Deoxynivalenol and Nivalenol Production by Fusarium culmorum Isolates Differing in Aggressiveness Toward Winter Rye

Fusarium culmorum Produces NX-2 Toxin Simultaneously with Deoxynivalenol and 3-Acetyl-Deoxynivalenol or Nivalenol

Fusarium culmorum is a major pathogen of grain crops. Infected plants accumulate deoxynivalenol (DON), 3-acetyl-deoxynivalenol (3-ADON), or nivalenol (NIV), which are mycotoxins of the trichothecene B group. These toxins are also produced by F. graminearum species complex. New trichothecenes structurally similar to trichothecenes B but lacking the carbonyl group on C-8, designated NX toxins, were recently discovered in atypical isolates of F. graminearum from North America. Only these isolates and a few strains of a yet to be characterized Fusarium species from South Africa are known to produce NX-2 and other NX toxins. Here, we report that among 20 F. culmorum strains isolated from maize, wheat, and oat in Europe and Asia over a period of 70 years, 18 strains produced NX-2 simultaneously with 3-ADON and DON or NIV. Rice cultures of strains producing 3-ADON accumulated NX-2 in amounts corresponding to 2−8% of 3-ADON (1.2−36 mg/kg). A strain producing NIV accumulated NX-2 and NIV at comparable amounts (13.6 and 10.3 mg/kg, respectively). In F. graminearum, producers of NX-2 possess a special variant of cytochrome P450 monooxygenase encoded by TRI1 that is unable to oxidize C-8. In F. culmorum, producers and nonproducers of NX-2 possess identical TRI1; the reason for the production of NX-2 is unknown. Our results indicate that the production of NX-2 simultaneously with trichothecenes B is a common feature of F. culmorum.

Genome-wide association study for deoxynivalenol production and aggressiveness in wheat and rye head blight by resequencing 92 isolates of Fusarium culmorum

Background

Fusarium culmorum is an important pathogen causing head blight of cereals in Europe. This disease is of worldwide importance leading to reduced yield, grain quality, and contamination by mycotoxins. These mycotoxins are harmful for livestock and humans; therefore, many countries have strict regulatory limits for raw materials and processed food. Extensive genetic diversity is described among field populations of F. culmorum isolates for aggressiveness and production of the trichothecene mycotoxin deoxynivalenol (DON). However, the causes for this quantitative variation are not clear, yet. We analyzed 92 isolates sampled from different field populations in Germany, Russia, and Syria together with an international collection for aggressiveness and DON production in replicated field experiments at two locations in two years with two hosts, wheat and rye. The 30x coverage whole-genome resequencing of all isolates resulted in the identification of 130,389 high quality single nucleotide polymorphisms (SNPs) that were used for the first genome-wide association study in this phytopathogenic fungus.

Results

In wheat, 20 and 27 SNPs were detected for aggressiveness and DON content, respectively, of which 10 overlapped. Additionally, two different SNPs were significantly associated with aggressiveness in rye that were among those SNPs being associated with DON production in wheat. Most of the SNPs explained only a small proportion of genotypic variance (p_G), however, four SNPs were associated with major quantitative trait loci (QTLs) with p_G ranging from 12 to 48%. The QTL with the highest p_G was involved in DON production and associated with a SNP most probably located within the Tri4 gene.

Conclusions

The diversity of 92 isolates of F. culmorum were captured using a heuristic approach. Key phenotypic traits, SNPs, and candidate genes underlying aggressiveness and DON production were identified. Clearly, many QTLs are responsible for aggressiveness and DON content in wheat, both traits following a quantitative inheritance. Several SNPs involved in DON metabolism, among them the Tri4 gene of the trichothecene pathway, were inferred as important source of variation in fungal aggressiveness. Using this information underlying the phenotypic variation will be of paramount importance in evaluating strategies for successful resistance breeding.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07931-5.

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.

Trichothecenes in Cereal Grains - An Update

Trichothecenes are sesquiterpenoid mycotoxins produced by fungi from the order Hypocreales, including members of the Fusarium genus that infect cereal grain crops. Different trichothecene-producing Fusarium species and strains have different trichothecene chemotypes belonging to the Type A and B class. These fungi cause a disease of small grain cereals, called Fusarium head blight, and their toxins contaminate host tissues. As potent inhibitors of eukaryotic protein synthesis, trichothecenes pose a health risk to human and animal consumers of infected cereal grains. In 2009, Foroud and Eudes published a review of trichothecenes in cereal grains for human consumption. As an update to this review, the work herein provides a comprehensive and multi-disciplinary review of the Fusarium trichothecenes covering topics in chemistry and biochemistry, pathogen biology, trichothecene toxicity, molecular mechanisms of resistance or detoxification, genetics of resistance and breeding strategies to reduce their contamination of wheat and barley.

Utility of a Multilevel Modeling Approach to Investigate Differences in Isolation Frequency of Fusarium culmorum in Agricultural Soil Across the Inland Pacific Northwest

The plant pathogen Fusarium culmorum represents an inoculum source capable of contaminating grains with deoxynivalenol in the Inland Northwest region of the United States. A multilevel modeling approach utilizing varying intercepts for different sampling quadrats, fields, and iterations in the dataset was performed to characterize differences in isolation frequency of F. culmorum collected during a 2-year soil survey. Differences in the isolation frequency of F. culmorum varied the most by sampled field followed by quadrat and iteration, respectively. Higher relative elevation within the sampling region of a field limited the amount of F. culmorum recovered. The effect of annual climate variables was investigated using combinations of single-variable and multivariable model equations with linear and polynomial terms. The same data analysis approach was applied to an external dataset of F. culmorum isolation frequencies in grains from fields across eastern Australia. These results represent a case study for investigating variability within datasets containing overdispersed fungal counts and incorporating climate summaries as predictor variables.

Candidate gene based association mapping in Fusarium culmorum for field quantitative pathogenicity and mycotoxin production in wheat

Background

Quantitative traits are common in nature, but quantitative pathogenicity has received only little attention in phytopathology. In this study, we used 100 Fusarium culmorum isolates collected from natural field environments to assess their variation for two quantitative traits, aggressiveness and deoxynivalenol (DON) production on wheat plants grown in four different field environments (location-year combinations). Seventeen Fusarium graminearum pathogenicity candidate genes were assessed for their effect on the aggressiveness and DON production of F. culmorum under field conditions.

Results

For both traits, genotypic variance among isolates was high and significant while the isolate-by-environment interaction was also significant, amounting to approximately half of the genotypic variance. Among the studied candidate genes, the mitogen-activated protein kinase (MAPK) HOG1 was found to be significantly associated with aggressiveness and deoxynivalenol (DON) production, explaining 10.29 and 6.05% of the genotypic variance, respectively.

