Plant Pathogens Research Articles

Screening and stability verification of reference genes in Botrytis cinerea ZX2 fermentation

Botrytis cinerea, an airborne plant pathogen, holds the potential to synthesize sesquiterpenes, which have been used for the industrial production of abscisic acid. Previously, through our genetic technology, we obtained strain ZX2, whose main product 1´,4´-trans-ABA-diol is physiologically active in plants. In this study, 50 L of fed fermentation was carried out with ZX2 strain to study the stability of expression of TUA, TUB, ATC, EF-1, GAPDH, UCE and GTP genes. Four kinds of software (GeNorm, NormFinder, BestKeeper and Delta Ct) were used to analyze the expression stability of candidate genes, and finally the best reference gene was screened by RefFinder. Based on the results, the ACT was the most stable gene. It was used to normalize the expression levels of two genes related to 1´,4´-trans-ABA-diol production (hmgr and bcaba3) when fed-batch fermentation. Guide the selection of appropriate internal reference genes during the fermentation process to accurately quantify the relative transcription levels of target genes in B.cinerea ZX2.

Design, synthesis and antifungal activity of novel pyrazole-amide-isothiazole derivatives as succinate dehydrogenase inhibitors

To discover new fungicides to protect food safety and quality, thirty-four novel pyrazole-amide-isothiazole compounds were designed, synthesised by using scaffold hopping theory for the first time. The bioactivity of all the target compounds against five plant pathogens (Including Penicillium digitatum, Physalospora piricola, Helminthosporium maydis, Sclerotinia sclerotiorum and Botrytis cinerea) were determined, the results showed that most of the compounds exhibited certain biological activities against B. cinerea in vitro. Compounds 7-XHU-6 had better antifungal activities than fluopyram with the EC50 values were 1.02, 1.78 mg/L, respectively. Moreover, the SDH inhibiting activities results indicated that 7-XHU-6 possessed outstanding activities with an IC50 value of 0.47 mg/L which better than fluopyram (IC50 = 0.88 mg/L). Besides, the in vivo experiments indicated that compound 7-XHU-6 had excellent protection efficiency and therapeutic efficiency. In addition, molecular docking studies demonstrated that compound 7-XHU-6 (−10 kcal/mol) has superior binding energy compared to fluopyram (−8.6 kcal/mol).

Morphological and phylogenetic analyses reveal eight novel species of Pestalotiopsis (Sporocadaceae, Amphisphaeriales) from southern China.

Plants play an important role in maintaining the ecological balance of the biosphere, but often suffer from pathogenic fungi during growth. During our continuing mycological surveys of plant pathogens from terrestrial plants in Jiangxi and Yunnan provinces, China, 24 strains of Pestalotiopsis isolated from diseased and healthy tissues of plant leaves represented eight new species, viz. P.alpinicola, P.camelliicola, P.cyclosora, P.eriobotryae, P.gardeniae, P.hederae, P.machiliana and P.mangifericola. Multi-locus (ITS, tef1-α and tub2) phylogenetic analyses were performed using maximum-likelihood and Bayesian inference to reveal their taxonomic placement within Pestalotiopsis. Both molecular phylogenetic analyses and morphological comparisons supported them as eight independent taxa within Pestalotiopsis. Illustrations and descriptions of these eight taxa were provided, in conjunction with comparisons with closely related taxa in the genus. This work highlights the large potential for new fungal species associated with diseased plant leaves.

First Report of Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae) in Oklahoma.

The corn leafhopper, Dalbulus maidis (DeLong and Wolcott) (Hemiptera: Cicadellidae), is an invasive insect that can cause damage to maize (Zea mays L.) in two ways: by direct feeding and the transmission of several plant pathogens. Dalbulus maidis is an invasive and serious economic pest of maize that has spread from its center of origin in Mexico to the southernmost parts of the United States. Prior to 2024, corn leafhoppers had not been documented in Oklahoma, and their spread northward toward the United States corn belt is of significant concern. Here, we provide the first reports of the insect in maize in several Oklahoma counties. Insect specimens were collected at various commercial and experimental field sites by Oklahoma State University research and extension personnel. The identity of the insect species was validated through morphological and molecular taxonomy. The presence records for the corn leafhopper presented here provide valuable information for future monitoring and management efforts of this economically important pest and disease.

Bioprospecting Endophytic Fungi of Forest Plants for Bioactive Metabolites with Antibacterial, Antifungal, and Antioxidant Potentials.

