Species composition, toxigenic potential and aggressiveness of Fusarium isolates causing Head Blight of barley in Uruguay

Effect of Quantitative Wheat Resistance on the Aggressiveness of Fusarium graminearum

Little is known about the selection pressures acting on plant pathogen populations, especially those applied by quantitative forms of resistance. Fusarium graminearum causes Fusarium head blight in wheat, producing significant yield losses and mycotoxin contamination. Quantitative host resistance is the best method to control Fusarium head blight. However, there needs to be more understanding of how disease resistance affects the evolution of plant pathogens. The aim of this study was to determine if the presence or absence of wheat resistance influenced the fitness components and genomic regions of F. graminearum. Thirty-one isolates from highly susceptible and 25 isolates from moderately resistant wheat lines were used. Isolate aggressiveness was measured by the area under the disease progress curve, visually damaged kernels, and deoxynivalenol contamination. The in vitro growth rate and spore production were also measured. Two whole-genome scans for selection were conducted with 333,297 single-nucleotide polymorphisms. One scan looked for signatures of selection in the entire sample, and the other scan was for divergent selection between the isolates from moderately resistant wheat and highly susceptible wheat. The subsample of isolates from highly susceptible wheat was primarily aggressive. Several regions of the F. graminearum genome with signatures for selection were identified. The moderately resistant wheat varieties used in this study did not select more aggressive isolates, suggesting that quantitative resistance is a durable method to control Fusarium head blight.

Characterization of Fusarium species causing head blight of highland barley (qingke) in Tibet, China

Most of the research on the characterization of Fusarium species focused on wheat, barley, rice, and maize in China. However, there has been limited research in highland barley (qingke). Recently, Fusarium head blight (FHB) of qingke was recently observed in Tibet, China, especially around the Brahmaputra River. To gain a better understanding of the pathogens involver, 201 Fusarium isolates were obtained from qingke samples in 2020. Among these isolates, the most abundant species was F. avenaceum (45.3 %), followed by F. equiseti (27.8 %), F. verticillioides (13.9 %), F. acuminatum (9.0 %), F. flocciferum (3.5 %), and F. proliferatum (0.5 %). The distribution of Fusarium species varied along the Brahmaputra River, with F. avenaceum being predominant in the midstream and downstream regions, while F. equiseti was more common in the upstream region. Chemical analyses of all the isolates revealed the production of different mycotoxins by various Fusarium species. It was found that enniatins were produced by F. acuminatum, F. avenaceum, and F. flocciferum, beauvericin (BEA) and fumonisins were produced F. proliferatum and F. verticillioides, and zearalenone (ZEN) and nivalenol (NIV) were produced by F. equiseti. Pathogenicity test showed that F. avenaceum was more aggressive in causing FHB compared to F. acuminatum, F. equiseti, and F. flocciferum. The disease severity, measured by the area under the disease progress curve (AUDPC), was significantly positively (P < 0.01) correlated with the concentration of total toxins produced by each species. Furthermore, all the Fusarium strains which were used for pathogenicity test were susceptible to carbendazim, and the 50 % effective concentration (EC50) ranged from 0.406 μg/mL to 0.673 μg/mL with an average EC50 of 0.551 ± 0.012 μg/mL.

In Vitro Sensitivity Test of Fusarium Species from Weeds and Non-Gramineous Plants to Triazole Fungicides

