Determination of the trichothecene mycotoxin chemotypes and associated geographical distribution and phylogenetic species of the Fusarium graminearum clade from China

Detoxifying bacterial genes for deoxynivalenol epimerization confer durable resistance to Fusarium head blight in wheat

Fusarium head blight (FHB) and the presence of mycotoxin deoxynivalenol (DON) pose serious threats to wheat production and food safety worldwide. DON, as a virulence factor, is crucial for the spread of FHB pathogens on plants. However, germplasm resources that are naturally resistant to DON and DON-producing FHB pathogens are inadequate in plants. Here, detoxifying bacteria genes responsible for DON epimerization were used to enhance the resistance of wheat to mycotoxin DON and FHB pathogens. We characterized the complete pathway and molecular basis leading to the thorough detoxification of DON via epimerization through two sequential reactions in the detoxifying bacterium Devosia sp. D6-9. Epimerization efficiently eliminates the phytotoxicity of DON and neutralizes the effects of DON as a virulence factor. Notably, co-expressing of the genes encoding quinoprotein dehydrogenase (QDDH) for DON oxidation in the first reaction step, and aldo-keto reductase AKR13B2 for 3-keto-DON reduction in the second reaction step significantly reduced the accumulation of DON as virulence factor in wheat after the infection of pathogenic Fusarium, and accordingly conferred increased disease resistance to FHB by restricting the spread of pathogenic Fusarium in the transgenic plants. Stable and improved resistance was observed in greenhouse and field conditions over multiple generations. This successful approach presents a promising avenue for enhancing FHB resistance in crops and reducing mycotoxin contents in grains through detoxification of the virulence factor DON by exogenous resistance genes from microbes.

Population Genetic Analyses and Trichothecene Genotype Profiling of Fusarium pseudograminearum Causing Wheat Crown Rot in Henan, China

In China, Fusarium pseudograminearum has emerged as a major pathogen causing Fusarium crown rot (FCR) and caused significant losses. Studies on the pathogen's properties, especially its mating type and trichothecene chemotypes, are critical with respect to disease epidemiology and food/feed safety. There are currently few available reports on these issues. This study investigated the species composition, mating type idiomorphs, and trichothecene genotypes of Fusarium spp. causing FCR in Henan, China. A significant shift in F. pseudograminearum-induced FCR was found in the present study. Of the 144 purified strains, 143 were F. pseudograminearum, whereas only 1 Fusarium graminearum was identified. Moreover, a significant trichothecene-producing capability of F. pseudograminearum strains from Henan was observed in this work. Among the 143 F. pseudograminearum strains identified, F. pseudograminearum with a 15ADON genotype was found to be predominant (133 isolates), accounting for 92.36% of all strains, followed by F. pseudograminearum with a 3ADON genotype, whereas only one NIV genotype strain was detected. Overall, a relatively well-balanced 1:1 ratio of the F. pseudograminearum population was found in Henan. To the best of our knowledge, this is the first study that has examined the Fusarium populations responsible for FCR across the Henan wheat-growing region.

Phylogenetic Variation of Tri1 Gene and Development of PCR-RFLP Analysis for the Identification of NX Genotypes in Fusarium graminearum Species Complex

NX toxins have been described as a novel group of type A trichothecenes produced by members of the Fusarium graminearum species complex (FGSC). Differences in structure between NX toxins and the common type B trichothecenes arise from functional variation in the trichothecene biosynthetic enzyme Tri1 in the FGSC. The identified highly conserved changes in the Tri1 gene can be used to develop specific PCR-based assays to identify the NX-producing strains. In this study, the sequences of the Tri1 gene from type B trichothecene- and NX-producing strains were analyzed to identify DNA polymorphisms between the two different kinds of trichothecene producers. Four sets of Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) methods were successfully developed to distinguish the common type B trichothecene producers and NX producers within FGSC. These promising diagnostic methods can be used for high-throughput genotype detection of Fusarium strains as a step forward for crop disease management and mycotoxin control in agriculture. Additionally, it was found that the Tri1 gene phylogeny differs from the species phylogeny, which is consistent with the previous studies.

Global distribution, toxicity to humans and animals, biodegradation, and nutritional mitigation of deoxynivalenol: A review

Deoxynivalenol (DON) is one of the main types of B trichothecenes, and it causes health-related issues in humans and animals and imposes considerable challenges to food and feed safety globally each year. This review investigates the global hazards of DON, describes the occurrence of DON in food and feed in different countries, and systematically uncovers the mechanisms of the various toxic effects of DON. For DON pollution, many treatments have been reported on the degradation of DON, and each of the treatments has different degradation efficacies and degrades DON by a distinct mechanism. These treatments include physical, chemical, and biological methods and mitigation strategies. Biodegradation methods include microorganisms, enzymes, and biological antifungal agents, which are of great research significance in food processing because of their high efficiency, low environmental hazards, and drug resistance. And we also reviewed the mechanisms of biodegradation methods of DON, the adsorption and antagonism effects of microorganisms, and the different chemical transformation mechanisms of enzymes. Moreover, nutritional mitigation including common nutrients (amino acids, fatty acids, vitamins, and microelements) and plant extracts was discussed in this review, and the mitigation mechanism of DON toxicity was elaborated from the biochemical point of view. These findings help explore various approaches to achieve the best efficiency and applicability, overcome DON pollution worldwide, ensure the sustainability and safety of food processing, and explore potential therapeutic options with the ability to reduce the deleterious effects of DON in humans and animals.

Type A Trichothecene Metabolic Profile Differentiation, Mechanisms, Biosynthetic Pathways, and Evolution in Fusarium Species-A Mini Review

Trichothecenes are the most common Fusarium toxins detected in grains and related products. Type A trichothecenes are among the mycotoxins of greatest concern to food and feed safety due to their high toxicity. Recently, two different trichothecene genotypes within Fusarium species were reported. The available information showed that Tri1 and Tri16 genes are the key determinants of the trichothecene profiles of T-2 and DAS genotypes. In this review, polymorphisms in the Tri1 and Tri16 genes in the two genotypes were investigated. Meanwhile, the functions of genes involved in DAS and NEO biosynthesis are discussed. The possible biosynthetic pathways of DAS and NEO are proposed in this review, which will facilitate the understanding of the synthesis process of trichothecenes in Fusarium strains and may also inspire researchers to design and conduct further research. Together, the review provides insight into trichothecene profile differentiation and Tri gene evolutionary processes responsible for the structural diversification of trichothecene produced by Fusarium.

Effect of Crop Rotation on Fusarium Mycotoxins and Fusarium Species in Cereals in Sichuan Province (China)

The present study was performed to evaluate the effect of crop rotation on Fusarium mycotoxins and species in cereals in Sichuan Province. A total of 311 cereal samples were randomly collected and analyzed from 2018 to 2019 in Sichuan Province. The results of mycotoxin analysis showed that the major trichothecene mycotoxins in Sichuan Province were nivalenol (NIV) and deoxynivalenol (DON), and the mean concentration of total trichothecenes (including NIV, fusarenone X [4ANIV], DON, 3-acetyldeoxynivalenol [3ADON], and 15-acetyldeoxynivalenol [15ADON]) in wheat was significantly higher than that in maize and rice. The concentration of total trichothecenes in the succeeding crops was significantly higher than that in the previous crops. In addition, wheat grown after maize had reduced incidence and concentration of trichothecene mycotoxins compared with that grown after rice, and ratooning rice grown after rice had increased incidence and concentration of trichothecene mycotoxins. Our data indicated that Fusarium asiaticum with the NIV chemotype was predominant in wheat and rice samples, while the number of the NIV chemotypes of F. asiaticum and Fusarium meridionale and the 15ADON chemotype of Fusarium graminearum in maize were almost the same. Although the composition of Fusarium species was affected by crop rotations, there were no differences when comparing the same crop rotation except for the maize-wheat rotation. Moreover, the same species and chemotype of Fusarium strains originated from different crops in various rotations, but there were no significant differences in pathogenicity in wheat and rice. These results contribute to the knowledge of the effect of crop rotation on Fusarium mycotoxins and species affecting cereals in Sichuan Province, which may lead to improved strategies for control of Fusarium mycotoxins and fungal disease in China.

