Novel Sources of Resistance to Eastern Filbert Blight in Hazelnut

Eastern filbert blight (EFB), caused by the pyrenomycete Anisogramma anomala, is a serious threat to the hazelnut industry in the Pacific Northwest.  The fungus is endemic in the eastern United States where it occasionally produces small cankers on the wild American hazelnut (C. americana).  In contrast, most cultivars of the commercially important European hazelnut (C. avellana) are susceptible.  Recommended cultural practices including scouting, pruning out infected branches, and fungicide applications slow disease spread but are expensive.  Genetic resistance is the most promising control method.  Recent OSU releases carry a dominant allele for resistance from 'Gasaway'.  However, 'Gasaway' and some of its offspring have been infected by isolates from New Jersey, Minnesota, and Michigan.  There is an urgent need to find and study new sources of resistance.  We investigated 12 new sources of EFB resistance:  'Grand Traverse', C. heterophylla 'Ogyoo', 'Yoder #5', C. americana 'Rush', 'Uebov' and seven selections from a Forestry Institute in Moscow, Russia.  Seedling populations segregating for resistance were inoculated by either exposure of potted trees under a structure topped with diseased branches or greenhouse inoculation.  DNA extracted from these seedlings was amplified with primers for microsatellite markers on linkage group 6 (LG6).  Resistance from 'Grand Traverse' and C. heterophylla 'Ogyoo' was correlated with LG6 marker scores while resistance from 'Yoder #5' and 'Rush' was not.  Disease scores of seedlings segregating for resistance from 'Uebov' were correlated (r=0.72) with scores for the marker LG682-431, indicated that this resistance locus was also on linkage group 6.  Seven Moscow selections that remained free of EFB following greenhouse inoculation were crossed with susceptible parents and ~60 seedlings of each progeny were inoculated in the greenhouse.  Very few seedlings of Moscow selections N01, N01-06, and N01-07 remained free of disease and were likely escapes.  In contrast, seedlings of Moscow selections N23, N26, N27 and Moscow N37 segregated in a 1:1 ratio, indicating control by a single locus and a dominant allele for resistance.  Resistance from Moscow N26 appears to be on LG6, while resistance from N23, N27 and N37 was not correlated with an LG6 allele.  Resistance from these new sources will be mapped, and linked markers developed and used in pyramiding different resistance genes for durable EFB resistance.