Fusarium species are common plant pathogens that cause serious crop losses worldwide. Fusarium spp. colonize not only the main host plants, crops, but also alternative hosts. The effectiveness of fungicide use in disease management ranges from very successful to possibly promoting the growth of the pathogen. Triazole fungicides are widely used to control these pathogens due to their broad-spectrum activity and systemic nature. This paper reviews the sensitivity of 40 Fusarium strains isolated from weeds, non-gramineous plants, and spring wheat to metconazole, prothioconazole, and tebuconazole. The effect of fungicides was determined by the percentage inhibition of F. graminearum, F. culmorum, F. sporotrichioides, and F. avenaceum fungal mycelial growth. The 50% effective concentration (EC50) values of all isolates on metconazole were lower than 2.9 mg L-1, prothioconazole EC50 ranged from 0.12 to 23.6 mg L-1, and tebuconazole ranged from 0.09 to 15.6 mg L-1. At 0.00025-0.025 mg L-1, the fungicides were ineffective, except for the growth of the F. avenaceum species. It was observed that isolates from weeds were more sensitive to low concentrations of fungicide than isolates from crop plants. In general, information is scarce regarding the comparison of fungicide resistance in Fusarium isolates from weed and crop plants, making this study an additional contribution to the existing knowledge base.

Quantitative PCR (qPCR) for estimating the presence of Fusarium and its mycotoxins in barley grains

Members within the Fusarium sambucinum species complex (FSAMSC) are able to produce mycotoxins, such as deoxynivalenol (DON), nivalenol (NIV), zearalenone (ZEN) and enniatins (ENNs) in food products. Consequently, alternative methods for assessing the levels of these mycotoxins are relevant for quick decision-making. In this context, qPCR based on key mycotoxin biosynthetic genes could aid in determining the toxigenic fungal biomass, and could therefore infer mycotoxin content. The aim of this study was to verify the use of qPCR as a technique for estimating DON, NIV, ENNs and ZEN, as well as Fusarium graminearum sensu lato (s.l.) and F. poae in barley grains. For this purpose, 53 barley samples were selected for mycobiota, mycotoxin and qPCR analyses. ENNs were the most frequent mycotoxins, followed by DON, ZEN and NIV. 83% of the samples were contaminated by F. graminearum s.l. and 51% by F. poae. Pearson correlation analysis showed significant correlations for TRI12/15-ADON with DON, ESYN1 with ENNs, TRI12/15-ADON and ZEB1 with F. graminearum s.l., as well as ESYN1 and TRI12/NIV with F. poae. Based on the results, qPCR could be useful for the assessment of Fusarium presence, and therefore, provide an estimation of its mycotoxins' levels from the same sample.

Fusarium Species and Mycotoxins Associated with Sorghum Grains in Uruguay

Grain mold and stalk rot are among the fungal diseases that cause significant losses in sorghum worldwide and are caused by different Fusarium spp. The presence of Fusarium species in sorghum grains causes yield losses and mycotoxin contamination, which represents a risk to consumers. In this study, Fusarium graminearum species complex (FGSC) had a high incidence, followed by Fusarium fujikuroi species complex (FFSC) and F. incarnatum-equiseti species complex. Within FFSC, F. proliferatum, F. andiyazi, F. fujikuroi, F. thapsinum, F. verticillioides and F. subglutinans were identified, and this was the first report of F. fujikuroi in sorghum. The most frequent toxins found in sorghum samples were deoxynivalenol (DON) and zearalenone (ZEN). The presence of fumonisins and nivalenol (NIV) was detected at low levels. This study adds new knowledge about the occurrence of Fusarium species and mycotoxins in sorghum grains. Furthermore, this is the first report in Uruguay on fungicide sensitivity for Fusarium isolates from sorghum, which constitutes an important starting point for defining management practices to minimize fungal infection and mycotoxin contamination.

Different diagnostic approaches for the characterization of the fungal community and Fusarium species complex composition of Italian durum wheat grain and correlation with secondary metabolite accumulation

BACKGROUND

The evolution of the fungal communities associated with durum wheat was assessed using different diagnostic approaches. Durum wheat grain samples were collected in three different Italian cultivation macro-areas (north, center and south). Fungal isolation was realized by potato dextrose agar (PDA) and by deep-freezing blotter (DFB). Identification of Fusarium isolates obtained from PDA was achieved by partial tef1α sequencing (PDA + tef1α), while those obtained from DFB were identified from their morphological characteristics (DFB + mc). The fungal biomass of eight Fusarium species was quantified in grains by quantitative polymerase chain reaction (qPCR). Fungal secondary metabolites were analyzed in grains by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Correlations between Fusarium detection techniques (PDA + tef1α; DFB + mc and qPCR) and mycotoxins in grains were assessed.