The Different Metabolic Responses of Resistant and Susceptible Wheats to Fusarium graminearum Inoculation

Fusarium head blight (FHB) is a serious wheat disease caused by Fusarium graminearum (Fg) Schwabe. FHB can cause huge loss in wheat yield. In addition, trichothecene mycotoxins produced by Fg are harmful to the environment and humans. In our previous study, we obtained two mutants TPS1⁻ and TPS2⁻. Neither of these mutants could synthesize trehalose, and they produced fewer mycotoxins. To understand the complex interaction between Fg and wheat, we systematically analyzed the metabolic responses of FHB-susceptible and -resistant wheat to ddH₂O, the TPS⁻ mutants and wild type (WT) using NMR combined with multivariate analysis. More than 40 metabolites were identified in wheat extracts including sugars, amino acids, organic acids, choline metabolites and other metabolites. When infected by Fg, FHB-resistant and -susceptible wheat plants showed different metabolic responses. For FHB-resistant wheat, there were clear metabolic differences between inoculation with mutants (TPS1⁻/TPS2⁻) and with ddH₂O/WT. For the susceptible wheat, there were obvious metabolic differences between inoculation with mutant (TPS1⁻/TPS2⁻) and inoculation with ddH₂O; however, there were no significant metabolic differences between inoculation with TPS⁻ mutants and with WT. Specifically, compared with ddH₂O, resistant wheat increased the levels of Phe, p-hydroxy cinnamic acid (p-HCA), and chlorogenic acid in response to TPS⁻ mutants; however, susceptible wheat did not. Shikimate-mediated secondary metabolism was activated in the FHB-resistant wheat to inhibit the growth of Fg and reduce the production of mycotoxins. These results can be helpful for the development of FHB-resistant wheat varieties, although the molecular relationship between the trehalose biosynthetic pathway in Fg and shikimate-mediated secondary metabolism in wheat remains to be further studied.

Identification of Candidate Genes Associated with Trichothecene Biosynthesis in Fusarium graminearum Species Complex Combined with Transcriptomic and Proteomic Analysis

The Fusarium graminearum species complex is the main causal agent of wheat head blight worldwide. Trichothecenes produced by the pathogen in infected grains have important food safety implications. Previously reported studies on trichothecene production have all focused on the conditions conducive to mycotoxin production, while the molecular mechanisms of trichothecene biosynthesis in Fusarium strains under normal or non-inducing conditions are still unclear. Here, a global analysis of the fungal gene expression of three strains using the Affymetrix Fusarium GeneChip under non-inducing conditions is reported. Differentially expressed genes were identified among strains with different trichothecene-production ability, and some novel genes associated with trichothecene biosynthesis were found by bioinformatics analysis. To verify the transcriptome results, proteomic analyses of the three strains were conducted under the same culture conditions. In total, 69 unique fungal proteins were identified in 77 protein spots. Combined with transcriptome and proteome analysis, 27 novel genes were predicted to be associated with trichothecene mycotoxin production. A protein, encoded by FGSG_01403, was found to be associated with trichothecene production via proteome analysis. Gene knock-out mutations of FGSG_01403 resulted in mutants with increased production of trichothecenes. Future functional analysis of the candidate genes identified in this study may reveal new insights into the negative regulation of trichothecene production in the Fusarium graminearum species complex.

An Efficient Strategy Combining Immunoassays and Molecular Identification for the Investigation of Fusarium Infections in Ear Rot of Maize in Guizhou Province, China

Fusarium is one of the most important phytopathogenic and mycotoxigenic fungi that caused huge losses worldwide due to the decline of crop yield and quality. To systematically investigate the infections of Fusarium species in ear rot of maize in the Guizhou Province of China and analyze its population structure, 175 samples of rotted maize ears from 76 counties were tested by combining immunoassays and molecular identification. Immunoassay based on single-chain variable fragment (scFv) and alkaline phosphatase (AP) fusion protein was first employed to analyze these samples. Fusarium pathogens were isolated and purified from Fusarium-infected samples. Molecular identification was performed using the partial internal transcribed spacer (ITS) and translation elongation factor 1α (TEF-1α) sequences. Specific primers were used to detect toxigenic chemotypes, and verification was performed by liquid chromatography tandem mass spectrometry (LC-MS/MS). One-hundred and sixty three samples were characterized to be positive, and the infection rate was 93.14%. Sixteen species of Fusarium belonging to six species complexes were detected and Fusarium meridionale belonging to the Fusarium graminearum species complex (FGSC) was the dominant species. Polymerase chain reaction (PCR) identification illustrated that 69 isolates (56.10%) were potential mycotoxin-producing Fusarium pathogens. The key synthetic genes of NIV, NIV + ZEN, DON + ZEN, and FBs were detected in 3, 35, 7, and 24 isolates, respectively. A total of 86.11% of F. meridionale isolates carried both NIV- and ZEN-specific segments, while Fusarium verticillioides isolates mainly represented FBs chemotype. All the isolates carrying DON-producing fragments were FGSC. These results showed that there are different degrees of Fusarium infections in Guizhou Province and their species and toxigenic genotypes display regional distribution patterns. Therefore, scFv-AP fusion-based immunoassays could be conducted to efficiently investigate Fusarium infections and more attention and measures should be taken for mycotoxin contamination in this region.

A Novel Deoxynivalenol-Activated Wheat Arl6ip4 Gene Encodes an Antifungal Peptide with Deoxynivalenol Affinity and Protects Plants against Fusarium Pathogens and Mycotoxins

Deoxynivalenol (DON) is one of the most widespread trichothecene mycotoxins in contaminated cereal products. DON plays a vital role in the pathogenesis of Fusarium graminearum, but the molecular mechanisms of DON underlying Fusarium–wheat interactions are not yet well understood. In this study, a novel wheat ADP-ribosylation factor-like protein 6-interacting protein 4 gene, TaArl6ip4, was identified from DON-treated wheat suspension cells by suppression subtractive hybridization (SSH). The qRT-PCR result suggested that TaArl6ip4 expression is specifically activated by DON in both the Fusarium intermediate susceptible wheat cultivar Zhengmai9023 and the Fusarium resistant cultivar Sumai3. The transient expression results of the TaARL6IP4::GFP fusion protein indicate that TaArl6ip4 encodes a plasma membrane and nucleus-localized protein. Multiple sequence alignment using microscale thermophoresis showed that TaARL6IP4 comprises a conserved DON binding motif, ₆₇HXXXG₇₁, and exhibits DON affinity with a dissociation constant (K_D) of 91 ± 2.6 µM. Moreover, TaARL6IP4 exhibited antifungal activity with IC₅₀ values of 22 ± 1.5 µM and 25 ± 2.6 µM against Fusarium graminearum and Alternaria alternata, respectively. Furthermore, TaArl6ip4 interacted with the plasma membrane of Fusarium graminearum spores, resulting in membrane disruption and the leakage of cytoplasmic materials. The heterologous over-expression of TaArl6ip4 conferred greater DON tolerance and Fusarium resistance in Arabidopsis. Finally, we describe a novel DON-induced wheat gene, TaArl6ip4, exhibiting antifungal function and DON affinity that may play a key role in Fusarium–wheat interactions.

Natural Products from Medicinal Plants against Phytopathogenic Fusarium Species: Current Research Endeavours, Challenges and Prospects

Many Fusarium species are pathogenic, causing crop diseases during crop production and spoilage of agricultural products in both commercial and smallholder farming. Fusarium attack often results into food contamination, yield loss and increases in food insecurity and food prices. Synthetic fungicides have been used as a control strategy for the management of crop diseases caused by Fusarium pathogens. The negative effects associated with application of many synthetic pesticides has necessitated the need to search for alternative control strategies that are affordable and environmentally safe. Research on medicinal plants as control agents for Fusarium pathogens has received attention since plants are readily available and they contain wide variety of secondary metabolites that are biodegradable. The activities of solvent extracts, essential oils and compounds from medicinal plants have been tested against Fusarium phytopathogenic species. A summary of recent information on antifungal activity of plants against Fusarium species is valuable for the development of biopesticides. This paper reviews the antifungal research conducted on medicinal plants against Fusarium pathogens, over a 10-year period, from January 2012 to May 2021. We also highlight the challenges and opportunities of using natural products from medicinal plants in crop protection. Several databases (Science Direct and Web of Science) were used to obtain information on botanical products used to control Fusarium diseases on crops. Keywords search used included natural products, antifungal, Fusarium, crops diseases, phytopathogenic, natural compounds and essential oil.

The Distribution of Fusarium graminearum and Fusarium asiaticum Causing Fusarium Head Blight of Wheat in Relation to Climate and Cropping System

In the main wheat production area of China (the Huang Huai Plain [HHP]), both Fusarium graminearum and Fusarium asiaticum, the causal agents of Fusarium head blight (FHB), are present. We investigated whether the relative prevalence of F. graminearum and F. asiaticum is related to cropping systems and/or climate factors. A total of 1,844 Fusarium isolates were obtained from 103 fields of two cropping systems: maize-wheat and rice-wheat rotations. To maximize the differences in climatic conditions, isolates were sampled from the north and south HHP regions. Based on the phylogenetic analysis of EF-1α and Tri101 sequences, 1,207 of the 1,844 isolates belonged to F. graminearum, and the remaining 637 isolates belonged to F. asiaticum. The former was predominant in the northern region: 1,022 of the 1,078 Fusarium isolates in the north were F. graminearum. The latter was predominant in the southern region: 581 of the 766 Fusarium isolates belonged to F. asiaticum. Using an analysis based on generalized linear modeling, the relative prevalence of the two species was associated more with climatic conditions than with the cropping system. F. graminearum was associated with drier conditions and cooler conditions during the winter but also with warmer conditions in the infection and grain-colonization period as well as with maize-wheat rotation. The opposite was true for F. asiaticum. Except for the 15-acetyldeoxynvalenol genotype, the trichothecene chemotype composition of F. asiaticum differed between the two cropping systems. The 3-acetyldeoxynivalenol genotype was more prevalent in the maize-wheat rotation, whereas the nivalenol genotype was more prevalent in the rice-wheat rotation. The results also suggested that environmental conditions in the overwintering period appeared to be more important than those in the infection, grain-colonization, and preanthesis sporulation periods in affecting the relative prevalence of F. graminearum and F. asiaticum. More research is needed to study the effect of overwintering conditions on subsequent epidemic in the following spring.

