2019 ASHS Annual Conference

New disease-resistant hazelnut cultivars should allow for European hazelnut (Corylus avellana) production in the northeastern U.S. where eastern filbert blight (EFB) previously prevented the establishment of a commercial industry. While these EFB-resistant cultivars are adapted to a wide area, their male flowers (catkins) can be damaged by mid-winter cold in some regions, limiting the amount of pollen shed and reducing nut yields. Female flowers are considerably more cold-hardy, but elongated catkins are quite tender. Fortunately, the wild American hazelnut (Corylus americana), native to the eastern half of the United States and parts of southern Canada, is cross-compatible with the European hazelnut and is much less susceptible to catkin cold injury. However, female receptivity and pollen shed times differ between the species, and among selections within each species, and the incompatibly alleles of C. americana selections have not been identified. In this study, we investigated the feasibility of using American hazelnut selections as pollenizers for European hazelnut orchards. Previous work at Rutgers University identified selections of EFB-resistant, cold-hardy, American hazelnuts with large numbers of catkins and a range of pollen shedding times that spanned most of the pistillate flower receptivity period of the European hazelnut. A geographically diverse subset of these C. americana selections (n=15) were used in controlled crosses with diverse selections of C. avellana. Hazelnuts show sporophytic incompatibility, which is controlled by a single locus with 33 known alleles. Incompatibility testing was performed using fluorescence microscopy. Pollen collected from the American selections was evaluated for viability and used in controlled crosses on replicated clones of C. avellana, with C. avellana pollens used as controls for comparison. The percentage of cluster set (ratio of nuts set to females pollinated) was calculated for each pollen parent, and the physical appearance and defect percentages for each pollen source were noted for each female parent. These data, in combination with flowering phenology notes, identified S-alleles, and pollen viability data, will help determine the feasibility of American hazelnut selections as pollenizers in European hazelnut orchards, and possibly identify superior clones for this purpose for the emerging industry.