ANALYSIS OF RESISTANCE TO EASTERN FILBERT BLIGHT IN CORYLUS-AVELLANA

Inheritance of resistance to eastern filbert blight, caused by Anisogr amma anomala, in European hazelnut (Corylus avellana) was evaluated in the progeny of seven cultivars crossed in 12 combinations. The progen y 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 gree nhouse and the field, progeny produced by crossing VR6-28 with three s usceptible cultivars segregated 1:1 for complete resistance to eastern filbert blight, confirming a previous report that VR6-28 is heterozyg ous for a single, dominant resistance gene. Histograms of disease resp onses in progeny of the remaining six parents showed continuous distri butions for all crosses examined. Consequently, these parents were ana lyzed for general and specific combining abilities for each disease re sponse. In the field, general and specific combining ability were both significant (P < 0.05) for all disease responses, with general combin ing ability having twice the magnitude of specific combining ability. These results suggest these disease responses are controlled by additi ve 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 paren ts, Gem and Tonda di Giffoni, and the seed parent, Willamette. Heritab ility 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 pa rents to breed for hazelnuts exhibiting fewer and smaller cankers.