Analysis of the Fusarium graminearum Species Complex from Gramineous Weeds Near Wheat Fields in Jiangsu Province, China

Several weed species are known as alternative hosts of the Fusarium graminearum species complex (FGSC), and their epidemiological significance in Fusarium head blight (FHB) has been investigated; however, scant information is available regarding FGSC occurrence in weeds near Chinese wheat fields. To evaluate the potential role of gramineous weeds surrounding wheat fields in FHB, 306 FGSC isolates were obtained from 210 gramineous weed samples in 2018 in Jiangsu Province. Among them, 289 were Fusarium asiaticum, and the remainder were F. graminearum. Trichothecene genotype and mycotoxin analyses revealed that 74.3% of the F. asiaticum isolates were the 3-acetyldeoxynivalenol (3ADON) chemotype, and the remainder were the nivalenol (NIV) chemotype. Additionally, 82.4% of F. graminearum isolates were the 15-acetyldeoxynivalenol (15ADON) chemotype, and the remainder were the NIV chemotype. FHB severity and trichothecene analysis indicated that F. asiaticum isolates with the 3ADON chemotype were more aggressive than those with the NIV chemotype in wheat. 3ADON and NIV chemotypes of F. asiaticum isolated from weeds and wheat showed no significant differences in pathogenicity in wheat. All selected F. asiaticum isolates produced perithecia, with little difference between the 3ADON and NIV chemotypes. These results highlight the epidemiology of the FGSC isolated from weeds near wheat fields, with implications for reducing FHB inoculum in China.

Symptoms and pathogens diversity of Corn Fusarium sheath rot in Sichuan Province, China

To elucidate the symptoms and pathogens diversity of corn Fusarium sheath rot (CFSR), diseased samples were collected from 21 county-level regions in 12 prefecture-level districts of Sichuan Province from 2015 to 2018 in the present study. In the field, two symptom types appeared including small black spots with a linear distribution and wet blotches with a tawny or brown color. One hundred thirty-seven Fusarium isolates were identified based on morphological characteristics and phylogenetic analysis (EF1-α), and Koch's postulates were also assessed. The results identified the isolates as 8 species in the Fusarium genus, including F. verticillioides, F. proliferatum, F. fujikuroi, F. asiaticum, F. equiseti, F. meridionale, F. graminearum and F. oxysporum, with isolation frequencies of 30.00, 22.67, 15.33, 7.33, 6.00, 5.33, 3.33 and 1.33%, respectively. Fusarium verticillioides and F. proliferatum were the dominant and subdominant species, respectively. Two or more Fusarium species such as F. verticillioides and F. proliferatum were simultaneously identified at a mixed infection rate of 14.67% in the present study. The pathogenicity test results showed that F. proliferatum and F. fujikuroi exhibited the highest virulence, with average disease indices of 30.28 ± 2.87 and 28.06 ± 1.96, followed by F. equiseti and F. verticillioides, with disease indices of 21.48 ± 2.14 and 16.21 ± 1.84, respectively. Fusarium asiaticum, F. graminearum and F. meridonale showed lower virulence, with disease indices of 13.80 ± 2.07, 11.57 ± 2.40 and 13.89 ± 2.49, respectively. Finally, F. orysporum presented the lowest virulence in CFSR, with a disease index of 10.14 ± 1.20. To the best of our knowledge, this is the first report of F. fujikuroi, F. meridionale and F. asiaticum as CFSR pathogens in China.

Analysis of Fusarium graminearum Species Complex from Freshly Harvested Rice in Jiangsu Province (China)

Members of Fusarium graminearum species complex (FGSC) are the major pathogens that cause Fusarium head blight (FHB) in cereals worldwide. Symptoms of FHB on rice, including dark staining or browning of rice glumes, were recently observed in Jiangsu Province, China. To improve our understanding of the pathogens involved, 201 FGSC isolates were obtained from freshly harvested rice samples and identified by phylogenetic analyses. Among the 201 FGSC isolates, 196 were F. asiaticum and the remaining 5 were F. graminearum. Trichothecene chemotype and chemical analyses showed that 68.4% of the F. asiaticum isolates were the 3-acetyldeoxynivalenol (3ADON) chemotype and the remainder were the nivalenol (NIV) chemotype. All of the F. graminearum isolates were the 15-acetyldeoxynivalenol chemotype. Pathogenicity assays showed that both the 3ADON and NIV chemotypes of F. asiaticum could infect wheat and rice spikes. FHB severity and trichothecene toxin analysis revealed that F. asiaticum with the NIV chemotype was less aggressive than that with the 3ADON chemotype in wheat, while the NIV-producing strains were more virulent than the 3ADON-producing strains in rice. F. asiaticum isolates with different chemotypes did not show significant differences in mycelial growth, sporulation, conidial dimensions, or perithecial production. These findings would provide useful information for developing management strategies for the control of FHB in China.

Population Genomic Analysis Reveals a Highly Conserved Mitochondrial Genome in Fusarium asiaticum

Fusarium asiaticum is one of the pivotal members of the Fusarium graminearum species complex (FGSC) causing Fusarium head blight (FHB) on wheat, barley and rice in large parts of Asia. Besides resulting in yield losses, FHB also causes the accumulation of mycotoxins such as nivalenol (NIV) and deoxynivalenol (DON). The aim of this study was to conduct population studies on F. asiaticum from Southern China through mitochondrial genome analyses. All strains were isolated from wheat or rice from several geographic areas in seven provinces in Southern China. Based on geographic location and host, 210 isolates were selected for next generation sequencing, and their mitogenomes were assembled by GRAbB and annotated to explore the mitochondrial genome variability of F. asiaticum. The F. asiaticum mitogenome proves extremely conserved and variation is mainly caused by absence/presence of introns harboring homing endonuclease genes. These variations could be utilized to develop molecular markers for track and trace of migrations within and between populations. This study illustrates how mitochondrial introns can be used as markers for population genetic analysis. SNP analysis demonstrate the occurrence of mitochondrial recombination in F. asiaticum as was previously found for F. oxysporum and implied for F. graminearum. Furthermore, varying degrees of genetic diversity and recombination showed a high association with different geographic regions as well as with cropping systems. The mitogenome of F. graminearum showed a much higher SNP diversity while the interspecies intron variation showed no evidence of gene flow between the two closely related and sexual compatible species.

Natural Occurrence of Deoxynivalenol and Its Acetylated Derivatives in Chinese Maize and Wheat Collected in 2017

Deoxynivalenol (DON), along with 3-acetyl-deoxynivalenol (3-ADON) and 15-acetyl-deoxynivalenol (15-ADON), occur in grains and cereal products and is often hazardous to humans and livestock. In this study, 579 wheat samples and 606 maize samples intended for consumption were collected from China in 2017 and analyzed to determine the co-occurrence of type-B trichothecenes (DON, 3-ADON, and 15-ADON). All the wheat samples tested positive for DON, while 99.83% of the maize samples were DON-positive with mean DON concentrations of 165.87 and 175.30 μg/kg, respectively. Per the Chinese standard limits for DON, 3.63% of wheat and 2.97% of the maize samples were above the maximum limit of 1000 μg/kg. The DON derivatives (3-ADON and 15-ADON) were less frequently found and were present at lower levels than DON in wheat. 3-ADON and 15-ADON had incidences of 13.53% and 76.40%, respectively, in maize. By analyzing the distribution ratio of DON and its derivatives in wheat and maize, DON (95.51%) was the predominant toxin detected in wheat samples, followed by 3.97% for the combination of DON + 3-ADON, while DON + 3-ADON + 15-ADON and DON + 15-ADON were only found in 0.17% and 0.35% of wheat samples, respectively. Additionally, a large amount of the maize samples were contaminated with DON + 15-ADON (64.19%) and DON (22.11%). The samples with a combination of DON + 3-ADON and DON + 3-ADON + 15-ADON accounted for 1.32% and 12.21%, respectively. Only one maize sample did not contain all three mycotoxins. Our study shows the necessity of raising awareness of the co-occurrence of mycotoxin contamination in grains from China to protect consumers from the risk of exposure to DON and its derivatives.

