2019 ASHS Annual Conference

Two limiting factors of European hazelnut (Corylus avellana) cultivation in the northeastern US are the disease eastern filbert blight (EFB) and lack of cold hardiness of catkins (male flowers). Several EFB-resistant C. avellana breeding selections have been developed at Rutgers University and are near the point of commercial release; however, cold-hardy disease-resistant pollenizers have not yet been developed. Hazelnuts are monoecious, wind-pollinated, and self-incompatible. Therefore, more than one compatible genotype must be planted in an orchard for successful nut set. Clonal pollinizers that possess both cold hardiness and high quality nuts are desirable for the long term success of an eastern hazelnut industry. Their pollen shed period must also overlap the exertion of pistillate blooms of the main nut producing genotype(s) in the orchard. One approach to developing these plants is to utilize the native American hazelnut, C. americana, which is adapted to very cold regions, as both a donor of EFB resistance and cold hardiness of catkins. In this study, a large population of C. avellana × C. americana F₁ and advanced generation hybrids planted in 2012 were evaluated for response to EFB, nut and kernel qualities, and relative numbers of catkins/catkin health (lack of winter injury). Out of a population of over 2,300 trees from more 30 controlled crosses, 60 superior trees were selected from 16 progenies. These 60 selections were observed twice per week over winter 2018/2019 for phenology of male and female flowers and vegetative bud break in comparison to a panel of known European hazelnut cultivars. Results showed that the hybrid selections, while largely free from winter damage, were highly variable in their timing of pollen shed. A number of the selections appeared to bloom too late to provide adequate pollen coverage for most European hazelnuts. However, a subset bloomed at the correct time according to this year’s flowering period and included early-, mid-, and -late blooming options for European hazelnuts. These selections will evaluated for phenology again in 2020, with their S-alleles identified, pollen fertility examined, and the most promising clonally propagated and tested in multiple locations including New Jersey, Nebraska, Wisconsin, and Minnesota.