Micropropagation and selection of Corylus colurna rootstock genotypes

The removal of suckers from the base of self-rooted European hazelnut (Corylus avellana) plants in orchards is a costly agronomic practice. Grafting of European hazelnut on rootstocks of the Turkish hazelnut Corylus colurna is gaining increasing interest due to its reduced or absent production of suckers, that results in reduced cultivation costs and increased sustainability of orchards. Grafting of hazelnut is most performed on C. colurna seedlings while the selection and the availability of clonal C. colurna rootstocks are hampered by the difficulties in the propagation of this species by cuttings or mound layering. To address these challenges, we have adopted a large-scale systematic in vitro transfer of C. colurna genotypes from both explants and seeds. From two main areas (North of Italy and Serbia), 37 C. colurna genotypes were selected and transferred in vitro. After five subcultures, the most performing genotypes are currently being selected based on their multiplication rate, rooting ability, and grafting compatibility with the three Italian C. avellana varieties Tonda Gentile delle Langhe, Tonda Giffoni, and Nocchione. Preliminary results indicate that the multiplication rate of different genotypes becomes homogeneous over time, while the rooting rate is highly variable and strongly dependent on the genotype, ranging between a minimum of 54% and a maximum of 97%. Preliminary experiments showed that green grafting success rates between two genotypes of C. colurna used as rootstocks and the three main Italian varieties are promising, with some graft combinations reaching up to 80% of successful take. Further optimization of the ex vitro acclimatization and of the grafting techniques is ongoing to enhance the pipeline of grafted hazelnuts. The successful selection and characterization of new clonal genotypes of C. colurna could represent an important resource for both the hazelnut industry and the scientific research.