Eastern Filbert Blight Susceptibility of American × European Hazelnut Progenies

Abstract

Eastern filbert blight (EFB), caused by Anisogramma anomala, is a devastating disease of Corylus avellana, the European hazelnut of commerce, and is considered the primary limiting factor of production in eastern North America. Conversely, C. americana, the wild American hazelnut, is generally highly tolerant of EFB, although it lacks many horticultural attributes necessary for commercial nut production. Hybrids of C. americana and C. avellana combine the EFB resistance of the wild species with the improved nut quality of the European species. However, inheritance of EFB resistance from C. americana remains unclear with existing hybrids derived from a very limited selection of parents. To investigate this topic, C. americana and advanced-generation C. americana × C. avellana hybrids were crossed with susceptible C. avellana and the resulting seedlings exposed to EFB through field inoculations and natural disease spread. In the winter after their fifth growing season, plants were rated for the presence of EFB using an index of 0 (no disease) through 5 (all stems containing cankers). The three progeny related to C. americana ‘Rush’ segregated for resistance in a ratio of one resistant to one susceptible, suggesting the presence of a single dominant R gene. A wide array of disease responses was observed for the other progenies with some expressing little EFB resistance or tolerance and others showing a distribution of disease phenotypes typical of control by multiple genes. Overall, the results indicate that both qualitative and quantitative resistance is present in C. americana. They also suggest that the choice of C. americana parent as well as the C. avellana parent will play a significant role in obtaining useful levels of EFB resistance in hybrid offspring, although the degree of disease expression in the parents may not be a useful predictor of progeny performance. Thus, more research is needed to understand inheritance of resistance, especially in advanced-generation backcrosses to susceptible C. avellana.