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Durum wheat is one of the cereal crops that accumulates the highest concentrations of cadmium (Cd) and deoxynivalenol (DON) mycotoxin in its grains, thereby affecting the safety of products made of durum wheat grains (pasta and semolina). This study investigates

International audience; Cereal crops are frequently affected by toxigenic Fusarium species, among which the most common and worrying in Europe are Fusarium graminearum and Fusarium culmorum. These species are the causal agents of grain contamination with type B trichothecene (TCTB) mycotoxins. To help reduce the use of synthetic fungicides while guaranteeing low mycotoxin levels, there is an urgent need to develop new, efficient and environmentally-friendly plant protection solutions. Previously, F. graminearum proteins that could serve as putative targets to block the fungal spread and toxin production were identified and a virtual screening undertaken. Here, two selected compounds, M1 and M2, predicted, respectively, as the top compounds acting on the trichodiene synthase, a key enzyme of TCTB biosynthesis, and the 24-sterol-C-methyltransferase, a protein involved in ergosterol biosynthesis, were submitted for biological tests. Corroborating in silico predictions, M1 was shown to significantly inhibit TCTB yield by a panel of strains. Results were less obvious with M2 that induced only a slight reduction in fungal biomass. To go further, seven M1 analogs were assessed, which allowed evidencing of the physicochemical properties crucial for the anti-mycotoxin activity. Altogether, our results provide the first evidence of the promising potential of computational approaches to discover new anti-mycotoxin solutions

Enniatins are mycotoxins produced by Fusarium species contaminating cereals and various agricultural commodities. The co-occurrence of these mycotoxins in large quantities with other mycotoxins such as trichothecenes and the possible synergies in toxicity could lead to serious food safety problems. Using the agar dilution method, Ammoides pusilla was selected among eight Tunisian plants for the antifungal potential of its essential oil (EO) on Fusarium avenaceum mycelial growth and its production of enniatins. Two EO batches were produced and analyzed by GC/MS-MS. Their activities were measured using both contact assays and fumigant tests (estimated IC50 were 0.1 µL·mL−1 and 7.6 µL·L−1, respectively). The A. pusilla EOs and their volatiles inhibited the germination of spores and the mycelial growth, showing a fungistatic but not fungicidal activity. The accumulation of enniatins was also significantly reduced (estimated IC50 were 0.05 µL·mL−1 for the contact assays and 4.2 µL·L−1 for the fumigation assays). The most active batch of EO was richer in thymol, the main volatile compound found. Thymol used as fumigant showed a potent fungistatic activity but not a significant antimycotoxigenic activity. Overall, our data demonstrated the bioactivity of A. pusilla EO and its high potential to control F. avenaceum and its enniatins production in agricultural commodities.

International audience; Fusarium graminearum is a major fungal pathogen affecting crops of worldwide importance. F. graminearum produces type B trichothecene mycotoxins (TCTB), which are not fully eliminated during food and feed processing. Therefore, the best way to minimize TCTB contamination is to develop prevention strategies. Herein we show that treatment with the reduced form of the γ-core of the tick defensin DefMT3, referred to as TickCore3 (TC3), decreases F. graminearum growth and abrogates TCTB production. The oxidized form of TC3 loses antifungal activity, but retains anti-mycotoxin activity. Molecular dynamics show that TC3 is recruited by specific membrane phospholipids in F. graminearum and that membrane binding of the oxidized form of TC3 is unstable. Capping each of the three cysteine residues of TC3 with methyl groups reduces its inhibitory efficacy. Substitutions of the positively-charged residues lysine (Lys) 6 or arginine 7 by threonine had the highest and the lesser impact, respectively, on the anti-mycotoxin activity of TC3. We conclude that the binding of linear TC3 to F. graminearum membrane phospholipids is required for the antifungal activity of the reduced peptide. Besides, Lys6 appears essential for the anti-mycotoxin activity of the reduced peptide. Our results provide foundation for developing novel and environment-friendly strategies for controlling F. graminearum.

Consumption of cereals contaminated by mycotoxins poses health risks. For instance, Fumonisins B, mainly produced by Fusarium verticillioides and Fusarium proliferatum, and the type B trichothecene deoxynivalenol, typically produced by Fusarium graminearum, are highly prevalent on cereal grains that are staples of many cultural diets and known to represent a toxic risk hazard. In Peru, corn and other cereals are frequently consumed on a daily basis under various forms, the majority of food grains being sold through traditional markets for direct consumption. Here, we surveyed mycotoxin contents of market-bought grain samples in order to assess the threat these mycotoxins might represent to Peruvian population, with a focus on corn. We found that nearly one sample of Peruvian corn out of six was contaminated with very high levels of Fumonisins, levels mostly ascribed to the presence of F. verticillioides. Extensive profiling of Peruvian corn kernels for fungal contaminants could provide elements to refine the potential risk associated with Fusarium toxins and help define adapted food safety standards. This research was funded by the French National Alliance for Life Sciences and Health, grant number ENV201408. S.B. has received funding from the European Union's Horizon 2020 Framework program under the Marie Sklodowska-Curie Actions, agreement number 823935. P.V.O. was supported by a postdoctoral fellowship from the French National Research Institute for Sustainable Development (IRD) (04077858). JPC was a recipient of a doctoral fellowship from the Peruvian National Council for Science and Technology (212-2015-FONDECYT).

Fusarium graminearum is a fungal pathogen that can colonize small-grain cereals and maize and secrete type B trichothecene (TCTB) mycotoxins. The development of environmental-friendly strategies guaranteeing the safety of food and feed is a key challenge facing agriculture today. One of these strategies lies on the promising capacity of products issued from natural sources to counteract crop pests. In this work, the in vitro efficiency of sixteen extracts obtained from eight natural sources using subcritical water extraction at two temperatures was assessed against fungal growth and TCTB production by F. graminearum. Maritime pine sawdust extract was shown to be extremely efficient, leading to a significant inhibition of up to 89% of the fungal growth and up to 65% reduction of the mycotoxin production by F. graminearum. Liquid chromatography/mass spectrometry analysis of this active extract revealed the presence of three families of phenolics with a predominance of methylated compounds and suggested that the abundance of methylated structures, and therefore of hydrophobic compounds, could be a primary factor underpinning the activity of the maritime pine sawdust extract. Altogether, our data support that wood/forest by-products could be promising sources of bioactive compounds for controlling F. graminearum and its production of mycotoxins.

