Graduate Thesis Or Dissertation

 

Genetic variability in the eastern filbert blight pathosystem Pubblico Deposited

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  • The heritability 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. Progeny produced by crossing 'VR6-28' with three susceptible cultivars segregated 1:1 for complete resistance to eastern filbert blight. Histograms of disease responses in progeny of the remaining six parents showed continuous distributions for all crosses examined, thus general and specific combining ability values were calculated for each parent. Based on general combining ability values, high levels of partial resistance were transmitted by 'Gem', 'Tonda di Giffoni' and '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, suggesting that hazelnuts with fewer, smaller cankers can be bred from partially resistant parents. Variation in the ITS region was examined in 67 isolates of A. anomala collected from five geographically separated infection centers in Oregon and Washington. Sixty-six isolates yielded a PCR product 649 by in length. Fourteen restriction sites, three of which were polymorphic, were found in the ITS region, but little sequence divergence was observed between isolates within (-2%) and among (-2%) infection centers. The ITS sequence of A. anomala was most closely related to those of diaporthaceous pathogens of woody plants. Forty A. anomala isolates collected from seven geographic regions were examined for their ability to infect two European hazelnut clones: VR6-28, a selection that carries a single dominant gene for complete resistance, and Barcelona, a moderately susceptible cultivar. Two isolates, one from Ontario and one from Minnesota, caused small sunken lesions on 'VR6-28'. Isolates from all seven regions infected 'Barcelona'; there were no significant differences (P > 0.05) in isolate virulence among regions. Thirty-three isolates were examined with four RAPD primers. Based on cluster analysis of the RAPD products, some genetic variation attributable to geographic origin was apparent in the collected isolates. This observation, coupled with the fact that two isolates from different indigenous populations infected 'VR6-28', suggests the quarantine laws prohibiting the importation of hazelnuts from eastern North America to Oregon and Washington should be maintained.
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