Assessment of the ‘Gasaway’ source of resistance to eastern filbert blight in New Jersey

The disease eastern filbert blight (EFB), caused by Anisogramma anomala, severely limits hazelnut (Corylus avellana) production in North America. In the 1970s, ‘Gasaway’, a late-flowering pollenizer, was found to be resistant to EFB in the Pacific northwestern U.S., and to transmit its resistance in a predictable Mendelian pattern. Its subsequent use in breeding at Oregon State University led to the release of a number of EFB-resistant cultivars, including Jefferson, Yamhill, Dorris, Wepster, and McDonald, which are now being widely planted across the Willamette Valley of Oregon. However, some cultivars carrying the ‘Gasaway’ R-gene develop EFB in New Jersey. Thus, the utility of this resistance source for breeding plants adapted to the eastern U.S has not been fully evaluated. In this study, we examined the EFB response of seedlings from 31 different full-sib progenies expected to segregate for the ‘Gasaway’ R-gene. Trees were exposed to the disease over at least 5 years and evaluated on a scale of 0 to 5 (0 = resistant, 5 = highly susceptible). In general, we found the number of seedlings free of EFB (class 0) to be less than expected based on prior work in Oregon, but resistant individuals were identified in each progeny, indicating the presence of heritable resistance. When disease response classes 0, 1, and 2 were combined (resistant through highly tolerant) and considered as “resistant”, the expected ratio of resistant to susceptible trees was recovered, signifying that the single dominant allele alone continues to provide a predictable level of at least tolerance. Modifying genes/factors appear to play a role in the final disease response of the individual seedling. It is thus hypothesized that some cultivars selected as resistant in Oregon that develop cankers in New Jersey may lack the necessary modifying genetic factors for full protection in the east. Until these modifying genes are elucidated, long-term field evaluation remains necessary to identify selections that carry the ‘Gasaway’ R-gene and express a high level of resistance to EFB in the eastern U.S.