RESULTS

Alternaria and Fusarium showed the highest incidence among the fungal genera developed from grains. Within the Fusarium community, PDA + tef1α highlighted that F. avenaceum and F. graminearum were the most represented members, while, DFB + mc detected a high presence of F. proliferatum. Alternaria and Fusarium mycotoxins, principally enniatins, were particularly present in the grain harvested in central Italy. Deoxynivalenol was mainly detected in northern-central Italy.

CONCLUSIONS

The adoption of the different diagnostic techniques of Fusarium detection highlighted that, for some species, qPCR was the best method of predicting their mycotoxin contamination in grains. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Genetic diversity of toxigenic Fusarium verticillioides associated with maize grains, India

In the present investigation, prevalence, genetic diversity, and mycotoxin producing potential of Fusarium species associated with maize grain samples were studied from different geographical regions of India. The highest prevalence of Fusarium verticillioides was recorded as 88.52%, followed by F. coffeatum, F. foetens, and F. euwallaceae, 6.55%, 3.27%, and 1.63%, respectively. We isolated 54 strains of F. verticillioides, and their genetic diversity was studied by inter simple sequence repeats (ISSR). The ISSR fingerprints (AG) 8C and (AG) 8G showed 252 and 368 microsatellite sites in the genome of F. verticillioides and resulted in 99-100% repeatability and reproducibility. The Simpson (SID) and Shannon (H) indices (0.78 and 2.36) suggest that F. verticillioides strains exhibit moderate to high diversity. Molecular detection of fumonisin B1 (FB1) biosynthetic genes (FUM1 and FUM13) involved in FB1 production in F. verticillioides was confirmed by polymerase chain reaction (PCR). Furthermore, 91% of the strains were positive for FB1 production, which was affirmed by liquid chromatography with tandem mass spectrometry (LC-MS-MS). In-vitro appurtenance of F. verticillioides spores exhibited a high to moderate effect on the growth and development of the maize. The current finding demonstrated that most F. verticillioides strains showed a wide range of genetic diversity with varied toxigenic and pathogenic potentials. In conclusion, for the first time, F. coffeatum, F. foetens, and F. euwallaceae species were reported from maize grain samples in India. They were positive for FB1 and negatively affecting grain quality, which is a major concern in food safety.

Toxicity and preventive approaches of Fusarium derived mycotoxins using lactic acid bacteria: state of the art

Mycotoxin contamination of food and feed is a serious food safety issue and causes acute and chronic diseases in humans and livestock. Climatic and agronomic changes helps in the proliferation of fungal growth and mycotoxin production in food commodities. Mycotoxin contamination has attracted global attention due to its wide range of toxicity to humans and animals. However, physical and chemical management approaches in practice are unsafe for well-being due to their health-hazardous nature. Various antibiotics and preservatives are in use to reduce the microbial load and improve the shelf life of food products. In addition, the use of antibiotic growth promotors in livestock production may increase the risk of antimicrobial resistance, which is a global health concern. Due to their many uses, probiotics are helpful microbes that have a significant impact on food and nutrition. Furthermore, the probiotic potential of lactic acid bacteria (LAB) is employed in various food and feed preparations to neutralize mycotoxins, antimicrobial activities, balance the gut microbiome, and various immunomodulatory activities in both humans and livestock. In addition, LAB produces various antimicrobials, flavouring agents, peptides, and proteins linked to various food and health care applications. The LAB-based processes for mycotoxin management are more effective, eco-friendly, and low-cost than physical and chemical approaches. The toxicity, novel preventive measures, binding nature, and molecular mechanisms of mycotoxins' detoxification using LAB have been highlighted in this review.

