Hazelnut Pollenizers Affect Kernel Characteristics in European Hazelnuts (Corylus avellana)

Hazelnuts (Corylus sp.) are self-incompatible, monoecious, and wind-pollinated. They typically bloom in the winter and have cold hardy pistillate (female) flowers; however, their staminate (male) flowers can be damaged by freezing temperatures especially following winter warm spells. This is most pronounced in the commercial European species, C. avellana. Thus, a lack of cold-hardy pollenizers in a C. avellana orchard could lead to limited pollen production and low nut yields in regions with fluctuating winter temperatures. Interestingly, catkins of the wild American species C. americana and American x European hybrid selections have been found to have cold-tolerant catkins. Thus, despite poor nut characteristics, they have been considered for use as pollenizers in European hazelnut orchards to overcome frost damage issues. However, limited testing has been done to determine the effects of American and American x European hybrid pollen on the kernel characteristics of European cultivars. In March 2015, controlled crosses were made in duplicate between three European hazelnut mother trees (‘Yamhill’, ‘Santiam’, and H3R07P25) and six pollen parents (two Americana accessions, 2 Americana x European hybrids, and two European cultivars). All hazelnuts were harvested in August 2015, counted, dried, and a subset of 50 nuts was cracked out from each sample and evaluated. A subset of 20 kernels, rated as good, were then evaluated for sphericity, kernel weight, and kernel to percentage. The percentages of “good” kernels and averages for sphericity, kernel weight, and kernel percentage were analyzed across all crosses. A Fishers LSD test (P ≤.05) was run to determine if pollenizer and pollenizer x mother plant had a significant affect for each dependent variable. When the effects were found to be significant for a variable, pairwise comparisons of means were made within each mother plant. Results showed no seeds were set when using either American hazelnut parent as a pollenizer across all three European mother trees. However, similar seed set was found between the hybrid and European pollen parents. The data analysis showed significant differences between pollen sources in respect percentages of “good” kernels (freedom from defects). Thus, our preliminary results, based on this limited pool of parents, suggest wild American hazelnuts may have compatibility issues with European species. However, the American x European hybrid pollen parents tested resulted in similar seed set, nut and kernel characteristics as the European species and may prove to be useful, cold-hardy pollenizers.