Colletotrichum Species Research Articles

A New Biocontrol Agent Bacillus velezensis SF334 against Rubber Tree Fungal Leaf Anthracnose and Its Genome Analysis of Versatile Plant Probiotic Traits.

Natural rubber is an important national strategic and industrial raw material. The leaf anthracnose of rubber trees caused by the Colletotrichum species is one of the important factors restricting the yields of natural rubber. In this study, we isolated and identified strain Bacillus velezensis SF334, which exhibited significant antagonistic activity against both C. australisinense and C. siamense, the dominant species of Colletotrichum causing rubber tree leaf anthracnose in the Hainan province of China, from a pool of 223 bacterial strains. The cell suspensions of SF334 had a significant prevention effect for the leaf anthracnose of rubber trees, with an efficacy of 79.67% against C. siamense and 71.8% against C. australisinense. We demonstrated that SF334 can lead to the lysis of C. australisinense and C. siamense mycelia by causing mycelial expansion, resulting in mycelial rupture and subsequent death. B. velezensis SF334 also harbors some plant probiotic traits, such as secreting siderophore, protease, cellulase, pectinase, and the auxin of indole-3-acetic acid (IAA), and it has broad-spectrum antifungal activity against some important plant pathogenic fungi. The genome combined with comparative genomic analyses indicated that SF334 possesses most genes of the central metabolic and gene clusters of secondary metabolites in B. velezensis strains. To our knowledge, this is the first time a Bacillus velezensis strain has been reported as a promising biocontrol agent against the leaf anthracnose of rubber trees caused by C. siamense and C. australisinense. The results suggest that B. velezensis could be a potential candidate agent for the leaf anthracnose of rubber trees.

Guanosine-specific single-stranded ribonuclease effectors of a phytopathogenic fungus potentiate host immune responses.

Plants activate immunity upon recognition of pathogen-associated molecular patterns. Although phytopathogens have evolved a set of effector proteins to counteract plant immunity, some effectors are perceived by hosts and induce immune responses. Here, we show that two secreted ribonuclease effectors, SRN1 and SRN2, encoded in a phytopathogenic fungus, Colletotrichum orbiculare, induce cell death in a signal peptide- and catalytic residue-dependent manner, when transiently expressed in Nicotiana benthamiana. The pervasive presence of SRN genes across Colletotrichum species suggested the conserved roles. Using a transient gene expression system in cucumber (Cucumis sativus), an original host of C. orbiculare, we show that SRN1 and SRN2 potentiate host pattern-triggered immunity responses. Consistent with this, C. orbiculare SRN1 and SRN2 deletion mutants exhibited increased virulence on the host. In vitro analysis revealed that SRN1 specifically cleaves single-stranded RNAs at guanosine, leaving a 3'-end phosphate. Importantly, the potentiation of C. sativus responses by SRN1 and SRN2, present in the apoplast, depends on ribonuclease catalytic residues. We propose that the pathogen-derived apoplastic guanosine-specific single-stranded endoribonucleases lead to immunity potentiation in plants.

What's in my Pot? Six Colletotrichum Species Causing Anthracnose in Brazilian Pecan Orchards.

Pecan (Carya illinoinensis) is one important exotic forest crop cultivated in South America, specifically in Brazil, Uruguay, and Argentina. However, diseases such as anthracnose, favored by high humidity conditions and high summer temperatures, make its cultivation difficult, causing important loss to pecan farmers. This study used morphological and molecular approaches to identify the Colletotrichum species causing anthracnose in pecan plantations in Southern Brazil. The isolates obtained from pecan fruits with anthracnose symptoms were grouped through quantitative morphological characteristics into three distinct morphotypes. Molecular analysis of nuclear genes allowed the identification of six species of Colletotrichum causing anthracnose in pecan: C. nymphaeae, C. fioriniae, C. gloeosporioides, C. siamense, C. kahawae, and C. karsti. Three of these species are reported for the first time as causal agents of anthracnose in pecan. Therefore, these results provide an important basis for the adoption and/or development of anthracnose management strategies in pecan orchards cultivated in southern Brazil and neighboring countries.