Mycotoxins in small grains are a significant and long-standing problem. These contaminants may be produced by members of several fungal genera, including Alternaria, Aspergillus, Fusarium, Claviceps, and Penicillium. Interventions that limit contamination can be made both pre-harvest and post-harvest. Many problems and strategies to control them and the toxins they produce are similar regardless of the location at which they are employed, while others are more common in some areas than in others. Increased knowledge of host-plant resistance, better agronomic methods, improved fungicide management, and better storage strategies all have application on a global basis. We summarize the major pre- and post-harvest control strategies currently in use. In the area of pre-harvest, these include resistant host lines, fungicides and their application guided by epidemiological models, and multiple cultural practices. In the area of post-harvest, drying, storage, cleaning and sorting, and some end-product processes were the most important at the global level. We also employed the Nominal Group discussion technique to identify and prioritize potential steps forward and to reduce problems associated with human and animal consumption of these grains. Identifying existing and potentially novel mechanisms to effectively manage mycotoxin problems in these grains is essential to ensure the safety of humans and domesticated animals that consume these grains.

Background Increased contamination of European and Asian wheat and barley crops with “emerging” mycotoxins such as enniatins or beauvericin, produced by Fusarium avenaceum and Fusarium tricinctum, suggest that these phylogenetically close species could be involved in future food-safety crises. Results The mitochondrial genomes of F. tricinctum strain INRA104 and F. avenaceum strain FaLH27 have been annotated. A comparative analysis was carried out then extended to a set of 25 wild strains. Results show that they constitute two distinct species, easily distinguished by their mitochondrial sequences. The mitochondrial genetic variability is mainly located within the intergenic regions. Marks of variations show they have evolved (i) by Single Nucleotide Polymorphisms (SNPs), (ii) by length variations mediated by insertion/deletion sequences (Indels), and (iii) by length mutations generated by DNA sliding events occurring in mononucleotide (A)n or (T)n microsatellite type sequences arranged in a peculiar palindromic organization. The optionality of these palindromes between both species argues for their mobility. The presence of Indels and SNPs in palindrome neighbouring regions suggests their involvement in these observed variations. Moreover, the intraspecific and interspecific variations in the presence/absence of group I introns suggest a high mobility, resulting from several events of gain and loss during short evolution periods. Phylogenetic analyses of intron orthologous sequences suggest that most introns could have originated from lateral transfers from phylogenetically close or distant species belonging to various Ascomycota genera and even to the Basidiomycota fungal division. Conclusions Mitochondrial genome evolution between F. tricinctum and F. avenaceum is mostly driven by two types of mobile genetic elements, implicated in genome polymorphism. The first one is represented by group I introns. Indeed, both genomes harbour optional (inter- or intra-specifically) group I introns, all carrying putatively functional hegs, arguing for a high mobility of these introns during short evolution periods. The gain events were shown to involve, for most of them, lateral transfers between phylogenetically distant species. This study has also revealed a new type of mobile genetic element constituted by a palindromic arrangement of (A) n and (T) n microsatellite sequences whose presence was related to occurrence of SNPs and Indels in the neighbouring regions.

Enniatins (ENNs) that belong to the group of emerging mycotoxins are widespread contaminants of agricultural commodities. There is currently insufficient evidence to rule out health concerns associated with long-term exposure to ENNs and efforts must be strengthened to define a control strategy. While the potential of plant compounds to counteract the contamination with legislated mycotoxins has been reported, little remains known regarding ENNs. The present study evidenced for the first time the efficiency of hydroxycinnamic acids to inhibit the fungal growth and ENNs yield by Fusarium avenaceum. Notably, 0.5 mM of exogenous ferulic, caffeic, and p-coumaric acids led to a drastic reduction of ENNs synthesis in pH4 broths, with ferulic acid being the most potent. The ENNs production inhibitory activity of ferulic acid was shown to be associated with a significant down-regulation of the expression of ENNs biosynthetic genes. To further investigate the bioactivity of ferulic acid, its metabolic fate was characterized in fungal broths and the capacity of F. avenaceum to metabolize it through a C2-cleavage type degradation was demonstrated. Overall, our data support the promising use of ferulic acid in ENNs control strategies, either as part of an environmentally friendly plant-care product or as a biomarker of plant resistance.

Cereal grains and their processed food products are frequently contaminated with mycotoxins produced by the Fusarium genus. Enniatins (ENNs), which belong to the so-called “emerging mycotoxins” family, are among the most frequently found in small grain cereals. Health hazards induced by a chronic exposure to ENNs or an association of ENNs with other major mycotoxins is a risk that cannot be excluded given the current toxicological data. Thus, efforts must be pursued to define efficient control strategies to mitigate their presence in cereal grains. A key condition for achieving this aim is to gain deep and comprehensive knowledge of the factors promoting the appearance of ENNs in crop harvests. After an update of ENN occurrence data, this review surveys the scientific literature on the Fusarium species responsible for ENN contamination and covers the recent advances concerning the abiotic determinants and the genetic regulation of ENN biosynthesis.

International audience; The risk of contamination of agricultural commodities with mycotoxins affects every part of the world. Despite all the efforts of the past decades to improve control strategies to minimize the contamination levels of these toxic fungal metabolites including the implementation of good agricultural and manufacturing practices, there is currently no available strategies that allow ensuring the lack of mycotoxins in food and feed products. This is especially true for mycotoxins produced by Fusarium species that mostly contaminate cereal grains during crop cultivation and are only partially removed by processing. A key condition to strengthen prevention strategies is to increase the knowledge regarding the determinants and factors that govern the fungal growth and production of mycotoxins and lead to the contamination of agricultural commodities. To tackle this challenge, metabolomics is a method of choice. Indeed, metabolomics that allows exploring the connections between central metabolism and specialized fungal metabolic pathways is a golden tool to decipher the regulatory mechanisms of mycotoxin biosynthesis. Metabolomics is also a powerful tool to investigate the chemical interactions between toxigenic fungi and both the plant host and the surrounding microbial communities. Additionally, metabolomics has the potential to meet the challenge of simultaneously analyzing the major and so-called emerging mycotoxins together with their modified forms and is therefore a promising technology to increase the reliability of risk assessment. In this review, we intend to demonstrate how metabolomic applications could pave the avenue for new and efficient developments to mitigate food and feed contamination with mycotoxins.

