Efficacy of Plant Growth-Promoting Bacteria Bacillus cereus YN917 for Biocontrol of Rice Blast

Investigation of the mechanisms involved in the biocontrol activities of natural products from a marine soil bacterium against rice blast

BACKGROUND

Rice blast, caused by Pyricularia oryzae, is a devastating fungal disease threatening global rice production. Overreliance on chemical fungicides has raised environmental concerns and led to resistant strains, necessitating the development of sustainable alternatives. This study integrated marine microbiology and natural antifungal compounds to create eco-friendly alternatives to chemical fungicides for disease management.

RESULTS

We identified Pseudomonas aeruginosa R64 with broad-spectrum antimicrobial activity from mangrove soil in the Mai Po Nature Reserve. The R64 fermentation extract (RFE) exhibited multifaceted inhibition of P. oryzae, suppressing mycelial growth, conidiation, conidial germination and appressorial formation, while disturbing cell wall and membrane function. It also attenuated virulence by impairing appressorial penetration and invasive growth. Further chemical analysis identified phenazines and quinolines as the primary compounds in RFE, corroborated by PCR detection of corresponding phenazine biosynthetic gene clusters. Comparative bioassays with two main bioactive components of RFE, phenazine-1-carboxamide (PCN) and phenazine-1-carboxylic acid (PCA), against P. oryzae implicated PCN as the principal antifungal effector. RFE and PCN had higher efficacy than tricyclazole in P. oryzae growth inhibition, but were less effective than isoprothiolane. Furthermore, RFE and PCN displayed lower acute ecotoxicity to an environmental indicator organism than isoprothiolane, suggesting their potential as sustainable biopesticides for rice blast management.

CONCLUSION

Natural products from mangrove soil bacterium P. aeruginosa R64 inhibited key developmental and infection processes of P. oryzae, effectively reducing rice blast development. The promising disease inhibition and low ecotoxicity of mangrove-associated bacteria highlight their untapped potential for innovative, eco-friendly fungicide mining for sustainable agriculture. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Herbivory-induced green leaf volatiles increase plant performance through jasmonate-dependent plant-soil feedbacks

Plants influence each other chemically by releasing leaf volatiles and root exudates, but whether and how these two phenomena interact remains unknown. Here we demonstrate that volatiles that are released by herbivore-attacked leaves trigger plant-soil feedbacks, resulting in increased performance of different plant species. We show that this phenomenon is due to green leaf volatiles that induce jasmonate-dependent systemic defence signalling in receiver plants, which results in the accumulation of beneficial soil bacteria in the rhizosphere. These soil bacteria then increase plant growth and enhance plant defences. In maize, a cysteine-rich receptor-like protein kinase, ZmCRK25, is required for this effect. In four successive year-field experiments, we demonstrate that this phenomenon can suppress leaf herbivore abundance and enhance maize growth and yield. Thus, volatile-mediated plant-plant interactions trigger plant-soil feedbacks that shape plant performance across different plant species through broadly conserved defence signalling mechanisms and changes in soil microbiota. This phenomenon expands the repertoire of biologically relevant plant-plant interactions in space and time and holds promise for the sustainable intensification of agriculture.

Bioprospecting Bacteria From Psychrophilic Anaerobic Digestate for Potential Plant Growth-Promoting Attributes

The psychrophilic anaerobic digestion (PAD) system is a diverse and underexplored microbial ecosystem that typically harbors cold-adapted microorganisms with possible agronomic potential. The plant growth-promoting bacteria in the residue of PAD have the potential to enhance crop production, particularly during cold winter months. In this context, the characteristics of cultivable, cold-tolerant bacteria isolated from digestate obtained during PAD were investigated. Of the 20 isolates, 12 (60%) were able to solubilize phosphate from insoluble compounds at 15°C. Furthermore, nine (45%) and six (30%) isolates exhibited nitrogen fixation activity and produced indole acetic acid (IAA), respectively, while only two (10%) isolates were capable of producing siderophores. Hydrolytic enzyme production varied with cellulase production observed as a common trait since all isolates produced varying levels of cellulase ranging from 3.3 ± 0.5 to 15.3 ± 4 mm activity diameter. Isolates Comamonas sp._A3-1, Acinetobacter iwoffi_B5-1, and Pseudomonas sp._B5-5 displayed maximum cellulolytic activity with activity diameters of 13 ± 2, 13 ± 1.2, and 15.3 ± 4 mm, respectively. However, only two (10%) of the bacterial isolates produced protease with Pseudomonas sp._B5-5 demonstrating maximum proteolytic activity as depicted by an activity diameter of 11.3 ± 2.5 mm. Nucleotide sequence analysis of seven isolates, possessing multiple plant-beneficial traits, revealed their affiliation to three genera: Acinetobacter (57%), Comamonas (28.7%), and Pseudomonas (14%). Biolog Phenotype MicroArray plates revealed varied catabolic capability among bacterial strains, with isolate B5-5 demonstrating the highest metabolic diversity. The findings of this study revealed that cold-tolerant isolates from low-temperature AD possess promising plant growth-promoting characteristics, which indicates the potential of psychrophilic digestate for application in agriculture.

Characterization and identification of hot pepper-associated endospore-forming bacteria with potential applications as biofertilizers and in biocontrol of pepper wilt pathogens

BACKGROUND

Although hot pepper contributes significantly to Ethiopia's national economy, its production is hindered by devastating outbreaks of phytopathogens such as Fusarium wilt and Meloidogyne incognita disease complexes. It is known that bacteria in the pepper rhizosphere can promote plant growth by suppressing soil-borne pathogens and producing growth-promoting substances. Therefore, hot pepper-associated endospore-forming bacteria were evaluated for plant growth-promoting traits and in vitro antagonism to pepper wilt-causing pathogens, revealing some potentially valuable isolates.

RESULTS

One hundred and forty-seven heat-resistant endospore-forming rhizobacteria were recovered from 48 rhizosphere samples. Thirty-five of these isolates solubilized phosphate efficiently with solubilization index values of 2.8-10, and produced indole acetic acid (27. 31-59.16 µg/ml). Moreover, 20 isolates hydrolyzed chitin effectively, 21 of them reduced the radial growth of three pathogenic Fusarium oxysporum strains by between 26.7% and 79.2%, and cell-free supernatants of 12 isolates reduced the hatching of M. incognita eggs by 51-96.4% while also increasing juvenile mortality by 45-98.7%. After 16S rRNA gene sequence analysis, 31 of the isolates were identified as Bacillus spp. (B. siamensis, B. velezensis, and B. cereus; n = 26) and Paenibacillus polymyxa (n = 5).

CONCLUSIONS

The bacterial strains JUBC7 (B. cereus) and JUBC12 (B. siamensis) have multiple phytobeneficial traits that make them promising microbial inoculants for protecting high value crops against phytopathogens.