Conclusions

To the best of our knowledge, this is the first report of a protein kinase regulator explaining differences in field aggressiveness and mycotoxin production among individuals from natural populations of a plant pathogen.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-017-0511-9) contains supplementary material, which is available to authorized users.

Identification of Pathogenic Fusarium spp. Causing Maize Ear Rot and Potential Mycotoxin Production in China

Ear rot is a serious disease that affects maize yield and grain quality worldwide. The mycotoxins are often hazardous to humans and livestock. In samples collected in China between 2009 and 2014, Fusarium verticillioides and F. graminearum species complex were the dominant fungi causing ear rot. According to the TEF-1α gene sequence, F. graminearum species complex in China included three independent species: F. graminearum, F. meridionale, and F. boothii. The key gene FUM1 responsible for the biosynthesis of fumonisin was detected in all 82 F. verticillioides isolates. Among these, 57 isolates mainly produced fumonisin B₁, ranging from 2.52 to 18,416.44 µg/g for each gram of dry hyphal weight, in vitro. Three different toxigenic chemotypes were detected among 78 F. graminearum species complex: 15-ADON, NIV and 15-ADON+NIV. Sixty and 16 isolates represented the 15-ADON and NIV chemotypes, respectively; two isolates carried both 15-ADON and NIV-producing segments. All the isolates carrying NIV-specific segment were F. meridionale. The in vitro production of 15-ADON, 3-ADON, DON, and ZEN varied from 5.43 to 81,539.49; 6.04 to 19,590.61; 13.35 to 19,795.33; and 1.77 to 430.24 µg/g of dry hyphal weight, respectively. Altogether, our present data demonstrate potential main mycotoxin production of dominant pathogenic Fusarium in China.

Characterization of Nivalenol-Producing Fusarium culmorum Isolates Obtained from the Air at a Rice Paddy Field in Korea

Together with the Fusarium graminearum species complex, F. culmorum is a major member of the causal agents of Fusarium head blight on cereals such as wheat, barley and corn. It causes significant yield and quality losses and results in the contamination of grain with mycotoxins that are harmful to humans and animals. In Korea, F. culmorum is listed as a quarantine fungal species since it has yet to be found in the country. In this paper, we report that two isolates (J1 and J2) of F. culmorum were collected from the air at a rice paddy field in Korea. Species identification was confirmed by phylogenetic analysis using multi-locus sequence data derived from five genes encoding translation elongation factor, histone H3, phosphate permease, a reductase, and an ammonia ligase and by morphological comparison with reference strains. Both diagnostic PCR and chemical analysis confirmed that these F. culmorum isolates had the capacity to produce nivalenol, the trichothecene mycotoxin, in rice substrate. In addition, both isolates were pathogenic on wheat heads and corn stalks. This is the first report on the occurrence of F. culmorum in Korea.

Occurrence and molecular detection of toxigenic Aspergillus species in food grain samples from India

BACKGROUND

The aim of this study was to detect the presence of different mycotoxigenic Aspergillus species in major food grains from southern states of India, namely maize, paddy, groundnut and sorghum. A total of 200 isolates recovered from 320 grain samples from four southern states were tested for their toxin chemotypes using high-performance liquid chromatography (HPLC), high-performance thin layer chromatography (HPTLC) and polymerase chain reaction (PCR) methods. The diversity and distribution of the isolates were recorded in terms of their frequency, density, importance value index and diversity indices.

RESULTS

Among the different grain samples tested, 83% of groundnut, 69% of maize, 57% of sorghum and 29% of paddy samples had aflatoxin B1 (AFB1) levels above the allowed limit, while 82% of maize, 70% of sorghum, 42% of paddy and 17% of groundnut samples had ochratoxin A (OTA) concentrations higher than the permitted threshold (5 µg kg⁻¹).

CONCLUSION

Since the southern states of India are temperate regions, environmental factors, especially temperature and relative humidity, may be responsible for the high levels of mycotoxins present in the grains studied. Therefore there is a need to generate awareness among farmers and consumers about the possible adverse health effects of high levels of mycotoxins present in different food grains.

Rye grains and the soil derived from under the organic and conventional rye crops as a potential source of biological agents causing respiratory diseases in farmers

Introduction

Introduction: Due to the specific work environment, farmers are exposed to various biological occupational hazard. Among these factors significant are fungi present in the grain and also in the soil. The fungi may be the cause of human diseases including skin infections, asthma, allergic rhinitis and many others.

Aim

The aim of this study was to quantify and identify species of fungi colonizing rye grain samples and the soil under cultivation.

Material and methods

The material consisted of grain and soil samples from two agricultural systems: organic and conventional. To determine the concentration and composition of fungi in collected samples, two media: Malt Agar (MA, Becton, Dickinson and Company) and Potato Dextrose Agar (PDA, Becton, Dickinson and Company) were used. The composition of species in fungal flora was determined using macroscopic and microscopic methods. The isolates of fungi were ranked in the appropriate classes of biosafety BSL.

Results

The most frequently isolated fungi from organic rye grain, regardless of the media used, were species: Aureobasidium pullulans and Alternaria alternata. In conventional farms, most species isolated from rye grain were: Aureobasidium pullulans, Cladosporium oxysporum, Alternaria alternata and yeast-like fungi. Most often species isolated from the soil was Penicillium citreo-viride.

Conclusions

All the results of the research demonstrate the potential hazard to the health of people working in agriculture. Significant exposure of this professional group is associated with the presence of harmful biological agents present in the grain and soil from its cultivation.

Grain dust originating from organic and conventional farming as a potential source of biological agents causing respiratory diseases in farmers

Introduction

Agricultural producers are exposed to a number of different health risks associated with their work environment.

Aim

The objective of the study was to assess the degree of colonization by fungi in terms of quantity and in terms of variety of species the samples taken from the settled dust from combine threshing of rye cultivation from organic and conventional farms in the Province of Lublin.

Material and methods

This paper is a preliminary quantitative assessment of the species of fungi colonizing the samples of settled dust collected during combine threshing from organic and conventional farms in the Province of Lublin. One of the stages of the project was the classification of biosafety BSL (biosafety level) of selected isolates and API ZYM tests to evaluate the potential ability of isolates to cause adverse health effects. To determine the concentration and composition of fungi in collected samples plate dilution method was used with two media: Malt Agar and Potato Dextrose Agar.