International audience; BACKGROUND: Systemic infection through the seed is one of the routes used by the mycotoxinogenic pathogen Fusarium verticillioides for colonizing maize plants. The prohibition of the use of most chemical fungicides by the EU has promoted research on plant resistance inducers as an effective and sustainable alternative. Induction of a priming state in maize seeds might affect their susceptibility to contamination and accumulation of fumonisins. This state by application of a natural fertilizer called Chamae on maize seeds, was investigated in two varieties to control the colonization by the fungus and the accumulation of fumonisins B 1 , B 2 and B 3 , germinating seeds, dead plants and yield.RESULTS:After inoculation of F. verticillioides on germinating seeds, the colonization by the fungus and the accumulation of fumonisins were significantly lower in seedlings coming from treated seeds, but a significant number of plants stopped their development by necrosis. In a field trial, the 0.01% (v/v) application dilution showed a lower plant density, although the level of biomass at harvest was not affected.CONCLUSION: The priming state contributed to the control of F. verticillioides development from seed infection and fumonisin accumulation in the early stage of plant growth, without affecting the final crop yield, and could reduce fungicide use and environmental contamination. © 2018 Society of Chemical Industry

International audience; Fusarium head blight (FHB) is a major disease of wheat that has been studied worldwide but never in Algeria where high quantities of both durum wheat and common soft wheat are grown and traditionally consumed as semolina and bread. Fusarium root rot has also been observed in this country. Here we show that Fusarium culmorum seems to be the major pathogen associated with these diseases in Algeria. The type of mycotoxins produced by four F. culmorum isolates and their capacity to confer the disease on spike and accumulate type B trichothecenes in the grain was evaluated. Two strains produced deoxynivalenol, 3-acetyldeoxynivalenol and zearalenone in vitro. The two other strains produced nivalenol and fusarenone X. The four strains were used for artificial spray inoculations on wheat spikes to determine their potential in generating FHB symptoms and accumulating mycotoxins in local field conditions. A panel constituted of four durum wheat and four soft wheat varieties generally cultivated in Algeria and of two newly created durum wheat lines were evaluated. The results show a correlation between the level of invasion of the grain and the quantity of accumulated toxins with a large diversity depending on the cultivars. Interestingly, two local durum wheat varieties and the two new durum lines showed a promising level of resistance to FHB with significantly lower trichothecene accumulation. The content in phenolic compounds of the different varieties was assessed and evaluated as possible factor of resistance to trichothecene accumulation. This is the first report evaluating the wheat varieties cultivated in Algeria for their susceptibility to Fusarium Head Blight caused by local strains of F. culmorum in semi-arid bioclimatic condition.

Tick innate immunity involves humoral and cellular responses. Among the humoral effector molecules in ticks are the defensins which are a family of small peptides with a conserved γ-core motif that is crucial for their antimicrobial activity. Defensin families have been identified in several hard and soft tick species. However, little is known about the presence and antimicrobial activity of defensins from the Australian paralysis tick Ixodes holocyclus. In this study the I. holocyclus transcriptome was searched for the presence of defensins. Unique and non-redundant defensin sequences were identified and designated as holosins 1 – 5. The antimicrobial activity of holosins 2 and 3 and of the predicted γ-cores of holosins 1–4 (HoloTickCores 1–4), was assessed using Gram-negative and Gram-positive bacteria as well as the fungus Fusarium graminearum and the yeast Candida albicans. All holosins had molecular features that are conserved in other tick defensins. Furthermore holosins 2 and 3 were very active against the Gram-positive bacteria Staphylococcus aureus and Listeria grayi. Holosins 2 and 3 were also active against F. graminearum and C. albicans and 5 μM of peptide abrogate the growth of these microorganisms. The activity of the synthetic γ-cores was lower than that of the mature defensins apart from HoloTickCore 2 which had activity comparable to mature holosin 2 against the Gram-negative bacterium Escherichia coli. This study reveals the presence of a multigene defensin family in I. holocyclus with wide antimicrobial activity., JJV is supported by Project FIT (Pharmacology, Immunotherapy, nanoToxicology), which was funded by the European Regional Development Fund and acknowledges a grant from the research organization RVO: RO0516. Transcriptome analysis of I. holocyclus viscera and salivary glands was funded by the Australian Research Council linkage project LP120200836 and Elanco Animal Health. MT and AV would like to acknowledge generous funding by the Hessen State Ministry of Higher Education, Research and the Arts (HMWK) via the LOEWE Centre for Translational Biodiversity Genomics (LOEWE-TBG) and the LOEWE Center for Insect Biotechnology and Bioresources.

Fusarium graminearum is a major plant pathogen that causes devastating diseases of cereals and produces type B trichothecene (TCTB) mycotoxins in infected grains. A comprehensive understanding of the molecular and biochemical mechanisms underlying the regulation of TCTB biosynthesis is required for improving strategies to control the TCTB contamination of crops and ensuring that these strategies do not favor the production of other toxic metabolites by F. graminearum . Elucidation of the association of TCTB biosynthesis with other central and specialized processes was the focus of this study. Combined 1 H nuclear magnetic resonance ( 1 H NMR) and liquid chromatography-quadrupole time of flight-mass spectrometry (LC-QTOF-MS) analyses were used to compare the exo- and endometabolomes of F. graminearum grown under toxin-inducing and -repressing caffeic acid conditions. Ninety-five metabolites were putatively or unambiguously identified, including 26 primary and 69 specialized metabolites. Our data demonstrated that the inhibition of TCTB production induced by caffeic acid exposure was associated with significant changes in the secondary and primary metabolism of F. graminearum , although the fungal growth was not affected. The main metabolic changes were an increase in the accumulation of several polyketides, including toxic ones, alterations in the tricarboxylic organic acid cycle, and modifications in the metabolism of several amino acids and sugars. While these findings provide insights into the mechanisms that govern the inhibition of TCTB production by caffeic acid, they also demonstrate the interdependence between the biosynthetic pathway of TCTB and several primary and specialized metabolic pathways. These results provide further evidence of the multifaceted role of TCTB in the life cycle of F. graminearum . IMPORTANCE Fusarium graminearum is a major plant pathogen that causes devastating diseases of cereal crops and produces type B trichothecene (TCTB) mycotoxins in infected grains. The best way to restrict consumer exposure to TCTB is to limit their production before harvest, which requires increasing the knowledge on the mechanisms that regulate their biosynthesis. Using a metabolomics approach, we investigated the interconnection between the TCTB production pathway and several fungal metabolic pathways. We demonstrated that alteration in the TCTB biosynthetic pathway can have a significant impact on other metabolic pathways, including the biosynthesis of toxic polyketides, and vice versa. These findings open new avenues for identifying fungal targets for the design of molecules with antimycotoxin properties and therefore improving sustainable strategies to fight against diseases caused by F. graminearum . Our data further demonstrate that analyses should consider all fungal toxic metabolites rather than the targeted family of mycotoxins when assessing the efficacy of control strategies.