Comparative Effects of Bacillus strains applied Via Seed Biopriming and Soil Drenching Applications on the Morpho-Physiological and Transcriptional Aspects of Cotton

Biofertilizers are considered as a sustainable solution for promoting the growth and productivity of crops while reducing the dependence on chemical fertilizers. There is a growing need for the sustainable agricultural solutions to lessen the reliance on chemical fertilizers; thus, evaluating Bacillus strains as biofertilizers for cotton growth promotion can support eco-friendly and economically viable crop production. Therefore, the growth promoting potential of endophytic Bacillus altitudinis strain TM22 and B. atrophaeus strain MCM61 applied as soil drenching or seed treatment, was evaluated on cotton cv. 'SS32'. In vitro, the qualitative assay both TM22 and MCM61 showed proteolytic, amylolytic, lipolytic, cellulolytic, and chitinolytic activity. TM22 and MCM61 strains also demonstrated the ability to produce siderophores, indole 3-acetic acid (IAA), and phosphate solubilization. In the pot experiment, seed biopriming with TM22 and MCM61 had better performance regarding plant growth and biomass, photosynthetic pigments, stomatal conductance, and relative leaf water contents than the soil drenching application. The gene expression analysis of growth hormones-related genes demonstrated that TM22 and MCM61 showed an upregulated expression of ARF1, ARF18, EXP6, IAA9, GIB1b, and CKX6 while ERF and ERF17 genes were downregulated. Overall, these findings suggest that seed biopriming with B. altitudinis TM22 and B. atrophaeus MCM61 is an effective method with the potential to enhance the biomass of cotton.

Pine Rhizosphere Soil Microorganisms Enhance the Growth and Resistance of Pinus massoniana Against Nematode Infection

Pine wilt disease, caused by Bursaphelenchus xylophilus, poses severe ecological and economic threats to coniferous forests. This study isolated two fungal (Arthropsis hispanica, Penicillium sclerotiorum) and two bacterial (Bacillus amyloliquefaciens, Enterobacter hormaechei) strains from Pinus massoniana rhizospheres, evaluating their biocontrol potential against pine wood nematodes. Molecular characterization confirmed strain identities. In vitro assays demonstrated that combined fermentation filtrates of CSX134+CSZ71 and CSX60+CSZ71 significantly enhanced plant growth parameters (height, biomass) and root-associated soil enzyme activities (urease, acid phosphatase) in P. massoniana. Treated plants exhibited elevated defense enzyme activities and upregulated defense-related gene expression. The treatments achieved 75.07% and 69.65% nematode control efficacy, respectively, compared to controls. These findings highlight the potential of microbial consortia in activating systemic resistance and suppressing pine wilt disease through the dual mechanisms of growth promotion and defense induction.

Genomic and metabolomic insights into the antimicrobial compounds and plant growth-promoting potential of Bacillus velezensis B115

The B115 strain, isolated from the inter-root soil of healthy plants in a continuous cropping site of Panax notoginseng, was identified as Bacillus velezensis B115 by 16S rDNA sequence comparison and comparative genomic analysis. B115 is a strain of beneficial microorganisms present in the inter-root zone of plants, with favorable plant growth-promoting properties and antagonistic effects against the plant pathogen Fusarium oxysporum. However, the whole genome of B115 remains unclear, thus restricting its potential applications. To address this gap, the whole genome of B115 has been sequenced and annotated to elucidate the molecular mechanisms underlying its plant growth-promoting and antimicrobial activities. The genome analysis revealed that B115 comprises a single circular chromosome of 4,200,774 bp and a plasmid region 16,878 bp long, possessing a GC content of 45.95%. Moreover, 4349 protein-coding genes were predicted. Notably, the B115 genome contains a substantial number of genes (103) involved in the biosynthesis, transport, and catabolism of secondary metabolites. Through genome mining, 13 BGCs and 540 genes encoding secondary metabolites with predicted roles were identified, including members of the surfactin and fengycin families. Utilizing LC-MS/MS technologies, 2318 metabolites were detected in the fermentation broth of B. velezensis B115, encompassing compounds such as Corynebactin, Gamabufotalin, Pracinostat, Indoleacetic acid, (8)-Gingerol, Luteolin, Liquiritigenin, and other metabolites with antimicrobial, growth-promoting, antioxidant, and antitumor properties. By exploring secondary metabolite-related genes and predicting potential secondary metabolites from the B115 genome based on the whole-genome sequence results, we further elucidate the genomic basis for its ability to promote plant growth and inhibit pathogen activity.

Do Organic Amendments Foster Only Beneficial Bacteria in Agroecosystems?: The Case of Bacillus paranthracis TSO55

Bacterial strain TSO55 was isolated from a commercial field of wheat (Triticum turgidum L. subsp. durum), under organic amendments, located in the Yaqui Valley, Mexico. Morphological and microscopical characterization showed off-white irregular colonies and Gram-positive bacillus, respectively. The draft genome sequence of this strain revealed a genomic size of 5,489,151 bp, with a G + C content of 35.21%, N50 value of 245,934 bp, L50 value of 8, and 85 contigs. Taxonomic affiliation showed that strain TSO55 belongs to Bacillus paranthracis, reported as an emergent human pathogen. Genome annotation identified 5743 and 5587 coding DNA sequences (CDSs), respectively, highlighting genes associated with indole production, phosphate and potassium solubilization, and iron acquisition. Further in silico analysis indicated the presence of three CDSs related to pathogenicity islands and a high pathogenic potential (77%), as well as the presence of multiple gene clusters related to antibiotic resistance. The in vitro evaluation of plant growth promotion traits was negative for indole production and phosphate and potassium solubilization, and it was positive but low (18%) for siderophore production. The biosynthetic gene cluster for bacillibactin (siderophore) biosynthesis was confirmed. Antifungal bioactivity of strain TSO55 evaluated against wheat pathogenic fungi (Alternaria alternata TF17, Bipolaris sorokiniana TPQ3, and Fusarium incarnatum TF14) showed minimal fungal inhibition. An antibiotic susceptibility assay indicated resistance to three of the six antibiotics evaluated, up to a concentration of 20 µg/mL. The beta hemolysis result on blood agar reinforced TSO55's pathogenic potential. Inoculation of B. paranthracis TSO55 on wheat seedlings resulted in a significant decrease in root length (-8.4%), total plant height (-4.2%), root dry weight (-18.6%), stem dry weight (-11.1%), and total plant dry weight (-15.2%) compared to the control (uninoculated) treatment. This work highlights the importance of analyzing the microbiological safety of organic amendments before application. Comprehensive genome-based taxonomic affiliation and bioprospecting of microbial species introduced to the soil by organic agricultural practices and any microbial inoculant will prevent the introduction of dangerous species with non-beneficial traits for crops, which affect sustainability and generate potential health risks for plants and humans.

Comparative analysis of crab growth performance, enzyme activity, and microbiota between rice-crab coculture and pond farming systems

Introduction

To support the sustainable development of rice and aquaculture industries, various rice-animal coculture systems have been developed. One such system, the rice-crab coculture system (RCC), has been practiced for decades in northern China. However, studies on the crab physiological status in RCC remain limited. Microorganisms play a crucial role in aquaculture by influencing animal nutrition, health, nutrient cycling, water quality, and environmental impact. Research on the gut and environmental microbiota in RCC is scarce.

Methods

This study compared the growth performance, immune and digestive enzyme activities of crabs between RCC and traditional pond farming system (PF). In addition, the microbiota in crab guts, water, and sediment from both systems was investigated using 16S rRNA gene sequencing.

