|KUHNEM, P. - Federal University Of Rio Grande Do Sul|
|SPOLTI, P. - Federal University Of Rio Grande Do Sul|
|SILVA, C. - University Of Maringa|
|CILIATO, M. - University Of Maringa|
|TESSMAN, D. - University Of Maringa|
|DEL PONTE, E. - Federal University Of Rio Grande Do Sul|
Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2015
Publication Date: 2/15/2016
Publication URL: http://handle.nal.usda.gov/10113/5479628
Citation: Kuhnem, P.R., Ward, T.J., Silva, C.N., Spolti, P., Ciliato, M.L., Tessman, D.J., Del Ponte, E.M. 2016. Composition and toxigenic potential of the Fusarium graminearum species complex from maize ears, stalks and stubble in Brazil. Plant Pathology. 65(7):1185-1191. doi: 10.1111/PPA.12497.
Interpretive Summary: Fungi within the Fusarium graminearum species complex (FGSC) are responsible for Fusarium head blight (FHB) of wheat, Fusarium ear rot (FER) of corn, and economically destructive diseases of other cereals world-wide. These fungi also contaminate grain with trichothecene mycotoxins that pose a significant threat to food safety and animal health. As part of a project to establish a global picture of FHB pathogen diversity, we determined the prevalence of FGSC species and toxin types associated with corn in Brazil, and also characterized the influence of ecological factors on the composition of pathogen species and toxin types. Brazil harbors substantially greater FGSC diversity than is present in the United States, making it an ideal location to study the ecological factors and cropping practices that influence the distribution of pathogen and toxin types. F. meridionale with the nivalenol toxin type predominated among isolates from corn in Brazil, whereas F. graminearum with the 15ADON toxin type, and F. asiaticum with the nivalenol toxin type were dominant on wheat and rice, respectively. These results indicate that despite being able to incite disease on a wide variety of cereals, substantial differences in host preference exist among these pathogens. In addition, the results of this study indicated that ecological factors are also important, as the prevalence of F. cortaderiae increased with increasing field elevation, and F. graminearum was found to have a significantly higher rate of radial growth than the other species at 25°C, but not at 15°C. These results are also a significant concern for food safety and animal health, because nivalenol is potentially more toxic than DON, which is more common and widely regulated. As such, the results reported here are critical to promoting food safety and cereal production through improved understanding of pathogen ecology and the influence of host and ecological factors on pathogen and toxin distributions.
Technical Abstract: Detailed knowledge of the composition and toxigenic potential of the Fusarium graminearum species complex affecting maize crops in Brazil is lacking. A multilocus genotype approach was used to identify 539 isolates from three sub-collections: 1) maize kernels (n= 110) from five states spanning south and central Brazil), 2) maize stalks (n=134) from Paraná (PR, south) state, and maize stubble (n=295) from Rio Grande do Sul (RS, south) state. Overall, three species were found, in order of prevalence: F. meridionale (Fmer) (67%) with the nivalenol (NIV) genotype, F. graminearum (Fgra) (19%) with the 15-acetyl(A)deoxnivalenol(DON) genotype, and F. cortaderie (Fcor) (14%) of the NIV (49/74) or the 3-ADON genotype (25/74). Similar frequencies of these species were found for the sub-collection from maize kernels, but while Fmer was distributed across all locations, Fgra and Fcor were found mostly in RS state. Among isolates from maize stalks, the vast majority (97.8%) was assigned to Fmer and only three isolates were assigned to Fgra. In the stubble collection, Fmer was less dominant (53%) compared to the other collections, and species composition varied across the 15 fields with a shift towards Fcor as the most frequent species at high elevation sites (>600m). No differences in growth rate were observed among the species at 15 oC. However, Fgra grew significantly faster than the other species at 25 oC in an in vitro mycelial growth assay, and Fmer showed the widest range of variation across the isolates at both temperatures. This is the first detailed report of FGSC composition in Brazilian maize showing that a NIV-producing species is the main pathogen of maize, further suggesting the risk of NIV contamination in grains. These results also provide additional evidence of host preference among FGSC members affecting commercial cereal crops in Brazil.