International audience; Fusarium verticillioides infects maize ears, causing ear rot disease and contamination of grain with fumonisin mycotoxins. This contamination can be reduced by the presence of bioactive compounds in kernels that are able to inhibit fumonisin biosynthesis. To identify such compounds, we used kernels from a maize genotype with moderate susceptibility to F. verticillioides, harvested at the milk-dough stage (i.e., when fumonisin production initiates in planta), and applied a bioguided fractionation approach. Chlorogenic acid was the most abundant compound in the purified active fraction and its contribution to fumonisin inhibitory activity was up to 70%. Moreover, using a set of maize genotypes with different levels of susceptibility, chlorogenic acid was shown to be significantly higher in immature kernels of the moderately susceptible group. Altogether, our data indicate that chlorogenic acid may considerably contribute to either maize resistance to Fusarium ear rot, fumonisin accumulation, or both. We further investigated the mechanisms involved in the inhibition of fumonisin production by chlorogenic acid and one of its hydrolyzed products, caffeic acid, by following their metabolic fate in supplemented F. verticillioides broths. Our data indicate that F. verticillioides was able to biotransform these phenolic compounds and that the resulting products can contribute to their inhibitory activity.

International audience; Gibberella and Fusarium Ear Rot and Fusarium Head Blight are major diseases affecting European cereals. These diseases are mainly caused by fungi of the Fusarium genus, primarily Fusarium graminearum and Fusarium verticillioides. These Fusarium species pose a serious threat to food safety because of their ability to produce a wide range of mycotoxins, including type B trichothecenes and fumonisins. Many factors such as environmental, agronomic or genetic ones may contribute to high levels of accumulation of mycotoxins in the grain and there is an urgent need to implement efficient and sustainable management strategies to reduce mycotoxin contamination. Actually, fungicides are not fully efficient to control the mycotoxin risk. In addition, because of harmful effects on human health and environment, their use should be seriously restricted in the near future. To durably solve the problem of mycotoxin accumulation, the breeding of tolerant genotypes is one of the most promising strategies for cereals. A deeper understanding of the molecular mechanisms of plant resistance to both Fusarium and mycotoxin contamination will shed light on plant-pathogen interactions and provide relevant information for improving breeding programs. Resistance to Fusarium depends on the plant ability in preventing initial infection and containing the development of the toxigenic fungi while resistance to mycotoxin contamination is also related to the capacity of plant tissues in reducing mycotoxin accumulation. This capacity can result from two mechanisms: metabolic transformation of the toxin into less toxic compounds and inhibition of toxin biosynthesis. This last mechanism involves host metabolites able to interfere with mycotoxin biosynthesis. This review aims at gathering the latest scientific advances that support the contribution of grain antioxidant secondary metabolites to the mechanisms of plant resistance to Fusarium and mycotoxin accumulation.

International audience; Fusarium Head Blight and Gibberella Ear Rot, mainly caused by the fungi Fusarium graminearum and Fusarium culmorum, are two of the most devastating diseases of small-grain cereals and maize. In addition to yield loss, these diseases frequently result in contamination of kernels with toxic type B trichothecenes. The potential involvement of chlorogenic acid in cereal resistance to Fusarium Head Blight and Gibberella Ear Rot and to trichothecene accumulation was the focus of this study. The effects of chlorogenic acid and one of its hydrolyzed products, caffeic acid, on fungal growth and type B trichothecenes biosynthesis were studied using concentrations close to physiological amounts quantified in kernels and a set of F. graminearum and F. culmorum strains. Both chlorogenic and caffeic acids negatively impact fungal growth and mycotoxin production, with caffeic acid being significantly more toxic. Inhibitory efficiencies of both phenolic acids were strain-dependent. To further investigate the antifungal and anti "mycotoxin" effect of chlorogenic and caffeic acids, the metabolic fate of these two phenolic acids was characterized in supplemented F. graminearum broths. For the first time, our results demonstrated the ability of F. graminearum to degrade chlorogenic acid into caffeic, hydroxychlorogenic and protocatechuic acids and caffeic acid into protocatechuic and hydroxycaffeic acids. Some of these metabolic products can contribute to the inhibitory efficiency of chlorogenic acid that, therefore, can be compared as a "pro-drug". As a whole, our data corroborate the contribution of chlorogenic acid to the chemical defense that cereals employ to counteract F. graminearum and its production of mycotoxins.

International audience; The effect of natural phenolic acids was tested on the growth and production of T‐2 and HT‐2 toxins by Fusarium langsethiae and F. sporotrichioides, on Mycotoxin Synthetic medium. Plates treated with 0.5 mM of each phenolic acid (caffeic, chlorogenic, ferulic and p‐coumaric) and controls without phenolic acid were incubated for 14 days at 25 °C. Fungal biomass of F. langsethiae and F. sporotrichioides was not reduced by the phenolic acids. However, biosynthesis of T‐2 toxin by F. langsethiae was significantly reduced by chlorogenic (23.1%) and ferulic (26.5%) acids. Production of T‐2 by F. sporotrichioides also decreased with ferulic acid by 23% (p < 0.05). In contrast, p‐coumaric acid significantly stimulated the production of T‐2 and HT‐2 toxins for both strains. A kinetic study of F. langsethiae with 1 mM ferulic acid showed a significant decrease in fungal biomass, whereas T‐2 production increased after 10 days of incubation. The study of gene expression in ferulic supplemented cultures of F. langsethiae revealed a significant inhibition for Tri5, Tri6 and Tri12 genes, while for Tri16 the decrease in gene expression was not statistically significant. Overall, results indicated that phenolic acids had a variable effect on fungal growth and mycotoxin production, depending on the strain and the concentration and type of phenolic acid assayed.

International audience; This study aims to compare the role of the transcription factor Fgap1 in oxidative stress response for two Fusarium graminearum strains belonging to the two chemotypes DON/ADON and NIV/FX. While the response to H2O2 was shown to be chemotype dependent, an opposite result was observed for diamide: whatever the chemotype, the global level of TCTB (i.e. trichothecene B) production was strongly increased by the treatment with diamide. Fgap1 was shown to be involved in this regulation for both chemotypes. Our data show that the response to diamide is mediated by Fgap1 whatever the chemotype of the F. graminearum strains. However, the NIV/FX chemotype has developed higher antioxidant capacities in response to oxidative stress. But when this capacity is overwhelmed by an increment in the H2O2 level, the NIV/FX strains also responds by an increase in toxin accumulation.