Results

Crabs in RCC exhibited superior growth performance and higher enzymatic activities, including acid phosphatase (ACP), alkaline phosphatase (AKP), lipase (LPS), and trypsin (TRY). Significant differences were observed in microbiota composition across crab gut, water, and sediment samples, respectively. RCC crabs had a lower abundance of Bacteroidota and a higher abundance of Firmicutes in their gut microbiota. The RCC environment was enriched with beneficial bacteria such as Rhizobiales, Methylococcales, KD4-96, C39, Xanthomonadales, and Nitrosomonadaceae. Microbial function predictions confirmed enhanced methanotrophy and nitrogen fixation in the RCC.

Discussion

The RCC enhances the growth rate and immune capability of crabs. Crabs from RCC consume more animal-based nutrition, which results in distinct differences in gut microbiota composition and higher levels of LPS and TRY compared to those in PF. Additionally, RCC supports environmentally beneficial bacteria that contribute to greenhouse gas reduction, carbon and nitrogen fixation, organic matter decomposition, and ammonia oxidation, benefiting both the crabs and their ecosystem. These findings enhance our understanding of crab physiology and microbial communities in RCC and PF systems.

Comparison of Two Bacillus Strains Isolated from the Coastal Zone in Barley (Hordeum vulgare L.) Under Salt Stress

Salt stress is one of the most important abiotic stress factors that negatively affects sustainable crop production, agricultural productivity, and microbial life. Increasing salt stress negatively affects the growth and development of barley, posing a threat to global food security. It is now known that inoculation of plant growth-promoting rhizobacteria (PGPR) has significant potential in increasing stress tolerance and yield in agricultural products. This study focused on the effects of Bacillus cereus CUN6 and Bacillus thuringiensis SIRB2, isolated from the coastal zone and tested for their PGPR capacities, on physiological (root length, shoot length, biomass, dry weight) and biochemical (total chlorophyll, total protein, hydrogen peroxide, lipid peroxidation, peroxidase activity (POX), catalase activity (CAT)) analyses in Hordeum vulgare L. seedlings under salt stress. The results showed that the two bacterial inoculations alleviated the negative effects of salt stress by increasing the root-shoot length, biomass, dry weight, chlorophyll content, and total protein content in barley plants. However, B.thuringiensis increased growth and development especially in root length, biomass, and dry weight compared to B.cereus. On the other hand, B.cereus significantly increased root length, biomass, and chlorophyll content under salt stress; these increases were 17%, 5%, and 7%, respectively. B.thuringiensis chlorophyll content increased by 4% in 300 mM NaCl compared to the control. When compared in terms of the antioxidant defense system, B.thuringiensis inoculation was more effective on CAT activity, while B.cereus inoculation was more effective on POX activity. Under salt stress, B.cereus and B.thuringiensis inoculation significantly decreased H2O2 content in barley; these decreases were 16% and 10%, respectively. Additionally, TBARs content was significantly decreased by B.cereus and B.thuringiensis inoculation under salt stress; these decreases were determined as 8% and 9%, respectively, compared to the control. These results indicated that both bacterial inoculations can alleviate the salt tolerance of barley seedlings by regulating antioxidant metabolism. This research focused on the potential of B.cereus and B.thuringiensis as biofertilizers against salt stress in barley based on physiological and biochemical analysis.

Characterization of Endophytic Streptomyces rhizosphaericola Ahn75 and Its Potential for Biocontrol against Rice Blast

Plant endophyte Streptomyces are excellent candidates as biocontrol agents against the rice blast fungus, Magnaporthe oryzae. In this study, a novel strain Ahn75 with antifungal activity was isolated from healthy rice stem and identified as Streptomyces rhizosphaericola by phenotypic characterization and phylogenetic analysis based on 16S rRNA gene, multilocus and genome sequences. Inhibition test using culture filtrate showed that Ahn75 could effectively suppress M. oryzae, with mycelia growth inhibition rate of 80.88% and spore germination inhibition rate of 78.26%. Genome sequence analysis of strain Ahn75 showed 40 gene clusters of secondary metabolites and several genes related to plant growth promotion were predicted in the genome of Ahn75. Several antimicrobial compounds including valinomycin, tetrabutylammonium, and benzalkonium chloride, were also detected in the antifungal fraction from Ahn75 culture filtrate by liquid chromatography and high resolution mass spectrometry. Meanwhile, strain Ahn75 demonstrates UV tolerance under UV irradiation for 60 min, pH tolerance between pH6 and pH9, and a high halotolerance in 7% (w/v) of NaCl. Greenhouse experiments indicated that Ahn75 is able to colonize rice stems, roots, and leaves, which help rice to reduce the rice leaf blast incidence by 59.76%. All these findings suggest that strain Ahn75 could be a potential biocontrol agent for rice blast.

Roles of Phyllosphere Microbes in Rice Health and Productivity

The phyllosphere, comprising the aerial portions of plants, is a vibrant ecosystem teeming with diverse microorganisms crucial for plant health and productivity. This review examines the functional roles of phyllosphere microorganisms in rice (Oryza sativa), focusing on their importance in nutrient uptake, disease resistance, and growth promotion. The molecular mechanisms underlying these interactions are explored along with their potential applications in enhancing sustainable rice production. The symbiotic relationships between rice plants and their associated microorganisms are highlighted, offering insights into improved agricultural practices. Furthermore, this review addresses the challenges and future developments in translating laboratory findings into practical applications. By synthesizing current research, this comprehensive analysis serves as a valuable resource for leveraging phyllosphere microbes in rice farming and related fields.

Biocontrol Activity of Bacillus altitudinis CH05 and Bacillus tropicus CH13 Isolated from Capsicum annuum L. Seeds against Fungal Strains

In this study, seed-surface-associated bacteria from fresh fruits of Capsicum spp. were analyzed to explore potential isolates for biocontrol of phytopathogenic fungal strains. A total of 76 bacterial isolates were obtained from three different species of chili pepper (C. annuum L., C. pubescens R. & P., and C. chinense Jacq.), and two isolates were selected via mycelial growth inhibition assays based on their production of volatile organic compounds (VOCs) against six fungal strains. Genomic analysis identified these isolates as Bacillus altitudinis CH05, with a chromosome size of 3,687,823 bp and with 41.25% G+C, and Bacillus tropicus CH13, with a chromosome size of 5,283,706 bp and with 35.24% G+C. Both bacterial strains showed high mycelial growth inhibition capacities against Sclerotium rolfsii, Sclerotinia sp., Rhizoctonia solani, and Alternaria alternata but lower inhibition capacities against Colletotrichum gloesporoides and Fusarium oxysporum. VOC identification was carried out after 24 h of fermentation with 64 VOCs for B. altitudinis CH05 and 53 VOCs for B. tropicus CH13. 2,5-Dimethyl pyrazine and acetoin had the highest relative abundance values in both bacterial strains. Our findings revealed that seed-surface-associated bacteria on Capsicum spp. have the metabolic ability to produce VOCs for biocontrol of fungal strains and have the potential to be used in sustainable agriculture.