Polyphasic identification of two novel Colletotrichum species causing leaf spots on mangroves in Thailand

Polyphasic identification of two novel Colletotrichum species causing leaf spots on mangroves in Thailand

Evaluation of screening methods for anthracnose fruit rot resistance in chilli (Capsicum spp.)

Anthracnose fruit rot caused by Colletotrichum spp. is a serious production constraint causing severe marketable yield loss in chilli. Field evaluation of chilli accessions for resistance to Colletotrichum spp. depends on various factors affecting disease expression such as edaphic conditions, temperature, rainfall, humidity and other variables that are difficult to control, therefore considered less accurate. Also, high chances of cross contamination with different Colletotrichum species leads to inconclusive assays for specific pathogen species and isolate. To identify a stable and reliable screening method, various chilli accessions were subjected to in vitro pin-prick and non-wounding spray methods using a specific pathogen isolates. When chilli accessions were screened against C. gloeosporioides isolate ‘IHRCg-1’, the in vitro pin- prick method showed positive correlation with the non- wounding spray method, except in the accession PBC80. The change in bioassay influenced the disease reaction pattern in the accession PBC 80, probably the pin pricks break the basal cuticle defense mechanism that was retained in spray inoculation method indicating varied resistance pattern. However, in the accession PBC 81 stable resistance pattern was observed against isolates of both species viz., C. truncatum ‘IIHR Ct-1’ and C. gloeosporioides ‘IIHR Cg-1’ and in the accession PBC 80 against C. truncatum ‘IIHR Ct-1’ in both the inoculation methods that depicted the expression of resistance genes during both methods of inoculation. Based on disease development pattern, the red ripe chilli expressed a variant reaction to infection by C. truncatum and C. gloeosporioides. The peak anthracnose infection at 10 DAI and 14 DAI is an accurate duration to record ‘IIHR Cg-1’ and ‘IIHR Ct-1’ infection, respectively on chilli ripe fruit for assaying the resistance.

SCREENING OF MICROBIAL BIOPESTICIDES AGAINST POST-HARVEST FUNGAL PATHOGEN COLLETOTRICHUM SPP A PRELIMINARY STUDY

Most common fungal pathogens are found in Colletotrichum genus which cause economically significant anthracnose or blight disease in a variety of tropical and subtropical fruit and vegetables. Despite that, the excessive application of chemical pesticides in agriculture has caused many problems such as poor soil fertility, pollution and risk to human health due to the toxic accumulation of the pesticides in the soil. This study was carried out to isolate potential bacterial colonies from five different soil sources around Universiti Malaysia Terengganu and to the screen isolated bacteria for antagonistic effect against Colletotrichum species. In total, 50 bacterial strains were isolated and subjected to selective screening to distinguish bacterial strains capable of inhibiting Colletotrichum sp. Based on the selective screening, nine bacterial strains with different morphology were selected and tested further in quantitative screening by calculating their percentage of inhibition of radial growth (PIRG). The results showed that S5-H strain demonstrated the highest inhibition effect at (75.67 ±2.86)%, followed by S5-I strain (68.89 ±5.93)%, S5-D strain (66.89 ±6.15)%, S3-C strain (60.33 ±3.19)%, S5-F strain (57.89 ±4.66)%, S5-G strain (53 ±5.79)%, S2-I strain (41.33 ±7.26)%, S4-B strain (40 ±7.07)% and S3-D strain (38.33 ±8.90)%. Based on the results, bacterial isolate S5-H with yellow, round, convex and entire colony from mangrove muddy sediment was shown to have a potential to be utilized as biopesticides against Colletotrichum sp. Nevertheless, this study requires further work in the future focusing on species identification by 16S rRNA phylogeny and mechanism of action exhibited by S5-H strain.