Nivalenol Mycotoxin Concerns in Foods: An Overview on Occurrence, Impact on Human and Animal Health and Its Detection and Management Strategies

Mycotoxins are secondary metabolites produced by fungi that infect a wide range of foods worldwide. Nivalenol (NIV), a type B trichothecene produced by numerous Fusarium species, has the ability to infect a variety of foods both in the field and during post-harvest handling and management. NIV is frequently found in cereal and cereal-based goods, and its strong cytotoxicity poses major concerns for both human and animal health. To address these issues, this review briefly overviews the sources, occurrence, chemistry and biosynthesis of NIV. Additionally, a brief overview of several sophisticated detection and management techniques is included, along with the implications of processing and environmental factors on the formation of NIV. This review’s main goal is to offer trustworthy and current information on NIV as a mycotoxin concern in foods, with potential mitigation measures to assure food safety and security.

Trichothecene Genotype Profiling of Wheat Fusarium graminearum Species Complex in Paraguay

Paraguay is a non-traditional wheat-producing country in one of the warmest regions in South America. Fusarium Head Blight (FHB) is a critical disease affecting this crop, caused by the Fusarium graminearum species complex (FGSC). A variety of these species produce trichothecenes, including deoxynivalenol (DON) and its acetylated forms (3-ADON and 15-ADON) or nivalenol (NIV). This study characterized the phylogenetic relationships, and chemotype diversity of 28 strains within FGSC collected from wheat fields across different country regions. Phylogenetic analysis based on the sequence of elongation factor-1α gene (EF-1α) from 28 strains revealed the presence of four species in the FGSC: F. graminearum sensu stricto, F. asiaticum, F. meridionale and F. cortaderiae. Ten strains selected for further analysis revealed that all F. graminearum strains were 15-ADON chemotype, while the two strains of F. meridionale and one strain of F. asiaticum were NIV chemotype. Thus, the 15-ADON chemotype of F. graminearum sensu stricto was predominant within the Fusarium strains isolated in the country. This work is the first report of phylogenetic relationships and chemotype diversity among Fusarium strains which will help understand the population diversity of this pathogen in Paraguay.

Fusarium graminearum Species Complex: A Bibliographic Analysis and Web-Accessible Database for Global Mapping of Species and Trichothecene Toxin Chemotypes

Fusarium graminearum is ranked among the five most destructive fungal pathogens that affect agroecosystems. It causes floral diseases in small grain cereals including wheat, barley, and oats, as well as maize and rice. We conducted a systematic review of peer-reviewed studies reporting species within the F. graminearum species complex (FGSC) and created two main data tables. The first contained summarized data from the articles including bibliographic, geographic, methodological (ID methods), host of origin and species, while the second data table contains information about the described strains such as publication, isolate code(s), host/substrate, year of isolation, geographical coordinates, species and trichothecene genotype. Analyses of the bibliographic data obtained from 123 publications from 2000 to 2021 by 498 unique authors and published in 40 journals are summarized. We describe the frequency of species and chemotypes for 16,274 strains for which geographical information was available, either provided as raw data or extracted from the publications, and sampled across six continents and 32 countries. The database and interactive interface are publicly available, allowing for searches, summarization, and mapping of strains according to several criteria including article, country, host, species and trichothecene genotype. The database will be updated as new articles are published and should be useful for guiding future surveys and exploring factors associated with species distribution such as climate and land use. Authors are encouraged to submit data at the strain level to the database, which is accessible at https://fgsc.netlify.app.