Exploring plant growth promoting traits and biocontrol potential of new isolated Bacillus subtilis BS-2301 strain in suppressing Sclerotinia sclerotiorum through various mechanisms

Sclerotinia sclerotiorum (Lib.) de Bary is the causative agent of stem white mold disease which severely reduces major crop productivity including soybean and rapeseed worldwide. The current study aimed to explore plant growth-promoting traits and biocontrol of new isolated Bacillus subtilis BS-2301 to suppress S. sclerotiorum through various mechanisms. The results indicated that the BS-2301 exhibited strong biocontrol potential against S. sclerotiorum up to 74% both in dual culture and partition plate experiments. The BS-2301 and its crude extract significantly suppressed S. sclerotiorum growth involving excessive reactive oxygen species (ROS) production in mycelia for rapid death. Furthermore, the treated hyphae produced low oxalic acid (OA), a crucial pathogenicity factor of S. sclerotiorum. The SEM and TEM microscopy of S. sclerotiorum showed severe damage in terms of cell wall, cell membrane breakage, cytoplasm displacement, and organelles disintegration compared to control. The pathogenicity of S. sclerotiorum exposed to BS-2301 had less disease progression potential on soybean leaves in the detached leaf assay experiment. Remarkably, the strain also demonstrated broad-range antagonistic activity with 70%, and 68% inhibition rates against Phytophthora sojae and Fusarium oxysporum, respectively. Furthermore, the strain exhibits multiple plant growth-promoting and disease-prevention traits, including the production of indole-3-acetic acid (IAA), siderophores, amylases, cellulases and proteases as well as harboring calcium phosphate decomposition activity. In comparison to the control, the BS-2301 also showed great potential for enhancing soybean seedlings growth for different parameters, including shoot length 31.23%, root length 29.87%, total fresh weight 33.45%, and total dry weight 27.56%. The antioxidant enzymes like CAT, POD, SOD and APX under BS-2301 treatment were up-regulated in S. sclerotiorum infected plants along with the positive regulation of defense-related genes (PR1-2, PR10, PAL1, AOS, CHS, and PDF1.2). These findings demonstrate that the BS-2301 strain possesses a notable broad-spectrum biocontrol potential against different phytopathogens and provides new insight in suppressing S. sclerotiorum through various mechanisms. Therefore, BS-2301 will be helpful in the development of biofertilizers for sustainable agricultural practices.

Antagonistic Strain Bacillus velezensis JZ Mediates the Biocontrol of Bacillus altitudinis m-1, a Cause of Leaf Spot Disease in Strawberry

Biofertilizers are environmentally friendly compounds that can enhance plant growth and substitute for chemically synthesized products. In this research, a new strain of the bacterium Bacillus velezensis, designated JZ, was isolated from the roots of strawberry plants and exhibited potent antagonistic properties against Bacillus altitudinis m-1, a pathogen responsible for leaf spot disease in strawberry. The fermentation broth of JZ exerted an inhibition rate of 47.43% against this pathogen. Using an optimized acid precipitation method, crude extracts of lipopeptides from the JZ fermentation broth were obtained. The crude extract of B. velezensis JZ fermentation broth did not significantly disrupt the cell permeability of B. altitudinis m-1, whereas it notably reduced the Ca2+-ATPase activity on the cell membrane and markedly elevated the intracellular reactive oxygen species (ROS) concentration. To identify the active compounds within the crude extract, QTOF-MS/MS was employed, revealing four antimicrobial compounds: fengycin, iturin, surfactin, and a polyene antibiotic known as bacillaene. The strain JZ also produced various plant-growth-promoting substances, such as protease, IAA, and siderophore, which assists plants to survive under pathogen infection. These findings suggest that the JZ strain holds significant potential as a biological control agent against B. altitudinis, providing a promising avenue for the management of plant bacterial disease.

Streptomyces pratensis S10 Promotes Wheat Plant Growth and Induces Resistance in Wheat Seedlings against Fusarium graminearum

Fusarium graminearum, a devastating fungal pathogen, causes great economic losses to crop yields worldwide. The present study investigated the potential of Streptomyces pratensis S10 to alleviate F. graminearum stress in wheat seedlings based on plant growth-promoting and resistance-inducing assays. The bioassays revealed that S10 exhibited multiple plant growth-promoting properties, including the production of siderophores, 1-aminocyclopropane-1-carboxylic acid deaminase (ACC), and indole-3-acetic acid (IAA), phosphate solubilization, and nitrogen fixation. Meanwhile, the pot experiment demonstrated that S10 improved wheat plant development, substantially enhancing wheat height, weight, root activity, and chlorophyll content. Consistently, genome mining identified abundant genes associated with plant growth promotion. S10 induced resistance against F. graminearum in wheat seedlings. The disease incidence and disease index reduced by nearly 52% and 65% in S10 pretreated wheat seedlings, respectively, compared with those infected with F. graminearum only in the non-contact inoculation assay. Moreover, S10 enhanced callose deposition and reactive oxygen species (ROS) accumulation and induced the activities of CAT, SOD, POD, PAL, and PPO. Furthermore, the quantitative real-time PCR (qRT-PCR) results indicated that S10 pretreatment increased the expression of SA- (PR1.1, PR2, PR5, and PAL1) and JA/ET-related genes (PR3, PR4a, PR9, and PDF1.2) in wheat seedlings upon F. graminearum infection. In summary, S. pratensis S10 could be an integrated biological agent and biofertilizer in wheat seedling blight management and plant productivity enhancement.

Novel Bacillus and Prestia isolates from Dwarf century plant enhance crop yield and salinity tolerance

Soil salinity is a major environmental stressor impacting global food production. Staple crops like wheat experience significant yield losses in saline environments. Bioprospecting for beneficial microbes associated with stress-resistant plants offers a promising strategy for sustainable agriculture. We isolated two novel endophytic bacteria, Bacillus cereus (ADJ1) and Priestia aryabhattai (ADJ6), from Agave desmettiana Jacobi. Both strains displayed potent plant growth-promoting (PGP) traits, such as producing high amounts of indole-3-acetic acid (9.46, 10.00 µgml-1), ammonia (64.67, 108.97 µmol ml-1), zinc solubilization (Index of 3.33, 4.22, respectively), ACC deaminase production and biofilm formation. ADJ6 additionally showed inorganic phosphate solubilization (PSI of 2.77), atmospheric nitrogen fixation, and hydrogen cyanide production. Wheat seeds primed with these endophytes exhibited enhanced germination, improved growth profiles, and significantly increased yields in field trials. Notably, both ADJ1 and ADJ6 tolerated high salinity (up to 1.03 M) and significantly improved wheat germination and seedling growth under saline stress, acting both independently and synergistically. This study reveals promising stress-tolerance traits within endophytic bacteria from A. desmettiana. Exploiting such under-explored plant microbiomes offers a sustainable approach to developing salt-tolerant crops, mitigating the impact of climate change-induced salinization on global food security.

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.