Evolutionary history of the cytochrome P450s from Colletotrichum species and prediction of their putative functional roles during host-pathogen interactions

The genomes of species belonging to the genus Colletotrichum harbor a substantial number of cytochrome P450 monooxygenases (CYPs) encoded by a broad diversity of gene families. However, the biological role of their CYP complement (CYPome) has not been elucidated. Here, we investigated the putative evolutionary scenarios that occurred during the evolution of the CYPome belonging to the Colletotrichum Graminicola species complex (s.c.) and their biological implications. The study revealed that most of the CYPome gene families belonging to the Graminicola s.c. experienced gene contractions. The reductive evolution resulted in species restricted CYPs are predominant in each CYPome of members from the Graminicola s.c., whereas only 18 families are absolutely conserved among these species. However, members of CYP families displayed a notably different phylogenetic relationship at the tertiary structure level, suggesting a putative convergent evolution scenario. Most of the CYP enzymes of the Graminicola s.c. share redundant functions in secondary metabolite biosynthesis and xenobiotic metabolism. Hence, this current work suggests that the presence of a broad CYPome in the genus Colletotrichum plays a critical role in the optimization of the colonization capability and virulence.

A novel partitivirus conferring hypovirulence by affecting vesicle transport in the fungus Colletotrichum.

Colletotrichum spp. are economically important phytopathogenic fungi that cause anthracnose in a variety of plant species worldwide. Hypovirulence-associated mycoviruses provide new options for the biological control of plant fungal diseases. Here, we found a novel partitivirus from Colletotrichum alienum and named it Colletotrichum alienum partitivirus 1 (CaPV1). CaPV1 contained two dsRNA segments encoding an RNA-dependent RNA polymerase and a capsid protein and was classified under the genus Gammapartitivirus of the family Partitiviridae. CaPV1 significantly decreased host virulence, mycelial growth, appressorial development, and appressorium turgor but increased conidial production with abnormal morphology. In addition, CaPV1 could be successfully transfected into other Colletotrichum species, including C. fructicola, C. spaethianum, and C. gloeosporioides, and caused hypovirulence, indicating the broad application potential of this virus. CaPV1 caused significant transcriptional rewiring of the host fungus C. alienum. Notably, some genes related to vesicle transport in the CaPV1-infected strain were downregulated, consistent with the impaired endocytosis pathway in this fungus. When the Rab gene CaRab7, which is associated with endocytosis in vesicle transport, was knocked out, the virulence of the mutants was reduced. Overall, our findings demonstrated that CaPV1 has the potential to control anthracnose caused by Colletotrichum, and the mechanism by which Colletotrichum induces hypovirulence is caused by affecting vesicle transport.IMPORTANCEColletotrichum is a kind of economically important phytopathogenic fungi that cause anthracnose disease in a variety of plant species worldwide. We found a novel mycovirus of the Gammapartitivirus genus and Partitiviridae family from the phytopathogenic fungus Colletotrichum alienum and named it CaPV1. This study revealed that CaPV1 infection significantly decreased host virulence and fitness by affecting mycelial growth, appressorial development, and appressorium turgor. In addition, CaPV1 could also infect other Colletotrichum species, including C. fructicola, C. spaethianum, and C. gloeosporioides, by viral particle transfection and resulting in hypovirulence of these Colletotrichum species. Transcriptomic analysis showed that CaPV1 caused significant transcriptional rewiring of the host fungus C. alienum, especially the genes involved in vesicle transport. Moreover, endocytosis and gene knockout assays demonstrated that the mechanism underlying CaPV1-induced hypovirulence is, at least in part, caused by affecting the vesicle transport of the host fungus. This study provided insights into the mechanisms underlying the pathogenesis of Colletotrichum species and mycovirus-fungus interactions, linking the role of mycovirus and fungus vesicle transport systems in shaping fungal pathogenicity.