Bioinformatics and Transcriptome Analysis of CFEM Proteins in Fusarium graminearum

Fusarium blight of wheat is usually caused by Fusarium graminearum, and the pathogenic fungi will secrete effectors into the host plant tissue to affect its normal physiological process, so as to make it pathogenic. The CFEM (Common in Fungal Extracellular Membrane) protein domain is unique to fungi, but it is not found in all fungi. The CFEM protein contained in F. graminearum may be closely related to pathogenicity. In this study, 23 FgCFEM proteins were identified from the F. graminearum genome. Then, features of these proteins, such as signal peptide, subcellular localization, and transmembrane domains, etc., were analyzed and candidate effectors were screened out. Sequence alignment results revealed that each FgCFEM protein contains one CFEM domain. The amino acids of the CFEM domain are highly conserved and contain eight spaced cysteines, with the exception that FgCFEM8, 9, and 15 lack two cysteines and three cysteines were missed in FgCFEM18 and FgCFEM22. A recently identified CFEM_DR motif was detected in 11 FgCFEMs, and importantly we identified two new conserved motifs containing about 29 and 18 amino acids (CFEM_WR and CFEM_KF), respectively, in some of FgCFEM proteins. Transcriptome analysis of the genes encoding CFEM proteins indicated that all the CFEM-containing genes were expressed during wheat infection, with seven and six genes significantly up- and down-regulated, respectively, compared with in planta and in vitro. Based on the above analysis, FgCFEM11 and FgCFEM23 were predicted to be F. graminearum effectors. This study provides the basis for future functional analyses of CFEM proteins in F. graminearum.

Species diversity and mycotoxin production by members of the Fusarium tricinctum species complex associated with Fusarium head blight of wheat and barley in Italy

Fusarium head blight (FHB) is a global cereal disease caused by a complex of Fusarium species. In Europe, the main species responsible for FHB are F. graminearum, F. culmorum and F. poae. However, members of the F. tricinctum species complex (FTSC) have become increasingly important. FTSC fusaria can synthesize mycotoxins such as moniliformin (MON), enniatins (ENNs) and several other biologically active secondary metabolites that could compromise food quality. In this study, FTSC isolates primarily from Italian durum wheat and barley, together with individual strains from four non-graminaceous hosts, were collected to assess their genetic diversity and determine their potential to produce mycotoxins in vitro on rice cultures. A multilocus DNA sequence dataset (TEF1, RPB1 and RPB2) was constructed for 117 isolates from Italy and 6 from Iran to evaluate FTSC species diversity and their evolutionary relationships. Phylogenetic analyses revealed wide genetic diversity among Italian FTSC isolates. Among previously described FTSC species, F. avenaceum (FTSC 4) was the most common species in Italy (56/117 = 47.9%) while F. tricinctum (FTSC 3), and F. acuminatum (FTSC 2) accounted for 11.1% (13/117) and the 8.5% (10/117), respectively. The second most detected species was a new and unnamed Fusarium sp. (FTSC 12; 32/117 = 19%) resolved as the sister group of F. tricinctum. Collectively, these four phylospecies accounted for 111/117 = 94.9% of the Italian FTSC collection. However, we identified five other FTSC species at low frequencies, including F. iranicum (FTSC 6) and three newly discovered species (Fusarium spp. FTSC 13, 14, 15). Of the 59 FTSC isolates tested for mycotoxin production on rice cultures, 54 and 55 strains, respectively, were able to produce detectable levels of ENNs and MON. In addition, we confirmed that the ability to produce bioactive secondary metabolites such as chlamydosporol, acuminatopyrone, longiborneol, fungerin and butanolide is widespread across the FTSC.

Occurrence, mitigation and in vitro cytotoxicity of nivalenol, a type B trichothecene mycotoxin - Updates from the last decade (2010-2020)

The present review aims to give an overview of the literature of the last decade (2010-2020) concerning the occurrence of the type B trichothecene mycotoxin nivalenol (NIV) and its in vitro toxicity, with the purpose of updating information regarding last researches on this mycotoxin. The most recent studies on the possible methods for preventing Fusarium spp. growth and NIV production are also discussed. Recently, various environmental factors have been shown to influence strongly NIV occurrence. However, Fusarium spp. of the NIV genotype have been found almost worldwide. With regard to NIV cytotoxicity, NIV has been reported to cause a marked decrease in cell proliferation in different mammalian cells. In particular, the recent data suggest that organs containing actively proliferating cells represent the main targets of NIV. Moreover, NIV resulted to cause immunosuppression, gastrointestinal toxicity and genotoxicity. However, sufficient evidence of carcinogenicity in humans is currently lacking, and the International Agency for Research on Cancer (IARC) classifies it as a group 3 carcinogen. Further researches and the discovery of effective treatment strategies to prevent NIV contamination and to counteract its toxicity are urgently required against this common food-borne threat to human health and livestock.