Results

Most commonly isolated fungi in settled dust samples collected during combine threshing from organic farms, on PDA medium were: Alternaria alternata and Aureobasidium pullulans. Cultures on MA medium were dominated by Alternaria alternata, Mycelia sterilia and Fusarium poae. In samples of dust from conventional crops, the predominant species was Alternaria alternata on PDA medium and on MA medium.

Conclusions

The obtained results show a potential risk of people involved in agricultural work.

Incidence and multiplex PCR based detection of trichothecene chemotypes of Fusarium culmorum isolates collected from freshly harvested Maize kernels in Southern India

Hundred Fusarium culmorum strains, isolated from freshly harvested maize grain samples from Southern parts of India, were incubated in czapek-dox medium and analyzed for trichothecene (DON/NIV) production. The mPCR assay was standardized targeting trichothecene metabolic pathway genes viz., Tri6, Tri7, Tri13 for detection of trichothecene (DON/NIV) chemotypes and rDNA gene for specific detection of F. culmorum species. Primers for targeted genes were designed and used to predict whether these isolates could produce deoxynivalenol/nivalenol, 94 isolates were able to produce DON/NIV by mPCR assay. Chemical analysis of DON/NIV was carried out for mPCR positive isolates by high performance-thin layer chromatography (HPTLC). To check the practical usefulness of developed mPCR assay, 150 field samples of maize were evaluated and results were compared with conventional HPTLC method. Out of 150 samples, 34% samples stayed as a positive for NIV contamination whereas 44% were found to have deoxynivalenol contamination. Moreover, mPCR results are equivocally matched with the HPTLC chemical analysis for field samples. Chemotyping of F. culmorum isolates were reported for the first time from India, and highlights the important potential of F. culmorum to contaminate maize with DON/NIV.

Fusarium culmorum: causal agent of foot and root rot and head blight on wheat

Fusarium culmorum is a ubiquitous soil-borne fungus able to cause foot and root rot and Fusarium head blight on different small-grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in contamination of the grain with mycotoxins. This review summarizes recent research activities related to F. culmorum, including studies into its population diversity, mycotoxin biosynthesis, mechanisms of pathogenesis and resistance, the development of diagnostic tools and preliminary genome sequence surveys. We also propose potential research areas that may expand our basic understanding of the wheat-F. culmorum interaction and assist in the management of the disease caused by this pathogen.

TAXONOMY

Fusarium culmorum (W.G. Smith) Sacc. Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Fusarium.

DISEASE SYMPTOMS

Foot and root rot (also known as Fusarium crown rot): seedling blight with death of the plant before or after emergence; brown discoloration on roots and coleoptiles of the infected seedlings; brown discoloration on subcrown internodes and on the first two/three internodes of the main stem; tiller abortion; formation of whiteheads with shrivelled white grains; Fusarium head blight: prematurely bleached spikelets or blighting of the entire head, which remains empty or contains shrunken dark kernels. IDENTIFICATION AND DETECTION: Morphological identification is based on the shape of the macroconidia formed on sporodochia on carnation leaf agar. The conidiophores are branched monophialides, short and wide. The macroconidia are relatively short and stout with an apical cell blunt or slightly papillate; the basal cell is foot-shaped or just notched. Macroconidia are thick-walled and curved, usually 3-5 septate, and mostly measuring 30-50 × 5.0-7.5 μm. Microconidia are absent. Oval to globose chlamydospores are formed, intercalary in the hyphae, solitary, in chains or in clumps; they are also formed from macroconidia. The colony grows very rapidly (1.6-2.2 cm/day) on potato dextrose agar (PDA) at the optimum temperature of 25 °C. The mycelium on PDA is floccose, whitish, light yellow or red. The pigment on the reverse plate on PDA varies from greyish-rose, carmine red or burgundy. A wide array of polymerase chain reaction (PCR) and real-time PCR tools, as well as complementary methods, which are summarised in the first two tables, have been developed for the detection and/or quantification of F. culmorum in culture and in naturally infected plant tissue.

HOST RANGE

Fusarium culmorum has a wide range of host plants, mainly cereals, such as wheat, barley, oats, rye, corn, sorghum and various grasses. In addition, it has been isolated from sugar beet, flax, carnation, bean, pea, asparagus, red clover, hop, leeks, Norway spruce, strawberry and potato tuber. Fusarium culmorum has also been associated with dermatitis on marram grass planters in the Netherlands, although its role as a causal agent of skin lesions appears questionable. It is also isolated as a symbiont able to confer resistance to abiotic stress, and has been proposed as a potential biocontrol agent to control the aquatic weed Hydrilla spp.

USEFUL WEBSITES

http://isolate.fusariumdb.org/; http://sppadbase.ipp.cnr.it/; http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html; http://www.fgsc.net/Fusarium/fushome.htm; http://plantpath.psu.edu/facilities/fusarium-research-center; http://www.phi-base.org/; http://www.uniprot.org/; http://www.cabi.org/; http://www.indexfungorum.org/

Factors influencing deoxynivalenol accumulation in small grain cereals

Deoxynivalenol (DON) is a mycotoxin produced by the plant pathogenic fungi Fusarium graminearum and F. culmorum. These and other closely related fungi cause a disease known as Fusarium head blight (FHB) in small grain cereals. Other mycotoxins produced by FHB-causing fungi include nivalenol, T-2 toxin, and zearalenone. Ingestion of mycotoxin-contaminated food and feed can lead to toxicosis in humans and animals, respectively. DON is the predominant and most economically important of these mycotoxins in the majority of small grain-producing regions of the world. This review examines the factors that influence DON accumulation in small grain cereals from an agricultural perspective. The occurrence and economic importance of FHB and DON in small grain cereals, epidemiological factors and cereal production practices that favor FHB development and DON accumulation in grain under field conditions, and regulatory/advisory standards for DON in food and feed are discussed. This information can be used to develop strategies that reduce DON accumulation in grain before harvest and to mitigate the human and animal health risks associated with DON contamination of food and feed.

Fusarium head blight development and trichothecene accumulation in point inoculated Fusarium infected wheat heads

Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schwein) Petch] is the predominant causal agent of Fusarium head blight (FHB), an economically important disease of wheat, in North America. Warm and humid environments at and shortly after anthesis favour FHB. FHB results in yield losses and quality losses in infected grain due to the accumulation of mycotoxins produced by the invading fungus. The objective of this study was to characterise the influence of different F. graminearum isolates and host resistance on FHB development and mycotoxin accumulation. A series of two greenhouse experiments were established where five single isolates of F. graminearum were tested. Three wheat cultivars were examined: Alsen (moderately resistant), 2375 (moderately susceptible) and Wheaton (susceptible). In the point-inoculation experiments, ca. 1000 conidia were placed into a central spikelet of spikes at anthesis. Point-inoculated spikelets were sampled at different growth stages up to soft dough stage. Samples from both experiment series were analysed for mycotoxins. The susceptible cultivar Wheaton had both the highest FHB severity and mycotoxin accumulation. The spread of symptoms both below and above the inoculated central spikelet was significantly higher in 2375 and Wheaton than Alsen. Though deoxynivalenol (DON) did not peak and decline in all experiments, when a peak in the DON content was present it was earlier in 2375 (early milk) than in either Alsen (early dough) or Wheaton (late milk). Though the isolates did not rank similarly in all experiments and in all cultivars, generally isolates Butte86Ada-11 and B63A were more aggressive and isolates 49-3 and B45A were less aggressive in terms of disease severity and mycotoxin accumulation.