Pathogenicity of Colletotrichum species isolated from rotten fruit and asymptomatic flowers of loquat in Nagasaki Prefecture, Japan and characterization of C. nagasakiense Takata & Kyoko Watan. sp. nov

Pathogenicity of Colletotrichum species isolated from rotten fruit and asymptomatic flowers of loquat in Nagasaki Prefecture, Japan and characterization of C. nagasakiense Takata & Kyoko Watan. sp. nov

Characterization and evaluation of Bacillus subtilis GYUN-2311 as a biocontrol agent against Colletotrichum spp. on apple and hot pepper in Korea.

Crop plants are vulnerable to a variety of diseases, including anthracnose, caused by various species of Colletotrichum fungi that damages major crops, including apples and hot peppers. The use of chemical fungicides for pathogen control may lead to environmental pollution and disease resistance. Therefore, we conducted this research to develop a Bacillus subtilis-based biological control agent (BCA). B. subtilis GYUN-2311 (GYUN-2311), isolated from the rhizosphere soil of an apple orchard, exhibited antagonistic activity against a total of 12 fungal pathogens, including eight Colletotrichum species. The volatile organic compounds (VOCs) and culture filtrate (CF) from GYUN-2311 displayed antifungal activity against all 12 pathogens, with 81% control efficiency against Fusarium oxysporum for VOCs and 81.4% control efficacy against Botryosphaeria dothidea for CF. CF also inhibited germination and appressorium formation in Colletotrichum siamense and C. acutatum. The CF from GYUN-2311 showed antifungal activity against all 12 pathogens in different media, particularly in LB medium. It also exhibited plant growth-promoting (PGP) activity, lytic enzyme activity, siderophore production, and the ability to solubilize insoluble phosphate. In trials on apples and hot peppers, GYUN-2311 effectively controlled disease, with 75 and 70% control efficacies against C. siamense in wounded and unwounded apples, respectively. Similarly, the control efficacy of hot pepper against C. acutatum in wounded inoculation was 72%. Combined application of GYUN-2311 and chemical suppressed hot pepper anthracnose to a larger extent than other treatments, such as chemical control, pyraclostrobin, TK®, GYUN-2311 and cross-spraying of chemical and GYUN-2311 under field conditions. The genome analysis of GYUN-2311 identified a circular chromosome comprising 4,043 predicted protein-coding sequences (CDSs) and 4,096,969 bp. B. subtilis SRCM104005 was the strain with the highest average nucleotide identity (ANI) to GYUN-2311. AntiSMASH analysis identified secondary metabolite biosynthetic genes, such as subtilomycin, bacillaene, fengycin, bacillibactin, pulcherriminic acid, subtilosin A, and bacilysin, whereas BAGEL analysis confirmed the presence of competence (ComX). Six secondary metabolite biosynthetic genes were induced during dual culture in the presence of C. siamense. These findings demonstrate the biological control potential of GYUN-2311 against apple and hot pepper anthracnose.

Genome evolution and transcriptome plasticity is associated with adaptation to monocot and dicot plants in Colletotrichum fungi.

Colletotrichum fungi infect a wide diversity of monocot and dicot hosts, causing diseases on almost all economically important plants worldwide. Colletotrichum is also a suitable model for studying gene family evolution on a fine scale to uncover events in the genome associated with biological changes. Here we present the genome sequences of 30 Colletotrichum species covering the diversity within the genus. Evolutionary analyses revealed that the Colletotrichum ancestor diverged in the late Cretaceous in parallel with the diversification of flowering plants. We provide evidence of independent host jumps from dicots to monocots during the evolution of Colletotrichum, coinciding with a progressive shrinking of the plant cell wall degradative arsenal and expansions in lineage-specific gene families. Comparative transcriptomics of 4 species adapted to different hosts revealed similarity in gene content but high diversity in the modulation of their transcription profiles on different plant substrates. Combining genomics and transcriptomics, we identified a set of core genes such as specific transcription factors, putatively involved in plant cell wall degradation. These results indicate that the ancestral Colletotrichum were associated with dicot plants and certain branches progressively adapted to different monocot hosts, reshaping the gene content and its regulation.