The Research of Antagonistic Endophytic Bacterium Bacillus velezensis CSUFT-BV4 for Growth Promotion and Induction of Resistance to Anthracnose in Camellia oleifera

Camellia oleifera (C. oleifera) is one of the four main, woody, edible oil tree species in the world, while C. oleifera anthracnose is mainly caused by the fungus Colletotrichum fructicola (C. fructicola), which severely affects the yield of C. oleifera and the quality of tea oil. Bacillus velezensis (B. velezensis) CSUFT-BV4 is an antagonistic endophytic bacterium isolated from healthy C. oleifera leaves. This study aimed to investigate the biocontrol potential of strain CSUFT-BV4 against C. oleifera anthracnose and its possible functional mechanism, and to determine its growth-promoting characteristics in host plants. In vitro, CSUFT-BV4 was shown to have efficient biofilm formation ability, as well as significant functions in the synthesis of metabolic substances and the secretion of probiotic substances. In addition, the CSUFT-BV4 fermentation broth also presented efficient antagonistic activities against five major C. oleifera anthracnose pathogens, including C. fructicola, C. gloeosporioides, C. siamense, C. camelliae, and C. kahawae, and the inhibition rate was up to 73.2%. In vivo, it demonstrated that the growth of C. oleifera treated with CSUFT-BV4 fermentation broth was increased in terms of stem width, plant height, and maximum leaf area, while the activities of various defense enzymes, e.g., superoxide dismutase (SOD), phenylalanine aminotransferase (PAL), and polyphenol oxidase (PPO), were effectively increased. The remarkable antagonistic activities against C. oleifera anthracnose, the growth-promoting characteristics, and the induction of host defense responses indicate that endophytic bacterium CSUFT-BV4 can be effectively used in the biological control of C. oleifera anthracnose in the future, which will have a positive impact on the development of the C. oleifera industry.

Beneficial Microorganisms as Bioprotectants against Foliar Diseases of Cereals: A Review

Cereal production plays a major role in both animal and human diets throughout the world. However, cereal crops are vulnerable to attacks by fungal pathogens on the foliage, disrupting their biological cycle and photosynthesis, which can reduce yields by 15-20% or even 60%. Consumers are concerned about the excessive use of synthetic pesticides given their harmful effects on human health and the environment. As a result, the search for alternative solutions to protect crops has attracted the interest of scientists around the world. Among these solutions, biological control using beneficial microorganisms has taken on considerable importance, and several biological control agents (BCAs) have been studied, including species belonging to the genera Bacillus, Pseudomonas, Streptomyces, Trichoderma, Cladosporium, and Epicoccum, most of which include plants of growth-promoting rhizobacteria (PGPRs). Bacillus has proved to be a broad-spectrum agent against these leaf cereal diseases. Interaction between plant and beneficial agents occurs as direct mycoparasitism or hyperparasitism by a mixed pathway via the secretion of lytic enzymes, growth enzymes, and antibiotics, or by an indirect interaction involving competition for nutrients or space and the induction of host resistance (systemic acquired resistance (SAR) or induced systemic resistance (ISR) pathway). We mainly demonstrate the role of BCAs in the defense against fungal diseases of cereal leaves. To enhance a solution-based crop protection approach, it is also important to understand the mechanism of action of BCAs/molecules/plants. Research in the field of preventing cereal diseases is still ongoing.

Isolation and Identification of Culturable Bacteria from South China Seawater and Preliminary Screening of Marine Biocontrol Bacteria

Marine microorganisms have evolved special metabolic pathways to produce numerous bioactive substances with novel structures and unique functions. This study analyzed the diversity of culturable bacteria in marine water samples from the South China Sea and screened the isolated bacteria with pathogenic fungi. A total of 200 culturable strains of 72 different bacteria were obtained from 56 water samples from the South China Sea. They belonged to three phyla and four classes, namely Gammaproteobacteria, Alphaproteobacteria, Bacilli and Actinomycetia. Bacilli was the dominant class, comprising up to 59.72%, followed by Gammaproteobacteria (20.83%). Bacillus, Pseudomonas, Paenibacillus and Rhizobium were the most dominant genera. Among these strains, HY-88 and HY-91 encoding BamC, FenB and PKSI genes were selected and identified as Bacillus subtilis. The respective inhibition rates of the HY-88 caused by plate confrontation against Magnaporthe grisea, Fusarium oxysporum, Botrytis cinerea, anthrax and Botrytis cinerea were 90.91%, 54.29%, 52.17% and 51.72%, in comparison with HY-91 86.36%, 48.57%, 47.83% and 34.48%. In addition, the supernatant of HY-88 showed a lesion inhibition rate of 74.5%, which was significantly higher than HY-91 (60.55%). In addition, HY-88 and HY-91 showed strong antifungal activity to Colletotrichum viniferum on detached Shine Muscat grapes. Tolerance tests showed that the HY-88 and HY-91 grew at 10-40 °C, 7-10% NaCl and pH 3-11. HY-88 and HY-91 could inhibit various fungal plant diseases, which lays a foundation for the development of new biopesticides.

Bacillus velezensis BV01 Has Broad-Spectrum Biocontrol Potential and the Ability to Promote Plant Growth

To evaluate the potential of a bacterial strain as a fungal disease control agent and plant growth promoter, its inhibitory effects on phytopathogens such as Bipolaris sorokiniana, Botrytis cinerea, Colletotrichum capsici, Fusarium graminearum, F. oxysporum, Neocosmospora rubicola, Rhizoctonia solani, and Verticillium dahliae were investigated. The results showed that the inhibitory rates in dual-culture and sterile filtrate assays against these eight phytopathogens ranged from 57% to 83% and from 36% to 92%. The strain was identified as Bacillus velezensis based on morphological and physiological characterization as well as phylogenetic analyses of 16S rRNA and the gyrase subunit A protein (gyrA) regions. The results demonstrated that B. velezensis was able to produce fungal cell-wall-degrading enzymes, namely, protease, cellulase, and β-1,3-glucanase, and the growth-promotion substances indole-3-acetic acid (IAA) and siderophore. Furthermore, B. velezensis BV01 had significant control effects on wheat root rot and pepper Fusarium wilt in a greenhouse. Potted growth-promotion experiments displayed that BV01 significantly increased the height, stem diameter, and aboveground fresh and dry weights of wheat and pepper. The results imply that B. velezensis BV01, a broad-spectrum biocontrol bacterium, is worth further investigation regarding its practical applications in agriculture.

Genomic and metabolomic insights into the antimicrobial compounds and plant growth-promoting potential of Bacillus velezensis Q-426

BACKGROUND

The Q-426 strain isolated from compost samples has excellent antifungal activities against a variety of plant pathogens. However, the complete genome of Q-426 is still unclear, which limits the potential application of Q-426.

RESULTS

Genome sequencing revealed that Q-426 contains a single circular chromosome 4,086,827 bp in length, with 4691 coding sequences and an average GC content of 46.3%. The Q-426 strain has a high degree of collinearity with B. velezensis FZB42, B. velezensis SQR9, and B. amyloliquefaciens DSM7, and the strain was reidentified as B. velezensis Q-426 based on the homology analysis results. Many genes in the Q-426 genome have plant growth-promoting activity, including the secondary metabolites of lipopeptides. Genome mining revealed 14 clusters and 732 genes encoding secondary metabolites with predicted functions, including the surfactin, iturin, and fengycin families. In addition, twelve lipopeptides (surfactin, iturin and fengycin) were successfully detected from the fermentation broth of B. velezensis Q-426 by ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS/MS), which is consistent with the genome analysis results. We found that Q-426 produced indole-3-acetic acid (IAA) at 1.56 mg/l on the third day of incubation, which might promote the growth of plants. Moreover, we identified eighteen volatile compounds (VOCs, including 2-heptanone, 6-methylheptan-2-one, 5-methylheptan-2-one, 2-nonanone, 2-decanone, 2-undecanone, 2-dodecanone, 2-tridecanone, 2-tetradecanone, 2-nonadecanone, pentadecanoic acid, oleic acid, dethyl phthalate, dibutyl phthalate, methyl (9E,12E)-octadeca-9,12-dienoate), pentadecane, (6E,10E)-1,2,3,4,4a,5,8,9,12,12a-decahydro-1,4-methanobenzo[10]annulene, and nonanal) based on gas chromatograph-mass spectrometer (GC/MS) results.

