Breeding hazelnuts resistant to eastern filbert blight
Eastern filbert blight (EFB) is a serious disease of European hazelnut (Corylus avellana) in North America. The causal agent is the pyrenomycete Anisogramma anomala, which is endemic in the eastern United States. The fungus occasionally produces small cankers on the wild American hazelnut (C. americana), but most European cultivars are susceptible. Infection leads to perennial cankers, girdling of branches, and premature tree death. Cultural practices including scouting, pruning out infected branches, and fungicide applications slow disease spread but are expensive. Resistance in Gasaway is conferred by a dominant allele at a single locus on linkage group 6 (LG6), and five candidate genes have been identified. Oregon State University released Jefferson, Yamhill, Dorris, Wepster and McDonald and several pollinizers carry Gasaway resistance. Oregon growers have planted resistant cultivars and pollinizers, and plantings have expanded from 11,700 ha in 2009 to 24,000 ha in 2017. We are concerned that Gasaway resistance could be overcome by isolates now present in the eastern states or that a new race of the pathogen could arise in Oregon. In cooperation with Rutgers University, we continue to evaluate hazelnut germplasm, identify EFB-resistant selections, characterize them, and use them in breeding. More than 100 resistant accessions have been identified to date. EFB resistance from ten sources has been assigned to three different LGs. Resistance from six sources maps to LG6: Gasaway, OSU 408.040 (Minnesota), Culpla (Spain), Crvenje, Uebov (Serbia), and OSU 495.072 (southern Russia). Resistance from three sources maps to LG7: Ratoli (Spain), Yoder #5 (Ohio) and C. americana Rush. Resistance from Georgian OSU 759.010 maps to LG2. Many cases of segregation distortion have been noted, resulting in deviations from the expected 50% resistant seedlings. Different sources of resistance could be combined, hopefully leading to durable resistance that would sustain the industry in Oregon and allow expansion to new areas. Quantitative resistance, expressed as less infection, fewer cankers and smaller cankers is also useful and heritable.
Mehlenbacher, S.A. (2018). Breeding hazelnuts resistant to eastern filbert blight. Acta Hortic. 1226, 73-78
Corylus avellana, Anisogramma anomala, marker-assisted selection, quantitative resistance