Colletotrichum species (Glomerellales, Glomerellaceae) causing walnut anthracnose in China.

Colletotrichum species can function as plant pathogens, saprobes or endophytes on a wide variety of plant hosts and are considered amongst the ten most significant genera of plant pathogens globally. China contributes almost half the walnut production in the world. However, Colletotrichum species occurring on walnut remain largely unresolved in China. To explore the Colletotrichum species found on walnut in China, 470 walnut fruit or leaf samples with anthracnose were collected from 14 main walnut-producing regions across seven provinces. A total of 165 Colletotrichum strains were isolated from these samples. The Colletotrichum isolates were identified, based on morphological characteristics and sequence analyses of ACT, CHS-1, GAPDH, ITS and TUB2. Twelve species, including 11 known Colletotrichum species (C.boninense, C.citrulli, C.fioriniae, C.fructicola, C.godetiae, C.juglandicola, C.karsti, C.mengyinense, C.pandanicola, C.peakense and C.siamense) and a novel species (C.chinensis sp. nov.) were identified. The species distribution revealed regional prevalence as follows: C.mengyinense was the most dominant species in Gansu, C.mengyinense and C.siamense in Shandong, C.chinensis in Beijing, C.pandanicola in Shaanxi and C.godetiae in Yunnan. Colletotrichumsiamense was the sole species isolated in Sichuan and Xinjiang Provinces. Koch's postulates were fulfilled, demonstrating that all 12 species cause anthracnose on walnut. This is the first report of C.boninense, C.citrulli and C.karsti as pathogens of walnut anthracnose worldwide.

Colletotrichum siamense is responsible for anthracnose on Hymenaea stigonocarpa in Brazil

AbstractHymenaea stigonocarpa, popularly known as ‘jatobá’ or ‘jatobá‐do‐cerrado’, is a native plant widely distributed across Brazilian Cerrado areas. This plant is used for urban afforestation, human and animal feeding, and industry. Foliar lesions resembling anthracnose symptoms were observed on H. stigonocarpa in natural habitats and nurseries. Microscopic examination of acervuli indicated a Colletotrichum species as the cause of the anthracnose symptoms. Based on multilocus phylogenetic analyses including data from APN2, APN2‐MAT/IGS, CAL, GAP2‐IGS, GAPDH, GS and TUB2 alongside morphological characterization and pathogenicity tests, Colletotrichum siamense was confidently identified as the causal agent of H. stignocarpa anthracnose in Brazil.

Colletotrichum nanjingense sp. nov. and C. gloeosporioides s.s. Causing Leaf Tip Blight on Jasminum mesnyi in Nanjing, Jiangsu, China.

Jasminum mesnyi Hance is an important medicinal and ornamental plant. This species is native to South Central China and Vietnam and grows primarily in the subtropical biomes. In June 2022, 17 Colletotrichum strains were isolated from leaf tip blight on foliage of J. mesnyi in Nanjing, Jiangsu, China. Based on morphological characteristics and multilocus phylogenetic analyses of six genomic loci (ITS, CAL, ACT, TUB2, CHS-1, and GAPDH), a new species, namely, C. nanjingense, and a known species, namely, C. gloeosporioides s.s., were described and reported. Pathogenicity tests revealed that both species were pathogens causing leaf tip blight on J. mesnyi. The results provided necessary information for disease control and enhanced our understanding of the diversity of Colletotrichum species in China.

