2013 ASHS Annual Conference

Eastern filbert blight (EFB), caused by the fungus Anisogramma anomala, has prevented the development of European hazelnut (Corylus avellana) orchards in the eastern U.S. and causes economic losses in the Willamette Valley of Oregon, the center of commercial production.  The first European hazelnut cultivar identified with resistance to this disease was Gasaway, a late-blooming pollinizer that produces low yields of tiny nuts.  Despite its horticultural deficiencies, ‘Gasaway’ was shown to pass resistance to its offspring in a ratio of one resistant to one susceptible, which is indicative of a dominant allele in the heterozygous state at a single locus.  Since then, ‘Gasaway’ has been widely used in breeding at Oregon State University, Corvallis, OR, and new resistant cultivars are being planted on a large scale in Oregon.  However, in addition to the concern of using only a single gene for resistance in breeding, ‘Gasaway’ and its subsequently improved offspring were identified as being resistant in Oregon, a region where the fungus is not native.  Its initial introduction can be traced back to a single location in southwest Washington in the 1960s.  To examine the durability of the ‘Gasaway’ R-gene, many trees of ‘Gasaway’, its advanced-generation offspring (‘Jefferson’, ‘Yamhill’, ‘Theta’, ‘Zimmerman’, etc.), and several thousand progeny from controlled crosses expected to segregate for the R-gene, were evaluated over the past decade at Rutgers University, New Brunswick, NJ, a region with a different climate than Oregon and more diverse, endemic populations of A. anomala.  Overall, more EFB was found on these plants than was expected from previous studies in Oregon.  In this presentation, summarized results of multiple, replicated greenhouse inoculations and clonal and seedling field trials will be discussed, and supplemented by a recent population diversity study completed on A. anomala.  While EFB cankers were shown to develop on most trees containing the ‘Gasaway’ R-gene, cumulative evidence suggests the R-gene continues to provide a significant level of tolerance to native populations of A. anomala under high disease pressure.  Results also suggest that additional genetic factors/modifying genes are present that may be affected by environmental conditions and/or isolates of the fungus.  The presence or absence of these yet-to-be characterized genetic factors is likely playing a significant role in the differential phenotypes observed with plants known to contain the ‘Gasaway’ R-gene.