|DEL PONTE, EMERSON - Federal University Of Rio Grande Do Sul|
|SPOLTI, PIERRE - Federal University Of Rio Grande Do Sul|
|GOMES, LARISSA - Federal University Of Rio Grande Do Sul|
|NICOLLI, CAMILA - Federal University Of Rio Grande Do Sul|
|KUHNEM, PAULO - Federal University Of Rio Grande Do Sul|
|SILVA, CLEILTAN - University Of Maringa|
|TESSMANN, DAURI - University Of Maringa|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2014
Publication Date: 2/1/2015
Publication URL: http://handle.nal.usda.gov/10113/60525
Citation: 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.
Interpretive Summary: Fungi within the Fusarium graminearum species complex (FGSC) are responsible for Fusarium head blight (FHB) of wheat 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 toxins associated with FHB infected wheat in Brazil, and also characterized the influence of ecological factors and cropping practices on FHB pathogen and toxin composition in different regions and within individual fields. Species and toxin diversity was significantly greater than observed within the United States, and the NIV toxin type was a more significant component of the population in regions of Brazil with relatively higher acreage devoted to corn. This is a significant concern for food safety and animal health, because NIV is considered more toxic than DON, which is more common. In addition, we demonstrated that corn stubble within a field was not the primary source for fungi causing FHB infections in that field, that some FHB species are more competitive pathogens of wheat than other species, and that pathogen and toxin composition was influenced by field elevation above sea level. However, the previous crop (corn or soybean) did not influence FHB pathogen populations. Taken together, the data presented here suggest that host preference and ecological adaptation may regulate FHB pathogen composition and toxin contamination in wheat. 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 regional and field specific factors on FHB severity and toxin exposure potential.
Technical Abstract: A multiyear survey of >200 wheat fields in Paraná (PR) and Rio Grande do Sul (RS) states was conducted to assess the extent and distribution of Fusarium graminearum species complex (FGSC) diversity in the southern Brazilian wheat agroecosystem. Five species and three trichothecene genotypes were found among 671 FGSC isolates from Fusarium head blight (FHB)-infected wheat heads: F. graminearum (83%) of the 15-acetyldeoxynivalenol (15-ADON) genotype, F. meridionale (12.8%) and F. asiaticum (0.4%) of the nivalenol (NIV) genotype, and F. cortaderiae (2.5%) and F. austroamericanum (0.9%) with either the NIV or the 3-ADON genotype. Regional differences in FGSC composition were observed, with F. meridionale and the NIV type being significantly (P < 0.001) more prevalent in PR (>28%) than in RS (=9%). Within RS, F. graminearum was overrepresented in fields below 600 m in elevation and in fields with higher levels of FHB incidence (P < 0.05). Species composition was not significantly influenced by previous crop or the stage of grain development at sampling. Habitat-specific differences in FGSC composition were evaluated in three fields by characterizing a total of 189 isolates collected from corn stubble, air above the wheat canopy, and symptomatic wheat kernels. Significant differences in FGSC composition were observed among these habitats (P < 0.001). Most strikingly, F. meridionale and F. cortaderiae of the NIV genotype accounted for the vast majority (>96%) of isolates from corn stubble, whereas F. graminearum with the 15-ADON genotype was dominant (>84%) among isolates from diseased wheat kernels. Potential differences in pathogenic fitness on wheat were also suggested by a greenhouse competitiveness assay in which F. graminearum was recovered at much higher frequency (>90%) than F. meridionale from four wheat varieties inoculated with an equal mixture of F. graminearum and F. meridionale isolates. Taken together, the data presented here suggest that FGSC composition and, consequently, the trichothecene contamination in wheat grown in southern Brazil is influenced by host adaptation and pathogenic fitness. Evidence that F. meridionale and F. cortaderiae with the NIV genotype are regionally significant contributors to FHB may have significant implications for food safety and the economics of cereal production.