Proteomics-Based Data Integration of Wheat Cultivars Facing Fusarium graminearum Strains Revealed a Core-Responsive Pattern Controlling Fusarium Head Blight

Fusarium head blight (FHB), mainly occurring upon Fusarium graminearum infection in a wide variety of small-grain cereals, is supposed to be controlled by a range of processes diverted by the fungal pathogen, the so-called susceptibility factors. As a mean to provide relevant information about the molecular events involved in FHB susceptibility in bread wheat, we studied an extensive proteome of more than 7,900 identified wheat proteins in three cultivars of contrasting susceptibilities during their interaction with three F. graminearum strains of different aggressiveness. No cultivar-specific proteins discriminated the three wheat genotypes, demonstrating the establishment of a core proteome regardless of unequivocal FHB susceptibility differences. Quantitative protein analysis revealed that most of the FHB-induced molecular adjustments were shared by wheat cultivars and occurred independently of the F. graminearum strain aggressiveness. Although subtle abundance changes evidenced genotype-dependent responses to FHB, cultivar distinction was found to be mainly due to basal abundance differences, especially regarding the chloroplast functions. Integrating these data with previous proteome mapping of the three F. graminearum strains facing the three same wheat cultivars, we demonstrated strong correlations between the wheat protein abundance changes and the adjustments of fungal proteins supposed to interfere with host molecular functions. Together, these results provide a resourceful dataset that expands our understanding of the specific molecular events taking place during the wheat-F. graminearum interaction.

Production of Microsclerotia From Entomopathogenic Fungi and Use in Maize Seed Coating as Delivery for Biocontrol Against Fusarium graminearum

The commercial use of the entomopathogenic fungi Metarhizium spp. in biopesticides has gained more interest since the discovery that several species of this genus are able to colonize roots. In general, commercial products with Metarhizium are formulated based on conidia for insect pest control. The process of mass production, harvesting, and formulation of infective conidia can be detrimental for conidial viability. Entomopathogenic fungi such as Metarhizium spp. are able to produce high concentrations of resistant structures, known as microsclerotia, when grown in liquid media. Microsclerotia are desiccation tolerant, with excellent storage stability, and are capable of producing high quantities of infective conidia after rehydration. The aim of this study was to evaluate microsclerotia production by different isolates of Metarhizium spp. and determine the effect of microsclerotia coated onto maize seeds on plant growth in the presence of soil-borne pathogen Fusarium graminearum. On average, ~1 × 105 microsclerotia/mL were produced by selected isolates of M. anisopliae (A1080 and F672) and Metarhizium robertsii (F447). Microsclerotia were formulated as granules with diatomaceous earth and used for seed coating, after which propagules produced around 5 × 106 CFU/g of seeds. In the presence of the plant pathogen, maize plants grown from untreated seeds had the lowest growth, while plants treated with the Metarhizium microsclerotia had significantly greater growth than the control plants. Hyphae were observed growing on and in root tissues in all the Metarhizium spp. treatments but not in samples from control plants. Metarhizium hyphal penetration points' on roots were observed 1 month after sowing, indicating the fungi were colonizing roots as endophytes. The results obtained indicate that microsclerotia can be coated onto seeds, providing plant protection against soil plant pathogens and a method to establish Metarhizium in the ecto- and endo-rhizosphere of maize roots, allowing the persistence of this biocontrol agent.

