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  • Author or Editor: Shawn A. Mehlenbacher x
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Eastern filbert blight (EFB) is a serious fungal disease of european hazelnut (Corylus avellana) in North America. The causal agent is the pyrenomycete Anisogramma anomala, which is native in the eastern United States where it occasionally produces small cankers on the wild american hazelnut (C. americana). However, most commercial cultivars of european hazelnut are susceptible. Infection leads to perennial cankers, girdling of branches, and premature tree death. Cultural practices including scouting, pruning out infected branches, and fungicide applications are recommended to slow disease spread but are expensive and not completely effective. EFB resistance from ‘Gasaway’ is conferred by a dominant allele at a single locus and has been extensively used in the Oregon State University hazelnut breeding program, but there is concern that this resistance could be overcome by isolates now present in the eastern United States or that a new race of the pathogen could arise in Oregon. Segregation for EFB resistance from ‘Uebov’, a new source from Serbia, was studied in three progenies by a combination of structure exposure and greenhouse inoculation. The frequency of resistant seedlings following structure exposure was about 20% in all three progenies. The ratios failed to fit the expected 1:1 ratio but did fit a ratio of 1 resistant:3 susceptible, which would be expected if resistance were conferred by dominant alleles at two independent loci. Seedlings from a cross of susceptible selection OSU 741.105 and ‘Uebov’ were used to study correlation of disease response and presence of alleles at microsatellite marker loci. Resistance was highly correlated with the presence of alleles at marker loci on linkage group 6 (LG6), and these markers also showed segregation distortion. We conclude that EFB resistance from ‘Uebov’ maps to a single locus on LG6 in the same region as resistance from ‘Gasaway’, although only about 20% of the seedlings are resistant because of segregation distortion. ‘Uebov’ has large, well-filled, round nuts and is suitable as a parent in breeding for the in-shell market, but its low nut yields and a high frequency of shells with split sutures are the drawbacks. Its use would expand options for breeding and ‘Uebov’ resistance could be combined with other resistance alleles with an expectation of more durable EFB resistance. Durable resistance would not only sustain the hazelnut industry in Oregon but would also allow expansion of plantings to new areas.

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Filbertworm, Cydia latiferreana (Walsingham) (Lepidoptera: Tortricidae), is a key insect pest of hazelnuts in North America. Susceptibility to filbertworm was determined in 25 hazelnut cultivars represented by 44 trees at the USDA National Clonal Germplasm Repository in Corvallis, OR. In addition, shell thickness of 17 of the cultivars was measured at the thinnest and thickest points of the basal scar as well as at the side of the shell wall. Filbertworm infestation, which ranged from 2% to 89% per tree, as well as shell thickness varied significantly among the cultivars. Filbertworm infestation significantly increased with decreasing shell thickness at the basal scar, where filbertworm larvae typically penetrate the nut. The cultivar Siciliana had the overall thickest shells and lowest filbertworm infestation (6% ± 2% average for the cultivar), whereas ‘Frango 2’, ‘Casina’, and ‘Daviana’ had the thinnest shells and 76%, 55%, and 82% infested nuts, respectively. Nut infestation was not correlated with the thickness of the side wall. Our data suggest that a thicker basal scar in hazelnut cultivars contributes to resistance against filbertworm infestation.

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Eastern filbert blight (EFB), caused by Anisogramma anomala (Peck) E. Müller, is a devastating disease to european hazelnut (Corylus avellana L.) orchards in the Willamette Valley of Oregon. Selection OSU 408.040 showed no symptoms or signs of the fungus following greenhouse inoculations, and enzyme-linked immunosorbant assays (ELISAs) were negative. Segregation ratios in three progenies indicate that a single dominant gene controls the resistance. A total of 64 amplified fragment length polymorphism (AFLP) primer combinations were screened using three resistant and three susceptible individuals as well as the parents of the cross OSU 245.098 × OSU 408.040. Primer combinations that showed no more than one recombinant in these six seedlings were investigated in 30 additional seedlings. Markers that showed <15% recombination with resistance were amplified in the remaining seedlings of the population. Five AFLP markers linked in coupling to resistance were identified. B2-125 was located on one side of the resistance locus at a distance of 4.1 centimorgans (cM), while A4-265 (9.2 cM), C2-175 (5.9 cM) and D8-350 (2.5 cM) were on the other side, and A8-150 cosegregated with resistance. Three of these markers (B2-125, C2-175, and D8-350) were also linked in coupling in a similar order in seedlings from a second progeny. These markers may be useful in marker-assisted selection for eastern filbert blight resistance from hazelnut selection OSU 408.040.

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Eastern filbert blight is an economically significant disease in European hazelnut (Corylus avellana L.) production in the United States. Since genetic resistance is the only viable disease control strategy to this fungal disease caused by Anisogramma anomala (Peck) E. Müller, greenhouse and field screening of germplasm was undertaken to study the inheritance from known resistant sources and to identify new sources for inclusion in the breeding program. We confirmed that `Gasaway' resistance to this disease is conferred by a single dominant gene. No major gen was identified in the field-resistant cultivar Gem. Representatives of six Corylus species were screened to identify new resistant germplasm. Corylus cornuta Marshall var. cornuta, C. cornuta var. californica (A.DC.) Sharp, C. heterophylla Fischer, and C. sieboldiana Blume were highly resistant, as were most C. americana Marshall genotypes and one C. colurna L. clone tested, but C. jacquenontii Decaisne was highly susceptible. In several cases, hybrids of these species with susceptible C. avellana were also resistant. These new sources of resisstance are being incorporated in the resistance breeding effort.

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Analysis of the pedigrees of selected eastern United States freestone peach [Prunus persica (L.) Batsch] cultivars reveals high degrees of inbreeding and coancestry. Commonly used parents include ‘Admiral Dewey’, ‘Elberta’, ‘Halehaven’, ‘J.H. Hale’, ‘Rio Oso Gem’, and ‘St. John’. These cultivars and their progeny were used as parents primarily for superior fruit quality. Selection for fruit quality has led to the intensive use of relatively few cultivars and a restriction in freestone peach germplasm. Future progress in the development of high quality, cold hardy, disease- and insect-resistant cultivars will depend upon expansion of the germplasm base, and identification and interfusion of genes conferring desired tree and fruit characters into existing eastern United States peach germplasm.

Open Access