Within-field variation of Fusarium graminearum isolates for aggressiveness and deoxynivalenol production in wheat head blight

Fusarium head blight (FHB), caused by Fusarium graminearum sensu stricto (s.s.), causes tremendous annual yield losses in wheat worldwide. Variation of aggressiveness of isolates from individual field populations in terms of FHB infection and deoxynivalenol (DON) concentration in the host are important population parameters reflecting parasitic ability. Our main objective was to estimate the variation of both traits within three populations of F. graminearum s.s., each consisting of 30 single-spore isolates collected from small wheat fields in Germany, and to compare it with 11 isolates of a collection (F. graminearum collection) from four countries. The same isolates were characterized using 19 single-sequence repeat markers. All isolates were spray inoculated on a moderately resistant spring wheat cultivar at two field locations over 2 years (i.e., in four environments). The genotypic proportion of phenotypic variance (σ(2)(G)) within populations was significant (P < 0.01) for both traits, and the σ(2)(G) × environment interaction was even more important for mean FHB severity. Ranges in mean FHB severity and DON concentration in the host were only slightly smaller for the field populations than for the F. graminearum collection. Both traits were significantly (P < 0.05) correlated within and across populations. A further partitioning of σ(2)(G) revealed 72% of σ(2)(G) within and 28% of σ(2)(G) across populations for both traits. Molecular variance of the three populations was similarly distributed (73.6% within versus 26.4% between populations). In view of this high within-field variation for traits of parasitic ability and selection, neutral molecular markers, multiple resistance genes of different origin should be employed in wheat breeding programs to obtain a long-term stable FHB resistance.

Pathogenicity, symptom development, and mycotoxin formation in wheat by Fusarium species frequently isolated from sugar beet

Crop rotations with putative non-host crops such as sugar beet are often recommended to reduce Fusarium head blight (FHB) in cereals. However, recent observations have shown pathogenic, endophytic, and saprotrophic colonization of sugar beet with various Fusarium spp. Therefore, strains of seven species frequently isolated from sugar beet were tested for pathogenicity on wheat. Species-specific symptoms on heads and kernels were evaluated and the grains were analyzed for 20 mycotoxins with liquid chromatography-tandem mass spectrometry. Fusarium graminearum, F. culmorum, and F. cerealis from sugar beet caused typical FHB symptoms and mycotoxin contamination with deoxynivalenol and nivalenol, while a high incidence of black point was observed in heads inoculated with F. tricinctum or F. equiseti. Black point kernels revealed 3.4 to 14.5 times higher mycotoxin concentrations than symptomless grains, containing enniatin B1 at 38,000 μg/kg, moniliformin at 4,900 μg/kg, and 2-amino-14,16-dimethyloctadecan-3-ol at 5,500 μg/kg, as well as monoacetoxyscirpenol at 2,600 μg/kg and nivalenol at 3,800 μg/kg. Monitoring of these latter two species in the field is hampered by the lack of typical head symptoms after infection. In further experiments, the impact of sugar beet residues on FHB severity and the correlation between mycotoxin contamination of cereal lots and the amount of black point have to be evaluated.

Characterization and mycotoxigenic potential of Fusarium species in freshly harvested and stored sugar beet in Europe

Based on a 2-year field trial at two locations in Lower Saxony (Germany), 395 Fusarium isolates belonging to 13 species were collected from more than 3,000 sugar beet roots that were apparently healthy at harvest. In a comparative screen, subsamples were analyzed for Fusarium infection directly after harvest and after different storage conditions. Depending on the storage duration, a different species composition was observed. F. redolens was predominant in freshly harvested beets, while F. culmorum, F. cerealis, and F. graminearum comprised 50.0% (2006) and 84.8% (2007) of the Fusarium mycoflora of sugar beets subjected to long-term pile storage. Randomly selected isolates of all species detected were tested for pathogenicity to sugar beet, but only isolates of F. graminearum and F. sambucinum caused severe root symptoms. Overall, 34 isolates of all species detected were characterized for their mycotoxin profile in rice culture to determine potentially produced toxins for future analysis of sugar beet. A total of 26 Fusarium mycotoxins were detected by liquid chromatography-tandem mass spectrometry, including trichothecenes, zearalenone, and especially high amounts of beauvericin, enniatins, and moniliformin. Further work is required to analyze the natural occurrence of these mycotoxins in sugar beet.

Genotyping and phenotyping of Fusarium graminearum isolates from Germany related to their mycotoxin biosynthesis

Fusarium graminearum is the most important pathogen causing Fusarium head blight (FHB) of small cereal grains worldwide responsible for quantitative and qualitative yield losses. The presence in crops is often associated with mycotoxin contamination of foodstuff limiting its use for human and animal consumption. A collection of isolates of F. graminearum from Germany was characterized genetically and chemically for their potential to produce the B trichothecenes deoxynivalenol (DON) and nivalenol (NIV). Molecular methods with eight PCR assays were implemented based on functional Tri7 and Tri13 genes and on the tri5-tri6 intergenic region to differentiate between chemotaxonomic groups DON and NIV, resulting in a marked majority (61/63) of DON chemotypes. Mycotoxins produced on rice kernels were quantified by means of LC-MSMS including DON, NIV, 3-acetyl-DON (3-ADON), 15-acetyl-DON (15-ADON), DON-3-glucoside, fusarenon X, as well as zearalenone; all of them proving to be present in high concentration among the isolates. All DON-chemotype isolates also produced lower amounts of NIV with the amount being positively correlated (R²=0.89) to the DON amount. 15-ADON and 3-ADON are reported to be produced simultaneously by the isolates, the former dominating over the latter in all but one isolate. Fungal biomass, was quantified via ergosterol amount on rice. It was used to calculate specific mycotoxin production per biomass of isolates, ranging from 0.104 to 1.815mg DON mg-1 ergosterol, presenting a Gaussian distribution. Genotype and phenotype characterization revealed discrepancies with respect to mycotoxin production potential of the fungi, i.e. isolates from one chemotype were able to produce mycotoxins from other chemotypes in considerable amounts.

