileyae isolate VIZR 1.53 to C. arvense seedlings and its asymptomatic development in the leaves of aboveground shoots. The organic extracts from mycelium and culture filtrate of D. baileyae, as well as macrocidin A and macrocidin Z, displayed phytotoxicity both to C. arvense leaves and seedlings. Macrocidin A was only detected in the naturally infected leaf tissues of C. arvense showing WTD symptoms. Macrocidins A and Z demonstrated low antimicrobial and cytotoxic activities, exhibiting no entomotoxic properties. The data obtained within this study on the pathogenicity and metabolites of D. baileyae may be important for the rational evaluation of its prospects as a biocontrol agent.

Comparative Genomic and Functional Analysis of c-di-GMP Metabolism and Regulatory Proteins in Bacillus velezensis LQ-3.

Bacillus velezensis is a promising candidate for biocontrol applications. A common second messenger molecule, bis-(3,5)-cyclic-dimeric-guanosine monophosphate (c-di-GMP), has the ability to regulate a range of physiological functions that impact the effectiveness of biocontrol. However, the status of the c-di-GMP signaling pathway in biocontrol strain LQ-3 remains unknown. Strain LQ-3, which was isolated from wheat rhizosphere soil, has shown effective control of wheat sharp eyespot and has been identified as B. velezensis through whole-genome sequencing analyses. In this study, we investigated the intracellular c-di-GMP signaling pathway of LQ-3 and further performed a comparative genomic analysis of LQ-3 and 29 other B. velezensis strains. The results revealed the presence of four proteins containing the GGDEF domain, which is the conserved domain for c-di-GMP synthesis enzymes. Additionally, two proteins were identified with the EAL domain, which represents the conserved domain for c-di-GMP degradation enzymes. Furthermore, one protein was found to possess a PilZ domain, indicative of the conserved domain for c-di-GMP receptors in LQ-3. These proteins are called DgcK, DgcP, YybT, YdaK, PdeH, YkuI, and DgrA, respectively; they are distributed in a similar manner across the strains and belong to the signal transduction family. We selected five genes from the aforementioned seven genes for further study, excluding YybT and DgrA. They all play a role in regulating the motility, biofilm formation, and colonization of LQ-3. This study reveals the c-di-GMP signaling pathway associated with biocontrol features in B. velezensis LQ-3, providing guidance for the prevention and control of wheat sharp eyespot by LQ-3.

Pseudomonas thivervalensis K321, a promising and effective biocontrol agent for managing apple Valsa canker triggered by Valsa mali

Plant growth-promoting rhizobacteria (PGPR) have been reported to suppress various diseases as potential bioagents. It can inhibit disease occurrence through various means such as directly killing pathogens and inducing systemic plant resistance. In this study, a bacterium isolated from soil showed significant inhibition of Valsa mali. Morphological observations and phylogenetic analysis identified the strain as Pseudomonas thivervalensis, named K321. Plate confrontation assays demonstrated that K321 treatment severely damaged V. mali growth, with scanning electron microscopy (SEM) observations showing severe distortion of hyphae due to K321 treatment. In vitro twigs inoculation experiments indicated that K321 had good preventive and therapeutic effects against apple Valsa canker (AVC). Applying K321 on apples significantly enhanced the apple inducing systemic resistance (ISR), including induced expression of apple ISR-related genes and increased ISR-related enzyme activity. Additionally, applying K321 on apples can activate apple MAPK by enhancing the phosphorylation of MPK3 and MPK6. In addition, K321 can promote plant growth by solubilizing phosphate, producing siderophores, and producing 3-indole-acetic acid (IAA). Application of 0.2% K321 increased tomato plant height by 53.71%, while 0.1% K321 increased tomato fresh weight by 59.55%. Transcriptome analysis revealed that K321 can inhibit the growth of V. mali by disrupting the integrity of its cell membrane through inhibiting the metabolism of essential membrane components (fatty acids) and disrupting carbohydrate metabolism. In addition, transcriptome analysis also showed that K321 can enhance plant resistance to AVC by inducing ISR-related hormones and MAPK signaling, and application of K321 significantly induced the transcription of plant growth-related genes. In summary, an excellent biocontrol strain has been discovered that can prevent AVC by inducing apple ISR and directly killing V. mali. This study indicated the great potential of P. thivervalensis K321 for use as a biological agent for the control of AVC.