Resistance to Fusarium head blight and mycotoxin accumulation among 129 wheat cultivars from different ecological regions in China

A total of 129 wheat cultivars collected from local breeders in four ecological regions in China was evaluated for Fusarium head blight resistance after natural infection under epidemic conditions. The disease index was scored and seven toxins concentrations were determined by UPLC-MS/MS. The disease index ranged from 6.3 to 80.9% and a strong correlation was found between the regions from which the cultivars originate and disease index. The middle and lower reaches of Yangtze River Region showed the highest disease resistance, followed by the upper reaches of the Yangtze River Region. FHB resistance of cultivars from northern and southern Huanghuai Region was lowest and all cultivars in these regions are highly or moderately susceptible. Disease index was significantly correlated with toxin accumulation on nation scale, but no clear correlation was found within most ecological regions. The toxin accumulation was also not well correlated with resistant levels. As the incidence of FHB has increased dramatically over the last decade, improved FHB resistance in cultivars is urgently needed. We recommend that besides scoring for disease index also mycotoxin accumulation in cultivars is incorporated in breeding procedures and the evaluation of cultivars.

Can discrepancies between Fusarium graminearum trichothecene genotype and chemotype be explained by the influence of temperature in the relative production of 3-ADON and 15-ADON?

Wheat is one of the most important crops in Argentina and worldwide. One of the major diseases affecting the crop is the Fusarium Head Blight (FHB). It is an endemic disease caused mainly by Fusarium graminearum, the most common agent of FHB around the world. The infection is strongly influenced by environmental parameters and occurs mostly when there are favourable conditions of moisture and temperature during wheat anthesis or flowering. This destructive disease affects wheat, barley and other small grains and has the capability of destroying crops, causing great economic losses due to reduced grain quality, and the accumulation of significant levels of mycotoxins such as trichothecenes. The aim of this study was to evaluate the influence of temperature on mycotoxin biosynthesis, on three strains of F. graminearum of 15-ADON genotype and one of 3-ADON genotype, with different capacity of synthesizing DON, 3-ADON and 15-ADON. Trichothecene production of the strains at different temperatures (5, 10, 15, 20, 25, 30 and 35 °C) was evaluated after 7, 14, 21, 28 and 35 d of incubation. The optimum temperature to produce DON and 3-ADON was between 25 and 30 °C, but the maximum production of 15-ADON occurred at a lower temperature (10 °C) for all the strains. Conversely, the minimum production of DON and 3-ADON was recorded between 5 and 10 °C and of 15-ADON between 30 and 35 °C. A possible explanation for the similar accumulation of both acetyl derivatives by strains of different chemotype and genotypes could be that the acetyl derivatives biosynthesis is regulated by temperature.

Metabolic Changes of Fusarium graminearum Induced by TPS Gene Deletion

Fusarium head blight (FHB) mainly resulting from Fusarium graminearum (Fg) Schwabe is a notorious wheat disease causing huge losses in wheat production globally. Fg also produces mycotoxins, which are harmful to human and domestic animals. In our previous study, we obtained two Fg mutants, TPS1^- and TPS2^-, respectively, with a single deletion of trehalose 6-phosphate synthase (TPS1) and trehalose 6-phosphate phosphatase (TPS2) compared with the wild type (WT). Both mutants were unable to synthesize trehalose and produced fewer mycotoxins. To understand the other biochemical changes induced by TPS gene deletion in Fg, we comprehensively analyzed the metabolomic differences between TPS^- mutants and the WT using NMR together with gas chromatography-flame ionization detection/mass spectrometry. The expression of some relevant genes was also quantified. The results showed that TPS1^- and TPS2^- mutants shared some common metabolic feature such as decreased levels for trehalose, Val, Thr, Lys, Asp, His, Trp, malonate, citrate, uridine, guanosine, inosine, AMP, C10:0, and C16:1 compared with the WT. Both mutants also shared some common expressional patterns for most of the relevant genes. This suggests that apart from the reduced trehalose biosynthesis, both TPS1 and TPS2 have roles in inhibiting glycolysis and the tricarboxylic acid cycle but promoting the phosphopentose pathway and nucleotide synthesis; the depletion of either TPS gene reduces the acetyl-CoA-mediated mycotoxin biosynthesis. TPS2^- mutants produced more fatty acids than TPS1^- mutants, suggesting different roles for TPS1 and TPS2, with TPS2^- mutants having impaired trehalose biosynthesis and trehalose 6-phosphate accumulation. This may offer opportunities for developing new fungicides targeting trehalose biosynthesis in Fg for FHB control and mycotoxin reduction in the FHB-affected cereals.

Isolation, Molecular Identification and Mycotoxin Profile of Fusarium Species Isolated from Maize Kernels in Iran

Fusarium species are among the most important fungal pathogens of maize, where they cause severe reduction of yield and accumulation of a wide range of harmful mycotoxins in the kernels. In order to identify the Fusarium species and their mycotoxin profiles associated to maize ear rot and kernel contamination in Iran, a wide sampling was carried out from field in ten major maize-producing provinces in Iran, during 2015 and 2016. From 182 samples of maize kernels, 551 strains were isolated and identified as belonging to Fusarium genus. Among the 234 representative strains identified at species level by translation elongation factor (EF-1α) sequences, the main Fusarium species were F. verticillioides and F. proliferatum, together representing 90% of the Iranian Fusarium population, and, to a lesser extent, F. incarnatum equiseti species complex (FIESC), F. thapsinum and F. redolens. Fumonisin (FBs) production by F. verticillioides and F. proliferatum representative strains was analysed, showing that all strains produced FB₁. None of F. verticillioides strains produced FB₂ nor FB₃, while both FB₂ and FB₃ were produced only by F. proliferatum. Total mean of FBs production by F. verticillioides was higher than F. proliferatum. The occurrence of different Fusarium species on Iranian maize is reason of great concern because of the toxigenic risk associated to these species. Moreover, the diversity of the species identified increases the toxigenic risk associated to Fusarium contaminated maize kernels, because of the high possibility that a multi-toxin contamination can occur with harmful consequences on human and animal health.

Molecular Phylogenetic Relationships, Trichothecene Chemotype Diversity and Aggressiveness of Strains in a Global Collection of Fusarium graminearum Species

Fusarium head blight (FHB), caused principally by the species belonging to the Fusarium graminearum species complex (FGSC), is an important disease in wheat, barley, and other small grain crops worldwide. Grain infected with species in the FGSC may be contaminated with trichothecene mycotoxins such as deoxynivalenol (DON) and nivalenol (NIV). In this study, we characterized the phylogenetic relationships, chemotype diversity, phenotypic characters, and aggressiveness of 150 strains in FGSC collected from eight different countries. Phylogenetic analysis based on portions of translation elongation factor 1-α (EF-1α) gene from 150 strains revealed six species in the FGSC, F. graminearum s.s, F. asiaticum, F. meridionale, F. cortaderiae, F. boothii, and F. austroamericanum. In this collection, 50% of the strains were 15-acetyldeoxynivalenol (15-ADON), 35% were 3-acetyldeoxynivalenol (3-ADON) and 15% were NIV. Evaluation of strains on moderately resistant (MR) wheat cultivar Carberry indicated that there is no significant difference among the species for FHB disease severity (DS), fusarium damaged kernel percentage (FDK%) and DON production. However, significant differences were observed among the chemotypes. Results showed significantly higher FHB DS, FDK%, DON production, growth rates, and macroconidia production for the 3-ADON strains than the 15-ADON and NIV strains. In addition, significant differences for FHB response variables were observed among the strains from different countries. Our results demonstrate that type and amount of trichothecene produced by a strain play a key role in determining the level of aggressiveness of that particular strain, regardless of the species.

Fusarium Toxins in Chinese Wheat since the 1980s

Wheat Fusarium head blight (FHB), caused by Fusarium species, is a widespread and destructive fungal disease. In addition to the substantial yield and revenue losses, diseased grains are often contaminated with Fusarium mycotoxins, making them unsuitable for human consumption or use as animal feed. As a vital food and feed ingredient in China, the quality and safety of wheat and its products have gained growing attention from consumers, producers, scientists, and policymakers. This review supplies detailed data about the occurrence of Fusarium toxins and related intoxications from the 1980s to the present. Despite the serious situation of toxin contamination in wheat, the concentration of toxins in flour is usually lower than that in raw materials, and food-poisoning incidents have been considerably reduced. Much work has been conducted on every phase of toxin production and wheat circulation by scientific researchers. Regulations for maximum contamination limits have been established in recent years and play a substantial role in ensuring the stability of the national economy and people's livelihoods.

