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J.L. Olsen, S.A. Mehlenbacher, and A.N. Azarenko

Hazelnuts, (Corylus avellana L.), are wind-pollinated, monoecious, mostly dichogamous, and self-incompatible. About 90% of the cultivars studied are protandrous. Anthesis of the pistillate flower is temperature-dependent and occurs December through February, peaking in January. Stigmatic surfaces may remain receptive for up to 3 months. Four to 5 months separate pollination and fertilization of the ovule; the latter usually occurring between mid-May and the end of June in Oregon. A 10% pollinizer density has been the standard, with a recommended distance of 66 ft (20 m) or less between the main cultivar and the nearest pollinizer. Two or three different pollinizer cultivars, with different times of pollen shed, are recommended. The Oregon hazelnut industry is presently combating the fungal disease, eastern filbert blight, caused by Anisogramma anomala (Peck). Current management recommendations suggest reducing risk of infection are to reduce the most susceptible pollinizer cultivars to a density 5%, then gradually replace those left with immune or more resistant genotypes.

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China F. Lunde, Shawn A. Mehlenbacher, and David C. Smith

Ninety hazelnut (Corylus sp.) genotypes were surveyed for response to the eastern filbert blight pathogen [Anisogramma anomala (Peck) E. Müller] following greenhouse inoculation using a combination of enzyme-linked immunosorbent assay (ELISA) and visual inspection for cankers. Most were cultivars of the European hazelnut (Corylus avellana L.) and a few were interspecific hybrids. Six genotypes did not display signs of the pathogen or symptoms of disease: `Closca Molla', `Ratoli', `Yoder #5', `Potomac', `Medium Long', and `Grand Traverse'. `Closca Molla' and `Ratoli', both minor Spanish cultivars, are superior in many respects to `Gasaway', which has been extensively used as a completely resistant parent in breeding. `Potomac' and `Yoder #5' have C. americana Marsh. in their pedigrees, `Grand Traverse' is one-quarter C. colurna, and the origin of `Medium Long' is uncertain. The random amplified polymorphic DNA (RAPD) marker generated by primer UBC 152, which is linked to the single dominant resistance gene of `Gasaway', is absent in these six genotypes, and thus they appear to be novel sources of genetic resistance to this devastating disease.

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C.F. Lunde, M.S. Mehlenbacher, and D.C. Smith

A survey of hazelnut (Corylus avellana L.) genotypes for response to the eastern filbert blight pathogen [Anisogramma anomala (Peck) E. Müller] was performed. Seven varieties were discovered that did not display disease signs or symptoms when subjected to severe inoculation with A. anomala in the greenhouse and assayed for infection. These cultivars are `Closca Molla', `Ratoli', `Yoder #5', `Potomac', `Medium Long', `Grand Traverse' and `Zimmerman'. `Ratoli' and `Closca Molla', both minor varieties from Spain, are superior agronomic types to the resistant cultivar Gasaway, which has been the main resistance source used in the breeding program. Only `Zimmerman' carries the RAPD marker linked to resistance in populations segregating for the `Gasaway' gene. Three populations were created using, `Zimmerman', as the pollen parent in controlled crosses. These populations were inoculated with spores of the pathogen and assayed by indirect ELISA and by observation of canker incidence. Resistant phenotypes make up 84% of the populations, indicating that `Zimmerman' possesses resistance either distinct from or additional to that found in, `Gasaway'. A RAPD marker linked to the resistance gene in crosses with `Gasaway' cosegregates with the resistant phenotype in all three populations (0 cM, 3 cM, 4 cM). Mechanisms to explain the distortion in these populations are discussed. Further studies are required to characterize the mechanism and inheritance resistance in these other clones.

