Fusarium head blight (FHB) is a serious disease worldwide for small grains such as wheat and barley due to reduced yield and the contamination of grains with mycotoxins. The primary pathogen responsible for FHB in the United States is the fungus Fusarium graminearum. We propose to advance the knowledge of F. graminearum by mapping the genetic basis of variation in pathogenicity related traits that segregate in a natural population. Our long-term aim is to identify genes harboring functional variation that contributes to variation in important pathogen traits within emerging F. graminearum populations, such as pathogenicity, mycotoxin production, fungicide resistance, and other measures of fungal fitness, to provide targets for disease management. The identified genes will be used to select pathogen targets that are most appropriate for developing control strategies that will lead to strong and durable resistance to FHB. Our project objectives are to:1) Map the genetic basis of natural variation in 'pathogen potential' traits measured in laboratory experiments by using standard statistical methods for detecting associations between thousands of genetic variants and pathogen traits;2) Map the genetic basis of natural variation in plant-interaction traits in greenhouse experiments using the same genetic variants and statistical methods as in objective 1; and3) Confirm loci associated with variation in fungicide sensitivity and mycotoxin production using QTL mapping in multiple biparental populations.This proposal leverages genotyping results from our previous work and aims to clarify the connection between naturally occurring genotypic and phenotypic variation in F. graminearum. Our anticipated results will suggest targets for pathogen control and will lead to the development of markers for tracking the spread of more pathogenic lineages. Our population genomic approach will identify pathogen variants that contribute to their aggressiveness and potential for mycotoxin contamination, and this knowledge will lead to strategies to manage FHB outbreaks, reduce toxin contamination, and, through the development of simple genetic assays, predict outbreaks in new locations.