Monitoring of Fusarium Species and Trichothecene Genotypes Associated with Fusarium Head Blight on Wheat in Hebei Province, China

To clarify the changes in field populations of Fusarium head blight (FHB) pathogens over a decade, Fusarium species and trichothecene genotypes associated with FHB on wheat were monitored in Hebei province during the periods 2005–2006 and 2013–2016. Fusarium species determination was carried out by morphological identification, species-specific amplification and partial translation elongation factor (TEF-1α) gene sequencing. Trichothecene genotype prediction was carried out by primers 3CON/3NA/3D15A/3D3 or Tri13F/Tri13R, Tri303F/Tri303R and Tri315F/Tri315R. A total of 778 purified Fusarium isolates were recovered from 42 sampling sites in 17 counties during the period 2005–2006 and 1002 Fusarium isolates were recovered from 122 sampling sites in 65 counties during the period 2013–2016. F. graminearum was the predominant pathogen recovered during the periods 2005–2006 and 2013–2016. However, the pathogen composition differed slightly between the two periods. In 2005–2006, 752 out of 778 (96.7%) of the isolates belonged to F. graminearum. Two were identified as F. culmorum. Five other Fusarium species were also recovered, F. equiseti, F. verticillioides, F. proliferatum, F. subglutinans and F. chlamydosporum, with lower recoveries of 0.4%, 0.8%, 0.8%, 0.1% and 1.0%, respectively. Trichothecene genotype prediction showed that all the 752 F. graminearum isolates were of the 15-ADON genotype. Five Fusarium species were recovered from samples collected over the period 2013–2016. F. graminearum was again the predominant pathogen with an isolation frequency of 97.6%. F. pseudograminearum, F. asiaticum, F. culmorum and F. negundis were also isolated at a recovery of 1.4%, 0.7%, 0.2% and 0.1%, respectively. For the 2013–2016 isolates, 971 of the 978 F. graminearum strains were 15-ADON whereas seven isolates were of the 3-ADON type. All seven F. asiaticum isolates were of the NIV type and fourteen F. pseudograminearum isolates were classified as 3-ADON. F. pseudograminearum was first isolated from FHB in Hebei in 2013. Although the recovery of F. pseudograminearum is still low, it represents a small shift in the pathogen composition and trichothecene genotypes associated with FHB in Hebei province. As Fusarium crown rot of wheat caused by F. pseudograminearum is an increasing problem in Hebei province, it is appropriate to monitor the role of F. pseudograminearum in FHB in the future.

Trichothecene Genotypes of Fusarium graminearum Populations Isolated from Winter Wheat Crops in Serbia

Fusarium graminearum as the main causal agent of Fusarium head blight (FHB) and its ability to produce trichothecenes was investigated by molecular techniques. A total of 37 strains isolated from the wheat, harvested in Serbia in 2005, 2008 and 2015, and previously designated by morphological observation as F. graminearum, were used for trichothecene genotypes characterization. The strains were identified using the species-specific primer set FG16R/FG16F while genotypic characterization was done using specific TRI13 and TRI3 sequences of the trichothecene gene clusters. The PCR assays identified all strains as species of F. graminearum sensu stricto with the DON/15-ADON genotype. The quantification of the mycotoxin (DON) was performed using the biochemical assay. The high levels of DON (>20,000 µg kg-1) were recorded in all of the strains from 2005, four strains from 2008 and two strains from 2015. Weather data of the investigated seasons, showed that the optimal temperature, frequent rains and high relative humidity (RH) was very favourable for the development of F. graminearum, affecting the DON biosynthesis.

Variation in the Microbiome, Trichothecenes, and Aflatoxins in Stored Wheat Grains in Wuhan, China

Contamination by fungal and bacterial species and their metabolites can affect grain quality and health of wheat consumers. In this study, sequence analyses of conserved DNA regions of fungi and bacteria combined with determination of trichothecenes and aflatoxins revealed the microbiome and mycotoxins of wheat from different silo positions (top, middle, and bottom) and storage times (3, 6, 9, and 12 months). The fungal community in wheat on the first day of storage (T₀) included 105 classified species (81 genera) and 41 unclassified species. Four species had over 10% of the relative abundance: Alternaria alternata (12%), Filobasidium floriforme (27%), Fusarium graminearum (12%), and Wallemia sebi (12%). Fungal diversity and relative abundance of Fusarium in wheat from top silo positions were significantly lower than at other silo positions during storage. Nivalenol and deoxynivalenol in wheat were 13–34% higher in all positions at 3 months compared to T₀, and mycotoxins in wheat from middle and bottom positions at 6 to 12 months were 24–57% higher than at T₀. The relative abundance of toxigenic Aspergillus and aflatoxins were low at T₀ and during storage. This study provides information on implementation and design of fungus and mycotoxin management strategies as well as prediction models.

Host and Cropping System Shape the Fusarium Population: 3ADON-Producers Are Ubiquitous in Wheat Whereas NIV-Producers Are More Prevalent in Rice

In recent years, Fusarium head blight (FHB) outbreaks have occurred much more frequently in China. The reduction of burning of the preceding crop residues is suggested to contribute to more severe epidemics as it may increase the initial inoculum. In this study, a large number of Fusarium isolates was collected from blighted wheat spikes as well as from rice stubble with perithecia originating from nine sampling sites in five provinces in Southern China. Fusarium asiaticum dominated both wheat and rice populations, although rice populations showed a higher species diversity. Chemotype analysis showed that rice is the preferred niche for NIV mycotoxin producers that were shown to be less virulent on wheat. In contrast, 3ADON producers are more prevalent on wheat and in wheat producing areas. The 3ADON producers were shown to be more virulent on wheat, revealing the selection pressure of wheat on 3ADON producers. For the first time, members of the Incarnatum-clade of FusariumIncarnatum-Equiseti Species Complex (FIESC) were found to reproduce sexually on rice stubble. The pathogenicity of FIESC isolates on wheat proved very low and this may cause the apparent absence of this species in the main wheat producing provinces. This is the first report of the Fusarium population structure including rice stubble as well as a direct comparison with the population on wheat heads in the same fields. Our results confirm that the perithecia on rice stubble are the primary inoculum of FHB on wheat and that cropping systems affect the local Fusarium population.

The Major Fusarium Species Causing Maize Ear and Kernel Rot and Their Toxigenicity in Chongqing, China

Fusarium verticillioides, F. proliferatum, and F. meridionale were identified as the predominant fungi among 116 Fusarium isolates causing maize ear and kernel rot, a destructive disease in Chongqing areas, China. The toxigenic capability and genotype were determined by molecular amplification and toxin assay. The results showed that the key toxigenic gene FUM1 was detected in 47 F. verticillioides and 19 F. proliferatum isolates. Among these, F. verticillioides and F. proliferatum isolates mainly produced fumonisin B₁, ranging from 3.17 to 1566.44, and 97.74 to 11,100.99 µg/g for each gram of dry hyphal weight, with the averages of 263.94 and 3632.88 µg/g, respectively, indicating the F. proliferatum isolates on average produced about an order of magnitude more fumonisins than F. verticillioides did in these areas, in vitro. Only NIV genotype was detected among 16 F. meridionale and three F. asiaticum isolates. Among these, 11 F. meridionale isolates produced NIV, varying from 17.40 to 2597.34 µg/g. ZEA and DON toxins were detected in 11 and 4 F. meridionale isolates, with the toxin production range of 8.35-78.57 and 3.38-33.41 µg/g, respectively. Three F. asiaticum isolates produced almost no mycotoxins, except that one isolate produced a small amount of DON. The findings provide us with insight into the risk of the main pathogenic Fusarium species and a guide for resistance breeding in these areas.

A new point mutation in β2-tubulin confers resistance to carbendazim in Fusarium asiaticum

Resistance to benzimidazole fungicides in many phytopathogenic fungi is caused by specific point mutations in the β-tubulin gene (β-tubulin). However, the mutated locus and genotype of β-tubulin differ among phytopathogenic fungi. To validate the point mutation in Fusarium asiaticum β₂-tubulin that confers resistance to carbendazim and to analyze the molecular interaction between carbendazim and F. asiaticum β₂-tubulin. In this study, a new point mutation (GAG→GCG, E198A) at codon 198 of β₂-tubulin in a wild-type F. asiaticum strain was constructed by site-directed mutagenesis followed by a split marker strategy. The site-directed mutants were verified and exhibited a high level of resistance to carbendazim. In the absence of fungicide treatment, the biological characteristics did not differ between the site-directed mutants and the wild-type strain. Molecular docking between carbendazim and β₂-tubulin was carried out using the Surflex-Dock program in Sybyl X-2.0 version and the results indicated that the E198A mutation altered the configuration of β₂-tubulin, resulting in the change of the bonding sites and docking scores. We concluded that the point mutation of F. asiaticum β₂-tubulin conferring carbendazim resistance may not always be the bonding site for carbendazim.