CONCLUSIONS

We mined secondary metabolite-related genes from the genome based on whole-genome sequence results. Our study laid the theoretical foundation for the development of secondary metabolites and the application of B. velezensis Q-426. Our findings provide insights into the genetic characteristics responsible for the bioactivities and potential application of B. velezensis Q-426 as a plant growth-promoting strain in ecological agriculture.

Plant Growth Promotion Using Bacillus cereus

Plant growth-promoting bacteria (PGPB) appear to be a sensible competitor to conventional fertilization, including mineral fertilizers and chemical plant protection products. Undoubtedly, one of the most interesting bacteria exhibiting plant-stimulating traits is, more widely known as a pathogen, Bacillus cereus. To date, several environmentally safe strains of B. cereus have been isolated and described, including B. cereus WSE01, MEN8, YL6, SA1, ALT1, ERBP, GGBSTD1, AK1, AR156, C1L, and T4S. These strains have been studied under growth chamber, greenhouse, and field conditions and have shown many significant traits, including indole-3-acetic acid (IAA) and aminocyclopropane-1-carboxylic acid (ACC) deaminase production or phosphate solubilization, which allows direct plant growth promotion. It includes an increase in biometrics traits, chemical element content (e.g., N, P, and K), and biologically active substances content or activity, e.g., antioxidant enzymes and total soluble sugar. Hence, B. cereus has supported the growth of plant species such as soybean, maize, rice, and wheat. Importantly, some B. cereus strains can also promote plant growth under abiotic stresses, including drought, salinity, and heavy metal pollution. In addition, B. cereus strains produced extracellular enzymes and antibiotic lipopeptides or triggered induced systemic resistance, which allows indirect stimulation of plant growth. As far as biocontrol is concerned, these PGPB can suppress the development of agriculturally important phytopathogens, including bacterial phytopathogens (e.g., Pseudomonas syringae, Pectobacterium carotovorum, and Ralstonia solanacearum), fungal phytopathogens (e.g., Fusarium oxysporum, Botrytis cinerea, and Rhizoctonia solani), and other phytopathogenic organisms (e.g., Meloidogyne incognita (Nematoda) and Plasmodiophora brassicae (Protozoa)). In conclusion, it should be noted that there are still few studies on the effectiveness of B. cereus under field conditions, particularly, there is a lack of comprehensive analyses comparing the PGP effects of B. cereus and mineral fertilizers, which should be reduced in favor of decreasing the use of mineral fertilizers. It is also worth mentioning that there are still very few studies on the impact of B. cereus on the indigenous microbiota and its persistence after application to soil. Further studies would help to understand the interactions between B. cereus and indigenous microbiota, subsequently contributing to increasing its effectiveness in promoting plant growth.

Effects of a Microbial Restoration Substrate on Plant Growth and Rhizosphere Microbial Community in a Continuous Cropping Poplar

In poplar cultivation, continuous cropping obstacles affect wood yield and soil-borne diseases, primarily due to structural changes in microbes and fungus infection. The bacterium Bacillus cereus BJS-1-3 has strong antagonistic properties against pathogens that were isolated from the rhizosphere soil of poplars. Poplar rhizospheres were investigated for the effects of Bacillus cereus BJS-1-3 on microbial communities. Three successive generations of soil were used to replant poplar seedlings. BJS-1-3 inoculated poplars were larger, had higher plant height and breast height diameter, and had a greater number of total and culturable bacteria than non-inoculated controls. B. cereus BJS-1-3 inoculated poplar rhizospheres were sequenced, utilizing the Illumina MiSeq platform to analyze changes in diversity and structure. The fungi abundance and diversity in the BJS-1-3 rhizosphere were significantly lower than in the control rhizosphere. In comparison to the control group, Bacillus sp. constituted 2.87% and 2.38% of the total bacterial community, while Rhizoctonia sp. constituted 2.06% and 6.00% of the total fungal community. Among the potential benefits of B. cereus BJS-1-3 in poplar cultivation is that it enhances rhizosphere microbial community structure and facilitates the growth of trees.

Identification of Enolase 1 as a Potential Target for Magnaporthe oryzae: Integrated Proteomic and Molecular Dynamics Simulation

Rice blast is an essential factor affecting rice yield and quality, which is caused by Magnaporthe oryzae (M. oryzae). Isobavachalcone (IBC) is a botanical fungicide derived from the seed extract of the Leguminosae plant Psoralea corylifolia L. and has shown an excellent rice blast control effect in field applications. To explore the potential targets of rice blast control, the analysis of the differentially expressed proteins (DEPs) between the liquid culture medium of mycelium treated by 10 mg/L of IBC for 2 h and the control group indicated that Enolase 1 (ENO1) was the most significantly down-regulated DEP with a fold change value of 0.305. In vitro experiments showed that after treating liquid culture mycelium with 10 mg/L of IBC for 0.5, 1, 2, 4, and 8 h, the enzymatic activity of ENO1 in the IBC experimental groups was 0.97, 0.75, 0.52, 0.44, and 0.39 times as much as in the control groups, respectively. To further explore the molecular interaction and binding mode between IBC and ENO1, the three-dimensional structure of ENO1 was established based on homology modeling. Molecular docking and molecular dynamics simulation showed that IBC had a pi-pi stacking effect with the residue TYR_365, a hydrogen bond interaction with the residue ARG_393, and hydrophobic interactions with non-polar residues ALA_361, LYS_362, and VAL_371 of ENO1. These findings indicated that ENO1 is a potential target of M. oryzae, which would pave the way for screening novel effective fungicides targeting ENO1.

Effects of rice blast biocontrol strain Pseudomonas alcaliphila Ej2 on the endophytic microbiome and proteome of rice under salt stress

Introduction

Soil salinity is a prevalent environmental stress in agricultural production. Microbial inoculants could effectively help plants to alleviate salt stress. However, there is little knowledge of the biocontrol strain Pseudomonas alcaliphila Ej2 mechanisms aiding rice plants to reduce the adverse effects caused by salt stress.

Methods

We performed integrated field and greenhouse experiments, microbial community profiling, and rice proteomic analysis to systematically investigate the Ej2 mechanism of action.

Results

The results displayed that biocontrol strain Ej2 increased shoot/root length and fresh/dry weight compared with control under salt stress. Meanwhile, strain Ej2 has the ability to control rice blast disease and promote rice growth. Furthermore, the microbial community analysis revealed that the alpha-diversity of Ej2-inoculated plants was higher than the control plants, expect the Shannon index of the bacterial microbiome and the Ej2-inoculated samples clustered and separated from the control samples based on beta-diversity analysis. Importantly, the enriched and specific OTUs after Ej2 inoculation at the genus level were Streptomyces, Pseudomonas, Flavobacterium, and Bacillus. Moreover, we observed that Ej2 inoculation influenced the rice proteomic profile, including metabolism, plant-pathogen interactions, and biosynthesis of unsaturated fatty acids. These results provide comprehensive evidence that Ej2 inoculation induced the rice endophytic microbiome and proteomic profiles to promote plant growth under salt stress.

