‘Gasaway' Source of Resistance to Eastern Filbert Blight Provides a Predictable Level of Tolerance but Not Complete Resistance in New Jersey

The disease eastern filbert blight (EFB), caused by the fungus Anisogramma anomala, limits hazelnut (Corylus avellana) production in North America.  Further, its management causes significant expense in Oregon, where 99% of the U.S. crop is grown.  The development and use of resistant cultivars is considered to be the most effective management strategy.  In the 1970s, ‘Gasaway’, a late-flowering pollinizer, was found to be resistant to EFB in the Pacific northwestern U.S.  It was later shown to carry a dominant allele at a single locus in a heterozygous state that conferred resistance to its offspring in a predictable Mendelian pattern.  ‘Gasaway’ was subsequently used in breeding at Oregon State University.  A number of improved, EFB-resistant cultivars have since been released, several which are now being widely planted in Oregon.  To examine the usefulness of the ‘Gasaway’ source of resistance in New Jersey where climatic conditions and isolates of the pathogen differ, clonal trees of ‘Gasaway’ and its offspring ‘Delta’, ‘Epsilon’, ‘Gamma’, ‘Jefferson’, ‘Santiam’, ‘Theta’, VR20-11, ‘Yamhill’, and ‘Zimmerman’ were evaluated, with some being observed for over a decade.  Further, a total of 32 full-sibling progenies representing 1339 plants segregating for ‘Gasaway’ resistance were also evaluated.  Here we present a comprehensive summary of our observations on the ‘Gasaway’ related plants.  Our results strongly show that the single dominant allele continues to provide a useful and predictable level of high tolerance (not complete resistance) inherited in a simple Mendelian pattern.  However, yet-to-be described modifying genes/factors support the final phenotype, which can range from completely resistant to only moderately tolerant.  Until the modifying factors are elucidated, long-term field evaluation and selection remains necessary to identify recombinants that express the highest levels of resistance.