Effect of different storage conditions on the mycotoxin contamination of Fusarium culmorum-infected and non-infected wheat straw

Mycotoxins are known to affect the health and performance of farm animals. In contrast to cereal grains, the straw is only rarely analysed for mycotoxins, although contaminated straw could additionally expose farm animals to mycotoxins. For this reason, two experiments were carried out to examine the effect of pre-harvest Fusarium infection (inoculation with F. culmorum) and different storage conditions on the mycotoxin concentrations in straw. In the first experiment, both the inoculated and the identically cultivated control straw were stored in rectangular bales either in a barn or outdoors for a time period of 32 weeks (farm-scale experiment). The second experiment was aimed to examine the mycotoxin concentrations during storage under controlled conditions in a temperature-controlled climatic chamber, with target dry matter contents of 86%, 82% and 78% using 1.5-l preservation jars (laboratory-scale experiment). While the concentration of deoxynivalenol and its derivates decreased in the farm-scale experiment when inoculated straw was stored outdoors, the zearalenone concentration increased within the same time period. The latter effect was also detected for the control straw. These opposite effects were probably caused by the massive water uptake during the outdoor storage. The only effect we observed in the laboratory-scale experiment with dry matter contents between 78% and 86% was a more pronounced decrease of the 3-acetyl-deoxynivalenol concentrations in the inoculated straw with increasing moisture contents.

The effect of silver nanoparticles on phytopathogenic spores of Fusarium culmorum

The aim of the present experiment was to investigate the influence of silver nanoparticles on Fusarium culmorum (W.G. Smith) Sacc. (FC) spores. The silver nanoparticles were produced by the high-voltage arc discharge method. To test the effect of silver nanoparticles on FC spores, 3 parameters were tested. One of these parameters was the vegetative mycelial growth in 2 experiments. The first involved the growth of FC spores on potato dextrose agar (PDA) medium after contact with 0.12–10 ppm of silver nanoparticles, and the second the growth of spores after contact with 0.12–2.5 ppm solutions of silver, but with culturing on 3 types of media (PDA, nutrient-poor PDA, and agar) instead. The next parameter was the formation of spores after the mycelia were cultured. The last parameter was spore germination in a 2.5 ppm solution of silver nanoparticles. A significant reduction in mycelial growth was observed for spores incubated with silver nanoparticles. This relationship was dependent on the incubation time and type of growth medium, but did not depend significantly on the concentration of silver nanoparticles up to 2.5 ppm. The sporulation test showed that, relative to control samples, the number of spores formed by mycelia increased in the culture after contact with silver nanoparticles, especially on the nutrient-poor PDA medium. The 24 h incubation of FC spores with a 2.5 ppm solution of silver nanoparticles greatly reduced the number of germinating fragments and sprout length relative to the control.

Double mutation in tomato ribosomal protein L3 cDNA confers tolerance to deoxynivalenol (DON) in transgenic tobacco

The contamination of mycotoxins associated with head blight of wheat and other grains caused by Fusarium graminearum is chronic threat to crop, human and animal health throughout the world. Deoxinevalenol (DON), produced by the fungus, belonging to class trichothecene is believed to act as a virulence factor in fungal pathogenesis by inhibiting eukaryotic protein synthesis, thereby blocking or delaying the expression of defense related proteins induced by host plant. The putative site of action of DON is 60s ribosomal protein L3 (RPL3). In order to reduce the effects of DON in the host plants, we modified tomato RPL3 (LeRPL3) to introduce W25R/H259Y mutations so that amino acid residue 258 is changed from tryptophan to arginine and 259 from histidine to tyrosine. Transgenic tobacco plants expressing these modified LeRPL3 cDNAs were tested for growth pattern of T1 seedlings in presence of DON. When seedling of these transgenic tobacco plants were compared for growth in the presence of DON, a significant difference in growth rate and the ability to undergo differentiation was observed among those plants expressing the modified version of the Rp13 gene, compared to those expressing the wild-type Rp13 gene. Expression of the tagged gene product indicates that is was not due to somaclonal variation. These results indicate a possible mechanism of host plant resistance to the fungal pathogen F. graminearum among the susceptible cereal species based on the expression ofmodified Rp13 genes.

Real-time PCR Quantification and Mycotoxin Production of Fusarium graminearum in Wheat Inoculated with Isolates Collected from Potato, Sugar Beet, and Wheat

ABSTRACT Fusarium graminearum causes Fusarium head blight (FHB) in small grains worldwide. Although primarily a pathogen of cereals, it also can infect noncereal crops such as potato and sugar beet in the United States. We used a real-time polymerase chain reaction (PCR) method based on intergenic sequences specific to the trichodiene synthase gene (Tri5) from F. graminearum. TaqMan probe and primers were designed and used to estimate DNA content of the pathogen (FgDNA) in the susceptible wheat cv. Grandin after inoculation with the 21 isolates of F. graminearum collected from potato, sugar beet, and wheat. The presence of nine mycotoxins was analyzed in the inoculated wheat heads by gas chromatography and mass spectrometry. All isolates contained the Tri5 gene and were virulent to cv. Grandin. Isolates of F. graminearum differed significantly in virulence (expressed as disease severity), FgDNA content, and mycotoxin accumulation. Potato isolates showed greater variability in producing different mycotoxins than sugar beet and wheat isolates. Correlation analysis showed a significant (P < 0.001) positive relationship between FgDNA content and FHB severity or deoxynivalenol (DON) production. Moreover, a significant (P < 0.001) positive correlation between FHB severity and DON content was observed. Our findings revealed that F. graminearum causing potato dry rot and sugar beet decay could be potential sources of inoculum for FHB epidemics in wheat. Real-time PCR assay provides sensitive and accurate quantification of F. graminearum in wheat and can be useful for monitoring the colonization of wheat grains by F. graminearum in controlled environments, and evaluating wheat germplasms for resistance to FHB.