Trichothecenes are a group of toxic secondary metabolites produced mainly by Fusarium graminearum (teleomorph: Gibberella zeae) during the infection of crop plants, including wheat, maize, barley, oats, rye and rice. Some fungal genes involved in trichothecene biosynthesis have been shown to encode regulatory proteins. However, the global regulation of toxin biosynthesis is still enigmatic. In addition to the production of secondary metabolites belonging to the trichothecene family, F. graminearum produces the red pigment aurofusarin. The gene regulation underlying the production of aurofusarin is not well understood. The velvet gene (veA) is conserved in various genera of filamentous fungi. Recently, the veA gene from Aspergillus nidulans has been shown to be the key component of the velvet complex regulating development and secondary metabolism. Using blast analyses, we identified the velvet gene from F. graminearum, FgVe1. Disruption of FgVe1 causes several phenotypic effects. However, the complementation of this mutant with the FgVe1 gene restores the wild-type phenotypes. The in vitro phenotypes include hyperbranching of the mycelium, suppression of aerial hyphae formation, reduced hydrophobicity of the mycelium and highly reduced sporulation. Our data also show that FgVe1 modulates the production of the aurofusarin pigment and is essential for the expression of Tri genes and the production of trichothecenes. Pathogenicity studies performed on flowering wheat plants indicate that FgVe1 is a positive regulator of virulence in F. graminearum.

Fungal interactions of Fusarium verticillioides and F. graminearum in maize ears and the impact on fungal development and toxin accumulation were investigated in a 2-year field study at two locations in France. Maize ears were inoculated either with a spore mixture of F. graminearum and F. verticillioides or using a sequential inoculation procedure consisting of a first inoculation with F. graminearum followed by a second with F. verticillioides 1 week later. Toxin and fungal biomass were assessed on mature kernels, using HPLC and quantitative PCR. Correlation between the levels of DNA and toxin was high concerning F. graminearum DNA and deoxynivalenol (R² = 0·73) and moderate for F. verticillioides DNA and fumonisin (R² = 0·44). Fusarium graminearum DNA either decreased in mixed inoculations or was not influenced by subsequent inoculations with F. verticillioides, compared to single inoculations. In contrast, F. verticillioides DNA either significantly increased or was not affected in mixed and sequential inoculations. In two of the replicates, it can be assumed that natural contamination by F. verticillioides was favoured by previous contamination with F. graminearum. Overall, the results suggest that F. verticillioides has competitive advantages over the F. graminearum strains. Additionally, the data provide, for the first time, key evidence that previous contamination by F. graminearum in maize ears can facilitate subsequent infections by F. verticillioides.

International audience; The present study was aimed at characterizing the ability of lactic acid bacteria isolated from maize to repress the growth of fumonisin-producing fungi. A total of 67 isolates were screened for their antifungal activity against Fusarium proliferatum and Fusarium verticillioides by using the overlay method. The most efficient antifungal isolate was identified as Pediococcus pentosaceus (L006), on the basis of physiological and biochemical characterization and 16S rRNA gene sequencing. Production of the antifungal metabolite by this isolate commenced at the end of the growth exponential phase (8 h) and reached a maximum level after a long period of incubation (120 h). The antifungal metabolites produced were shown to be heat stable, resistant to proteolytic enzyme treatments, and pH dependent. The exact chemical nature of these substances remains to be clarified.

Reducing production of type B trichothecenes by Fusarium graminearum on cereals is necessary to control contamination, prevent yield reduction and protect human and animal health. Thus, an understanding of how trichothecene biosynthesis is induced is essential. The effect of ambient pH on fungal growth, toxin biosynthesis and expression of TRI genes was studied during in vitro liquid culture of F. graminearum on minimal medium. Fungal development stopped at day 3 after a sharp pH drop in the medium. At the same time, induction of TRI gene expression was observed and toxin began accumulating 1 day later. Acidification seems a determinant of induction, as neither the toxin nor the TRI genes were detected when the pH was maintained neutral. Shifting from neutral to acidic pH by mycelium transfer induced TRI gene expression and toxin accumulation. The regulation of toxin production by ambient pH appears to be specific to some TRI genes since TRI5, located in the core FgTRI5 cluster, showed an immediate induction while TRI101, located elsewhere in the genome, showed a more progressive response. The regulation of trichothecene biosynthesis by the ambient pH appears to be a general mechanism, independent of strain or chemotype, as all tested strains, including F. graminearum and F. culmorum species, showed a regulation of toxin production in response to the ambient pH. We conclude that, in vitro, external acidification is required for induction of TRI gene expression.

International audience; Fumonisins are mycotoxins mainly produced by two Fusarium species: F. verticillioides and F. proliferatum. These toxins are of great concern due to their widespread contamination in maize and their adverse effects on animal and human health. In the past decade, progress was made in identifying the genes required for fumonisin biosynthesis. Additionally, molecular mechanisms involved in the regulation of fumonisin production have been very recently elucidated. By covering the latest advances concerning the factors modulating fumonisin production, this review aims at presenting an integrated approach of the overall mechanisms involved in the regulation of fumonisin biosynthesis during maize kernel colonization.

International audience; The effect of ferulic acid, the most abundant phenolic acid in wheat bran, was studied in vitro on type B trichothecene biosynthesis by Fusarium. It was demonstrated that ferulic acid is an efficient inhibitor of mycotoxin production by all strains of Fusarium tested, including different chemotypes and species. To analyse the mechanism of toxin biosynthesis inhibition by ferulic acid, expression of representative Tri genes, involved in the trichothecene biosynthesis pathway, was monitored by real-time RT-PCR. A decrease in the level of Tri gene expression was measured, suggesting that inhibition of toxin synthesis by ferulic acid could be regulated at the transcriptional level. Moreover, toxin production was shown to be reduced proportionally to the initial amount of ferulic acid added in the culture medium. Addition of ferulic acid either at the spore germination step or to a mycelial culture resulted in the same final inhibitory effect on mycotoxin accumulation. A cumulative inhibitory effect on trichothecene biosynthesis was even observed with successive supplementation of ferulic acid. Ferulic acid, which content varies among wheat varieties, could then play an important role in modulating trichothecene biosynthesis by Fusarium in some wheat varieties.

International audience; Kinetics of fungal spread and Trichothecenes B (TCT B) contamination were achieved using four hybrids of Maize characterized by different levels of resistance. Inoculation was performed using a toxigenic Fusarium graminearum strain 5 days after flowering into the silk channel. In addition, phenolic acids composition was evaluated at the different grain filling stages for the four hybrids. Results are discussed with regards to a potential involvement of phenolic acids in limitation of toxins accumulation and resistance level.