CHITOSAN INHIBITS THE <i>IN VITRO</i> DEVELOPMENT OF <i>Colletotrichum</i> SP. FROM BANANA (<i>Musa x paradisiaca</i> L.) FRUITS

The banano (Musa x paradisiaca L.) is a tropical fruit, susceptible to infection by Colletotrichum sp. Fungicides are the most typical approach for controlling postharvest infections. Concerns regarding its negative impact on human health and the environment have prompted the quest for alternate remedies. Because of its antimicrobial activity, chitosan is an environmentally friendly alternative. This study aimed to determine the influence of chitosan on the in vitro development of Colletotrichum sp. isolated from banana fruits. Inhibition mycelial growth, spore concentration and spore germination were evaluated in three chitosan concentrations, 0.5 %, 1.0 % and 1.5 %. Optical, fluorescence, and scanning electron microscopy were used to examine the impact of chitosan on spore growth and morphology. We observed that chitosan solutions inhibited Colletotrichum species in vitro. Chitosan at 1.5 % significantly decreased the percentage of mycelial growth inhibition and spore concentration in comparison with the control. Compared to the control, a concentration of 1.5 % chitosan considerably decreased the mycelial growth and spore concentration. In addition, a complete inhibition of spore germination and a low mycelium content was observed with 1.0% and 1.5% chitosan, controlling the in vitro development of Colletotrichum sp. in banana fruits.

Assessment of Candidate Reference Genes for Gene Expression Studies Using RT-qPCR in Colletotrichum fructicola from Litchi.

Litchi (Litchi chinensis Sonn.) is a tropical fruit originating from southern China that is currently cultivated in subtropical and tropical regions worldwide. Litchi anthracnose, caused by Colletotrichum fructicola, a dominant species of Colletotrichum spp., is an important disease of litchi that damages the fruits in fields and in post-harvest storage. Real-time quantitative PCR (RT-qPCR) is a common technique with which to detect the expression of and function of target genes quickly and precisely, and stable reference genes are crucial. However, there is no comprehensive information on suitable reference genes of C. fructicola present. Here, we designed eight candidate genes (GAPDH, α-tubulin, 18S, β-tubulin, EF1a, TATA, RPS5, and EF3) using RefFinder software (programs: geNorm, ΔCt, BestKeeper, and NormFinder) to investigate their reliability in the detection of C. fructicola under five different treatments (fungal development stage, temperature, UV, culture medium, and fungicide). The results showed the optimal reference genes under different conditions: EF1a and α-tubulin for developmental stage; α-tubulin and β-tubulin for temperature; α-tubulin and RPS5 for UV treatment; RPS5 and α-tubulin for culture medium; α-tubulin, GAPDH, and TATA for fungicide treatments. The corresponding expression patterns of HSP70 (Heat shock protein 70) were significantly different when the most and the least stable reference genes were selected when treated under different conditions. Our study provides the first detailed list of optimal reference genes for the analysis of gene expression in C. fructicola via RT-qPCR, which should be useful for future functional studies of target genes in C. fructicola.

Gene Family Expansion during the Adaptation of Colletotrichum gloeosporioides to Woody Plants.

Gene gains/losses during evolution are critical for the adaptation of organisms to new environments or hosts. However, it remains unknown whether gene family expansions facilitated the adaptation of phytopathogenic fungi to woody plants. In this study, we compared the newly sequenced genome of the Colletotrichum gloeosporioides strain CFCC80308 with the genomes of two other C. gloeosporioides strains, Cg-14 and Lc-1, isolated from Persea americana and Liriodendron leaves, respectively. The genes in the expanded families, which were associated with plant surface signal recognition, encoded various proteins, including glycosyde hydrolases (GHs) and cytochrome P450. Interestingly, there was a substantial increase in the number of GH family genes in CFCC80308. Specifically, there were 368 enriched genes in the GH families (e.g., GH1, GH3, GH10, GH12, GH15, GH16, GH17, GH18, GH25, GH32, GH53, GH61, GH76, and GH81); the expression levels of these genes were highly up-regulated during the infection of poplar trees. Additionally, the GH17 family was larger in CFCC80308 than in C. gloeosporioides strains Cg-14 and Lc-1. Furthermore, the expansion of the MP65-encoding gene family during the adaptation of Colletotrichum species to woody plants was consistent with the importance of gene gains/losses for the adaptation of organisms to their environments. This study has clarified how C. gloeosporioides adapted to woody plants during evolution.

