Progress breeding hybrid hazelnuts (Corylus americana × Corylus avellana) in the United States

The disease eastern filbert blight, caused by Anisogramma anomala, and poor adaptation to cold temperatures limits where European hazelnut (Corylus avellana) production can occur in the US. Since the early 1900s, breeders have turned to the wild American hazelnut (C. americana) as a donor for disease resistance and wider adaptation. However, interspecific hybridization efforts have been intermittent and early breeding efforts lacked genetic diversity, especially regarding the European parents. Further, instead of the selection and clonal propagation of improved hybrid cultivars, many nurseries chose to distribute open-pollinated, seed-derived planting stock to growers. While many of these seed-derived orchards have proved to be disease resistant and adapted to cold regions, they also had low average yields ha^-1 and poor-quality nuts. Thus, despite progress in developing adapted materials, early efforts did not result in commercially viable hybrid hazelnut cultivars. Over the past decade, however, the scenario has changed. Multiple organizations are now working earnestly toward the goal of developing widely-adapted commercial-quality cultivars. They include the Hybrid Hazelnut Consortium (HHC), comprising Rutgers University, Oregon State University, The University of Nebraska-Nebraska Forest Service, the Arbor Day Foundation, and the University of Missouri, as well as the Upper Midwest Hazelnut Development Initiative (UMHDI) that includes the University of Minnesota and the University of Wisconsin. Controlled breeding efforts, in addition to selection of improved individuals from the earlier established seed-derived orchards, are ongoing and yielding improved clonal plant materials. Multi-location yield trials have been established and new hybrid cultivars, like ‘OSU 541.147’ “The Beast™”, are being released with many improved selections in the pipeline. In this review, we discuss progress with hybrid hazelnut breeding by the HHC and UMHDI and outline future goals and approaches for the wide expansion of hazelnut production regions.