The growing emergence of multi-drug resistant microbial strains has kept the scientific world searching for novel bioactive compounds with specific chemical characteristics. Accordingly, researchers have started exploring the understudied metabolites from endophytes as a new source of bioactive compounds. In this context, the current study was designed to evaluate the bioactive properties of endophytic fungi from the Mokrzański forest in Wrocław, Poland that have not yet been fully researched. Forty-three endophytic fungi were isolated from twelve distinct plants. Following their cultivation, fungal extracts were separately prepared from biomass and cell-free filtrates, and their antibacterial, antifungal (against human and plant pathogens), and antioxidant properties were examined. Five promising fungi after screening were identified to possess all of these activities. These strains and their respective plant hosts were Trichoderma harzianum BUK-T (Fagus sylvatica), Aspergillus ochraceus ROB-L1 (Robinia pseudoacacia), Chaetomium cochliodes KLON-L1, Fusarium tricinctum KLON-L2 (Acer platanoides), and Penicillium chrysogenum SOS-B2 (Pinus sylvestris). Moreover, gamma irradiation at several doses (Gy) was separately applied to the fungal cultures to study their effects on the recorded activities. Finally, compounds after preparative thin-layer chromatography fractionation of the five fungal strains were identified by GC-MS. These findings suggest that the isolated endophytic fungi could serve as novel sources of bioactive metabolites with antibacterial, antifungal, and antioxidant properties, potentially paving the way for future research and the development of new bioactive compounds.

Above‐ and belowground plant pathogens along elevational gradients: patterns and potential mechanisms

Plant pathogens are important for community assembly and ecosystem functioning and respond to a variety of abiotic and biotic factors, which may change along elevational gradients. Thus, elevational gradients are a valuable model system for exploring how environmental, plant community and soil factors influence pathogen communities. Yet, how these factors influence pathogens in natural ecosystems remains poorly understood. We examined the dynamics of plant fungal pathogens along elevational gradients, as well as the mechanisms shaping these dynamics, by combining a field survey on the Tibetan Plateau with a global meta‐analysis. In the field survey, increasing elevation was associated with a decrease in soil fungal pathogen richness but not in foliar fungal disease symptoms. Elevation was primarily related to soil fungal pathogen richness through abiotic factors, whereas no association was found between elevation and foliar fungal diseases. The meta‐analysis confirmed the generality of our field survey results: elevation was associated with a decrease in soil fungal pathogen richness, but it had no consistent relationship with foliar fungal diseases or pathogens. Thus, above‐ and belowground plant pathogen communities showed distinct elevational patterns, providing new insights into underlying mechanisms.

The first complete genome of Robbsia andropogonis reveals its arsenal of virulence system causing leaf spot disease of areca palm

Robbsia andropogonis is one of the most destructive leaf spot disease pathogens of numerous host plants and causes heavy economic damage. In the present study, the complete genome of R. andropogonis strain BLB1, causing the leaf spot disease of areca palm, was generated using a hybrid method combining ONT PromethION long reads and BGISEQ-500 short reads. The resulting genome consists of seven replicons totaling 6,828,120 bp, and 5,808 genes were annotated, including 788 virulence-related genes. Function analysis showed that genes involved in metabolism were the most abundant group. Impressively, the bacteria were well-equipped with four, two, and four sets of type three, four, and six secretion systems, respectively, highlighting the virulence features of R. andropogonis BLB1. As the first complete genome sequence of the species of genus Robbsia, the BLB1 genome provides a solid foundation for investigation of mechanisms underlying the pathogen virulence and disease control, and will promote further discovery and characterization of the genus Robbsia.

Quantification of the fungal pathogen Didymella segeticola in Camellia sinensis using a DNA-based qRT-PCR assay.

