1a. Objectives (from AD-416):
The overall goal of this project is to contribute to the effective control of toxigenic Fusarium, especially those responsible for FHB of small grain cereals, in order to enhance food safety and crop production in the U.S. and around the world. The proposed project is designed to produce a robust evolutionary framework for understanding the genetic and phenotypic diversity, geographic distribution and population biology of toxigenic fusaria, and will result in novel technologies for the rapid detection, identification and control of toxigenic fusarial pathogens of critical importance to food safety and food security. This framework will also support and facilitate work by the global Fusarium research community. The specific objectives are: Objective 1: characterize the genetic diversity and mycotoxin potential of Fusarium head blight and other fusarial pathogens, develop novel pathogen detection technologies, and expand web-accessible informational database to facilitate the rapid and accurate identification of toxigenic fusaria via the Internet. Objective 2: Determine the global population structure of F. graminearum and identify genetic variation associated with population-level difference in growth, reproduction, and toxin accumulation phenotypes as a means to improve pathogen modeling and surveillance. Objective 3: Characterize the mechanisms that drive the diversification and adaptive evolution of virulence genes in Fusarium genomes as well as host defense genes involved in immunogenicity and disease response.
1b. Approach (from AD-416):
Toxins produced by plant-pathogenic Fusarium pose a significant threat to food safety and place a major burden on the world’s agricultural economy. The primary objectives of the proposed research are to: 1) Characterize the genetic diversity and mycotoxin potential of Fusarium head blight (FHB) and other fusarial pathogens, develop novel pathogen detection technologies, and expand web-accessible informational databases to facilitate the rapid and accurate identification of toxigenic fusaria via the Internet, 2) Determine the global population structure of F. graminearum and identify genetic variation associated with population-level differences in growth, reproduction, and toxin accumulation phenotypes as a means to improve pathogen modeling and surveillance, and 3) Characterize the mechanisms that drive the diversification and adaptive evolution of virulence genes in Fusarium genomes as well as host defense genes involved in immunogenicity and disease response. These complementary objectives are directed at developing robust pathogen control strategies through elucidating the evolution, population structure, phenotypic diversity, host range, geographic distribution and adaptive potential of toxigenic fusaria. In addition, the planned research will produce enhanced methods for identification and characterization (e.g. toxin type, toxin accumulation potential, and host preference) of Fusarium responsible for mycotoxin contamination of cereals and other food. The information and molecular tools developed as a result of this project will address the needs of small grain cereal producers, food and feed processors, the U.S. Department of Agriculture (USDA) Federal Grain Inspection Service (FGIS), the USDA Animal and Plant Health Inspection Service (APHIS), and the Food and Drug Administration (FDA).
3. Progress Report:
The origin, distribution, and evolution of a novel type A trichothecene toxin (NX toxin) was determined. Probes targeting the genetic variation responsible for the NX toxin type were developed and integrated into a published multilocus genotyping assay for rapid identification of strains with the ability to produce NX toxin. A combination of molecular surveillance and population genetic analyses were used to demonstrate significant regional differences in the composition and toxin production capacity of Fusarium head blight (FHB) pathogen populations in North America. Significant regional differences in the rate and nature of genetic exchange between introduced and native pathogen populations were demonstrated. Molecular characterization of FHB species and toxin diversity provided additional evidence of host specialization among FHB pathogen and toxin types, with different species and toxins predominating on wheat, corn, and rice. These analyses also demonstrated that the major FHB pathogen of wheat in Mexico is different than in the United States. In joint research with agricultural scientists in Japan, New Zealand, and collaborators at the Pennsylvania State University, we conducted a detailed genetic analysis of a novel FHB pathogen that we discovered within the U.S. infecting Dactylis glomerata (orchard grass), one of the world’s most important forage grasses. Mycotoxin analyses established that this novel FHB pathogen could produce the trichothecene mycotoxin nivalenol in planta as well as detectable amounts of the estrogenic mycotoxin zearalenone in vitro. Pathogenicity tests also revealed that the orchard grass isolates could induce head blight symptoms on wheat. Given the economic importance of FHB pathogens and their toxins to U.S. and global agriculture, we formally described the orchard grass pathogen as F. dactylidis to foster accurate communication of it within the scientific community. In collaborative research with fungal biologists at the Centraalbureau voor Schimmelcultures Biodiversity Center, Utrecht, The Netherlands and collaborators at the Pennsylvania State University, Pennsylvania, we increased the utility of two web-accessible sites (Fusarium multilocus sequence typing (MLST), http://www.cbs.knaw.nl/Fusarium; and Fusarium-ID, http://isolate.fusariumdb.org) by depositing multilocus DNA sequence data from our pathogen genetic diversity studies in both databases. These dedicated web-accessible sites were developed to facilitate rapid and accurate identification of toxigenic and pathogenic fusaria via the Internet. In addition, the Fusarium MLST website was updated to provide detailed instructions on how to query the database with a DNA sequence from an unknown. These two dedicated sites facilitate global epidemiological studies and contribute to improved disease surveillance and global monitoring via the Internet. In addition, the multilocus DNA sequence data deposited in Fusarium MLST and Fusarium-ID has proven to be extraordinarily useful in developing molecular surveillance technologies for monitoring the global movement of FHB and other fusarial pathogens and their toxins. The overarching goal of this research is to develop potential control and intervention strategies so that fusaria and their toxins do not enter the food chain.