Involvement of trichothecenes in fusarioses of wheat, barley and maize evaluated by gene disruption of the trichodiene synthase (Tri5) gene in three field isolates of different chemotype and virulence

SUMMARY Fusarium graminearum is the main causative agent of Fusarium head blight on small grain cereals and of ear rot on maize. The disease leads to dramatic yield losses and to an accumulation of mycotoxins. The most dominant F. graminearum mycotoxins are the trichothecenes, with deoxynivalenol and nivalenol being the most prevalent derivatives. To investigate the involvement of trichothecenes in the virulence of the pathogen, the gene coding for the initial enzyme of the trichothecene pathway was disrupted in three field isolates, differing in chemotype and in virulence. From each isolate three individual disruption mutants were tested for their virulence on wheat, barley and maize. Despite the different initial virulence of the three wild-type progenitor strains on wheat, all disruption mutants caused disease symptoms on the inoculated spikelet, but the symptoms did not spread into other spikelets. On barley, the trichothecene deficient mutants showed no significant difference compared to the wild-type strains: all were equally aggressive. On maize, mutants derived from the NIV-producing strain caused less disease than their wild-type progenitor strain, while mutants derived from DON-producing strains caused the same level of disease as their progenitor strains. These data demonstrate that trichothecenes influence the virulence of F. graminearum in a highly complex manner, which is strongly host as well as moderately chemotype specific.

A highly efficient transient protoplast system for analyzing defence gene expression and protein-protein interactions in rice

SUMMARY The transient assay system based on mesophyll or cultured cell-derived protoplasts has been exploited in several plant species and has become a powerful tool for rapid gene functional analysis and biochemical manipulations. However, the system has not been widely used in rice owing to the difficulties in large-scale isolation of viable rice protoplasts from leaves or suspension-cultured cells. Here, we describe a significantly improved method to isolate a large number of protoplasts from stem and sheath tissues of both young and mature plants. High-level coexpression of multiple constructs and efficient suppression of exogenous and endogenous genes were observed in the stem- and sheath-derived protoplasts. A transient green fluorescent protein and luciferase-based reporter system for defence-related genes expression analysis has been established, which is useful for screening and characterizing genes involved in rice defence signalling pathways. Furthermore, a protoplast-based bimolecular fluorescence complementation (BiFC) system for the detection of protein-protein interactions in living rice cells was developed. The YFP complementation of two split-YFP halves mediated by homodimerization of the GUS and SPIN1, a cell-death related protein, was observed in transfected protoplasts. In combination with genetic, genomic and proteomic approaches, the established versatile protoplast transient assay system will facilitate large-scale functional analysis of defence-related genes in rice.

Differentiation inside multicelled macroconidia of Fusarium culmorum during early germination

Multicelled conidia are formed by many fungal species, but germination of these spores is scarcely studied. Here, the germination and the effects of antimicrobials on multicompartment macroconidia of Fusarium culmorum were investigated. Germ-tube formation was mostly from apical compartments. The intracellular pH (pH(in)) of the different individual cells of the macroconidia was monitored during germination. The pH(in) varied among different compartments and during different stages of germination. The internal pH was lowest in ungerminated cells and rose during germ-tube formation and was highest in new germ tubes. Antifungal compounds affect the pH(in) and differentiation of the conidia. The pH(in) inside the macroconidial compartments was lowered very fast in the presence of nystatin (1 and 4 microg/ml). At sublethal doses (0.3 microg/ml), the apical compartments were preferentially targeted showing lower pH(in) values. The reduced germination capacity of apical compartments under these conditions was compensated by an increased germination capacity of middle compartments.

Epidemiology of mycotoxigenic fungi associated with Fusarium ear blight and apple blue mould: A review

Research on the epidemiology of plant diseases is briefly reviewed, focusing on two diseases caused by mycotoxin-producing pathogens: Fusarium ear (or head) blight (FEB or FHB) of small grain cereals and apple blue mould (Penicillium expansum). Pathogen development during its key life cycles is discussed in relation to important environmental factors and host resistance. Current control methods are also reviewed, focusing on cultural and biological methods. The future challenge is to understand the relationships between disease severity, fungal biomass and the production of associated mycotoxins in order to minimize risks of both disease damage to crop yields and threat to human health posed by mycotoxins.

Assessment of trichothecene chemotypes ofFusarium culmorumoccurring in Europe

Fusarium trichothecenes are a group of fungal toxic metabolites whose synthesis requires the action of gene products from three different genetic loci. We evaluated, both chemically and by PCR assays, 55 isolates of Fusarium culmorum from eight European countries and different host plants for their ability to produce trichothecenes. Specific sequences in the Tri6-Tri5 intergenic region were associated with deoxynivalenol production. Sequences in the Tri3 gene were also associated with deoxynivalenol production and specific primer sets were selected from these sequences to identify 3-acetyl-deoxynivalenol or 15-acetyl-deoxynivalenol chemotypes. Specific sequences in the Tri5 and Tri7 genes were associated with the nivalenol chemotype but not with the deoxynivalenol chemotype. Two chemotypes were identified by chemical analysis and confirmed by PCR. Strains of the nivalenol chemotype produced nivalenol (up to 260 microg g(-1)) and 4-acetyl-nivalenol (up to 60 microg g(-1)), strains with the 3-acetyl-deoxynivalenol chemotype produced deoxynivalenol (up to 1700 microg g(-1)) and 3-acetyl-deoxynivalenol (up to 600 microg g(-1)). Three strains of F. culmorum from France, previously reported as 15-acetyl-deoxynivalenol producers, had the 3-acetyl-deoxynivalenol chemotype. The results are consistent with data from other European countries on the occurrence of the nivalenol and 3-acetyl-deoxynivalenol chemotypes and provide support for the hypothesis that European isolates of F. culmorum producing deoxynivalenol belong only to the 3-acetyl-deoxynivalenol chemotype. The production of trichothecenes from F. culmorum isolates from walnut (3-acetyl-deoxynivalenol chemotype) and leek (nivalenol chemotype) is reported for the first time.

Resistance in wheat to Fusarium infection and trichothecene formation

The state of the art in Fusarium head blight resistance research is reviewed with reference to breeding for genetic resistance to Fusarium in wheat in practice. Fusarium graminearum and F. culmorum produce the trichothecene mycotoxin deoxynivalenol (DON). DON has phytotoxic properties and is an important aggressiveness factor in head blight. Head blight resistance in wheat is not specific for either F. graminearum or F. culmorum. Resistance components include resistance to penetration, resistance to colonization and mechanisms that influence kernel DON content. The resistance to Fusarium in wheat is a quantitative trait with relative high heritability and controlled by a few genes with major effect. A major quantitative trait locus (QTL) for head blight resistance from the Chinese variety Sumai 3 has been identified and verified by several research groups via molecular marker analysis. Research is now directed at identifying additional QTLs to make accumulation of resistance genes in elite wheat lines possible. The policy of official variety list trials may affect the head blight resistant level of future wheat varieties by excluding candidate varieties that are a too susceptible to Fusarium. A higher level of Fusarium head blight will guarantee lower risks for the farmer of crop loss due to reduced grain yield, low quality and mycotoxin contamination.