International audience; This review describes the naturally occurring mechanisms in cereals that lead to a reduction of Fusarium trichothecene mycotoxin accumulation in grains. A reduction in mycotoxin contamination in grains could also limit fungal infection, as trichothecenes have been reported to act as virulence factors. The mechanisms explaining the low toxin accumulation trait, generally referred to as type V resistance to Fusarium, can be subdivided into two classes. Class 1 includes mechanisms by which the plants chemically transform the trichothecenes, leading to their degradation or detoxification. Among the detoxification strategies, glycosylation of trichothecenes is a natural process already reported in wheat. According to the structure and the toxicity of trichothecenes, two other detoxification processes, acetylation and de-epoxidation, can be expressed, at least in transgenic plants. Class 2 comprises mechanisms that lead to reduced mycotoxin accumulation by inhibition of their biosynthesis through the action of plant endogenous compounds. These include both grain constitutive compounds and compounds induced in response to pathogen infection. There are already many compounds with antioxidant properties, like phenolic compounds, peptides or carotenoids, and with prooxidant properties, like hydrogen peroxide or linoleic acid-derived hydroperoxides, that have been described as ‘modulators’ of mycotoxin biosynthesis. This review addresses for the first time different studies reporting specific in vitro effects of such compounds on the biosynthesis of Fusarium mycotoxins. A better understanding of the natural processes limiting accumulation of trichothecenes in the plant will open the way to the development of novel breeding varieties with reduced ‘mycotoxin risk’.

International audience; Growth and production of type-B trichothecenes mycotoxins by the Fusarium graminearum strain CBS 185.32 were compared in GYEP medium supplemented with Mg2+ at different concentrations (0–4 mM). Mg2+ led to a strong decrease in toxin accumulation without affecting the mycelial growth, suggesting a specific Mg2+ effect on fungal secondary metabolism. Expression of Tri5, Tri6, and Tri12 genes was followed throughout the time courses of type-B trichothecenes (TCTB) yield in standard and 2 mM Mg2+-supplemented GYEP media. Mg2+ addition significantly decreased Tri5, Tri6, and Tri12 expression. The inhibition of toxin production by Mg2+ was shown to be highly correlated with inhibition of Tri5 transcription and, to a lesser extend, of Tri6 and Tri12. This is the first report of a transcriptional control of TCTB production by Mg2+.

Liquid cultures of Fusarium graminearum were supplemented with H2O2 or other oxidative compounds. The accumulation kinetics of the resulting trichothecenes were monitored. At non-lethal concentrations, the H2O2 treatments modulated toxin accumulation, dependent on the method of supplementation. When H2O2 was added at the same time as the inoculation, higher levels of toxins accumulated 30 days later. Conversely, adding H2O2 2 or 7 days after inoculation had little effect. When H2O2 was added daily over the course of the culture, the accumulation of trichothecenes was rapidly and strongly enhanced. The fungus may adapt to oxidative stress when the first exposure to H2O2 occurs at the beginning of the culture course. The highest toxin levels were measured when the H2O2 was added daily. The importance of the first hours of culture was confirmed: pre-treating conidia with H2O2 does not affect their germination kinetics but leads to a reduction in the yield of trichothecenes 40 days later. The H2O2 regulation of this trichothecene accumulation may be specific, as paraquat, another pro-oxidant compound, inhibits their production. Since H2O2 is a major component of the oxidative burst occurring in pathogen/host interactions, these data support the theory that trichothecenes may act as virulence factors.

National audience; Le cadmium et les mycotoxines sont parmi les contaminants les plus fréquents qui affectent la sécurité sanitaire des grains de blé et de leurs produits dérivés. Le cadmium est un élément trace naturellement présent dans l’environnement. Il est facilement absorbé par la plante et se retrouve dans les grains où il s’accumule. La contamination en mycotoxines des grains de blé est essentiellement liée à la présence d’espèces fusariennes toxinogènes et en particulier en Europe de Fusarium graminearum, producteur de Déoxynivalenol (DON, trichothécènes de type B). Les teneurs en Cd et en DON dans les grains destinés à l’alimentation humaine sont strictement réglementées en Europe (EC N°1881/2006 et EC N°856/2005 respectivement). Pour l’instant il n’existe pas de compréhension complète sur la "réponse" du blé à l’accumulation du Cd. Des éléments laissent penser que sa toxicité pourrait induire au niveau de la plante des dommages oxydatifs. Ce stress induit par le Cd et son accumulation dans les grains sont deux facteurs qui peuvent influencer l'infection, le développement et la mycotoxinogenèse de Fusarium. En effet il a déjà été montré que H2O2 et le magnésium modulaient la biosynthèse des trichothécènes (Pinson-Gadais et al, 2008;. Ponts et al., 2007). Pour mieux comprendre les mécanismes de cocontamination et l’impact de leurs interactions éventuelles sur leur accumulation dans les grains, nous avons donc étudié l’effet du stress induit par la présence du Cd sur l’installation de Fusarium. Deux hypothèse ont été posées : (i) la présence de Cd dans les grains est-elle un facteur capable de moduler la production de mycotoxines ? (directe sur l’expression des gènes impliqués dans la voie de biosynthèse ou indirecte par l’induction d’un stress oxydant dans les cellules fongiques), (ii) la présence de Cd dans le sol induit-elle un stress oxydant au niveau des tissus végétaux qui impacterait l’installation de Fusarium et sa capacité à produire des fusariotoxines ? Nous avons mené deux types d’expérimentation : la 1ère consistait à inoculer F.graminearum sur des grains de blé dur issus de plantes cultivées sur des sols avec différents niveaux de contamination de Cd. La 2ème menée "In vitro" avait pour objectif d’étudier l’effet du Cd sur le développement et la toxinogènese de F. graminearum et F. culmorum. Nous avons ainsi montré un effet du Cd sur F.graminearum et F.culmorum, modulant son développement et sa production de toxines. L’intensité de cet effet dépend de la souche et de l’espèce. L’interaction entre ces deux contaminants demande à être élucidée, par une compréhension fine des mécanismes de modulation mis en jeu.