Persistence and Microbiome Modification in Rhizoctonia solani-Inoculated Rhizosphere Following Amendment with a Bacillus Biocontrol Agent

Bacterial biocontrol agents that antagonize soilborne pathogens are increasingly considered alternatives to chemical pesticides, but their in vivo efficacy is often inconsistent, restricting commercial use. The efficacy of a biocontrol agent can depend on rhizosphere competence and its interaction with native microbiomes, which can affect ecosystem functioning. This study investigated the capacity of a Bacillus cereus sensu lato biocontrol strain (S-25) to persist on roots and in the rhizosphere of cucumber and evaluated its impact on bacterial and fungal community composition in the rhizosphere in the absence and presence of Rhizoctonia solani, the causative agent of damping-off disease in young seedlings. Following amendment, S-25 abundance in the cucumber rhizosphere decreased by two orders of magnitude but remained relatively high for the duration of the experiment, in contrast to the root surface, where it was not detected. Amendment with S-25 significantly reduced the incidence of disease caused by R. solani without reducing the relative abundance of the fungal pathogen. Interestingly, R. solani did not substantially alter the rhizosphere microbial community, whereas S-25 reduced bacterial diversity and facilitated a shift in community composition, with increased relative abundance of Acidobacteriota and Actinomycetota, and reduced abundance of Pseudomonadota, Bacteroidota, and Verrucomicrobiota. Collectively, this study provides important insights into the mode of persistence of biocontrol agents and their effect on native microbiomes in the rhizosphere of pathogen-inoculated plants. It demonstrates that amendment can significantly alter local microbiomes and suggests that optimizing amendment regimes or selecting strains with higher rhizosphere competence can enhance future biocontrol agents.

Biocontrol and growth promotion potential of Bacillus velezensis NT35 on Panax ginseng based on the multifunctional effect.

The Bacillus velezensis strain NT35, which has strong biocontrol ability, was isolated from the rhizosphere soil of Panax ginseng. The antifungal effects of the NT35 strain against the mycelium and spore growth of Ilyonectria robusta, which causes ginseng rusty root rot, were determined. The inhibitory rate of I. robusta mycelial growth was 94.12% when the concentration of the NT35 strain was 107 CFU·mL-1, and the inhibitory rates of I. robusta sporulation and spore germination reached 100 and 90.31%, respectively, when the concentration of the NT35 strain was 104 and 108 CFU·mL-1, respectively. Strain NT35 had good prevention effects against ginseng rust rot indoors and in the field with the control effect 51.99%, which was similar to that of commercial chemical and biocontrol agents. The labeled strain NT35-Rif160-Stre400 was obtained and colonized ginseng roots, leaves, stems and rhizosphere soil after 90 days. Bacillus velezensis NT35 can induce a significant increase in the expression of five defensive enzyme-encoding genes and ginsenoside biosynthesis-related genes in ginseng. In the rhizosphere soil, the four soil enzymes and the microbial community improved during different periods of ginseng growth in response to the biocontrol strain NT35. The NT35 strain can recruit several beneficial bacteria, such as Luteimonas, Nocardioides, Sphingomonas, and Gemmatimonas, from the rhizosphere soil and reduce the relative abundance of Ilyonectria, Fusarium, Neonectria and Dactylonectria, which cause root rot and rusty root rot in ginseng plants. The disease indices were significantly negatively correlated with the abundances of Sphingomonas and Trichoderma. Additionally, Sphingomonadales, Sphingomonadaceae and actinomycetes were significantly enriched under the NT35 treatment according to LEfSe analysis. These results lay the foundation for the development of a biological agent based on strain NT35.

New Strain of Bacillus amyloliquefaciens G1 as a Potential Downy Mildew Biocontrol Agent for Grape

To obtain effective biocontrol strains for downy mildew of grape, 38 endophytic bacteria were isolated from fruits, seeds, and old stems of six grape varieties. Using spot inoculation mixtures of sporangial suspensions of Plasmopara viticola and biocontrol bacterial suspension, this screen yielded three strains (G1, G5, and G9) with good antagonistic effects against P. viticola. The growth inhibition rate was 100%, which was comparable to the effect of the positive control Bacillus subtilis strain CN181. The enzyme activity and the metabolites of strain G1 were examined on casein hydrolysate medium, sodium carboxymethyl cellulose agar plates, and chrome azurol sulfonate (CAS) agar plates. The antifungal protein component was identified by liquid chromatography–mass spectrometry (LC–MS). The results showed that strain G1 was more effective against Plasmopara viticola after two field trials, and the inhibition rates of strain G1 on the seventh day of the two field trials were 47.5% and 36.9%, respectively. Strain G1 was identified as Bacillus amyloliquefaciens based on morphological examination and 16S rDNA sequence analysis. It produced proteases, cellulases, and siderophores. Crude protein of the strain mainly included the putative segregation protein SpoVG, which inhibited P. viticola.

