Trichothecene and beauvericin mycotoxin production and genetic variability inFusarium poaeisolated from wheat kernels from northern Italy

Debunking the Myth of Fusarium poae T-2/HT-2 Toxin Production

Fusarium poae is commonly detected in field surveys of Fusarium head blight (FHB) of cereal crops and can produce a range of trichothecene mycotoxins. Although experimentally validated reports of F. poae strains producing T-2/HT-2 trichothecenes are rare, F. poae is frequently generalized in the literature as a producer of T-2/HT-2 toxins due to a single study from 2004 in which T-2/HT-2 toxins were detected at low levels from six out of forty-nine F. poae strains examined. To validate/substantiate the observations reported from the 2004 study, the producing strains were acquired and phylogenetically confirmed to be correctly assigned as F. poae; however, no evidence of T-2/HT-2 toxin production was observed from axenic cultures. Moreover, no evidence for a TRI16 ortholog, encoding a key acyltransferase shown to be necessary for T-2 toxin production in other Fusarium species, was observed in any of the de novo assembled genomes of the F. poae strains. Our findings corroborate multiple field-based and in vitro studies on FHB-associated Fusarium populations which also do not support the production of T-2/HT-2 toxins with F. poae and therefore conclude that F. poae should not be generalized as a T-2/HT-2 toxin producing species of Fusarium.

Searching for the Fusarium spp. Which Are Responsible for Trichothecene Contamination in Oats Using Metataxonomy to Compare the Distribution of Toxigenic Species in Fields from Spain and the UK

The contamination of oats with Fusarium toxins poses a high risk for food safety. Among them, trichothecenes are the most frequently reported in European oats, especially in northern countries. The environmental conditions related to the climate change scenario might favour a distribution shift in Fusarium species and the presence of these toxins in Southern European countries. In this paper, we present an ambitious work to determine the species responsible for trichothecene contamination in Spanish oats and to compare the results in the United Kingdom (UK) using a metataxonomic approach applied to both oat grains and soil samples collected from both countries. Regarding T-2 and HT-2 toxin producers, F. langsethiae was detected in 38% and 25% of the oat samples from the UK and Spain, respectively, and to the best of our knowledge, this is the first report of the detection of this fungus in oats from Spain. The relevant type B trichothecene producer, F. poae, was the most frequently detected Fusarium species in oats from both origins. Other important trichothecene producers, such as the Fusarium tricinctum species complex or Fusarium cerealis, were also frequently detected in oat fields. Many Fusarium toxins, including T-2 and HT-2 toxins, deoxynivalenol, or nivalenol, were detected in oat samples. The results obtained in this work revealed a clear change in the distribution of trichothecene producers and the necessity to establish the potential of these species to colonize oats and their ability to produce mycotoxins.

Genetic Divergence and Chemotype Diversity in the Fusarium Head Blight Pathogen Fusarium poae

Fusarium head blight is a disease caused by a complex of Fusarium species. F. poae is omnipresent throughout Europe in spite of its low virulence. In this study, we assessed a geographically diverse collection of F. poae isolates for its genetic diversity using AFLP (Amplified Fragment Length Polymorphism). Furthermore, studying the mating type locus and chromosomal insertions, we identified hallmarks of both sexual recombination and clonal spread of successful genotypes in the population. Despite the large genetic variation found, all F. poae isolates possess the nivalenol chemotype based on Tri7 sequence analysis. Nevertheless, Tri gene clusters showed two layers of genetic variability. Firstly, the Tri1 locus was highly variable with mostly synonymous mutations and mutations in introns pointing to a strong purifying selection pressure. Secondly, in a subset of isolates, the main trichothecene gene cluster was invaded by a transposable element between Tri5 and Tri6. To investigate the impact of these variations on the phenotypic chemotype, mycotoxin production was assessed on artificial medium. Complex blends of type A and type B trichothecenes were produced but neither genetic variability in the Tri genes nor variability in the genome or geography accounted for the divergence in trichothecene production. In view of its complex chemotype, it will be of utmost interest to uncover the role of trichothecenes in virulence, spread and survival of F. poae.