Map-based cloning identifies velvet A as a critical component of virulence in Fusarium pseudograminearum during infection of wheat heads

Although better known as a pathogen of wheat stem bases, Fusarium pseudograminearum also causes Fusarium head blight. A natural isolate of F. pseudograminearum was identified that showed severely reduced virulence towards wheat heads and a map-based cloning approach was undertaken to identify the genetic basis of this phenotype. Using a population of 95 individuals, a single locus on chromosome 1 was shown to be responsible for the low virulence. Fine mapping narrowed the region to just five possible SNPs of which one was in the F. pseudograminearum homologue of velvet A. Knockout mutants of velvet A, which were non-pathogenic towards wheat, confirmed that velvet A regulates virulence in this pathogen. The mutation in velvet A was only found in a single field isolate and the origin of the mutation is unknown.

Fungicides may have differential efficacies towards the main causal agents of Fusarium head blight of wheat

BACKGROUND

Fusarium head blight (FHB) is a complex disease of wheat and barley caused by several Fusarium species. In recent years, a variation in the composition of the FHB community has been observed in several wheat cultivation areas across the world. In detail, F. avenaceum and F. poae increased their frequencies, while, a lower F. graminearum and F. culmorum incidence was simultaneously observed. These shifts within the FHB complex might have been caused by different factors, including the selective pressure caused by fungicides used to control the disease in the field. Therefore, the present study was carried out to evaluate, both in in vitro experiments and in field trials, the activity of commonly used fungicides of wheat (tebuconazole, metconazole, prothioconazole and prochloraz) towards the above mentioned four Fusarium species.

RESULTS

A preliminary in vitro assay revealed that low concentrations of all tested fungicides caused the incomplete reduction of fungal development. Furthermore, F. poae and F. avenaceum showed, at the same time, a lower sensitivity to all tested fungicides. In field trials, all fungicides showed an activity against the four Fusarium species. However, F. avenaceum exhibited a reduced sensitivity to metconazole. The lower efficacy of metconazole towards F. avenaceum was also confirmed by an additional in vitro experiment on several F. avenaceum and F. graminearum different strains.

CONCLUSION

The selective pressure exerted by the extensive use of certain fungicides may influence population dynamics of Fusarium species due to their different sensitivity. © 2020 Society of Chemical Industry.

Characterization of the Fusarium sambucinum species complex and detection of multiple mycotoxins in Brazilian barley samples

This study investigated the fungal diversity in Brazilian barley samples, focusing on the Fusarium sambucinum species complex and the presence of multiple mycotoxins: aflatoxins B1, B2, G1, G2 beauvericin (BEA), enniatins (ENNs) A, A1, B, and B1, deoxynivalenol (DON), fumonisins (FB) B1 and B2, HT-2 and T-2 toxins, nivalenol (NIV) and ochratoxin A (OTA) from two different regions, São Paulo (SP) and Rio Grande do Sul (RS). The majority of the isolates belonged to the Fusarium sambucinum species complex (FSAMSC), with F. graminearum s.s. characterized as the major contaminant. F. meridionale and F. poae were the second most frequent fungi isolated from SP and RS, respectively. All of the F. graminearum s.s. isolates demonstrated 15-ADON genotype, whereas F. poae and F. meridionale were all NIV. The majority of the F. cortaderiae isolates were NIV, with only one 3-ADON genotype. Mycotoxin analysis revealed that none of the samples were contaminated by aflatoxins, OTA, FB2 and type A trichothecenes, however, all of the samples were contaminated with at least one Fusarium toxin. Contamination by DON, ZEA, ENNB and ENNB1 levels were significantly higher in RS. Co-contamination of BEA, DON, ENNs, NIV and ZEA in 18.5% and 24.2% of the analyzed samples was observed, from SP and RS respectively. More than 20% of the samples from RS presented DON and ZEA levels above the regulations established by Europe and Brazil. The results provide further information on the FSAMSC from South America and detected multiple Fusarium toxins in barley samples. This highlights the importance for further studies on the possible interactions of these mycotoxins in order to determine potential risks to animal health.