Antagonistic and Plant Growth-Promoting Properties of Streptomyces F2 Isolated from Vineyard Soil

Streptomyces can produce secondary metabolites with a wide range of activities and is often used in agriculture as a biocontrol strain to control soil-borne diseases. Screening and isolation from infected soil is an effective method to obtain active strains. In this study, the best antagonistic inter-root growth-promoting bacteria were isolated from grapevine inter-root soil samples, and strain F2 was identified as Streptomyces sp. based on morphological, physiological, and biochemical characteristics as well as 16S rDNA sequencing results. The results showed that the fermentation broth/liquid and sterile filtrate of strain F2 exhibited antagonistic effects against 10 plant pathogens, with an inhibition rate reaching up to 80%. Notably, two of them exhibited remarkable inhibitory effects against Phytophthora capsici with inhibition rates of 80.58% and 87.71%, respectively. The P. capsici leaf control experiment revealed that the control effect of strain F2 fermentation liquid on P. capsici filaments was 61.09%. Furthermore, indoor pot experiments demonstrated that the fermentation liquid of strain F2 had a significant inhibitory effect on pepper blight, with a maximum inhibition of 83.31%. Antagonistic factor analysis indicated that strain F2 had specific organophosphorus hydrolysis, nitrogen fixation, extracellular protease secretion, and IAA production capabilities. Additionally, root treatment with strain F2’s fermentation liquid significantly enhanced capsicum growth. Taking together, Streptomyces F2 not only exhibits a wide-spectrum antagonistic effect against plant pathogens but also promotes plant growth, which suggests that Streptomyces F2 can be used as an effective biological control resource and provides important theoretical support for the application of Streptomyces F2.

A potent endophytic fungus Purpureocillium lilacinum YZ1 protects against Fusarium infection in field-grown wheat.

Fusarium diseases pose a severe global threat to major cereal crops, particularly wheat. Existing biocontrol strains against Fusarium diseases are believed to primarily rely on antagonistic mechanisms, but not widely used under field conditions. Here, we report an endophytic fungus, Purpureocillium lilacinum YZ1, that shows promise in combating wheat Fusarium diseases. Under glasshouse conditions, YZ1 inoculation increased the survival rate of Fusarium graminearum (Fg)-infected wheat seedlings from 0% to > 60% at the seedling stage, and reduced spikelet infections by 70.8% during anthesis. In field trials, the application of YZ1 resulted in an impressive 89.0% reduction in Fg-susceptible spikelets. While a slight antagonistic effect of YZ1 against Fg was observed on plates, the induction of wheat systemic resistance by YZ1, which is distantly effective, non-specific, and long-lasting, appeared to be a key contributor to YZ1's biocontrol capabilities. Utilizing three imaging methods, we confirmed YZ1 as a potent endophyte capable of rapid colonization of wheat roots, and systematically spreading to the stem and leaves. Integrating dual RNA-Seq, photosynthesis measurements and cell wall visualization supported the link between YZ1's growth-promoting abilities and the activation of wheat systemic resistance. In conclusion, endophytes such as YZ1, which exhibits non-antagonistic mechanisms, hold significant potential for industrial-scale biocontrol applications.

Lipopeptides from Bacillus velezensis ZLP-101 and their mode of action against bean aphids Acyrthosiphon pisum Harris

