Population Differentiation Within in North America.

, a biotrophic ascomycete in the order Diaporthales, causes eastern filbert blight (EFB) of hazelnuts ( spp.). Until recently, little has been documented on its genetic diversity and population structure. In this study, 18 simple sequence repeat markers were used to fingerprint 182 accessions of the fungus originating from across North America. Our results, based on summary statistics of the allelic data, a discriminant analysis of principal components (DAPC) scatterplot, an unweighted pair group method with arithmetic mean (UPGMA) dendrogram, and analysis of multilocus genotypes, show that exhibits considerable genetic diversity across multiple populations. Eleven clusters were resolved from the DAPC scatterplot, five of which were validated by statistically supported clusters in the UPGMA dendrogram. The 11 DAPC clusters were statistically significant via an analysis of molecular variance. Dendrogram topology and DAPC scatterplot groups showed some correlation with collection origin; samples collected in proximity tended to cluster together and be genetically similar. However, some locations held populations that were diverse and some populations with a high degree of similarity had disparate origins, suggesting movement by humans. Overall, the results demonstrate the presence of multiple, genetically distinct populations of in North America and serve as a reference to assist in understanding and managing EFB.