1. The distribution of Fusarium head blight (FHB) pathogens and toxin contamination of cereals are influenced by host preference. Fungi within the Fusarium graminearum species complex (FGSC) are responsible for FHB of cereal crops world-wide. FHB significantly reduces crop yield and results in contamination of grain with trichothecene mycotoxins, such as deoxynivalenol (DON) and nivalenol (NIV), which pose a significant threat to food safety and animal health. In collaboration with scientists in Brazil, ARS scientists in Peoria, Illinois, demonstrated significant regional and crop-specific differences in FHB pathogen and toxin diversity. The results suggest that wheat is most susceptible to F. graminearum and the DON toxin type, whereas Fusarium species with the NIV toxin type predominated on rice. In addition, we demonstrated that pathogen and toxin composition was influenced by field elevation above sea level. The results indicate that rice could serve as a reservoir for FHB pathogens with the NIV toxin type, enabling these pathogens to cause disease and NIV contamination of wheat in regions where rice production is significant. These results are critical to promoting food safety through improved understanding of ecological and host-specific factors that shape FHB pathogen diversity and toxin exposure potential.
2. Detection and characterization of a novel trichothecene mycotoxin produced by Fusarium head blight (FHB) pathogens. Fusarium graminearum and related fungi are responsible for FHB and other economically destructive diseases of cereal crops world-wide. In addition, these fungi contaminate grain with mycotoxins that pose a significant threat to food safety and animal health and represent enormous losses of food and feed worldwide as well as to high costs for monitoring and mycotoxin management to protect consumers. ARS scientists in St. Paul, Minnesota, and Peoria, Illinois, in collaboration with scientists in Austria identified strains of F. graminearum from the Upper Midwest of the United States that produce a previously unknown trichothecene toxin, termed NX toxin. We determined the chemical structure of this novel toxin and described why it is not detectable by analytical methods that are widely used for mycotoxin monitoring. In addition, we demonstrated that NX toxin has nearly the same toxicity to plants and animals as deoxynivalenol (DON), which is regulated in many countries. Finally, the gene responsible for the ability to produce NX toxin was identified and a genetic test was developed to rapidly identify fungi capable of producing the novel NX toxin. These results are critical to promoting food safety and cereal production through improved mycotoxin monitoring and improved understanding of fungal diversity that can inform efforts to breed cereals with broad resistance to FHB.
3. etection of significant changes in Fusarium head blight (FHB) pathogen populations and toxin types in the Upper Midwest. Fusarium graminearum causes FHB in wheat and barley, and contaminates grains with trichothecene mycotoxins that are a significant threat to food safety and crop production. In collaboration with ARS scientists in St. Paul, Minnesota and in Peoria, Illinois, documented significant changes in the composition of FHB pathogen populations and toxin types in the Upper Midwest. Strains from a new pathogen population increased by approximately 4 fold between 1999 and 2013 and their range expanded southward toward the border between Minnesota and South Dakota. This change is a significant concern for cereal production and food safety as strains from the new population have previously been shown to grow more quickly, to be more aggressive on some lines of wheat, and to accumulate more trichothecene toxin in grain than strains from the traditional FHB population in the Upper Midwest. These results are critical to promoting food safety and cereal production through improved detection of novel FHB pathogens and toxin types, and through plant quarantine and variety improvement efforts that account for the entire spectrum of FHB pathogen and toxin type diversity.