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Jeff Olsen

Hazelnuts in Oregon are grown on 30,000 acres by ≈1000 orchardists in the Willamette Valley. Their annual production accounts for 3% to 5% of the world's hazelnut tonnage. The trees are grown in a single trunk system wrtb an average spacing of 20 feet between trees. Mechanical harvestihg is done in October. The industry employs an Integrated Pest Management approach, utilizing combinations of scouting, trapping, and biological control. The main insect pests are filbertworm, filbert leafroller, obliquebanded leafroller, and filbert aphids. The aphid parasite Trioxys pallidus was imported from Europe and successfully established in Oregon. Eastern Filbert Blight, Anisogramma anomala, a fungus disease, is the most serious disease problem in the industry. Annual applications of nitrogen to the soil and boron applied to the foliage are routine for Oregon's hazelnut growers. OSU research has quantified the importance of good light distribution in the tree canopy for increased nut production. OSU recommends a 5-year rotational pruning program. Some growers use mechanical hedging instead of hand pruning. OSU is home to the world's largest hazelnut breeding program. `Barcelona' is still the main, cultivar grown, while `Ennis' is the main in-shell variety. There is growing interest in planting varieties with a high percent kernel, such as `Casina', `Willamette', and `Lewis'.

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Thomas J. Molnar, Sara N. Baxer, and Joseph C. Goffreda

An eastern filbert blight resistance screening technique was developed that reduces the time required to identify susceptible Corylus avellana L. seedlings from the previously reported 14 to 16 months after inoculation to 6 to 7 months. To accomplish this, hazelnuts were harvested at maturity, treated with GA3, germinated, and grown for about 8 weeks at 24 °C day/18 °C night with 16-hour daylengths. Seedlings were then moved to a humidity chamber and inoculated with ascospores of Anisogramma anomala (Peck) E. Müller 3 times over 2 weeks by misting until run off with a solution of 1 × 106 ascospores/mL in sterile distilled water. Following inoculation, seedlings were returned to the original greenhouse for 8 weeks and then were moved to a 10 to 15 °C day/5 to 10 °C night greenhouse with natural daylengths for 4 weeks. They were then moved to a 4 °C cold room for 8 weeks to receive chilling. Afterwards, seedlings were returned to a greenhouse at 24 °C day/18 °C night where stromata development was visible in 4 to 6 weeks.

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J.L. Olsen

Oregon State University (OSU) developed an integrated pest management (IPM) program for hazelnut (Corylus avellana.) in the early 1980s, through a USDA grant. Sampling schemes and action thresholds were refined over a period of 4 years for the filbertworm (Cydia latiferreana), filbert aphid (Myzocallis coryli), filbert leafroller (Archips rosanus.), and obliquebanded leafroller (Choristoneura rosaceana), which are the most important insect pests in Oregon hazelnuts. A classical biological approach was employed in the mid-1980s when the filbert aphid parasitoid, Trioxys pallidus, was imported from Europe. Grower survey results for 1981 and 1997 showed that the amount of pesticides applied for filbert aphid control has declined by 93%. The registration of synthetic pyrethroids for filbertworm control and the use of pheromone trapping have reduced the amount of active ingredient applied in the industry by 96%. The annual cost savings to Oregon hazelnut growers due to use of the OSU IPM program are estimated at $0.5 million. Current research focuses on the use of less toxic insecticides, such as insect growth regulators for filbertworm and leafroller control. The most serious hazelnut disease, eastern filbert blight (EFB) caused by the fungus Anisogramma anomala was first reported in the Pacific northwestern U.S. in 1973. It has spread its way through two thirds of the hazelnut acreage. Current OSU IPM recommendations include preventative fungicide sprays in spring, scouting for and cutting out infections, and replacement of the most susceptible cultivars when possible. The long-term approach to EFB control is the development of EFB immune varieties.

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Clarice J. Coyne, Shawn A. Mehlenbacher, and David C. Smith

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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Honglin Chen, Shawn A. Mehlenbacher, and David C. Smith

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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Clarice J. Coyne, Shawn A. Mehlenbacher, Kenneth B. Johnson, John N. Pinkerton, and David C. Smith