First Report of Colletotrichum fructicola, C. rhizophorae sp. nov. and C. thailandica sp. nov. on Mangrove in Thailand.

Colletotrichum, a genus within the phylum Ascomycota (Fungi) and family Glomerellaceae are important plant pathogens globally. In this paper, we detail four Colletotrichum species found in mangrove ecosystems. Two new species, Colletotrichum rhizophorae and C. thailandica, and a new host record for Colletotrichum fructicola were identified in Thailand. Colletotrichum tropicale was collected from Taiwan's mangroves and is a new record for Rhizophora mucronata. These identifications were established through a combination of molecular analysis and morphological characteristics. This expanded dataset for Colletotrichum enhances our understanding of the genetic diversity within this genus and its associations with mangrove ecosystems. The findings outlined herein provide data on our exploration of mangrove pathogens in Asia.

Detection of DNA using gold nanoparticle-coated silica nanoparticles

We report a sensitive lateral flow assay (LFA) in which the assay colour change originated from reporter labels constructed from silica spheres (radius = 450 nm) coated with approximately 3.9 × 103 gold nanoparticles (radius = 8.5 nm). These reporter labels were modified with DNA and deposited in the conjugation area of an LFA device assembled on wax-patterned Fusion 5 paper. Test and control zones of the device were pre-loaded with capture probe formed by avidin-coated mesoporous silica nanoparticles attached with biotin-tagged DNA sequences. Proof-of-concept was demonstrated by the detection of a partial sequence of the actin gene of Colletotrichum truncatum. The DNA target could be detected with an LOD of 46 pM, which was 5 times lower than a comparative assay using gold nanoparticles alone. The assay showed good selectivity against the Colletotrichum species C. scovillei and C. gloeosporioides, as well as against DNA from the fungal genera Aspergillus niger and Alternaria alternata. There was negligible change in sensor response over storage for one month at room temperature. The LFA was used to detect PCR products following extraction from mycelium.

Blueberry floral probiotics: nectar microbes inhibit the growth of Colletotrichum pathogens.

To identify whether microorganisms isolated from blueberry flowers can inhibit the growth of Colletotrichum, an opportunistic plant pathogen that infects flowers and threatens yields, and to assess the impacts of floral microbes and Colletotrichum pathogens on artificial nectar sugars and honey bee consumption. The growth inhibition of Colletotrichum (Colletotrichum acutatum, Colletotrichum fioriniae, and Colletotrichum gloeosporioides) was screened using both artificial nectar co-culture and dual culture plate assays. All candidate nectar microbes were screened for antagonism against a single C. acutatum isolate. Then, the top four candidate nectar microbes showing the strongest inhibition of C. acutatum (Neokomagataea thailandica, Neokomagataea tanensis, Metschnikowia rancensis, and Symmetrospora symmetrica) were evaluated for antagonism against three additional C. acutatum isolates, and single isolates of both C. fioriniae and C. gloeosporioides. In artificial nectar assays, single and three-species cultures inhibited the growth of two of four C. acutatum isolates by ca. 60%, but growth of other Colletotrichum species was not affected. In dual culture plate assays, inhibition was observed for all Colletotrichum species for at least three of four selected microbial antagonists (13%‒53%). Neither honey bee consumption of nectar nor nectar sugar concentrations were affected by any microbe or pathogen tested. Selected floral microbes inhibited growth of all Colletotrichum species in vitro, although the degree of inhibition was specific to the assay and pathogen examined. In all microbial treatments, nectar sugars were preserved, and honey bee preference was not affected.