TRI Genotyping and Chemotyping: A Balance of Power

Fusarium is among the top 10 most economically important plant pathogens in the world. Trichothecenes are the principal mycotoxins produced as secondary metabolites by select species of Fusarium and cause acute and chronic toxicity in animals and humans upon exposure either through consumption and/or contact. There are over 100 trichothecene metabolites and they can occur in a wide range of commodities that form food and feed products. This review discusses strategies to mitigate the risk of mycotoxin production and exposure by examining the Fusarium-trichothecene model. Fundamental to mitigation of risk is knowing the identity of the pathogen. As such, a comparison of current, recommended molecular approaches for sequence-based identification of Fusaria is presented, followed by an analysis of the rationale and methods of trichothecene (TRI) genotyping and chemotyping. This type of information confirms the source and nature of risk. While both are powerful tools for informing regulatory decisions, an assessment of the causes of incongruence between TRI genotyping and chemotyping data must be made. Reconciliation of this discordance will map the way forward in terms of optimization of molecular approaches, which includes data validation and sharing in the form of accessible repositories of genomic data and browsers for querying such data.

The ER Lumenal Hsp70 Protein FpLhs1 Is Important for Conidiation and Plant Infection in Fusarium pseudograminearum

Heat shock protein 70s (Hsp70s) are a class of molecular chaperones that are highly conserved and ubiquitous in organisms ranging from microorganisms to plants and humans. Hsp70s play key roles in cellular development and protecting living organisms from environmental stresses such as heat, drought, salinity, acidity, and cold. However, their functions in pathogenic fungi are largely unknown. Here, a total of 14 FpHsp70 genes were identified in Fusarium pseudograminearum, including 3 in the mitochondria, 7 in the cytoplasm, 2 in the endoplasmic reticulum (ER), 1 in the nucleus, and 1 in the plastid. However, the exon–intron boundaries and protein motifs of the FpHsp70 have no consistency in the same subfamily. Expression analysis revealed that most FpHsp70 genes were up-regulated during infection, implying that FpHsp70 genes may play important roles in F. pseudograminearum pathogenicity. Furthermore, knockout of an ER lumenal Hsp70 homolog FpLhs1 gene reduced growth, conidiation, and pathogenicity in F. pseudograminearum. These mutants also showed a defect in secretion of some proteins. Together, FpHsp70s might play essential roles in F. pseudograminearum and FpLhs1 is likely to act on the development and virulence by regulating protein secretion.

Comparing genotype and chemotype of Fusarium graminearum from cereals in Ontario, Canada

Fusarium graminearum is responsible for production of the mycotoxin deoxynivalenol (DON) on maize and wheat in Ontario, Canada. It has been understood since the early 1980s that in most parts of Canada, the predominant chemotype of F. graminearum is 15ADON, and not the 3ADON chemotype mainly found in Europe and Asia. The discovery of F. graminearum strains that did not produce DON but the structurally related 7-α hydroxy, 15-deacetylcalonectrin (3ANX) and its hydrolysis product 7-α hydroxy, 3,15-dideacetylcalonectrin to (NX) demonstrated that we still have a lot to learn about this well studied but complicated fungus. We conducted a survey of maize and wheat samples from Ontario farms. In the 2015 crop year, we isolated 86 strains and tested a representative subset of 20 using the published genetic probes for assessing genotype. We also developed a targeted LC-MS/MS method for the identification and quantitation of known toxins from this species to determine chemotype. The results showed that 80% of our strains produced some 3ANX in addition to 15ADON and one strain produced 3ANX and no 15ADON. Comparison of chemical data with genotyping revealed that in more than 50% of the cases there was no clear agreement. These data demonstrate the importance of chemical analysis for understanding the toxigenic potential of strains, especially using a LC-MS method that is capable of differentiating 3ADON and 15ADON. For this collection, genotyping of isolates did not produce reliable information on the chemotype. This is the first report of 3ANX toxin production concurrently with 15ADON and suggests that the 3ANX producers in North America likely originated from the 15ADON background.