Identification and trichothecene genotypes of Fusarium graminearum species complex from wheat in Taiwan

BACKGROUND

Fusarium head blight (FHB) of wheat caused by Fusarium graminearum species complex (FGSC) is a devastating disease worldwide. The pathogens not only reduce the yield of wheat, but also impact the quality of wheat by contamination with trichothecene mycotoxins. A systematic investigation on the pathogens of FHB in Taiwan is lacking. Here, molecular and morphological approaches were used to identify species of the Taiwanese FGSC isolates and determine their trichothecene genotypes.

RESULTS

In this study, a total of 195 isolates of FGSC from diseased wheat were collected from 8 areas of northern and central Taiwan. All isolates were subjected to seedling inoculation for verification of pathogenicity. The pathogenic isolates were genetically characterized by sequence characterized amplified region (SCAR), PCR- restriction fragment length polymorphism (RFLP), phylogenetic analysis and fixed nucleotides to clarify their phylogenetic species, and by PCR assays of TRI genes to determine trichothecene genotypes. They were identified as F. asiaticum, F. graminearum sensu stricto, F. meridionale and an unknown species. Isolates of F. asiaticum were the major causal agents (98%) in this investigated population and were comprised of SCAR type 5 (75%), SCAR type 4 (21%) and SCAR type 3 (2%). Their trichothecene genotypes were either 15-acetyl-deoxynivalenol (15-ADON) (83%) or nivalenol (NIV) genotype (17%). These genetic characterizations indicated that F. asiaticum (15-ADON SCAR type 5) accounts for 60% of this Taiwanese population. Virulence assay on wheat heads indicated virulence of F. asiaticum isolates in subpopulations divided by SCAR types or trichothecene genotypes were comparable, suggesting other factors influence the unequal subpopulation sizes.

CONCLUSIONS

This is the first study that FGSC isolates in Taiwan were systematically collected and characterized. In addition to F. graminearum sensu stricto and F. meridionale, F. asiaticum with 15-ADON genotype was identified as the predominate species in Taiwan. In contrast to Chinese and Japanese populations that F. asiaticum isolates were typically of 3-ADON or NIV genotype, the predominate 15-ADON genotype in Taiwanese population was unique among F. asiaticum populations and represented the southernmost 15-ADON genotype population in East Asia.

The septins FaCdc3 and FaCdc12 are required for cytokinesis and affect asexual and sexual development, lipid metabolism and virulence in Fusarium asiaticum

Septins are a highly conserved family of GTP-binding proteins that contribute to many cellular and metabolic functions, including cell polarity, cytokinesis, cell morphogenesis and pathogenesis. In this study, we characterized the septins FaCdc3 and FaCdc12 in the filamentous fungus Fusarium asiaticum. The functions of FaCdc3 and FaCdc12 were evaluated by constructing deletion mutants of FaCdc3 and FaCdc12, designated ΔFaCdc3-5 and ΔFaCdc12-71, respectively. The deletion mutants exhibited a reduced rate of mycelial growth, increased aerial hyphae formation, irregularly shaped hyphae, reduced conidiation and a lack of sexual reproduction in wheat kernels. Histochemical analysis revealed that the conidia and hyphae of ΔFaCdc3-5 and ΔFaCdc12-71 formed large lipid droplets (LDs). ΔFaCdc3-5 and ΔFaCdc12-71 also exhibited increased resistance to agents that induce osmotic stress and damage the cell membrane and cell wall. In addition, the hyphae and conidia of the two mutants formed fewer septa than those of the wild-type and exhibited aberrant nuclear distribution. Pathogenicity assays showed that ΔFaCdc3-5 and ΔFaCdc12-71 exhibited reduced virulence on wheat spikelets, which was indirectly correlated with a reduced level of deoxynivalenol accumulation. All of these defects were restored by genetic complementation of the two mutants with the parental FaCdc3 and FaCdc12. These results indicate that FaCdc3 and FaCdc12 play a critical role in various cellular processes in F. asiaticum.

Geographic distribution of phylogenetic species of the Fusarium graminearum species complex and their 8-ketotrichothecene chemotypes on wheat spikes in Iran

Isolates of the Fusarium graminearum species complex (FGSC, n = 446) were collected from wheat spikes from northern and western regions of Iran with a history of Fusarium head blight (FHB) occurrences. The trichothecene mycotoxin genotypes/chemotypes, the associated phylogenetic species, and geographical distribution of these isolates were analyzed. Two phylogenetic species, Fusarium asiaticum and F. graminearum, were identified and were found to belong to sequence characterized amplified region (SCAR) groups V and I. Isolates from F. asiaticum species lineage 6 were within SCAR group V, whereas F. graminearum species lineage 7 were of SCAR group I. Of the 446 isolates assayed, 274 were F. asiaticum species predominantly of the nivalenol (NIV) genotype, while other isolates were either deoxynivalenol (DON) plus 3-acetyldeoxynivalenol (3-AcDON) or DON plus 15-acetyldeoxynivalenol (15-AcDON) genotype. Based on Tri7 gene sequences, a new subpopulation of 15-AcDON producers was observed among F. asiaticum strains in which 11-bp repeats were absent in the Tri7 sequences. The trichothecene chemotype was confirmed and quantified by high-performance liquid chromatography (HPLC) in 46 FGSC isolates. Isolates produced NIV (33.4-108.2 μg/g) and DON (64.7-473.6 μg/g) plus either 3-AcDON (51.4-142.4 μg/g) or 15-AcDON (24.1-99.3 μg/g). Among FGSC isolates, F. asiaticum produced the highest levels of trichothecenes. Using BIOCLIM based on the climate data of 20-year during 1994-2014, modelling geographical distribution of FGSC showed that F. asiaticum was restricted to warmer and humid areas with a median value of mean annual temperature of about 17.5 °C and annual rainfall of 658 mm, respectively (P < 0.05). In contrast, F. graminearum (only 15-AcDON producers) was restricted to cooler and drier areas, with a median value of the mean annual temperature of 14.4 °C and an annual rainfall of 384 mm, respectively (P < 0.05). Based on climate parameters at anthesis, the recorded distribution of F. graminearum and F. asiaticum was similar to that based on BIOCLIM parameters. Therefore, geographic differences on the wheat-growing areas in Iran have had a significant effect on distribution of FGSC and their trichothecene chemotypes.

Analysis of Fusarium graminearum Species Complex from Wheat-Maize Rotation Regions in Henan (China)

Fusarium head blight (FHB) and maize stalk rot (MSR), caused by members of the Fusarium graminearum species complex (FGSC), are among the most destructive and economically important diseases in the world. Species identity and the trichothecene chemotype of 312 members of the FGSC from diseased wheat spikes and maize stalks in Henan was determined using phylogenetic analyses and a polymerase chain reaction trichothecene chemotype assay. F. graminearum sensu stricto accounted for more than 93% of the FGSC isolates associated with FHB (N = 168) and MSR (N = 130). The remaining isolates were F. asiaticum. Significant differences were found in the frequencies of the two species within the hosts (P < 0.01). However, the frequencies of the same species in FHB and MSR were similar (P > 0.05) for wheat and maize isolates, indicating that the composition of the FGSC with respect to wheat and maize in these fields varied little. The 15-acetyl-deoxynivalenol (15-ADON) trichothecene chemotype represented 92.7 and 98.5% of isolates from wheat (N = 167) and maize (N = 130), respectively. However, the 3-acetyl-deoxynivalenol chemotype was found in 6.7% of wheat isolates, and the nivalenol chemotype in 1.5% of MSR isolates and in 0.6% of FHB isolates. Mycelial growth at different concentrations of carbendazim and difenoconazole did not differ between F. graminearum sensu stricto and F. asiaticum. These results suggest that the 15-ADON chemotype of F. graminearum sensu stricto is the predominant pathogen that causes wheat- and maize-related diseases in this region. Copyright © 2017 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Fitness of three chemotypes of Fusarium graminearum species complex in major winter wheat-producing areas of China

In China, Fusarium head blight is caused mainly by the Fusarium graminearum species complex (FGSC), which produces trichothecene toxins. The FGSC is divided into three chemotypes: 3-acetyldeoxynivalenol (3-ADON), 15-acetyldeoxynivalenol (15-ADON), and nivalenol (NIV). In order to predict the geographical changes in the distribution of these chemotype populations in major winter wheat-producing areas in China, the biological characteristics of twenty randomly selected isolates from each of the three chemotypes were studied. No significant difference was exhibited in the growth rate of 3-ADON, 15-ADON, and NIV isolates at 15°C. At 20°C and 25°C, the growth rate of 15-ADON isolates was the highest. At 30°C, the growth rate of NIV and 3-ADON isolates was significantly higher than that of 15-ADON isolates. The 15-ADON isolates produced the highest quantities of perithecia and two to three days earlier than the other two populations at each temperature, and released more ascospores at 18°C. The aggressiveness test on wheat seedlings and ears indicated there was no significant difference between the 3-ADON and 15-ADON isolates. However, the aggressiveness of NIV isolates was significantly lower than that of the 3-ADON and 15-ADON isolates. The DON content in grains from heads inoculated with the 3-ADON isolates was higher than the content of 15-ADON and NIV isolates. The results showed that 15-ADON population had the advantage in perithecia formation and ascospore release, and the 3-ADON population produced more DON in wheat grains. We suggested that distribution of these three chemotype populations may be related to these biological characteristics.

