Hazelnut (Corylus spp.) breeding

Hazelnut is an economically important tree nut whose production is mostly destined to the confectionery industry with a demand that currently exceeds supply. Its cultivation remains substantially based on named selections from local, wild vegetation. Public breeding programs were not initiated until the 1960s and only two, both in the USA, are in operation today that are relatively large. Oregon State University has produced new cultivars with Gasaway resistance to the fungus Anisogramma anomala, causal agent of eastern filbert blight (EFB), a major disease in North America; these cultivars are being widely planted. In China, cold-hardy hybrid cultivars from Corylus heterophylla and C. avellana were recently released and are planted in northeastern China. In the past 25 years, molecular markers have facilitated a much better understanding of genetic diversity in the genus Corylus, aided the construction of linkage maps and allowed for marker-assisted selection for disease resistance. The genome of C. avellana was sequenced and assembled, and DNA markers identified from the transcriptome, providing the basis for the isolation of important genes, including those related to nut quality and adaptive and phenological traits. Many new genotypes expressing eastern filbert blight (EFB) resistance have been identified in the germplasm, and subsequent linked DNA markers developed, allowing new approaches to breeding for durable resistance. Micropropagation is routinely used in the USA, Chile and Italy for multiplication, but work with other in vitro techniques is less advanced. Genetic engineering has not been developed in hazelnut due to regeneration difficulties from somatic tissues but recent advances have established a protocol for organogenesis. More research is being carried out to assemble a high-quality hazelnut genome and achieve somatic embryogenesis. The results from this research will provide knowledge and tools enabling the isolation of genes and molecular markers, and the application of genome editing techniques to hazelnut.