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Analysis of Resistance to Eastern Filbert Blight in Corylus avellana

Inheritance of resistance to eastern filbert blight, caused by Anisogramma anomala, in European hazelnut (Corylus avellana) was evaluated in the progeny of seven cultivars crossed in 12 combinations. The progeny were subjected to inoculation with A. anomala in the greenhouse and in the field. Three disease responses were measured: disease incidence, number of cankers, and proportion of wood diseased. In both the greenhouse and the field, progeny produced by crossing VR6-28 with three susceptible cultivars segregated 1:1 for complete resistance to eastern filbert blight, confirming a previous report that VR6-28 is heterozygous for a single, dominant resistance gene. Histograms of disease responses in progeny of the remaining six parents showed continuous distributions for all crosses examined. Consequently, these parents were analyzed for general and specific combining abilities for each disease response. In the field, general and specific combining ability were both significant (P < 0.05) for all disease responses, with general combining ability having twice the magnitude of specific combining ability. These results suggest these disease responses are controlled by additive gene action in the cultivars examined, with nonadditive gene action being of some importance. Based on general combining ability values, high levels of partial resistance were transmitted by the pollen parents, Gem and Tonda di Giffoni, and the seed parent, Willamette. Heritability of disease incidence, number of cankers, and proportion of wood diseased were calculated to be 0.21, 0.39, and 0.47, respectively, for this set of nine crosses after the first exposure period in the field. This suggests that it will be possible to use partially resistant parents to breed for hazelnuts exhibiting fewer and smaller cankers.