Influence of environmental factors on the biosynthesis of type B trichothecenes by isolates of Fusarium spp. from Spanish crops

Various species of Fusarium can produce trichothecene mycotoxins that contaminate food commodities and can represent a risk for human and animal health. In this paper, a full factorial design was applied to study the influence of incubation temperature, water activity (a(w)) and type of isolate on the production of deoxynivalenol (DON), nivalenol (NIV) and 3-acetyldeoxynivalenol (3-AcDON) in corn kernel cultures by three isolates of Fusarium graminearum and three isolates of Fusarium culmorum from crops grown in Spain. The tested temperatures were 15, 20, 28 and 32 degrees C. The a(w)-values were 0.960, 0.970 and 0.980. Moisture of cultures (within the studied range) did not affect significantly production of trichothecenes; however, the temperature affected significantly mycotoxin production and the optimal values were 28, 20 and 15 degrees C for DON, NIV and 3-AcDON, respectively. Four additional isolates of F. graminearum and two additional isolates of F. culmorum were examined for production of these mycotoxins at the optimal temperatures. Of the seven isolates of F. graminearum, four produced DON (0.88-3.97 microg/g), seven produced NIV (1.53-124 microg/g), and three produced 3-AcDON (0.65-10.6 microg/g). Of the five isolates of F. culmorum, four produced DON (1.20-4.93 microg/g), four produced NIV (6.94-701 microg/g), and four produced 3-AcDON (0.83-7.70 microg/g). Practically all isolates seem to belong to the NIV-chemotype. This is the first study done with regard to interaction between strain and ecological variables on type B trichothecene production by isolates of these two species from crops grown in Spain.

Host genetic effect on deoxynivalenol accumulation in fusarium head blight of barley

ABSTRACT One of the major concerns with Fusarium head blight (FHB) of barley is the potential health risks to livestock and humans through the accumulation of the mycotoxin deoxynivalenol (DON) in infected grain. To define the role of the host in DON accumulation during the early stages of disease development, we conducted a series of greenhouse experiments. We inoculated single spikelets of greenhouse-grown plants with Fusarium graminearum, moved the plants to a dew chamber, and harvested the inoculated spikelets after 72 h for DON analysis. We conducted a quantitative trait locus (QTL) analysis using a genetic mapping population, constructed with the parents Stander and Frederickson, that segregated for DON accumulation after single-spikelet inoculation in two experiments. A single QTL on chromosome 3 explained 18 and 35% of the phenotypic variation in the two experiments. To validate this QTL for DON accumulation, we used a DNA marker to select near-isogenic lines from a family from the mapping population that was segregating at this QTL. Disease symptom development was similar between the nearisogenic lines; however, the mean DON concentration of the lines homozygous for the allele from the high DON parent was 2.5-fold more than the lines homozygous for the alternate allele. A time course experiment showed that this effect on toxin accumulation was observed at 10 days post inoculation. The near-isogenic lines developed in this study should prove useful for further exploration of the role of DON in FHB.

Genetic Mapping of Pathogenicity and Aggressiveness of Gibberella zeae (Fusarium graminearum) Toward Wheat

ABSTRACT Gibberella zeae is the major fungal pathogen of Fusarium head blight of wheat and produces several mycotoxins that are harmful to humans and domesticated animals. We identified loci associated with pathogenicity and aggressiveness on an amplified fragment length polymorphism based genetic map of G. zeae in a cross between a lineage 6 nivalenol producer from Japan and a lineage 7 deoxynivalenol producer from Kansas. Ninety-nine progeny and the parents were tested in the greenhouse for 2 years. Progeny segregated qualitatively (61:38) for pathogenicity:nonpathogenicity, respectively. The trait maps to linkage group IV, which is adjacent to loci that affect colony pigmentation, perithecium production, and trichothecene toxin amount. Among the 61 pathogenic progeny, the amount of disease induced (aggressiveness) varied quantitatively. Two reproducible quantitative trait loci (QTL) for aggressiveness were detected on linkage group I using simple interval analysis. A QTL linked to the TRI5 locus (trichodiene synthase in the trichothecene pathway gene cluster) explained 51% of the variation observed, and a second QTL that was 50 centimorgans away explained 29% of the phenotypic variation. TRI5 is tightly linked to the locus controlling trichothecene toxin type. The two QTLs, however, were likely part of the same QTL using composite interval analysis. Progeny that produced deoxynivalenol were, on average, approximately twice as aggressive as those that produced nivalenol. No transgressive segregation for aggressiveness was detected. The rather simple inheritance of both traits in this interlineage cross suggests that relatively few loci for pathogenicity or aggressiveness differ between lineage 6 and 7.

Production of trichothecenes and other secondary metabolites by Fusarium culmorum and Fusarium equiseti on common laboratory media and a soil organic matter agar: an ecological interpretation

Fusarium culmorum and F. equiseti were characterized with regard to production of trichothecenes and other secondary metabolites. Results following growth on laboratory media are interpreted with the aim of increasing the understanding of fungal metabolism in the field environment. While trichothecene production was detected for 94 of 102 F. culmorum isolates, only 8 of 57 F. equiseti isolates were positive. Profiles of secondary metabolites were compared by following growth on yeast extract sucrose agar (YES), potato sucrose agar (PSA), and an agar medium, prepared from soil organic matter (SOM), which was included to simulate growth conditions in soil. SOM supported the production of chrysogine by F. culmorum. The two species utilized the media differently. F. culmorumproduced zearalenone (ZEA) on YES, whereas some F. equiseti isolates produced ZEA on PSA. Other F. equiseti isolates produced equisetin. These differences may reflect that F. culmorum depends on a pathogenic life style while F. equiseti has a more saprotrophic mode of existence.

Arabidopsis is susceptible to the cereal ear blight fungal pathogens Fusarium graminearum and Fusarium culmorum

The fungal pathogens Fusarium graminearum and F. culmorum cause ear blight disease on cereal crops worldwide. The disease lowers both grain quality and grain safety. Disease prevalence is increasing due to changes in cropping practices and the difficulties encountered by plant breeders when trying to introgress the polygene-based resistance. The molecular basis of resistance to Fusarium ear blight in cereal species is poorly understood. This is primarily due to the large size of cereal genomes and the expensive resources required to undertake gene function studies in cereals. We therefore explored the possibility of developing various model floral infection systems that would be more amenable to experimental manipulation and high-throughput gene function studies. The floral tissues of tobacco, tomato, soybean and Arabidopsis were inoculated with Fusarium conidia and this resulted in disease symptoms on anthers, anther filaments and petals in each plant species. However, only in Arabidopsis did this initial infection then spread into the developing siliques and seeds. A survey of 236 Arabidopsis ecotypes failed to identify a single genotype that was extremely resistant or susceptible to Fusarium floral infections. Three Arabidopsis floral mutants that failed to develop anthers and/or functional pollen (i.e. agamous-1, apetala1-3 and dad1) were significantly less susceptible to Fusarium floral infection than wild type. Deoxynivalenol (DON) mycotoxin production was also detected in Fusarium-infected flowers at >1 ppm. This novel floral pathosystem for Arabidopsis appears to be highly representative of a serious cereal crop disease.

