Breeding hazelnuts resistant to eastern filbert blight

S.A. Mehlenbacher, B.J. Heilsnis, R.T. Mooneyham, J.W. Snelling
Eastern filbert blight (EFB) is caused by the ascomycete Anisogramma anomala, which is endemic to the eastern United States where it causes little damage to the wild Corylus americana but causes severe cankers on most cultivars of the commercially important European hazelnut, Corylus avellana. Unfortunately, the fungus was introduced to the Pacific Northwest (USA) and is now present throughout Oregon’s Willamette Valley where 99% of the US hazelnut crop is produced. Host genetic resistance was first noted in the pollinizer ‘Gasaway’ and resistance was later shown to be conferred by a dominant allele at a single locus on linkage group 6 (LG6). Many new orchards were planted following the release of resistant cultivars by Oregon State University, including several for the blanched kernel market, and the area increased from 12,000 ha in 2009 to 35,000 ha today. Two RAPD markers have been used for marker-assisted selection for ‘Gasaway’ resistance for the past 25 years. Some fungal isolates in the eastern USA can overcome ‘Gasaway’ resistance, prompting a search for other sources of resistance. More than 100 highly resistant accessions have been identified from diverse origins, and major resistance genes mapped using simple sequence repeat (SSR) markers, and placed on LGs 6, 2 and 7. SSR markers allow the pyramiding of major resistance genes. The breeding program also uses quantitative resistance and has identified dozens of selections with few and smaller cankers. Quantitative resistance is heritable and is considered more durable. The genome sequence of ‘Jefferson’, which carries ‘Gasaway’ resistance, serves as our reference. We sequenced the genomes of a dozen others with different resistance genes using Pacific Biosciences technology, and diversity panels of C. avellana and C. americana using Illumina technology. These genome sequences will be useful in developing new markers for fine mapping resistance regions and studying important traits. With improved knowledge of the pathogen over the past 35 years, and our expanded collection of hazelnut genetic resources, we anticipate release of additional resistant cultivars for the kernel and in-shell markets.
Mehlenbacher, S.A., Heilsnis, B.J., Mooneyham, R.T. and Snelling, J.W. (2023). Breeding hazelnuts resistant to eastern filbert blight. Acta Hortic. 1362, 557-562
DOI: 10.17660/ActaHortic.2023.1362.75
hazelnut, filbert, Corylus avellana, Anisogramma anomala, disease resistance, nut breeding

Acta Horticulturae