Population Structure Analysis of Eastern Filbert Blight Resistant Hazelnut (Corylus spp.) Germplasm

Eastern filbert blight (EFB) severely limits hazelnut production in the eastern U.S., and its spread to Oregon's Willamette Valley now threatens the primary U.S. commercial hazelnut production region.  Work is currently being done at Rutgers University to develop commercially acceptable hazelnut cultivars with durable resistance to this disease.  An important goal of the breeding program is the maintenance of genetic diversity within the breeding lines, which can be assessed using simple sequence repeat (SSR) markers.  In this study, 170 newly selected EFB-resistant and tolerant seedlings from foreign germplasm collections, as well as 178 reference cultivars including EFB-resistant breeding selections representing a wide spectrum of geographic origins, were analyzed using 17 genomic SSR markers.  Genetic analysis was performed using the program STRUCTURE 2.3.3 to confirm prior cluster analysis results, as well as to discern the most parsimonious number of populations present within the hazelnut germplasm.   Results of the analysis grouped hazelnuts into 11 populations, and an AMOVA performed using GenAlEx 6.5 showed that the post-facto groups were all significantly different (P ≤ 0.001).  This analysis sheds light on the relationships of the new EFB-resistant seedlings in comparison to known sources of resistance and other reference cultivars.  Knowing these relationships can allow breeders to better utilize and maintain a high level of genetic diversity in their EFB-resistance breeding efforts.