Improvement of asexual propagation and Anisogramma anomala detection protocols to facilitate applied breeding of new Corylus avellana and C. americana x C. avellana germplasm

Though hazelnut (Corylus L.) breeding has a long history, the discipline is still in the early stages of its development. Global hazelnut production continues to rely on wild selections and local cultivars in many countries. The lack of new cultivar development is a consequence of underutilization of the wide genetic diversity that exists within the genus and an exceptionally long breeding cycle. This cycle requires a minimum of eight years from seed to seed (generation time) and an additional nine years for selected individuals to proceed through replicated performance trials to cultivar release. At present, layering techniques are the primary method for asexual propagation of Corylus selections during the breeding cycle. While effective, that technique is relatively archaic and yields of successful cuttings are low. Propagation by cuttings provides an alternative with a higher production potential; however, variable root induction rates and bud abscission among traditional Corylus cultivars currently limit this approach. A recent study suggests use of ethylene-blocking compounds in combination with low auxin levels may help overcome these challenges. Presently, the efficacy of these treatments is known for only a narrow selection of C. avellana genotypes. In addition to working to overcome challenges associated with propagation, breeding efforts have expanded germplasm collections to increase sources of eastern filbert blight (EFB) resistance. Screening for EFB resistance greatly complicates breeding efforts because Anisogramma anomala (the causal pathogen of EFB) contains notable genetic and pathogenic variation. Screening U.S. collections for EFB resistance is largely done by phenotyping, which is problematic because A. anomala has a 12- to 16-month symptomless latent period that delays the culling of susceptible plants. Refinement of recently developed real-time polymerase chain reaction (PCR) protocols that provide early detection of EFB susceptible seedlings would greatly improve the capacity and pace of cultivar development. This thesis focuses on ways to increase breeding efficiency by improving: 1) protocols used to propagate stem cuttings and, 2) early detection of EFB susceptibility in seedling populations. A hybrid hazelnut (C. americana x C. avellana) progeny population was used in two experiments to observe adventitious rooting and bud abscission after treatment with low indole-3-butyric acid (IBA) (≥1000 ppm) and low IBA plus ethylene-inhibiting silver nitrate. Using subterminal softwood stem cuttings, adventitious root formation occurred at a rate of 62% or greater and bud abscission was not observed in either experiment. These results indicate adventitious rooting of softwood stems cuttings is a promising method for hybrid hazelnut breeders to use. To address the EFB screening bottleneck, a real-time PCR protocol for A. anomala detection in stem tissue was adapted by increasing the size of stem tissue sampled by 2-3 fold. This modification allowed for successful detection of anomala infection in symptomless seedlings 30 days after inoculation. Detection success was not improved by later (55 and 90 days) sampling. In addition to improving early diagnosis of A. anomala infection, this assay could be used to study A. anomala growth and development following infection