The fungal pathogen Didymella segeticola causes leaf spot and leaf blight on tea plant (Camellia sinensis), leading to production losses and affecting tea quality and flavor. Accurate detection and quantification of D. segeticola growth in tea plant leaves are crucial for diagnosing disease severity or evaluating host resistance. In this study, we monitored disease progression and D. segeticola development in tea plant leaves inoculated with a GFP-expressing strain. By contrast, a DNA-based qRT-PCR analysis was employed for a more convenient and maneuverable detection of D. segeticola growth in tea leaves. This method was based on the comparison of D. segeticola-specific DNA encoding a Cys2His2-zinc-finger protein (NCBI accession number: OR987684) in relation to tea plant Cs18S rDNA1. Unlike ITS and TUB2 sequences, this specific DNA was only amplified in D. segeticola isolates, not in other tea plant pathogens. This assay is also applicable for detecting D. segeticola during interactions with various tea cultivars. Among the five cultivars tested, 'Zhongcha102' (ZC102) and 'Fuding-dabaicha' (FDDB) were more susceptible to D. segeticola compared with 'Longjing43' (LJ43), 'Zhongcha108' (ZC108), and 'Zhongcha302' (ZC302). Different D. segeticola isolates also exhibited varying levels of aggressiveness towards LJ43. In conclusion, the DNA-based qRT-PCR analysis is highly sensitive, convenient, and effective method for quantifying D. segeticola growth in tea plant. This technique can be used to diagnose the severity of tea leaf spot and blight or to evaluate tea plant resistance to this pathogen.

Genomic Characterization and Establishment of a Genetic Manipulation System for Trichoderma sp. (Harzianum Clade) LZ117.

Trichoderma species have been reported as masters in producing cellulolytic enzymes for the biodegradation of lignocellulolytic biomass and biocontrol agents against plant pathogens and pests. In our previous study, a novel Trichoderma strain LZ117, which shows potent capability in cellulase production, was isolated. Herein, we conducted multilocus phylogenetic analyses based on DNA barcodes and performed time-scaled phylogenomic analyses using the whole genome sequences of the strain, annotated by integrating transcriptome data. Our results suggest that this strain represents a new species closely related to T. atrobrunneum (Harzianum clade). Genes encoding carbohydrate-active enzymes (CAZymes), transporters, and secondary metabolites were annotated and predicted secretome in Trichoderma sp. LZ117 was also presented. Furthermore, genetic manipulation of this strain was successfully achieved using PEG-mediated protoplast transformation. A putative transporter gene encoding maltose permease (Mal1) was overexpressed, which proved that this transporter does not affect cellulase production. Moreover, overexpressing the native Cre1 homolog in LZ117 demonstrated a more pronounced impact of glucose-caused carbon catabolite repression (CCR), suggesting the importance of Cre1-mediated CCR in cellulase production of Trichoderma sp. LZ117. The results of this study will benefit further exploration of the strain LZ117 and related species for their applications in bioproduction.

Biocontrol potential of Bacillus velezensis SEC-024A against southern blight of industrial hemp

Agroathelia rolfsii is the causative agent of southern blight of industrial hemp, which is a soil-borne infection resulting in grave economic losses in industrial hemp (Cannabis sativa L.). Chemical pesticides are currently the primary means of controlling this disease, but their use is harmful to human health as well as to the environment. Urgent action is needed to screen eco-friendly biocontrol agents against this pathogen. An endophytic bacterium SEC-024A was isolated from the leaf tissue of industrial hemp and exhibited a significant antagonistic effect on A. rolfsii, with a plate inhibition rate of 80.5 % and a pot control effect of 74.1 %. Through whole genome sequencing, SEC-024A was identified to be Bacillus velezensis. It contained multiple gene clusters involved in secondary metabolite biosynthesis and the genes that promote plant growth, colonization, and pathogen defense. Bacillus velezensis SEC-024A produces volatile organic compounds (VOCs) that serve as its primary fungistatic agents. Nine VOCs produced by SEC-024A were detected through gas chromatography-mass spectrometry. These VOCs were individually tested for their antifungal effects. Four volatiles, namely isobutyric acid, tiglic acid, trans-2-octenal, and 2-decanone, exhibited notable inhibitory effects on A. rolfsii with EC50 values of 0.012, 0.038, 0.009, and 0.046 μL/mL, respectively. Additionally, trans-2-octenal demonstrated broad-spectrum antifungal activity against various soil-borne pathogens. Together, this study suggests that B. velezensis SEC-024A holds promise as a novel microbial agent for improving plant growth and controlling diseases.

Conserved perception of host and non-host signals via the a-pheromone receptor Ste3 in Colletotrichum graminicola.