Discussion

Understanding the biocontrol strain effects on the endophytic microbiome and rice proteomics will help us better understand the complex interactions between plants and microorganisms under salt stress. Furthermore, unraveling the mechanisms underlying salt tolerance will help us more efficiently ameliorate saline soils.

Use of beneficial bacterial endophytes: A practical strategy to achieve sustainable agriculture

Beneficial endophytic bacteria influence their host plant to grow and resist pathogens. Despite the advantages of endophytic bacteria to their host, their application in agriculture has been low. Furthermore, many plant growers improperly use synthetic chemicals due to having no or little knowledge of the role of endophytic bacteria in plant growth, the prevention and control of pathogens and poor access to endobacterial bioproducts. These synthetic chemicals have caused soil infertility, environmental contamination, disruption to ecological cycles and the emergence of resistant pests and pathogens. There is more that needs to be done to explore alternative ways of achieving sustainable plant production while maintaining environmental health. In recent years, the use of beneficial endophytic bacteria has been noted to be a promising tool in promoting plant growth and the biocontrol of pathogens. Therefore, this review discusses the roles of endophytic bacteria in plant growth and the biocontrol of plant pathogens. Several mechanisms that endophytic bacteria use to alleviate plant biotic and abiotic stresses by helping their host plants acquire nutrients, enhance plant growth and development and suppress pathogens are explained. The review also indicates that there is a gap between research and general field applications of endophytic bacteria and suggests a need for collaborative efforts between growers at all levels. Furthermore, the presence of scientific and regulatory frameworks that promote advanced biotechnological tools and bioinoculants represents major opportunities in the applications of endophytic bacteria. The review provides a basis for future research in areas related to understanding the interactions between plants and beneficial endophytic microorganisms, especially bacteria.

Bacillus cereus EC9 protects tomato against Fusarium wilt through JA/ET-activated immunity

The mechanisms of action and the limitations of effectiveness of natural biocontrol agents should be determined in order to convert them into end products that can be used in practice. Rhizosphere Bacillus spp. protect plants from various pathogens by displaying several modes of action. However, the ability of Bacillus spp. to control plant diseases depends on the interaction between the bacteria, host, and pathogen, and the environmental conditions. We found that soil drenching of tomato plants with the non-antifungal Bacillus cereus strain EC9 (EC9) enhances plant defense against Fusarium oxysporum f. sp. lycopersici (Fol). To study the involvement of plant defense-related phytohormones in the regulation of EC9-activated protection against Fol, we conducted plant bioassays in tomato genotypes impaired in salicylic acid (SA) accumulation, jasmonic acid (JA) biosynthesis, and ethylene (ET) production, and analyzed the transcript levels of pathways-related marker genes. Our results indicate that JA/ET-dependent signaling is required for EC9-mediated protection against Fol in tomato. We provide evidence that EC9 primes tomato plants for enhanced expression of proteinase inhibitor I (PI-I) and ethylene receptor4 (ETR4). Moreover, we demonstrated that EC9 induces callose deposition in tomato roots. Understanding the involvement of defense-related phytohormones in EC9-mediated defense against Fusarium wilt has increased our knowledge of interactions between non-antifungal plant defense-inducing rhizobacteria and plants.

Antagonistic potential of an Egyptian entomopathogenic nematode, compost and two native endophytic bacteria isolates against the root-knot nematode (Meloidogyne incognita) infecting potato under field conditions

Background

The root-knot nematode, Meloidogyne spp., are one of the most dominant and dangerous group of pests. The deformations and discolorations make tubers unmarketable and/or of less quality. Therefore, management of Meloidogyne spp. becomes an obligatory challenge that warrants intervention. Biological control agents are the best alternative tools for controlling plant-parasitic nematodes that comply with the requirements of the development of the green agriculture and that reduce the reliance on these harmful chemicals. Therefore, this study aimed to evaluate the effectiveness of compost singly, and in combinations with the bio-agents Heterorhabditis bacteriophora, and two bacterial isolates Nem 212 and Nem 213 against the root-knot nematode Meloidogyne incognita infecting potato plants under field conditions.

Results

Among 15 bacterial isolates (Nem205-Nem219) obtained from the rhizosphere of tomato and eggplant from Giza, Egypt, the two isolates (Nem 212 and Nem 213) were molecularly characterized based on the partial 16S rDNA sequencing analysis. These two bacterial isolates were deposited in the GenBank as Bacillus cereus Nem 212 and B. cereus Nem 213 and were tested against M. incognita J2s in vitro. Results showed that the cell filtrates of B. cereus Nem 212 and B. cereus Nem 213 gave the highest percentage of M. incognita J2s mortality (100%), after 48 h of the in vitro application. Moreover, all the applied treatments significantly suppressed the reproductive of M. incognita on potato plants and enhanced the potato crop yield under the field conditions. Compost enriched with B. cereus Nem 212 cell suspension was the most effective treatment. The combination between the bacterial cell suspension and the compost offered an increase in the disease curing and the potato plant growth and yield production, compared to the treatment with compost alone. The entomopathogenic nematode, Heterorhabditis bacteriophora, was relatively less effective in controlling M. incognita on potato, compared to B. cereus Nem 212 and/or B. cereus Nem 213 treatments. However, when compost was enriched with H. bacteriophora, it increased its capability to control the nematodes.

Conclusions

This study provides insights into the practical usage of EPNs H. bacteriophora, and the endophytic bacteria (B. cereus Nem 212 or B. cereus Nem 213) as biocontrol agents against M. incognita on potato plants. The application of compost enriched with the bacterial cell suspensions of either B. cereus Nem 212 or B. cereus Nem 213 and H. bacteriophora within Galleria mellonella cadaver proved efficient control of M. incognita infecting potato plants and improved the growth and yield of potato plants under field conditions.

Biological control and plant growth promotion properties of Streptomyces albidoflavus St-220 isolated from Salvia miltiorrhiza rhizosphere

Root rot disease caused by Fusarium oxysporum is a devastating disease of Salvia miltiorrhiza and dramatically affected the production and quality of Sa. miltiorrhiza. Besides the agricultural and chemical control, biocontrol agents can be utilized as an additional solution. In the present study, an actinomycete that highly inhibited F. oxysporum was isolated from rhizosphere soil and identified as based on morphological and molecular characteristics. Greenhouse assay proved that the strain had significant biological control effect against Sa. miltiorrhiza root rot disease and growth-promoting properties on Sa. miltiorrhiza seedlings. To elucidate the biocontrol and plant growth-promoting properties of St-220, we employed an analysis combining genome mining and metabolites detection. Our analyses based on genome sequence and bioassays revealed that the inhibitory activity of St-220 against F. oxysporum was associated with the production of enzymes targeting fungal cell wall and metabolites with antifungal activities. Strain St-220 possesses phosphate solubilization activity, nitrogen fixation activity, siderophore and indole-3-acetic acid production activity in vitro, which may promote the growth of Sa. miltiorrhiza seedlings. These results suggest that St. albidoflavus St-220 is a promising biocontrol agent and also a biofertilizer that could be used in the production of Sa. miltiorrhiza.