Les fusarioses de l'épi principalement causées par Fusarium graminearum et Fusarium verticillioides sont deux maladies majeures affectant les céréales européennes. Ces deux champignons constituent une menace pour la qualité sanitaire des récoltes du fait de leur capacité à produire des mycotoxines, dont les trichothécènes de type B et les fumonisines. La sélection variétale est un des leviers les plus prometteurs pour pouvoir espérer contrôler efficacement et durablement les teneurs en mycotoxines dans les céréales. L’obtention de génotypes suffisamment résistants pour garantir des niveaux de mycotoxines les plus faibles possibles implique cependant une meilleure compréhension des mécanismes de résistance des plantes à la Fusariose et à l’accumulation de mycotoxines. Une des composantes de cette résistance est liée à leur capacité à réduire l'accumulation de mycotoxines dans les grains. Cette capacité peut résulter de deux mécanismes : la transformation métabolique de la toxine en composés moins toxiques et l'inhibition de la biosynthèse de la toxine. Ce second mécanisme met en jeu les phytomicronutriments présents dans les grains capables de moduler les voies de biosynthèse. Cet article a pour objectif de synthétiser les avancées scientifiques les plus récentes qui permettent de préciser quels sont les phytomicronutriments présents dans les grains jouant un rôle clef dans les mécanismes de résistance des plantes à la Fusariose et accumulation de mycotoxines., Gibberella and Fusarium Ear Rot mainly caused by Fusarium graminearum and Fusarium verticillioides, are two major diseases affecting European cereals. The two former fungi are a serious threat to food safety because of their ability to produce a wide range of mycotoxins, including type B trichothecenes and fumonisins. The breeding of tolerant genotypes is one of the most promising strategies to efficiently control mycotoxins in cereals. This objective cannot be achieved without a better understanding of plant resistance mechanisms to Fusarium and mycotoxin accumulation. One component of this resistance is related to the ability of plant tissues to reduce mycotoxin accumulation. This capacity results from two mechanisms: metabolic transformation of the toxin into less toxic compounds and the inhibition of toxin biosynthesis. This second mechanism involves the occurrence of phytomicronutriments that are able to modulate the biosynthesis of mycotoxins. This article aims at gathering the latest scientific advances that makes it possible to specify which grain phytomicronutriments play a key role in the mechanisms of plant resistance to Fusarium and mycotoxin accumulation

article présenté lors du colloque 'Phytomicronutriments' qui s’est tenu à Avignon le 16 décembre 2014.; National audience; Gibberella and Fusarium Ear Rot mainly caused by Fusarium graminearum and Fusarium verticillioides, are two major diseases affecting European cereals. The two former fungi are a serious threat to food safety because of their ability to produce a wide range of mycotoxins, including type B trichothecenes and fumonisins. The breeding of tolerant genotypes is one of the most promising strategies to efficiently control mycotoxins in cereals. This objective cannot be achieved without a better understanding of plant resistance mechanisms to Fusarium and mycotoxin accumulation. One component of this resistance is related to the ability of plant tissues to reduce mycotoxin accumulation. This capacity results from two mechanisms: metabolic transformation of the toxin into less toxic compounds and the inhibition of toxin biosynthesis. This second mechanism involves the occurrence of phytomicronutriments that are able to modulate the biosynthesis of mycotoxins. This article aims at gathering the latest scientific advances that makes it possible to specify which grain phytomicronutriments play a key role in the mechanisms of plant resistance to Fusarium and mycotoxin accumulation; Les fusarioses de l'épi principalement causées par Fusarium graminearum et Fusarium verticillioides sont deux maladies majeures affectant les céréales européennes. Ces deux champignons constituent une menace pour la qualité sanitaire des récoltes du fait de leur capacité à produire des mycotoxines, dont les trichothécènes de type B et les fumonisines. La sélection variétale est un des leviers les plus prometteurs pour pouvoir espérer contrôler efficacement et durablement les teneurs en mycotoxines dans les céréales. L’obtention de génotypes suffisamment résistants pour garantir des niveaux de mycotoxines les plus faibles possibles implique cependant une meilleure compréhension des mécanismes de résistance des plantes à la Fusariose et à l’accumulation de mycotoxines. Une des composantes de cette résistance est liée à leur capacité à réduire l'accumulation de mycotoxines dans les grains. Cette capacité peut résulter de deux mécanismes : la transformation métabolique de la toxine en composés moins toxiques et l'inhibition de la biosynthèse de la toxine. Ce second mécanisme met en jeu les phytomicronutriments présents dans les grains capables de moduler les voies de biosynthèse. Cet article a pour objectif de synthétiser les avancées scientifiques les plus récentes qui permettent de préciser quels sont les phytomicronutriments présents dans les grains jouant un rôle clef dans les mécanismes de résistance des plantes à la Fusariose et accumulation de mycotoxines.

International audience; Redox sensing is of primary importance for fungi to cope with oxidant compounds found in their environment. Plant pathogens are particularly subject to the oxidative burst during the primary steps of infection. In the budding yeast Saccharomyces cerevisiae, it is the transcription factor Yap1 that mediates the response to oxidative stress via activation of genes coding for detoxification enzymes. In the cereal pathogen Fusarium graminearum, Fgap1 a homologue of Yap1 was identified and its role was investigated. During infection, this pathogen produces mycotoxins belonging to the trichothecenes family that accumulate in the grains. The global regulation of toxin biosynthesis is not completely understood. However, it is now clearly established that an oxidative stress activates the production of toxins by F. graminearum. The involvement of Fgap1 in this activation was investigated. A deleted mutant and a strain expressing a truncated constitutive form of Fgap1 were constructed. None of the mutants was affected in pathogenicity. The deleted mutant showed higher level of trichothecenes production associated with overexpression of Tri genes. Moreover activation of toxin accumulation in response to oxidative stress was no longer observed. Regarding the mutant with the truncated constitutive form of Fgap1, toxin production was strongly reduced. Expression of oxidative stress response genes was not activated in the deleted mutant and expression of the gene encoding the mitochondrial superoxide dismutase MnSOD1 was up-regulated in the mutant with the truncated constitutive form of Fgap1. Our results demonstrate that Fgap1 plays a key role in the link between oxidative stress response and F. graminearum secondary metabolism.

International audience; The potential involvement of antioxidants (alpha-tocopherol, lutein, zeaxanthin, beta-carotene, and ferulic acid) in the resistance of maize varieties to Fusarium ear rot was the focus of this study. These antioxidants were present in all maize kernel stages, indicating that the fumonisin-producing fungi (mainly Fusarium verticillioides and Fusarium proliferatum) are likely to face them during ear colonization. The effect of these compounds on fumonisin biosynthesis was studied in F. verticillioides liquid cultures. In carotenoid-treated cultures, no inhibitory effect of fumonisin accumulation was observed while a potent inhibitory activity was obtained for sublethal doses of a-tocopherol (0.1 mM) and ferulic acid (1 mM). Using a set of genotypes with moderate to high susceptibility to Fusarium ear rot, ferulic acid was significantly lower in immature kernels of the very susceptible group. Such a relation was nonexistent for tocopherols and carotenoids. Also, ferulic acid in immature kernels ranged from 3 to 8.5 mg/g, i.e., at levels consistent with the in vitro inhibitory concentration. Overall, our data support the fact that ferulic acid may contribute to resistance to Fusarium ear rot and/or fumonisin accumulation.