Understanding the interactions between fungal plant pathogens and host roots is crucial for developing effective disease management strategies. This study investigates the molecular mechanisms underpinning the chemotropic responses of the maize anthracnose fungus Colletotrichum graminicola to maize root exudates. Combining the generation of a deletion mutant with monitoring of disease symptom development and detailed analysis of chemotropic growth using a 3D-printed device, we identify the 7-transmembrane G-protein coupled receptor (GPCR) CgSte3 as a key player in sensing both plant-derived class III peroxidases and diterpenoids. Activation of CgSte3 initiates signaling through CgSo, a homolog to the Cell Wall Integrity Mitogen-Activated Protein Kinase (CWI MAPK) pathway scaffold protein identified in other filamentous fungi, facilitating the pathogen's growth towards plant defense molecules. The NADPH oxidase CgNox2 is crucial for peroxidase sensing but not for diterpenoid detection. These findings reveal that CgSte3 and CWI MAPK pathways are central to C. graminicola's ability to hijack plant defense signals, highlighting potential targets for controlling maize anthracnose.

Plant PR1 rescues condensation of the plastid iron-sulfur protein by a fungal effector.

Plant pathogens secrete numerous effectors to promote host infection, but whether any of these toxic proteins undergoes phase separation to manipulate plant defence and how the host copes with this event remain elusive. Here we show that the effector FolSvp2, which is secreted from the fungal pathogen Fusarium oxysporum f. sp. lycopersici (Fol), translocates a tomato iron-sulfur protein (SlISP) from plastids into effector condensates in planta via phase separation. Relocation of SlISP attenuates plant reactive oxygen species production and thus facilitates Fol invasion. The action of FolSvp2 also requires K205 acetylation that prevents ubiquitination-dependent degradation of this protein in both Fol and plant cells. However, tomato has evolved a defence protein, SlPR1. Apoplastic SlPR1 physically interacts with and inhibits FolSvp2 entry into host cells and, consequently, abolishes its deleterious effect. These findings reveal a previously unknown function of PR1 in countering a new mode of effector action.

Spatial trajectories of coffee harvesting in large-scale plantations: Ecological and management drivers and implications

CONTEXTCoffee is produced under different management systems and scales of production categorized as Syndromes of Production. The “Capitalist Syndrome” is characterized by large-scale and high-density planting farms that may promote the development of plant pathogens like coffee leaf rust (CLR). Harvesting dynamics are also affected by the syndrome of production and generate spatial trajectories that could contribute to the dispersal of pathogens across and within plantations. However, these spatial trajectories have not yet been described, nor their relationship with the syndrome of production, and even less its potential ecological implications for pathogen dispersal. OBJECTIVEDescribe and analyze the daily spatial movement of coffee harvesters in two large-scale capitalist plantations, an organic and a conventional plantation, and systematize the drivers that might explain the differences in the spatial trajectories. METHODSUsing State-Space Models, we recorded and analyzed the spatial movements of harvesters. We then constructed a driver tree for harvest dynamics, which incorporated qualitative variables related to the environment, coffee biology, and management aspects reported by the harvesters or in previous studies. RESULTS AND CONCLUSIONSThe model differentiated two kinds of movements: 1) when trees have berries, harvesters remain in the coffee rows or areas nearby (Collect state; 94–98 % of the steps); 2) when not, harvesters make longer steps within the harvesting location or move to another area (Search state; 2–6 % of the steps). In the organic plantation, the Search state had a longer-tailed step-length distribution than in the conventional plantation, resulting in a significantly larger visited area per worker (p < 0.05). This might be directly related to the lower interplant ripening percentage or smaller harvesting locations (“pantes”) per number of harvesters. The number of harvested trees might be affected by the fruit load or the coffee variety, among others. Harvesting movements that explore a larger area, either by visiting more plants or by changing locations on the same day, could create more foci of CLR infection across the plantation. SIGNIFICANCEThese results constitute an initial analysis of harvesting trajectories and highlight practices that can reduce the potential impact of human dispersal of pathogens, like shorter harvesting trajectories by working fewer hours a day or avoiding harvesting at the end of the maturation season when few trees have berries and harvesters have to travel medium to long distances. This calls for organic coffee management that could prevent diseases and guarantee just and safe conditions for workers.

Biological Control of Microbial Pectinolytic Plant Pathogens Causing Soft Rot of Fruits and Vegetables.

