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Eastern filbert blight (EFB), caused by the fungus Anisogramma anomala, is the primary limiting factor to growing European hazelnuts, Corylus avellana, in New Jersey and much of the eastern United States. Anisogramma anomala is native to North America where it is found naturally occurring on populations of the wild American hazelnut, Corylus americana. While infection by A. anomala causes little damage to the wild American hazelnut, it causes severe cankering, branch dieback, and frequently death of its European relative. Consequently, previous attempts at commercial hazelnut production failed in the east, however, hazelnuts were found to thrive in coastal Washington and Oregon and this area quickly became the center of the United States hazelnut industry. This success was due to being outside the native range of A. anomala as well as having a maritime climate well suited for many available European commercial cultivars. Currently, the United States is ranked 3rd in world production, producing 3.4 % of the world crop behind Turkey (66.9 %) and Italy (17.3 %), with 99% of the United States crop grown in the Willamette Valley of Oregon. Recent major advances in hazelnut genetics and breeding, expanded germplasm resources, and a greatly improved understanding of eastern filbert blight have set the stage for the dramatic expansion of hazelnut culture throughout eastern North America. The goal of the work presented in this dissertation was to contribute to these advances in support of developing an efficient and effective hazelnut genetic improvement program at Rutgers University. This includes efforts to: (1) develop a better understanding of A. anomala's pathogenic variation and the broad-based usefulness of available sources of host resistance; (2) survey a new and diverse collection of hazelnut germplasm from the Russian Federation and the Crimean peninsula of Ukraine for response to inoculation with A. anomala, in an effort to identify new sources of high genetic resistance to the disease; (3) develop an accelerated disease screening technique to more efficiently identify genotypes highly resistant to EFB; and (4) initiate population improvement programs to develop superior cultivars and to demonstrate the opportunities for substantial long-term genetic improvement of hazelnuts.
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