BackgroundNatural products are important sources for the discovery of new biopesticides to control the worldwide destructive pests Acyrthosiphon pisum Harris. Here, insecticidal substances were discovered and characterized from the secondary metabolites of the bio-control microorganism Bacillus velezensis strain ZLP-101, as informed by whole-genome sequencing and analysis.ResultsThe genome was annotated, revealing the presence of four potentially novel gene clusters and eight known secondary metabolite synthetic gene clusters. Crude extracts, prepared through ammonium sulfate precipitation, were used to evaluate the effects of strain ZLP-101 on Acyrthosiphon pisum Harris aphid pests via exposure experiments. The half lethal concentration (LC50) of the crude extract from strain ZLP-101 against aphids was 411.535 mg/L. Preliminary exploration of the insecticidal mechanism revealed that the crude extract affected aphids to a greater extent through gastric poisoning than through contact. Further, the extracts affected enzymatic activities, causing holes to form in internal organs along with deformation, such that normal physiological activities could not be maintained, eventually leading to death. Isolation and purification of extracellular secondary metabolites were conducted in combination with mass spectrometry analysis to further identify the insecticidal components of the crude extracts. A total of 15 insecticidal active compounds were identified including iturins, fengycins, surfactins, and spergualins. Further insecticidal experimentation revealed that surfactin, iturin, and fengycin all exhibited certain aphidicidal activities, and the three exerted synergistic lethal effects.ConclusionsThis study improved the available genomic resources for B. velezensis and serves as a foundation for comprehensive studies of the insecticidal mechanism by Bacillus velezensis ZLP-101 in addition to the active components within biological control strains.

Bacillus amyloliquefaciens LM-1 Affects Multiple Cell Biological Processes in Magnaporthe oryzae to Suppress Rice Blast.

Magnaporthe oryzae, one of the most destructive rice pathogens, causes significant losses during the rice harvest every year. Bacillus amyloliquefaciens has been explored in many crops as a potential biocontrol agent. However, the mechanisms of B. amyloliquefaciens controled rice blast are not fully understood. Here, a biocontrol strain LM-1, isolated from a contaminated medium, was identified as B. amyloliquefaciens using morphological observation, physiological and biochemical tests, and 16S rDNA sequencing. LM-1 inhibited the growth and pathogenicity of M. oryzae and Bipolaris oryzae (Breda de Haan) Shoem. The mycelia of M. oryzae co-cultured with LM-1 were enlarged and broken by fluorescence microscopy using calcofluor white. LM-1 inhibited the mycelia of M. oryzae from producing conidia. Genes itu, srf, and fenB were detected in LM-1. Furthermore, the supernatant of LM-1 interfered with the appressorium formation of M. oryzae, blocked conidial cell death, and reduced autophagy degradation but did not affect the normal germination of rice seeds and seeding growth. Additionally, we observed hypersensitivity reactions, reactive oxygen species, and iron accumulation reduction in rice cells inoculated with supernatant. Our study reveals that LM-1 has a control effect on rice blast and affects cell wall integrity, sporulation, appressorium formation, cell death, and autophagy.

Biocontrol potential of epiphytic bacteria against Xanthomonas citri pathotypes A and A*

BackgroundCitrus canker caused by the bacterium Xanthomonas citri (Hasse 1915) is known as a dangerous disease that has serious economic impacts on citrus production in many tropical and subtropical countries. In Iran, Citrus canker disease has caused significant damage to various citrus fruits, particularly limes. Nowadays, employing antagonistic bacteria as an effective and environmentally friendly method for plant disease management has gained special importance.ResultsCitrus leaf samples were collected from different regions of Iran, and after isolating epiphytic bacteria, ex planta and in planta investigations concerning antagonistic activities of the isolates against Xanthomonas citri pathotypes A and A* were performed. A total of 94 epiphytic bacterial isolates were isolated from citrus aerial parts. Based on biochemical, physiological, morphological, and genotypic tests, it was determined that these bacteria belong to the Bacillus and Staphylococcus genera. The highest inhibition activity against the pathogenic bacterium was related to isolates D4 and D5. Using the molecular method and the resulting dendrogram, it was found that these isolates were most similar to Bacillus amyloliquefaciens. The present findings demonstrated that pathogenicity test on key lime leaves infected with X. citri pathotypes A and A*, along with the application of the biocontrol strain B. amyloliquefaciens, resulted in a significant reduction in the number of canker lesions.ConclusionThe results strongly suggested that the identified antagonistic bacterial isolates hold promising potential as biocontrol agents for managing citrus bacterial canker disease.