It is crucial to implement appropriate measures to prevent the spread of plant pathogens that lead to the decay of fruits and vegetables. From this perspective, we evaluated the biocontrol potential of five Bacillus-plant growth promoting rhizobacteria (PGPR) strains against twenty-one pectinolytic phytopathogens causing soft rot in fruits and vegetables. These phytopathogens had been previously studied. Three in vitro methods were utilized to accomplish this objective: competition, extraction of bioactive substances, and direct confrontation. The inhibitory effect of the direct confrontation method resulted in a slower growth of 11 microbial plant pathogens. In addition, it was noted that 11 strains of plant pathogens generated inhibitory constituents, while 15 plant pathogens produced inducible inhibitory substances. Furthermore, volatile inhibitory compounds were detected in the six tested strains. Overall, strains of PGPR-Bacillus demonstrated strong antifungal and antibacterial properties against phytopathogens. These PGPR can be regarded as potential biocontrol agents for soft microbial rot in fruits and vegetables as well as producers of substances that effectively suppress plant diseases.

Exploring the Potential of Macroalgae for Sustainable Crop Production in Agriculture.

Marine macroalgae, which typically colonize coastal areas, are simple plant organisms. They live on rocks in coastal regions and are classified into red, brown, and green macroalgae. These algae are an important natural resource in agriculture due to their ability to enhance the structural, chemical, and biological properties of soil. Marine macroalgae can be used to produce various biocidal molecules that are effective in controlling plant pathogens. Much of the literature on marine macroalgae and their derivatives focuses primarily on the pharmaceutical field, while their use in agriculture is still considered secondary. However, various studies and experiments have demonstrated their potential to play a significant role in crop protection and enhancement. This review aims to highlight the various applications of macroalgae in plant production. It also emphasizes the biotechnological importance of marine macroalgae derivatives as biofertilizers, molecules for controlling insects and microorganisms, and as plant growth conditioners. Compounds from macroalgae, such as fatty acids, carotenoids, polyphenols, and carbohydrates, are being investigated for their fungicidal, antimicrobial, and antiviral effects against various plant pathogens. Beyond enhancing crop production, macroalgae can also be considered multifunctional bioinoculants suitable for use in organic farming.

RNA interference: a promising biotechnological approach to combat plant pathogens, mechanism and future prospects.

Plant pathogens and other biological pests represent significant obstacles to crop Protection worldwide. Even though there are many effective conventional methods for controlling plant diseases, new methods that are also effective, environmentally safe, and cost-effective are required. While plant breeding has traditionally been used to manipulate the plant genome to develop resistant cultivars for controlling plant diseases, the emergence of genetic engineering has introduced a completely new approach to render plants resistant to bacteria, nematodes, fungi, and viruses. The RNA interference (RNAi) approach has recently emerged as a potentially useful tool for mitigating the inherent risks associated with the development of conventional transgenics. These risks include the use of specific transgenes, gene control sequences, or marker genes. Utilizing RNAi to silence certain genes is a promising solution to this dilemma as disease-resistant transgenic plants can be generated within a legislative structure. Recent investigations have shown that using target double stranded RNAs via an effective vector system can produce significant silencing effects. Both dsRNA-containing crop sprays and transgenic plants carrying RNAi vectors have proven effective in controlling plant diseases that threaten commercially significant crop species. This article discusses the methods and applications of the most recent RNAi technology for reducing plant diseases to ensure sustainable agricultural yields.

Bioactivity of a dihydroxy flavone produced by Penicillium EU0013 against the wilt pathogen of tomato

Bioassay-guided isolation of a dihydroxy flavone from the cell extract of Penicillium EU0013 was carried out using preparative LCMS and the structure was interpreted using 1D and 2D NMR spectra. The fungus was fermented in three different nutrient media i.e. Glucose Nutrient Broth, Glucose Peptone Yeast Broth, and Yeast Extract Broth and the cell extract was obtained using organics. Comparative LCMS profiles of the fungus confirmed the enhanced production of dihydroxy flavone in GPYB media. In this study, the pathogenicity of the dihydroxy flavone is reported for the first time against Fusarium oxysporum f.sp. lycopersici, wilt causing pathogen of a tomato plant. In MIC experiments, the compound inhibited the pathogen at 80 µg mL−1. Molecular docking studies of the compound with Fol tomatinase showed five binding interactions. These docking studies may help explore dihydroxy flavones as a lead for developing new fungicides to prevent wilt disease in tomatoes.