Toxigenic profiles and trinucleotide repeat diversity of Fusarium species isolated from banana fruits

Infesting Fusarium species isolated from banana fruit samples were identified and quantified by morphological, mycotoxicological and molecular tools. A total of 19 Fusarium isolates were obtained: F. semitectum was most predominant (26%), followed by F. proliferatum (16%), F. circinatum (16%), F. chlamydosporum (10.5%), F. solani (10.5%), F. oxysporum (10.5%) and F. thapsinum (5%). Fumonisin B1, deoxynivalenol and zearalenone contents were assayed by high-performance liquid chromatography (HPLC). Seventeen isolates, belonging to F. chlamydosporum, F. circinatum, F. semitectum, F. solani, F. thapsinum, F. proliferatum and Fusarium spp., produced mycotoxins when cultured on rice medium. Fumonisin was produced by all of the studied Fusarium isolates, except F. oxysporum, at a concentration of over 1 μg/mL. F. citrinium isolates 4 and 5 and F. solani isolate 3 were the most potent producers of deoxynivalenol. We compared the 19 Fusarium isolates based on the bands amplified by 10 microsatellite primers. Of these, seven primers, (TCC)5, (TGG)5, (GTA)5, (ATG)5, (TAC)5, (TGC)5 and (TGT)5, yielded a high number of bands and different mean number of alleles. The similarity level between isolates was calculated using a simple matching coefficient. Dendrograms were constructed by the unweighted pair-group method with arithmetical averages (UPGMA). Two main clusters were observed. The interspecific genetic similarity between Fusarium spp. isolates was between 40% and 58% and the intraspecific similarity from 58% to 100%, indicating a high degree of genetic diversity in the tested isolates. Some unexpected genetic similarities were observed among the isolates, indicating non-agreement between morphological and molecular identification of the isolates.

Co-occurrence of type A and B trichothecenes and zearalenone in wheat grown in northern Italy over the years 2009-2011

The occurrence of the most widespread type A and B trichothecenes and of zearalenone was surveyed in soft and durum wheat produced in northern Italy. A total of 293 wheat fields, grown in the years 2009-2011, were surveyed; for each field, weather and cropping system data were collected. The results indicated a high deoxynivalenol incidence, with durum always more contaminated than soft wheat; in 2010, the percentage of durum wheat samples exceeding the European Commission legal limit was 39.6%. As regards type A trichothecenes, widespread contamination was observed in 2010. In soft wheat, an incidence of 70% and 85% was found for T-2 and HT-2 toxins, respectively; all the durum wheat samples were contaminated. The trichothecene contamination was affected by weather conditions; copious rainfall and high relative humidity (RH) during flowering occurred in 2010, when the highest contamination of both type A and B trichothecenes was found.

Deoxynivalenol and other selected Fusarium toxins in Swedish wheat--occurrence and correlation to specific Fusarium species

Wheat is often infected by Fusarium species producing mycotoxins, which may pose health risks to humans and animals. Deoxynivalenol (DON) is the most important Fusarium toxin in Swedish wheat and has previously been shown to be produced mainly by Fusarium graminearum. However, less is known about the co-occurrence of DON and F. graminearum with other toxins and Fusarium species in Sweden. This study examined the distribution of the most important toxigenic Fusarium species and their toxins in winter wheat (2009 and 2011) and spring wheat (2010 and 2011). DNA from seven species was quantified with qPCR and the toxin levels were quantified with a multitoxin analysis method based on liquid chromatography/electrospray ionisation-tandem mass spectrometry (HPLC/ESI-MS/MS). The method enabled detection of many fungal metabolites, including DON, zearalenone (ZEA), nivalenol (NIV), T-2 toxin, HT-2 toxins, moniliformin (MON), beauvericin (BEA), and enniatins (ENNs). It was found that Fusarium poae and Fusarium avenaceum were present in almost all samples. Other common Fusarium species were F. graminearum and F. culmorum, present in more than 70% of samples. Several species occurred at lower DNA levels in 2011 than in other years, but the reverse was true for F. graminearum and Fusarium langsethiae. The most prevalent toxins were ENNs, present in 100% of samples. DON was also common, especially in spring wheat, whereas ZEA and NIV were common in 2009 and in winter wheat, but less common in 2011 and in spring wheat. Only three samples of spring wheat contained T-2 or HT-2 above LOQ. Annual mean levels of several mycotoxins were significantly lower in 2011 than in other years, but the reverse applied for DON. The strongest correlations between mycotoxin and Fusarium DNA levels were found between F. avenaceum and ENNs (r(2) = 0.67) and MON (r(2) = 0.62), and F. graminearum and DON (r(2) = 0.74). These results show that several Fusarium species and toxins co-occur in wheat. The highest toxin levels were detected in spring wheat and DON and ENNs, the latter belonging to the group of so called "emerging toxins", which were the most prevalent toxins and those occurring at the highest levels.

Sequence divergence of the enniatin synthase gene in relation to production of beauvericin and enniatins in Fusarium species

Beauvericin (BEA) and enniatins (ENNs) are cyclic peptide mycotoxins produced by a wide range of fungal species, including pathogenic Fusaria. Amounts of BEA and ENNs were quantified in individual rice cultures of 58 Fusarium strains belonging to 20 species, originating from different host plant species and different geographical localities. The species identification of all strains was done on the basis of the tef-1α gene sequence. The main aim of this study was to analyze the variability of the esyn1 gene encoding the enniatin synthase, the essential enzyme of this metabolic pathway, among the BEA- and ENNs-producing genotypes. The phylogenetic analysis based on the partial sequence of the esyn1 gene clearly discriminates species producing exclusively BEA from those synthesizing mainly enniatin analogues.

