Hazelnut Accessions from Russia and Crimea Transmit Resistance to Eastern Filbert Blight

Abstract

Eastern filbert blight (EFB), caused by the fungus Anisogramma anomala, severely restricts production of European hazelnuts ( Corylus avellana) in North America. The planting of EFB-resistant cultivars is considered to be the most effective disease management strategy. In 2002, a seed-based germplasm collection was made in Russia and Crimea to add diversity to the U.S. hazelnut collection and search for new sources of resistance. The resulting seedlings were grown and evaluated in both Oregon and New Jersey—in Oregon, seedlings were first evaluated for horticultural traits (i.e., nut and kernel characteristics, yield) with improved selections later subjected to the EFB pathogen, whereas in New Jersey, all seedlings were first exposed to EFB with the horticultural traits of the survivors examined later. From a total of 1299 seedlings grown in Oregon, 68 Russian and 29 Crimean improved selections were identified. In this study, they were clonally propagated and evaluated for disease response after being exposed to A. anomalathrough greenhouse inoculations and/or exposure under a structure topped with diseased wood. Out of 1,285 seedlings planted in New Jersey, nearly all died from EFB; however, ~70 resistant or highly tolerant trees were identified. As part of this study, 11 improved EFB-resistant seedlings were selected and crossed with susceptible male parents to examine inheritance of resistance. Fourteen progenies represented by 1,584 seedlings were field planted in 2010 and 2011, annually exposed to high levels of A. anomala,and evaluated for EFB response in January 2015. A rating scale of 0 (no signs or symptoms of EFB) to 5 (all stems containing cankers) was used. Results in Oregon showed that three selections from Russia and one from Crimea remained free of disease after multiple exposures. In New Jersey, all eleven accessions transmitted resistance to a useful number (24% to 59%) of their offspring. Interestingly, all progenies showed a clear bimodal distribution of resistant (rating = 0) and highly susceptible trees (rating = 4 or 5) with few intermediate individuals, which indicates genetic control by one or a small number of major genes. The proportions of resistant trees differed among the accessions, with five parents producing progenies that segregated in a ratio of 1 resistant: 1 susceptible, four in a ratio of 1 resistant: 3 susceptible, and two producing an abundance of resistant seedlings. Additional work, including R-gene mapping, is needed to examine whether or not these selections represent different R-genes. Overall, our findings highlight and document the value of the new hazelnut germplasm from Russia and Crimea which holds substantial promise for the breeding of improved cultivars.