Molecular phylogenetic and estimation of evolutionary divergence and biogeography of the family Schizoparmaceae and allied families (Diaporthales, Ascomycota)

The Diaporthales includes 32 families, many of which are important plant pathogens, endophytes and saprobes, e.g., members of the families Pseudoplagiostomataceae, Pyrisporaceae and Schizoparmaceae. Nucleotide sequences derived from five genetic loci including: ITS, LSU, TEF1-α, TUB2 and RPB2 were used for Bayesian evolutionary analysis to determine divergence times and evolutionary relationships within the Schizoparmaceae. Molecular clock analyses revealed that the ancestor of Schizoparmaceae split during the Upper Cretaceous period approximately 75.7 Mya (95 % highest posterior density of 60.3–91.3 Mya). Reconstructing ancestral state in phylogenies (RASP) with using the Bayesian Binary Markov chain Monte Carlo (BBM) Method to reconstruct the historical biogeography for the family Schizoparmaceae indicated its most likely origin in Africa. Based on taxonomic and phylogenetic analyses, the Pseudoplagiostomataceae and Pyrisporaceae relationships were clarified and a total of four species described herein. For Pseudoplagiostomataceae, three new species and one known species that include, Pseudoplagiostoma fafuense sp. nov., Ps. ilicis sp. nov., Ps. sanmingense sp. nov. and Ps. bambusae are described and a key of Pseudoplagiostomataceae is provided. With respect to Pyrisporaceae, we considered Pseudoplagiostoma castaneae to be a synonym of Pyrispora castaneae. In addition, a new species of Schizoparmaceae, Coniella fujianensis sp. nov. is described and illustrated.

Efficacy of Bacillus spp. Isolates for Application as Biofertilizer in Tomato (Solanum lycospersicum L.) Cultivation

Certain species of Bacillus are considered rhizobacteria that promote plant growth, inhibit the growth of plant pathogens and deleterious rhizospheric microorganisms. The aim of this study was to determine the stimulatory effect of Bacillus subtilis KBM1 and Bacillus venezensis KBM1 on the growth and disease reduction of tomato plants in Côte d'Ivoire. In this respect, three substrates consisting of soil only, sawdust only and a mixture of soil and sawdust were inoculated with the two bacteria, then left to ferment for twenty-four (24) hours. The biofertilizers obtained after fermentation were used to assess their effects on the development of potted tomatoes. Growth parameters, infection rate and mortality rate of tomato plants were measured regularly during 6 weeks of cultivation. A search for tomato pathogenic fungi was carried out to demonstrate the efficacy of Bacillus strains isolates on plant health. The results obtained showed that Bacillus subtilis KBM1 and Bacillus venezensis KBM1 had a positive impact on plant growth of tomato plants grown. Infection and mortality rates of 0% were observed for tomato plants grown on the three substrates inoculated with these two bacteria. No pathogenic fungi were isolated from the organs of tomato plants grown on the three substrates fermented with the bacteria. However, on untreated control plants, a variety of pathogenic fungi, namely Fusarium sp, Phytophtora sp, Cladosporium sp, Rhizoctonia sp, Colletotrichum sp, Penicillium sp, Rhizopus sp and Trichoderma sp were observed. However, the Bacillus subtilis KBM1 treatment stood out from Bacillus venezensis KBM1 with the best results for the growth parameters measured. In view of these results, these two bacteria could be used to produce an effective biofertilizer for tomato cultivation in Côte d'Ivoire.

The role of foraging pollinators in assembling the flower microbiota and transmitting the fire blight pathogen Erwinia amylovora.

Flowers serve as hubs for biotic interactions with pollinators and microbes, which can significantly impact plant reproduction and health. Previous studies have shown that the flower microbiota undergoes dynamic assembly processes during anthesis. However, the influence of foraging pollinators on the assembly and dispersal of the flower microbiota and the transmission of plant pathogens remains poorly understood. In this study, we used insect exclusion netting to investigate the role of pollinators in the assembly of the microbiota on apple stigma and the transmission of the fire blight pathogen Erwinia amylovora. We found that excluding pollinators had a minor impact on the community diversity and composition of the apple stigma microbiota, while the flower's developmental stage had a strong influence. Additionally, pollinator exclusion altered bacterial dispersal and the relative abundance of different bacterial species, including E. amylovora, suggesting that pollinators play a role in transmitting plant pathogens. Using a reporter system, we demonstrated that bumble bees can transmit the fire blight pathogen from an infected flower under controlled growth conditions. Our study highlights the importance of intrinsic and pollinator-independent microbes as sources of inoculum for the stigma microbiota and underscores the role of foraging pollinators in vectoring plant pathogens.