A rapid and reliable assay for screening European hazelnut (Corylus avellana L.) genotypes for quantitative resistance to eastern filbert blight [Anisogramma anomala (Peck) E. Müller] was tested by comparing two methods using the same clones. In the first assay, disease spread was followed for five consecutive years (1992-96) in a field plot planted in 1990. Measured responses included disease incidence (the presence or absence of cankers) and total canker length, quantified as the length of perennially expanding cankers. The second assay consisted of annually exposing replicated sets of 2-year-old, potted trees to artificially high doses of pathogen inoculum and measuring incidence and canker lengths at the end of the next growing season. The potted trees were exposed to inoculum in 1990, 1992, 1993, and 1994. Compared to the field plot, disease incidence and total canker length were higher in all the potted-tree experiments. Nonetheless, disease responses of individual clones in the two screening methods were significantly correlated in some contrasts (rs = 0.97 between 1996 field and 1995 potted trees). However, for a few clones (`Camponica', `Tombul Ghiaghli', and `Tonda di Giffoni'), disease developed slowly in the field plot, but disease incidence on these clones averaged > 30% in most of the potted-tree studies. Disease responses also were significantly correlated among some of the potted-tree experiments (rs = 0.72 for the comparison of 1994 to 1995). Highly susceptible and highly resistant hazelnut clones were identified by both methods. However, the field plot method was superior to the potted-tree method for distinguishing among moderately resistant clones. `Bulgaria XI-8', `Gem', `Camponica', `Tombul Ghiaghli', and `Tonda di Giffoni' were identified as promising sources of quantitative resistance to eastern filbert blight.

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China F. Lunde, Shawn A. Mehlenbacher, and David C. Smith

Eastern filbert blight (EFB), caused by the fungus Anisogramma anomala (Peck) E. Müller, is an important disease of european hazelnut (Corylus avellana L.) in the Pacific northwestern United States. In 1989, a chance seedling free of EFB was discovered adjacent to a severely diseased orchard near Troutdale, Ore. This selection, subsequently named `Zimmerman', was crossed with three susceptible selections. Based on morphological characters and incompatibility alleles, we speculated that `Zimmerman' (S1 S3) was a hybrid between `Barcelona' (S1 S2) and `Gasaway' (S3 S26). The three seedling populations were inoculated with spores of the pathogen in a greenhouse test and assayed by indirect enzyme-linked immunosorbent assay (ELISA) and by observation of canker incidence. The observed segregation fit a 3 resistant : 1 susceptible ratio in all three progenies, in contrast to the 1 : 1 ratio found when the resistant pollinizer `Gasaway' was crossed to susceptible genotypes. Random amplified polymorphic DNA (RAPD) marker UBC 152800 linked to the resistance gene in `Gasaway' co-segregated with the resistant phenotype in all three populations with 2%, 4%, and 6% recombination, respectively. Seed germination and transplanting records did not provide evidence of selection in favor of resistant seedlings. Pollen germination was 71% in `Gasaway', 29% in `Zimmerman', and 18% in `Barcelona', indicating possible selection at the gametophytic level. Subsequently 16 resistant seedlings of `Zimmerman' were crossed with the highly susceptible selection OSU 313.078. Segregation fit a 3 : 1 ratio in 14 of the 16 progenies, and showed a surplus of resistant seedlings in the other two. None showed a 1 : 1 segregation. Resistance co-segregated with two RAPD markers that flank the `Gasaway' resistance allele. To test allelism of resistance from `Gasaway' and `Zimmerman', VR 6-28 with resistance from `Gasaway' was crossed with `Zimmerman'. Eight resistant selections from this progeny were crossed with OSU 313.078. Five of the eight progenies segregated 3 : 1, two progenies segregated 1 : 1, and OSU 313.078 × OSU 720.056 gave only resistant offspring. The ratios indicate that OSU 720.056 is homozygous resistant and that `Zimmerman' and `Gasaway' share a common resistance allele. Reciprocal translocations have been reported in hazelnut cultivars, including `Barcelona', the leading cultivar in Oregon. `Zimmerman' appears to be a hybrid of `Barcelona' and `Gasaway', but because of cytogenetic abnormalities, `Zimmerman' may have inherited two copies of the chromosome region that contain the resistance locus and flanking RAPD markers. If the region containing the resistance were attached to two independent centromeres, a 3 : 1 segregation ratio for disease response and flanking markers would be expected, and we propose this as the most likely explanation. Resistance from `Gasaway' and `Zimmerman' has been called “immunity” or “complete resistance.” However, we noted a few seedlings with small cankers, nearly all of which lacked sporulating stromata. Flanking RAPD markers indicate that the resistance allele is present in these seedlings. Although not “immune” or “completely resistant,” `Gasaway' and `Zimmerman' transmit a very high level of resistance.