2019 ASHS Annual Conference

Eastern filbert blight (EFB), caused by Anisogramma anomala, is a primary limiting factor of hazelnut cultivation in North America. The fungus, native to the eastern US and southern Canada, causes severe stem cankers and branch die-back on susceptible plants, which includes most cultivars of European hazelnut, Corylus avellana. Fortunately, the pollenizer ‘Gasaway’ was identified as resistant in the 1970s and found to transmit a dominant allele at a single locus that confers resistance to EFB. To date, ‘Gasaway’ has been used in breeding at Oregon State University to develop improved, EFB-resistant cultivars for the Oregon hazelnut industry, which produces 99% of US hazelnuts. However, research at Rutgers University showed that some of the ‘Gasaway’ protected plants, while remaining resistant in Oregon, developed EFB in the field in New Jersey. Fortunately, most infections remained minor, with reduced canker lengths and fewer cankers per stem compared to known susceptible plants. This scenario changed dramatically in 2016 when multiple ‘Gasaway’ protected plants were found to express a high number of large cankers. The following two years confirmed this apparent change in response to EFB, with many trees, including ‘Gasaway’ itself, showing significant amounts of disease unlike that previously reported. To examine this observation more critically, controlled inoculations were performed using A. anomala collected from these large cankers and applied to replications of five cultivars (Yamhill, Jefferson, Dorris, McDonald, and Felix) that carry the R-gene. A similar control population was exposed to A. anomala using inoculum collected from known susceptible trees lacking the R-gene. Results showed that 87% of the trees exposed to the “Gasaway” inoculum expressed EFB. This is in contrast to only 20% of trees exposed to the “general” inoculum developing cankers. Further, the average proportion of disease wood of the infected trees in the “Gasaway” inoculum group was 21.7%, whereas the proportion of disease wood in the “general” inoculum group was only 6.7%. Finally, the average canker length of the “Gasaway” and “general” group was 30.1 cm and 9.7 cm, respectively. These results strongly suggest a difference in virulence between the two sources of inoculum, and when combined with the field observations, suggest that a ‘Gasaway’- virulent strain of A. anomala is now present in New Jersey that greatly reduces the effectiveness of the R-gene. A second round of the study, supported by DNA fingerprinting of the fungus, is underway.