Mycotoxigenic Potentials of Fusarium Species in Various Culture Matrices Revealed by Mycotoxin Profiling

In this study, twenty of the most common Fusarium species were molecularly characterized and inoculated on potato dextrose agar (PDA), rice and maize medium, where thirty three targeted mycotoxins, which might be the secondary metabolites of the identified fungal species, were detected by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Statistical analysis was performed with principal component analysis (PCA) to characterize the mycotoxin profiles for the twenty fungi, suggesting that these fungi species could be discriminated and divided into three groups as follows. Group I, the fusaric acid producers, were defined into two subgroups, namely subgroup I as producers of fusaric acid and fumonisins, comprising of F. proliferatum, F. verticillioides, F. fujikuroi and F. solani, and subgroup II considered to only produce fusaric acid, including F. temperatum, F. subglutinans, F. musae, F. tricinctum, F. oxysporum, F. equiseti, F. sacchari, F. concentricum, F. andiyazi. Group II, as type A trichothecenes producers, included F. langsethiae, F. sporotrichioides, F. polyphialidicum, while Group III were found to mainly produce type B trichothecenes, comprising of F. culmorum, F. poae, F. meridionale and F. graminearum. A comprehensive picture, which presents the mycotoxin-producing patterns by the selected fungal species in various matrices, is obtained for the first time, and thus from an application point of view, provides key information to explore mycotoxigenic potentials of Fusarium species and forecast the Fusarium infestation/mycotoxins contamination.

Temporal dynamics, population characterization and mycotoxins accumulation of Fusarium graminearum in Eastern China

Trichothecene genotype composition, mycotoxin production, genetic diversity, and population structure were analyzed, using 185 Fusarium strains collected from wheat (Triticum aestivum L.) throughout the Jiangsu province during 1976, 1983, 1998, 2006, and 2014. The results showed that 3-acetyldeoxynivalenol (3ADON) was consistently the predominant type in this region over 40 years, and the nivalenol (NIV) type has emerged since 1998. Long-term rotation of wheat and rice (Oryza sativa L.), rather than fungicide application, crop fitness, or weather conditions, might be the main cause of this phenomenon. The genetic diversity results from two toxin synthetic genes, Pks4 and Tri10, and variable number of tandem repeat (VNTR) markers revealed the largest variance within the population in 1998, which was also the year with the highest production of mycotoxins. Population differentiation analysis indicated that major temporal population comparisons from the same area were not significantly differentiated. Our results showed that dominant species could maintain genetic stability for a long time, and Pks4 would be of utility in genetic and population studies.

Aerobic De-Epoxydation of Trichothecene Mycotoxins by a Soil Bacterial Consortium Isolated Using In Situ Soil Enrichment

Globally, the trichothecene mycotoxins deoxynivalenol (DON) and nivalenol (NIV) are among the most widely distributed mycotoxins that contaminate small grain cereals. In this study, a bacterial consortium, PGC-3, with de-epoxydation activity was isolated from soil by an in situ soil enrichment method. Screening of 14 soil samples that were sprayed with DON revealed that 4 samples were able to biotransform DON into de-epoxydized DON (dE-DON). Among these, the PGC-3 consortium showed the highest and most stable activity to biotransform DON into dE-DON and NIV into dE-NIV. PGC-3 exhibited de-epoxydation activity at a wide range of pH (5–10) and temperatures (20–37 °C) values under aerobic conditions. Sequential subculturing with a continued exposure to DON substantially reduced the microbial population diversity of this consortium. Analyses of the 16S rDNA sequences indicated that PGC-3 comprised 10 bacterial genera. Among these, one species, Desulfitobacterium, showed a steady increase in relative abundance, from 0.03% to 1.55% (a 52-fold increase), as higher concentrations of DON were used in the subculture media, from 0 to 500 μg/mL. This study establishes the foundation to further develop bioactive agents that can detoxify trichothecene mycotoxins in cereals and enables for the characterization of detoxifying genes and their regulation.

Genotypes and Characteristics of Phenamacril-Resistant Mutants in Fusarium asiaticum

Fusarium asiaticum is a critical pathogen of Fusarium head blight (FHB) in the southern part of China. The fungicide phenamacril has been extensively used for controlling FHB in recent years, which reduced both FHB severity and mycotoxin production. Our previous report indicated that resistance of F. asiaticum to phenamacril was related to mutations in myosin5. A recent article revealed that the resistance level of phenamacril-resistant mutants was associated with the genotypes of myosin5 in these mutants. In total, we obtained 239 resistant isolates by fungicide domestication, and 82 resistant mutants were randomly selected for further study. Of these mutants, 25.6, 7.3, and 67.1% showed low resistance (LR), moderate resistance (MR), and high resistance (HR), respectively, to phenamacril determined by 50% effective concentration values. Point mutations A135T, V151M, P204S, I434M, A577T, R580G/H, or I581F led to LR. Point mutations S418R, I424R, and A577G were responsible for MR and point mutations K216R/E, S217P/L, or E420K/G/D conferred HR. Interestingly, all of the mutations concentrated in the myosin5 motor domain and mutations conferring HR occurred at codon 217 and 420, which we called the core region. Homology modeling revealed that mutations far from the core region led to a lower resistance degree. Phenotype assays revealed that the most highly resistant mutants did not significantly change pathogenicity but decreased conidia production compared with the wild type, which may slow down the formation of the resistant pathogen population in the fields.

Nucleotide polymorphisms and protein structure changes in the Fg16 gene of Fusarium graminearum sensu stricto

Fusarium graminearum is one of the most important causes of wheat scab in different parts of the world. This fungus is able to produce widespread trichothecene mycotoxins such as nivalenol (NIV) and deoxynivalenol (DON) which are harmful for both human and animals. The Fg16 target is located in chromosome 1 of the F. graminearum genome coding for a hypothetical protein whose function is not yet known. The Fg16 gene is involved in lipid biosynthesis and leads to sexual development during colonization in wheat stalks. This gene is used to detect F. graminearum and determine the lineage of F. graminearum complex species. In the present study, polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) and DNA sequencing methods were employed in screening for genetic variation in 172 F. graminearum s.s. isolates. The PCR reaction forced the amplification of 410-bp fragments of Fg16. Two single nucleotide polymorphisms (T82C and A352T) and one amino acid exchange (C65S) with three patterns (TA/TA, CT/CT and TA/CT genotypes) were found in the Fg16 gene fragment. Two haplotypes, 1A and 1B, were identified within F. graminearum s.s. populations in northern and western regions of Iran. Two different secondary structures of protein were predicted for CT/CT and TA/CT genotypes of Fg16 gene. The average diversity levels detected were relatively high (He: 0.3238; Heu: 0.334; Ho: 0.2894; mean PIC: 0.514; mean Shannon's information index: 0.4132; mean number of alleles per locus: 1.473). On the basis of the obtained results, it was revealed that the Fg16 gene had a high degree of polymorphism that can be considered for future control programming strategies and thus the associations between the SSCP patterns with different traits of F. graminearum such as wheat colonization, perithecium formation on stalk tissues and lineage discrimination should be investigated.

Myosins FaMyo2B and Famyo2 Affect Asexual and Sexual Development, Reduces Pathogenicity, and FaMyo2B Acts Jointly with the Myosin Passenger Protein FaSmy1 to Affect Resistance to Phenamacril in Fusarium asiaticum

We previously reported that mutations occurred in the gene myosin5 were responsible for resistance to the fungicide phenamacril in Fusarium graminearum. Here, we determined whether there is a functional link between phenamacril resistance and the myosin proteins FaMyo2B and Famyo2 in Fusarium asiaticum, which is the major causal agent of Fusarium head blight in China. We found that FaMyo2B acts jointly with FaSmy1 to affect resistance to phenamacril in F. asiaticum. We also found that FaMyo2B disruption mutant and Famyo2 deletion mutant were defective in hyphal branching, conidiation, and sexual reproduction. ΔFamyo2 also had an enhanced sensitivity to cell wall damaging agents and an abnormal distribution of septa and nuclei. In addition, the FaMyo2B and Famyo2 mutants had reduced pathogenicity on wheat coleoptiles and flowering wheat heads. Taken together, these results reveal that FaMyo2B and Famyo2 are required for several F. asiaticum developmental processes and activities, which help us better understand the resistance mechanism and find the most effective approach to control FHB.