Antifungal Activity and Plant Growth-Promoting Properties of Bacillus mojovensis B1302 against Rhizoctonia Cerealis

Rhizoctonia cerealis is a worldwide soil-borne pathogenic fungus that significantly infects wheat and causes sharp eyespot in China. However, the biocontrol strains used for the control of Rhizoctonia cerealis are insufficient. In the present study, antagonistic strain B1302 from the rhizosphere of wheat were isolated and identified as Bacillus mojovensis based on their morphological, physiological, and biochemical characteristics, and their 16S rDNA sequence. Culture filtrate of strain B1302 had a broad antifungal spectrum. In order to improve the antifungal activity of B1302, response surface methodology (RSM) was used to optimize the culture conditions. The final medium composition and culture conditions were 13.2 g/L of wheat bran, 14.1 g/L of soybean meal, 224 r/min of rotation speed, 7.50 of initial pH, and 1.5 × 10⁸ CFU/mL of inoculation amount at 35 °C for a culture duration of 72 h. B. mojavensis B1302 inhibited the hyphae growth of R.cerealis and produced hydrolytic enzymes (protease, chitinase, and glucanase), IAA, and had N-fixing potentiality and P-solubilisation capacity. It can also promote wheat seedling growth in potted plants. The disease incidence and index of wheat seedlings were consistent with the effect of commercial pesticides under treatment with culture filtrate. The biocontrol efficacy of culture filtrate was significant—up to 65.25%. An animal toxicological safety analysis suggested that culture filtrate was safe for use and could be developed into an effective microbial fungicide to control wheat sharp eyespot.

Alcaligenes faecalis Juj3 alleviates Plasmodiophora brassicae stress to cabbage via promoting growth and inducing resistance

Clubroot is a devastating disease threatening global cruciferous vegetable production caused by Plasmodiophora brassicae (Pb). We have evaluated the positive effects of the Alcaligenes faecalis Juj3 on cabbage growth promotion and Pb stress alleviation through pot and field experiments. The Juj3 strain was isolated from a healthy cabbage rhizosphere with growth-promoting characteristics and was identified as A. faecalis based on morphological traits and phylogeny. Seed germination assays revealed that Juj3 inoculation enhances cabbage bud shoot and root growth. In pot experiments, inoculation with Juj3 fermentation powder at cabbage sowing dates significantly improved the seedling biomass. Combining seed treatments with root irrigation after transplanting considerably reduced the clubroot disease index and resulted in appreciable biocontrol efficacy (83.7%). Gene expression analyses of cabbage after Juj3 inoculation showed that PR2 and EIN3 expression were significantly up-regulated. Physiologically, Juj3 inoculation enhanced cabbage chlorophyll content and root activity in a normal environment. Irrespective of whether plants were under normal environment or Pb stresses, Juj3 improved photosynthesis. Field trial analyses revealed that Juj3 exhibits satisfactory biocontrol efficacy in cabbage (51.4%) and Chinese cabbage (37.7%). Moreover, Juj3 could also enhance cabbage and Chinese cabbage biomass to improve the yield quality. These findings pave the way for future use of A. faecalis as biocontrol agents for clubroot and reveal the great potential of the rhizobacterium for plant growth-promoting applications in agriculture and horticulture.

Biopriming for induction of disease resistance against pathogens in rice

Rice is attacked by an armada of pathogens. Present review provides a critical evaluation of the potential of different biotic agents used to protect rice yield drop from pathogenicity and an account of unexplored areas, which might be taken into consideration to manage rice diseases. Rice (Oryza sativa L.), is the most important staple food of Asian countries. Rice production is significantly limited by a diversity of pathogens, leading to yield loss and deficit in current rice supply. Application of agrochemicals of diverse types has been considered as the only option to control pathogens and enhance rice production, thereby causing environmental concerns and making the pathogens resistant to the active ingredients. Increase in population and resistance of pathogen towards agrochemicals put pressure on the agronomists to search for safe, novel, eco-friendly alternative ways to manage rice pathogens. Inducing resistance in rice by using different biotic/abiotic agents provides an environmental friendly alternative way to effectively manage bacterial, fungal, and viral rice pathogens. In recent years, a number of protocols have been developed for inducing pathogen resistance by bio-priming of rice. However, a comprehensive evaluation of the potential of different biotic agents to protect rice crop loss from pathogens is hitherto lacking due to which the research on induction of defense against pathogens in rice is discontinuous. This review deals with the detailed analysis of the bacterial and fungal agents used to induce defense against rice pathogens, their mode of application, mechanism (physiological, biochemical, and molecular) of defense induction, and effect of defense induction on the yield of rice. It also provides an account of gaps in the research and the unexplored areas, which might be taken into consideration to effectively manage rice pathogens.

Multi-Omics Techniques for Analysis Antifungal Mechanisms of Lipopeptides Produced by Bacillus velezensis GS-1 against Magnaporthe oryzae In Vitro

Magnaporthe oryzae is a fungal pathogen that causes rice blast, a highly destructive disease. In the present study, the bacteria strain GS-1 was isolated from the rhizosphere soil of ginseng and identified as Bacillus velezensis through 16S rRNA gene sequencing, whole genome assembly, and average nucleotide identity analysis. B. velezensis strain GS-1 exhibited significant antagonistic activity to several plant fungal pathogens. Through whole genome sequencing, 92 Carbohydrate-Active Enzymes and 13 gene clusters that encoded for secondary metabolites were identified. In addition, strain GS-1 was able to produce the lipopeptide compounds, surfactin, fengycin, and plantazolicin. The inhibitory effects of lipopeptide compounds on M. oryzae were confirmed, and the antagonistic mechanism was explored using transcriptomics and metabolomics analysis. Differential expressed genes (DEGs) and differential accumulated metabolites (DAMs) revealed that the inhibition of M. oryzae by lipopeptide produced by GS-1 downregulated the expression of genes involved in amino acid metabolism, sugar metabolism, oxidative phosphorylation, and autophagy. These results may explain why GS-1 has antagonistic activity to fungal pathogens and revealed the mechanisms underlying the inhibitory effects of lipopeptides produced by GS-1 on fungal growth, which may provide a theoretical basis for the potential application of B. velezensis GS-1 in future plant protection.

Role of Rhizospheric Bacillus megaterium HGS7 in Maintaining Mulberry Growth Under Extremely Abiotic Stress in Hydro-Fluctuation Belt of Three Gorges Reservoir

Plant growth-promoting rhizobacteria have been shown to play important roles in maintaining host fitness under periods of abiotic stress, and yet their effect on mulberry trees which regularly suffer drought after flooding in the hydro-fluctuation belt of the Three Gorges Reservoir Region in China remains largely uncharacterized. In the present study, 74 bacterial isolates were obtained from the rhizosphere soil of mulberry after drought stress, including 12 phosphate-solubilizing and 10 indole-3-acetic-acid-producing isolates. Bacillus megaterium HGS7 was selected for further study due to the abundance of traits that might benefit plants. Genomic analysis revealed that strain HGS7 possessed multiple genes that contributed to plant growth promotion, stress tolerance enhancement, and antimicrobial compound production. B. megaterium HGS7 consistently exhibited antagonistic activity against phytopathogens and strong tolerance to abiotic stress in vitro. Moreover, this strain stimulated mulberry seed germination and seedling growth. It may also induce the production of proline and antioxidant enzymes in mulberry trees to enhance drought tolerance and accelerate growth recovery after drought stress. The knowledge of the interactions between rhizobacteria HGS7 and its host plant might provide a potential strategy to enhance the drought tolerance of mulberry trees in a hydro-fluctuation belt.