Identification by PCR of Fusarium culmorum strains producing large and small amounts of deoxynivalenol

Thirty deoxynivalenol-producing F. culmorum strains, isolated from wheat grains, were incubated in vitro and analyzed for trichothecene production. Seventeen strains produced more than 1 ppm of deoxynivalenol and acetyldeoxynivalenol and were considered high-deoxynivalenol-producing strains, whereas 13 F. culmorum strains produced less than 0.07 ppm of trichothecenes and were considered low-deoxynivalenol-producing strains. For all strains, a 550-base portion of the trichodiene synthase gene (tri5) was amplified and sequenced. According to the tri5 data, the F. culmorum strains tested clustered into two groups that correlated with in vitro deoxynivalenol production. For three high-producing and three low-producing F. culmorum strains, the tri5-tri6 intergenic region was then sequenced, which confirmed the two separate clusters within the F. culmorum strains. According to the tri5-tri6 sequence data, specific PCR primers were designed to allow differentiation of high-producing from low-producing F. culmorum strains.

Production of culmorin compounds and other secondary metabolites by Fusarium culmorum and F. graminearum strains isolated from Norwegian cereals

Twenty-three Fusarium culmorum and 21 F. graminearum isolates were studied for their ability to produce mycotoxins and other secondary metabolites. The strains were cultivated on rice, and the extracts analysed by gas chromatography mass spectrometry (GC-MS) after derivatization with pentafluoropropionic (PFP) reagent. Two F. culmorum strains formed nivalenol and its acetylated derivatives (chemotype II), while all F. graminearum and the other F. culmorum isolates produced deoxynivalenol (DON) via 3-acetyldeoxynivalenol (3-acetyl-DON) (chemotype IA). 15-hydroxy-culmorin, followed by 5-hydroxy-culmorin were the main other metabolites produced F. culmorum, while 5-, 12- and an unidentified hydroxy-culmorin, suggested to be 14-hydroxy-culmorin, were the main metabolites of F. graminearum. The hydroxy-culmorin profile was found to be significantly different for the two Fusarium species. Minor amounts of about ten other hydroxy-culmorins, four hydroxy-culmorones and 3,13-dihydroxy- epiapotrichothecene were also detected in most cultures. Traces of sambucinol seemed to be present in some of the isolates, but were not detected in any significant amounts. The precursors in the biosynthetic sequence to 3-acetyldeoxynivalenol, 7,8-dihydroxycalonectrin and 15-deacetyl-7,8-dihydroxycalonectrin, were detected in most cultures. We also report the assignment of both the 1H and 13C NMR data of 15-deacetyl-7,8-dihydroxycalonectrin, which has only been reported incorrectly before.

Toxigenic potential of Fusarium culmorum strains isolated from French wheat

Sixty F. culmorum strains were isolated from wheat grains collected from different wheat-growing areas in France and from different cultivars. The isolates were grown on autoclaved wheat grain to assess their ability to produce trichothecenes and zearalenone. Fungal biomass was evaluated through the ergosterol grain content. All the isolates produced zearalenone (0.39-1660 mg kg(-1)). Thirty-five of the 60 F. culmorum produced nivalenol (0.11-11.7 mg kg(-1)), 12 of 60 produced fusarenone X (0.05-8.42 mg kg(-1)), five of 60 produced 15-acetyldeoxynivalenol (0.48-27.7 mg kg(-1)), 13 of 60 produced 3-acetyldeoxynivalenol (0.07-21.0 mg kg(-1) and 24 of 60 produced deoxynivalenol (0.92-51.9 mg kg(-1)). According to the results, the distribution of the different chemotypes as well as the high and the low mycotoxin-producing Fusarium strains could not be associated to geographical origin.

Fast methods for screening of trichothecenes in fungal cultures using gas chromatography-tandem mass spectrometry

The paper presents a fast method for trichothecene profiling and chemotaxonomic studies in species of Fusarium, Stachybotrys. Trichoderma and Memnoniella. Micro scale extracted crude Fusarium extracts were derivatised using pentafluoropropionic anhydride and analysed by gas chromatography with simultaneous full scan and tandem mass spectrometric detection. It was possible to monitor for up to four compounds simultaneous, making detection of acetyl T-2 toxin, T-2 toxin, HT-2 toxin, T-2 triol. T-2 tetraol, neosolaniol, iso-neosolaniol, scirpentriol, 4,15-diacetoxyscirpenol, 15-acetoxyscirpenol, 4-acetoxyscirpentriol, nivalenol, fusarenon-X, deoxynivalenol, 15-acetyl-deoxynivalenol and 3-acetyldeoxynivalenol possible during a 23-min GC run. A slightly modified method could detect trichothecenes produced by Stachybotrys, Memnoniella and Trichoderma, by hydrolysing crude extracts prior to derivatisation with heptafluorobuturyl imidazole. All types of derivatised extracts could be reanalysed using negative ion chemical ionisation (NICI) GC-MS for molecular mass determination and verification purposes. A retention time index could be used for correction in retention time drifts between sequences and worked both in EI+ and NICI mode.

Characterisation offusarium graminearum andF. culmorum isolates by mycotoxin production and aggressiveness to wheat

A total of 27Fusarium culmorum isolates from Germany and 41F. graminearum isolates from Kenya were investigated for aggressiveness and mycotoxin production on wheat ears. In addition, ergosterol content of the kernels from ears inoculated withF. graminearum was determined and theF. culmorum isolates were tested for mycotoxin productionin vitro. For both pathogens, isolates markedly differed in aggressiveness. 59% and 37% of theF. culmorum isolates produced NIV and DON, respectively,in vivo andin vitro. The DON-producing isolates also produced 3-acDONin vitro. The more aggressive isolates produced mainly DON while the less aggressive isolates produced mainly NIV. 12% and 85% of theF. graminearum isolates produced NIV and DON, respectively. The highly aggressive isolates produced higher amounts of DON, aggressiveness being highly correlated to DON content in the kernels. NIV-producing isolates were less aggressive. Ergosterol content of kernels was moderately correlated to aggressiveness but highly correlated to DON content. Disease severity was associated with kernel weight reduction.