Development of a PCR assay to detect the potential production of nivalenol in Fusarium poae

Fusarium species can produce mycotoxins, which can contaminate cereal-based food producing adverse effects for human and animal health. In recent years, the importance of Fusarium poae has increased within the Fusarium head blight complex. Fusarium poae is known to produce trichothecenes, especially nivalenol, a potent mycotoxin able to cause a variety of toxic effects. In this study, a specific primer pair was designed based on the tri7 gene to detect potential nivalenol-producing F. poae isolates. A total of 125 F. poae, four F. cerealis, two F. culmorum, one F. langsethiae, one F. sporotrichioides and seven F. graminearum, plus F. austroamericanum, F. meridionale, F. graminearum sensu stricto and F. cortaderiae from the NRRL collection were analysed, and only F. poae isolates gave a positive result for the presence of a 296-bp partial tri7 DNA fragment. Moreover, the primer set was tested from cereal seed samples where F. poae and other Fusarium species with a negative result for the specific reaction ( F. graminearum, F. oxysporum, F. chlamydosporum, F. sporotrichioides, F. equiseti and F. acuminatum) were isolated, and the expected fragment was amplified. We developed a rapid and reliable PCR assay to detect potential nivalenol-producing F. poae isolates.

Phylogenetic analyses and toxigenic profiles of Fusarium equiseti and Fusarium acuminatum isolated from cereals from Southern Europe

Fusarium equiseti and Fusarium acuminatum are toxigenic species that contaminate cereal crops from diverse climatic regions. They are common in Spanish cereals. The information available on their phylogenetics and toxigenic profiles is, however, insufficient to assist risk evaluation. In this work, phylogenetic analyses were performed using partial sequences of the translation elongation factor gene (EF-1α) of F. equiseti and F. acuminatum strains isolated from barley and wheat from Spain and other countries. The Northern and Southern European F. equiseti strains largely separated into two phylogenetically distinct clusters. This suggests the existence of two distinct populations within this species, explaining its presence in these regions of markedly different climate. Production of type A and B trichothecenes by the Spanish strains, examined in wheat cultures using a multitoxin analytical method, indicated that F. equiseti could produce deoxynivalenol and nivalenol and other trichothecenes, at concentrations that might represent a significant risk of toxin contamination for Southern European cereals. F. acuminatum showed low intraspecific genetic variability and 58% of the strains could produce deoxynivalenol at low level. Neither species was found to produce T-2 or HT-2 toxins. The present results provide important phylogenetic and toxigenic information essential for the accurate prediction of toxigenic risk.

Fusarium sibiricum sp. nov, a novel type A trichothecene-producing Fusarium from northern Asia closely related to F. sporotrichioides and F. langsethiae

Production of type A trichothecenes has been reported in the closely related species Fusarium langsethiae and F. sporotrichioides. Here, we characterized a collection of Fusarium isolates from Siberia and the Russian Far East (hereafter Asian isolates) that produce high levels of the type A trichothecene T-2 toxin and are similar in morphology to the type A trichothecene-producing F. langsethiae, and to F. poae which often produces the type B trichothecene nivalenol. The Asian isolates possess unique macroscopic and microscopic characters and have a unique TG repeat in the nuclear ribosomal intergenic spacer (IGS rDNA) region. In Asian isolates, the TRI1-TRI16 locus, which determines type A versus type B trichothecene production in other species, is more similar in organization and sequence to the TRI1-TRI16 locus in F. sporotrichioides and F. langsethiae than to that in F. poae. Phylogenetic analysis of the TRI1 and TRI16 gene coding regions indicates that the genes in the Asian isolates are more closely related to those of F. sporotrichioides than F. langsethiae. Phylogenetic analysis of the beta-tubulin, translation elongation factor, RNA polymerase II and phosphate permease gene sequences resolved the Asian isolates into a well-supported sister lineage to F. sporotrichioides, with F. langsethiae forming a sister lineage to F. sporotrichioides and the Asian isolates. The Asian isolates are conspecific with Norwegian isolate IBT 9959 based on morphological and molecular analyses. In addition, the European F. langsethiae isolates from Finland and Russia were resolved into two distinct subgroups based on analyses of translation elongation factor and IGS rDNA sequences. Nucleotide polymorphisms within the IGS rDNA were used to design PCR primers that successfully differentiated the Asian isolates from F. sporotrichioides and F. langsethiae. Based on these data, we formally propose that the Asian isolates together with Norwegian isolate IBT 9959 comprise a novel phylogenetic species, F. sibiricum, while the two subgroups of F. langsethiae only represent intraspecific groups.