International audience; The aim of this work was to study the effectiveness of a Pediococcus pentosaceus strain L006, isolated from maize leaf and previously characterised for its high antifungal efficiency, on fumonisin biosynthesis by Fusarium verticillioides. Studies performed in GYEP medium supplemented with amylopectin showed a significant increase in fumonisin production when the F. verticillioides strain was simultaneously co-inoculated with the P. pentosaceus strain or inoculated in a three-day-old culture of this lactic acid bacteria. Our studies also demonstrated that some extracellular metabolites produced in MRS medium by the P. pentosaceus strain L006 were able to significantly reduce fumonisin production in liquid medium as well as on maize kernels. Fumonisin yields by F. verticillioides inoculated on autoclaved maize kernels were reduced by a factor ranging from 75% to 80% after 20 days of incubation. Our results illustrate the potential risk linked to the use of an antagonistic bacterial agent to manage fumonisin contamination, while emphasizing the potential use of bacterial metabolites to counteract fumonisin accumulation in kernels.

International audience; Trichothecenes are a group of toxic secondary metabolites produced mainly by Fusarium graminearum (teleomorph: Gibberella zeae) during the infection of crop plants, including wheat, maize, barley, oats, rye and rice. Some fungal genes involved in trichothecene biosynthesis have been shown to encode regulatory proteins. However, the global regulation of toxin biosynthesis is still enigmatic. In addition to the production of secondary metabolites belonging to the trichothecene family, F. graminearum produces the red pigment aurofusarin. The gene regulation underlying the production of aurofusarin is not well understood. The velvet gene (veA) is conserved in various genera of filamentous fungi. Recently, the veA gene from Aspergillus nidulans has been shown to be the key component of the velvet complex regulating development and secondary metabolism. Using blast analyses, we identified the velvet gene from F. graminearum, FgVe1. Disruption of FgVe1 causes several phenotypic effects. However, the complementation of this mutant with the FgVe1 gene restores the wild-type phenotypes. The in vitro phenotypes include hyperbranching of the mycelium, suppression of aerial hyphae formation, reduced hydrophobicity of the mycelium and highly reduced sporulation. Our data also show that FgVe1 modulates the production of the aurofusarin pigment and is essential for the expression of Tri genes and the production of trichothecenes. Pathogenicity studies performed on flowering wheat plants indicate that FgVe1 is a positive regulator of virulence in F. graminearum.

Colloque « Pour des aliments sains : savoir maîtriser les risques en alimentation » à Toulouse le 28 novembre 2012.; National audience; Maintaining good safety and quality of cereals is tightly linked to the mastery of contamination of kernels with mycotoxins. These mycotoxins are mainly related to the presence of fungal species of the genera Aspergillus, Penicillium and Fusarium. Particularly stable, main of mycotoxins resist agri-food processing and end up in finished products. In Europe, the mycotoxins produced by Fusarium, especially the type B trichothecenes, are central concerns of the cereals sector. These mycotoxins are frequently found in the harvests and are known to induce several toxic disorders. Significant progresses have been recently achieved to identify and classify the agronomic factors linked with an increased risk of kernels contamination. However, at the present time, there is no existing cultivation strategy, that is fully effective to certify compliance with official limits set by the EC regulation since 2006. The continued progress of the definition of such strategies requires a greater knowledge about the diversity of toxigenic fungal species and on the mechanisms underlying the regulation of toxin biosynthesis. By generating new indicators more likely to promote the development of agronomic tools for the prediction and/or control of contamination, and enable a better assessment of the mycotoxin risk linked to the presence of Fusarium, studies from the different INRA laboratories aim to meet the economical, toxicological, and legal issues posed by these contaminants.; Une des composantes essentielles de la qualité sanitaire des céréales repose sur la maîtrise du risque de contamination en mycotoxines des grains. Ces mycotoxines sont liées principalement à la présence d’espèces fongiques des genres Aspergillus, Penicillium et Fusarium. Molécules particulièrement stables, résistantes aux procédés agro-alimentaires, les mycotoxines se retrouvent dans les produits finis. En Europe, les mycotoxines produites par Fusarium ou fusariotoxines (et en particulier les trichothécènes de type B) sont au centre des préoccupations des filières céréales du fait de leur occurrence fréquente et des multiples effets toxiques qui leur sont associés. Des progrès significatifs, réalisés ces dernières années, ont conduit à l’identification et à la hiérarchisation des facteurs agronomiques augmentant le risque de contamination des céréales. Cette connaissance n’a cependant pas permis de définir des stratégies suffisamment efficaces pour certifier le respect des limites réglementaires définies depuis 2006. La définition de ces stratégies ne pourra être obtenue sans une connaissance approfondie de la diversité des agents toxinogènes mais aussi des mécanismes de production et de régulation de la biosynthèse de ces métabolites toxiques. En générant de nouveaux indicateurs plus à même (i) de favoriser le développement d'outils agronomiques de prédiction et/ou de maîtrise des contaminations (ii) de permettre une meilleure évaluation du risque mycotoxique associé à la présence des fusariotoxines, les études menées par les différents laboratoires de l’INRA ont pour objectifs de répondre aux enjeux économiques, toxicologiques mais aussi réglementaires que posent ces contaminants.

International audience; Fusarium graminearum is the causal agent of Gibberella ear rot and produces trichothecene mycotoxins. Basic questions remain unanswered regarding the kernel stages associated with trichothecene biosynthesis and the kernel metabolites potentially involved in the regulation of trichothecene production in planta. In a two-year field study, F. graminearum growth, trichothecene accumulation, and phenolic acid composition were monitored in developing maize kernels of a susceptible and a moderately resistant variety using quantitative polymerase chain reaction and liquid chromatography coupled with photodiode array or mass spectrometry detection. Infection started as early as the blister stage and proceeded slowly until the dough stage. Then, a peak of trichothecene accumulation occurred and infection progressed exponentially until the final harvest time. Both F. graminearum growth and trichothecene production were drastically reduced in the moderately resistant variety. We found that chlorogenic acid is more abundant in the moderately resistant variety, with levels spiking in the earliest kernel stages induced by Fusarium infection. This is the first report that precisely describes the kernel stage associated with the initiation of trichothecene production and provides in planta evidence that chlorogenic acid may play a role in maize resistance to Gibberella ear rot and trichothecene accumulation.

National audience