4. Detection and characterization of a novel nivalenol toxin-producing head blight pathogen. Fungi within the B lineage of trichothecene toxin-producing fusaria are responsible for Fusarium head blight (FHB) of cereal crops world-wide. ARS scientists in Peoria, Illinois, in collaboration with scientists in Japan and New Zealand, discovered and characterized a novel FHB pathogen from Dactylis glomerata (orchard grass), one of the world’s most important forage grasses. Formally described as F. dactylidis, isolates of this novel FHB pathogen produced nivalenol mycotoxin in planta as well as low but detectable amounts of the estrogenic mycotoxin zearalenone in vitro. Results of a pathogenicity test revealed that F. dactylidis induced mild head blight on wheat. Results of this study help promote cereal production and food safety through improved detection of novel FHB pathogens and toxin types, and through plant quarantine and variety improvement efforts that account for the entire spectrum of FHB pathogen and toxin type diversity.
5. Evolution of resistance to cyanate fungicides by fungi that cause vascular wilts. Fungi within the Fusarium oxysporum species complex (FOSC) are responsible for scores of economically destructive vascular wilt diseases of vegetable and horticultural plants world-wide. The general purpose fungicide cyanate has been widely used in agriculture to control plant diseases, however some pathogens are resistant to cyanate fungicides. As part of a project to characterize the evolution of cyanate resistance, ARS scientists in Peoria, Illinois, in collaboration with scientists at Vanderbilt University and the Ohio State University, discovered a cluster of two genes responsible for cyanate degradation by vascular wilt pathogens within the FOSC. Analyses of 163 FOSC strains from a wide variety of hosts suggest that the gene cluster has been transferred between isolates, possibly in response to cyanates produced by plants and\or the use of cyanate fungicides in agriculture. These results are critical to promoting agricultural biosecurity, food safety, and informed plant breeding programs through improved understanding of the genetics of FOSC resistance to the widely used fungicide cyanate.
Del Ponte, E.M., Spolti, P., Ward, T.J., Gomes, L.B., Nicolli, C.P., Kuhnem, P.R., Silva, C.N., Tessmann, D.J. 2015. Regional and field-specific factors affect the composition of Fusarium head blight pathogens in subtropical no-till wheat agroecosystem of Brazil. Phytopathology. 105(2):246-254.
Aoki, T., Vaughan, M.M., McCormick, S.P., Busman, M., Ward, T.J., Kelly, A.C., O'Donnell, K., Johnston, P.R., Geiser, D.M. 2015. Fusarium dactylidis sp. nov., a novel nivalenol toxin-producing species sister to F. pseudograminearum isolated from orchard grass (Dactylis glomerata) in Oregon and New Zealand. Mycologia. 107(2):409-418.
Liang, J., Xayamongkhon, H., Broz, K.L., Dong, Y., McCormick, S.P., Abramova, S., Ward, T.J., Ma, Z.H., Kistler, H.C. 2014. Temporal dynamics and population genetic structure of Fusarium graminearum in the upper Midwestern United States. Fungal Genetics and Biology. 73:83-92.
Gomes, L.B., Ward, T.J., Badiale-Furlong, E., Del Ponte, E.M. 2015. Species composition, toxigenic potential and pathogenicity of Fusarium graminearum species complex isolates from southern Brazilian rice. Plant Pathology. 64(4):980-987.
Varga, E., Wiesenberger, G., Hametner, C., Ward, T.J., Dong, Y., Schofbeck, D., McCormick, S.P., Broz, K.L., Stuckler, R., Schuhmacher, R., Krska, R., Kistler, H.C., Berthiller, F., Adam, G. 2015. New tricks of an old enemy: isolates of Fusarium graminearum produce a type A trichothecene mycotoxin. Environmental Microbiology. 17(8):2588-2600.
Aamot, H.U., Ward, T.J., Brodal, G., Vralstad, T., Larsen, G., Klemsdal, S.S., Elameen, A., Uhlig, S., Hofgaard, I.S. 2015. Genetic and phenotypic diversity within the Fusarium graminearum species complex in Norway. European Journal of Plant Pathology. 142(3):501-519.
Scandiani, M.M., Luque, A.G., Razori, M.V., Ciancio Casalini, L., Aoki, T., O'Donnell, K., Cervigni, G.L., Spampinato, C.P. 2015. Metabolic profiles of soybean roots during early stages of Fusarium tucumaniae infection. Journal of Experimental Botany. DOI:10.1093/jxb/eru432.