Genetic Diversity of Anisogramma anomala and Its Implications for Breeding Eastern Filbert Blight Resistant Hazelnuts

Eastern filbert blight (EFB), caused by the fungus Anisogramma anomala, is a major limiting factor to commercial hazelnut production in North America.  Until now, little work has been done to analyze the genetic diversity of the fungus, which is endemic to a wide area of the eastern United States and spread to the Pacific Northwest in the 1960s.  This lack of knowledge hampers current breeding efforts to develop plants expressing durable resistance to EFB.  The goal of this project was to elucidate the genetic diversity and population structure of A. anomala using simple sequence repeat (SSR) markers.  A total of 26 SSR markers were used to amplify 204 isolates of the fungus collected from throughout North America.  Cluster and population structure analyses were performed on the resulting peak data to discern the genetic diversity and relationships among both individuals and populations of isolates.  The SSR marker summary statistics showed an average of nine alleles per loci and an average expected heterozygosity of 0.72, which indicates that the isolates tested were more genetically diverse than was initially hypothesized for A. anomala based on prior internal transcribed spacer region sequence studies.  Further, the cluster and population structure analysis showed distinct genetic differences between populations of isolates collected from different regions, as well as evidence for the spread of distinct isolates from one region to another. The results of the cluster and population structure analyses and their possible implications in terms of breeding hazelnut plants expressing durable resistance will be discussed.