Effect of environmental factors on Fusarium population and associated trichothecenes in wheat grain grown in Jiangsu province, China

The present study was performed to identify prevailing Fusarium species and the environmental factors affecting their frequencies and the contamination of grain with major mycotoxins in Jiangsu province. The precipitation levels were 184.2mm, 156.4mm, and 245.8mm in the years 2013-2015, respectively, and the temperature fluctuated by an average of 10.6±7.2°C in 2013, 10.9±7.2°C in 2014, and 10.6±6.3°C in 2015. Co-occurrence of deoxynivalenol (DON), 3-acetyldeoxynivalenol (3ADON), and 15-acetyldeoxynivalenol (15ADON) were observed in wheat. The average concentrations of DON were 879.3±1127.8, 627.8±640.5, and 1628.6±2,168.0μg/kg in 2013-2015, respectively. The average concentrations of 3ADON were 43.5±59.0, 71.2±102.5, and 33.5±111.9μg/kg in 2013-2015, respectively. We found that the average concentration of DON in wheat was positively correlated with precipitation (r=0.998, p<0.01), and 3ADON was negatively correlated with precipitation (r=-0.887, p<0.05). However, there was no correlation between precipitation and 15ADON or nivalenol (NIV). The differences in temperature were not as significant as the differences in rainfall amount over a short time period. Therefore, there were no correlations between temperature and the concentrations of trichothecenes, excluding 3ADON (r=0.996, p<0.01). Our data indicated that Fusarium asiaticum is the primary pathogenic fungus prevalent in the Fusarium head blight disease nursery. The trichothecene chemotype composition differed between Fusarium graminearum sensu stricto (s. str.) and F. asiaticum isolates. The 3ADON chemotype was found only among strains of F. asiaticum. The NIV chemotype was not observed among strains of F. graminearum, while the 15ADON chemotype represented 100% of the F. graminearum strains collected. The results of this study indicated no correlations between environmental conditions and the species or genetic chemotype composition of pathogens in Jiangsu province in 2013-2015.

The recent Fusarium mycotoxin situation in grain and feed in China

Fusarium mycotoxins, such as trichothecenes, zearalenone (ZEA) and fumonisins, are widely distributed in grain and animal feed and cause hazards to human and animal health. China, one of the largest producers of agricultural products and animal feed, constantly faces challenges in preventing and controlling Fusarium mycotoxins. The recent status of Fusarium mycotoxins in grain and feed is of interest to many stakeholders; however, no comprehensive review of this has been published to date. The objective of this article is to review the recent situation in China, including the contamination situation, its (probable) main causes and the updated regulations. Every district of China has been affected by Fusarium mycotoxin contamination to varying degrees, with the most seriously affected districts being East China, Central China and North China. The incidence rates of deoxynivalenol and ZEA were higher than those of other Fusarium mycotoxins in both grain and feed samples. It has been suggested that deoxynivalenol-3-glucoside should undergo the risk assessment and the development of a related legal limit in China. Among the multiple causes of Fusarium mycotoxin occurrence in China, geography and climate and the variable characteristics of plants are probably the two important causes. The latest legal limits for Fusarium mycotoxins in food were promulgated in 2011, and the legal limits in feed are in the process of being revised. This article aims to provide information for promoting an understanding of the recent situation and the challenges for combating Fusarium mycotoxin contamination of grain and feed in China.

Genotypes and Phenotypic Characterization of Field Fusarium asiaticum Isolates Resistant to Carbendazim in Anhui Province of China

Fusarium asiaticum is a causal agent of Fusarium head blight (FHB) of wheat in the southern part of China. Carbendazim has been extensively used for controlling FHB for more than 30 years, leading to the widespread carbendazim-resistant isolates in all major wheat-producing provinces in China, especially in Anhui Province. F. asiaticum isolates were collected throughout Anhui Province between 2010 and 2012 to monitor their sensitivity to carbendazim. In total, 74 of 899 single-spore isolates F. asiaticum were found to be resistant to carbendazim. Resistant isolates were collected from all of the sampled sites except Hefei of Anhui Province. The overall frequency of carbendazim resistance was shown to be 8.2%. Of the 74 isolates, 1, 68, and 5 had low resistance (LR), moderate resistance (MR) ,and high resistance (HR), respectively, to carbendazim. Five types of point mutations (F167Y, E198L, E198K, F200Y, and E198Q) in the β₂-tubulin gene conferring resistance to carbendazim were detected in the field-resistant isolates with frequencies of 89.2, 2.7, 4.1, 2.7, and 1.4%, respectively. The point mutations at codon 167, 198, or 200 of the β₂-tubulin gene were correlated with different levels of carbendazim resistance. Some of the sensitive and resistant isolates appeared to possess different biological characteristics; however, these might not be due to resistance. Because carbendazim resistance was generally widespread throughout Anhui Province, the sensitivity of F. asiaticum populations to carbendazim should be constantly monitored for the development of carbendazim resistance in natural populations.

The tubulin cofactor A is involved in hyphal growth, conidiation and cold sensitivity in Fusarium asiaticum

BACKGROUND

Tubulin cofactor A (TBCA), one of the members of tubulin cofactors, is of great importance in microtubule functions through participating in the folding of α/β-tubulin heterodimers in Saccharomyces cerevisiae. However, little is known about the roles of TBCA in filamentous fungi.

RESULTS

In this study, we characterized a TBCA orthologue FaTBCA in Fusarium asiaticum. The deletion of FaTBCA caused dramatically reduced mycelial growth and abnormal conidiation. The FaTBCA deletion mutant (ΔFaTBCA-3) showed increased sensitivity to low temperatures and even lost the ability of growth at 4°C. Microscopic observation found that hyphae of ΔFaTBCA-3 exhibited blebbing phenotypes after shifting from 25 to 4°C for 1- or 3-day incubation and approximately 72% enlarged nodes contained several nuclei after 3-day incubation at 4°C. However, hyphae of the wild type incubated at 4°C were phenotypically indistinguishable from those incubated at 25°C. These results indicate that FaTBCA is involved in cell division under cold stress (4°C) in F. asiaticum. Unexpectedly, ΔFaTBCA-3 did not exhibit increased sensitivity to the anti-microtubule drug carbendazim although quantitative real-time assays showed that the expression of FaTBCA was up-regulated after treatment with carbendazim. In addition, pathogenicity assays showed that ΔFaTBCA-3 exhibited decreased virulence on wheat head and on non-host tomato.

CONCLUSION

Taken together, results of this study indicate that FaTBCA plays crucial roles in vegetative growth, conidiation, temperature sensitivity and virulence in F. asiaticum.

α1-Tubulin FaTuA1 plays crucial roles in vegetative growth and conidiation in Fusarium asiaticum

The filamentous ascomycete Fusarium asiaticum contains two homologous genes FaTUA1 and FaTUA2 encoding α-tubulins. In this study, we found that FaTUA2 was dispensable for vegetative growth and sporulation in F. asiaticum. The deletion of FaTUA1 however led to dramatically reduced mycelial growth, twisted hyphae and abnormal nuclei in apical cells of hyphae. The FaTUA1 deletion mutant (ΔFaTuA1-5) also showed a significant decrease in conidiation, and produced abnormal conidia. Pathogenicity assays showed that ΔFaTuA1-5 exhibited decreased virulence on wheat head. Unexpectedly, the deletion of FaTUA1 led to resistance to high temperatures. In addition, ΔFaTuA2 showed increased sensitivity to carbendazim. Furthermore, increased FaTUA2 expression in ΔFaTuA1-5 partially restored the defects of the mutant in mycelial growth, conidial production and virulence, vice versa, increased FaTUA1 expression in the FaTUA2 deletion mutant also partially relieved the defect of the mutant in the delay of conidial germination. Taken together, these results indicate that FaTuA1 plays crucial roles in vegetative growth and development, and the functions of FaTuA1 and FaTuA2 are partially interchangeable in F. asiaticum.

Biogeography of Fusarium graminearum species complex and chemotypes: a review

Differences in the geographic distribution of distinct trichothecene mycotoxins in wheat and barley were first recorded two decades ago. The different toxicological properties of deoxynivalenol (DON), nivalenol (NIV) and their acetylated derivatives require careful monitoring of the dynamics of these mycotoxins and their producers. The phylogenetic species concept has become a valuable tool to study the global occurrence of mycotoxin-producing Fusarium species. This has revolutionised our views on the terrestrial distribution of trichothecene-producing Fusaria in the context of agronomics, climatic conditions, and human interference by the global trade and exchange of agricultural commodities. This paper presents an overview of the dynamics of the different trichothecene-producing Fusarium species as well as their chemotypes and genotypes across different continents. Clearly not one global population exists, but separate ones can be distinguished, sometimes even sympatric in combination with different hosts. A population with more pathogenic strains and chemotypes can replace another. Several displacement events appear to find their origin in the inadvertent introduction of new genotypes into new regions: 3-acetyl-DON-producing F. graminearum in Canada; 3-acetyl-DON-producing F. asiaticum in Eastern China; 15-acetyl-DON F. graminearum in Uruguay; and NIV-producing F asiaticum in the southern United States.