Screening, Identification, and Fermentation of a Biocontrol Strain against Peony Southern Blight and Extraction of Secondary Metabolites

A bacterial strain (WM-37) was isolated from soil and identified as Streptomyces rectiviolaceus on the basis of morphological, physiological, biochemical, and 16S rRNA characteristics. The strain was screened regarding its potential use for controlling the pathogen causing peony southern blight. To enhance the secondary metabolite yield, submerged fermentation was conducted according to a single-factor trial and response surface method. Metabolite production peaked under the following conditions: 250.00 mL flask containing 100.00 mL culture medium consisting of 20.00 g·L−1 soluble starch, 3.86 g·L−1 ammonium sulfate, 0.50 g·L−1 sodium chloride, 0.50 g·L−1 dipotassium phosphate, 0.50 g·L−1 magnesium sulfate, and 0.01 g·L−1 ferrous sulfate; inoculation amount, 7.74%; temperature, 30 °C; initial pH, 7.00; incubation time, 7 days; and rotational speed, 160 rpm. The fermentation broth was absorbed by D101 macroporous resin and eluted with an ethanol-water gradient, after which the eluate fractions with antifungal compounds were collected, evaporated, and concentrated to obtain a crude extract. This extract was dissolved in methanol and separated by high-performance liquid chromatography. The active compound was identified as azelaic acid (C9H16O4) on the basis of ultra-high-resolution mass spectrometry and analyses of publicly available data. These findings suggest that Streptomyces rectiviolaceus WM-37 may be a viable biocontrol agent effective against the pathogen responsible for peony southern blight.

Discovery of a Biocontrol Strain Trichaptum laricinum: Its Metabolites and Antifungal Activity against Pathogenic Fungus Colletotrichum anthrisci.

Finding safe and environmentally friendly fungicides is one of the important strategies in modern pesticide research and development. In this work, the antipathogenic effects of the fungus Trichaptum laricinum against the anthracnose pathogen Colletotrichum anthrisci were studied. The EtOAc extract of T. laricinum showed remarkable antifungal activity against C. anthrisci with an inhibition rate of 50% at 256 μg/mL. Bioguided isolation of the cultural broth of T. laricinum produced four new drimane sesquiterpenes, trichalarins A-D (1-4), and six other metabolites (5-10). Their structures were established by extensive spectroscopic methods, quantum chemical calculations, and single-crystal X-ray diffraction. All compounds exhibited antifungal activity against C. anthrisci with minimum inhibitory concentrations (MICs) of 8-64 μg/mL in vitro. Further in vivo assay suggested that compounds 2, 6, and 9 could significantly inhibit C. anthrisci growth in avocado fruit with inhibition rates close to 80% at the concentration of 256 μg/mL, while compounds 2 and 6 had an inhibition rate over 90% at the concentration of 512 μg/mL. The EtOAc extract of T. laricinum had no inhibitory effect on Pinus massoniana seed germination and growth at the concentration of 2 mg/mL, showing good environmental friendliness. Thus, the fungus T. laricinum could be considered as an ideal biocontrol strain, and its metabolites provided a diverse material basis for the antibiotic agents.

Efficacy of entomopathogenic fungi against Philaenus spumarius, the vector of Xylella fastidosa.

Xylella fastidiosa is an important causative agent of Olive Quick Decline Syndrome in the Apulia region of Italy. The current study evaluated the bioefficacy of three entomopathogenic fungal strains: Beauveria bassiana SGB7004, Metarhizium robertsii SGB1K, and Akanthomyces lecanii SGB4711 against Philaenus spumarius the main vector of this pathogen, under laboratory conditions. Pathogenicity bioassays were performed by dipping nymphs and adults of P. spumarius in an aqueous suspension of powdered fungal culture (PFC) or conidial suspension (CS) of the three fungal strains. Both B. bassiana SGB7004 and M. robertsii SGB1K affected the viability of nymphs, resulting in more than 80% mortality at 48 h post treatment, while the effect of A. lecanii SGB4711 was not statistically significant. On adults, all three biocontrol strains were effective in a time- and concentration-dependent manner. The PFCs of B. bassiana SGB7004, M. robertsii SGB1K, and A. lecanii SGB4711 at the highest concentration tested (120 mg mL-1) resulted in 97%, 83% and 27% mortality at the trial endpoint (120 h), respectively. Mycelial growth was observed on 38.5%, 37.0% and 61.5% of dead insects treated with B. bassiana SGB7004 (2.3 × 108 CFU mL-1), M. robertsii SGB1K (3.8 × 106 CFU mL-1) and A. lecanii SGB4711 (5.4 × 108 CFU mL-1), respectively. None of the PFCs of the tested strains was pathogenic when injected into nymph spittle. Beauveria bassiana SGB7004 and M. robertsii SGB1K significantly affected the survival of P. spumarius nymphs and adults, while A. lecanii SGB4711 was not effective on nymphs and only slightly effective against adults. © 2024 Society of Chemical Industry.