S01 - Session O10 - Breeding hazelnuts for resistance to eastern filbert blight

Authors: Shawn A. Mehlenbacher *

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 into the Pacific Northwest (USA) and is now present throughout Oregon's Willamette Valley where 99% of the U.S. 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 the 'Gasaway' resistance for the past 25 years. Some fungal isolates 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 have been mapped to LGs 2, 6 and 7 using simple sequence repeat (SSR) markers, which allow the pyramiding of major resistance genes. The breeding program also uses quantitative resistance and has identified dozens of selections with fewer 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. The genomes of a dozen others with different resistance genes have been sequenced and their EFB resistance regions have been aligned. Our knowledge of the pathogen and collection of genetic resources have improved over the past 35 years. We anticipate the release of additional resistant cultivars for the kernel and in-shell markets.