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X. Ferrán, J. Tous, A. Romero, J. Lloveras, and J.R. Pericón

In a 3-year experiment in two drip-irrigated orchards on the Mediterranean coast, boron (B) sprays applied at rates of 0.6 and 1.2 g per tree and a soil B application of 12 g per tree did not increase fruit set or production of Corylus avellana L. `Negret' and `Pauetet' hazelnuts with mid to low foliar B levels (14.3 to 21.8 μg·g-1 dry mass). The average fruit set and nut yields of the trials were, respectively, 66% and 3.54 kg per tree for `Pauetet', and 50% and 4.54 kg per tree for `Negret'. The lack of response to B applications might be due to 1) initial fruit set levels were high; 2) the current B recommendation guidelines (25 to 30 μg·g-1 dry mass) might be adequate for fruit set and yield; 3) the rates of B applied might be too low; and 4) weather and soil conditions, cultivars, and biennial bearing may have masked any response to foliar B application.

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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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Jordi Marsal, Joan Girona, and Mercè Mata

The influence of deficit irrigation on predawn leaf water potential (Ψpd) and leaf gas-exchange parameters was analyzed in almond [Prunus dulcis (Mill.) D.A. Webb] and compared to hazelnut (Corylus avellana L.). Both species were planted in adjacent plots in which four irrigation treatments were applied: T-100%, T-130%, and T-70%, which were irrigated at full crop evapotranspiration (ETc), 1.3 × ETc, and 0.7 × ETc, respectively, and a regulated deficit irrigation (RDI) treatment, which consisted of full irrigation for the full season, except from middle June to late August when 0.2 × ETc was applied. Under nonstressful conditions, hazelnut had a lower net CO2 assimilation rate (A) (12.2 μmol·m-2·s-1) than almond (15.5 μmol·m-2·s-1). Reductions in net CO2 assimilation rate (A) induced by decreases in Ψpd were higher in hazelnut than in almond. Gas-exchange activity from early morning to midday decreased in hazelnut for all irrigation treatments, but in almond increased in the well-watered treatments and decreased slightly or remained constant in the RDI. Hazelnut had a higher A sensitivity to variations in stomatal conductance (gs) than almond, especially at low gs values. The Ψpd values in almond and hazelnut of the T-100% and T-130% treatments were affected by decreasing values in midsummer, but in hazelnut Ψpd was probably also affected by sink kernel filling. These facts indicate that hazelnut RDI management could be more problematic than in almond.

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Jeff Olsen

Oregon's Willamette Valley is home to 99% of the U.S. domestic production of hazelnuts, Corylus avellana. There are currently around 30,000 acres of hazelnuts in Oregon. Hazelnuts are a relatively low resource input crop when compared to other orchard crops. They require few pesticide applications, and are harvested mechanically. Oregon State Univ. (OSU) developed an Integrated Pest Management (IPM) program for hazelnuts in the middle 1980s that is widely adopted in the industry today. Sampling schemes and action thresholds have been developed for the filbertworm (the most important insect pest), as well as: obliquebanded leafroller, filbert leafroller, and filbert aphids. In an example of classical biological control, a filbert aphid parasite, Trioxysis pallidus, was imported from Europe in 1984. Trioxysis has successfully established itself throughout the industry. As a result, the need for aphid control sprays has been significantly reduced. Current research in hazelnut IPM is focused on a “soft pesticide” program that features an insect growth regulator for filbertworm control. Recent research with isotopically labeled nitrogen seeks to improve the efficiency of nitrogen fertilization in the industry. The northern portion of the industry is affected by Eastern Filbert Blight. OSU research has secured registrations of effective fungicides and refined the control program for the blight. Work is being completed on a predictive model to quantify the extent of spore dispersal, based on accumulated rainfall.

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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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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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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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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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Chantalak Tiyayon and Anita Nina Azarenko

Pollen development is an important event in plant reproduction. Hazelnut (Corylus avellana) male flower differentiation starts in summer and pollen shed is in the winter. Hazelnut pollen shed can vary up to 3 months between early to late flowering genotypes. Microsporogenesis and microgametogenesis of hazelnut is not well understood. Pollen development and differentiation of nine genotypes, representing early to late blooming cultivars from the National Clonal Germplasm Repository in Corvallis, Ore., were studied. Catkins were collected weekly from Aug. to Nov. 2002. Tissue sections were examined under the light microscope. Microsporogenesis was divided into five stages: archesporial cells, sporogenous cells and parietal layers, pollen mother cells (PMC), tetrads, and microspores. Microgametogenesis was distinguished between young pollen grains (uninucleate) and mature pollen grains (binucleate). On 4 Aug., cultivars were at different developmental stages of microsporogenesis. Early blooming cultivars had PMCs present. Later-blooming cultivars only contained archesporial cells. PMCs were present in all cultivars by 22 Aug. Microspores were observed on 26 Sept. in all cultivars. This study contributes to a better understanding of male gametophyte development in hazelnut, which has increased our ability to correlate hazelnut pollen development with bloom phenology.

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Nahla V. Bassil, R. Botta, and S.A. Mehlenbacher

Three microsatellite-enriched libraries of the european hazelnut (Corylus avellana L.) were constructed: library A for CA repeats, library B for GA repeats, and library C for GAA repeats. Twenty-five primer pairs amplified easy-to-score single loci and were used to investigate polymorphism among 20 C. avellana genotypes and to evaluate cross-species amplification in seven Corylus L. species. Microsatellite alleles were estimated by fluorescent capillary electrophoresis fragment sizing. The number of alleles per locus ranged from 2 to 12 (average = 7.16) in C. avellana and from 5 to 22 overall (average = 13.32). With the exception of CAC-B110, di-nucleotide SSRs were characterized by a relatively large number of alleles per locus (≥5), high average observed and expected heterozygosity (Ho and He > 0.6), and a high mean polymorphic information content (PIC ≥ 0.6) in C. avellana. In contrast, tri-nucleotide microsatellites were more homozygous (Ho = 0.4 on average) and less informative than di-nucleotide simple sequence repeats (SSRs) as indicated by a lower mean number of alleles per locus (4.5), He (0.59), and PIC (0.54). Cross-species amplification in Corylus was demonstrated. These microsatellite markers were highly heterozygous and polymorphic and differentiated among genotypes of C. avellana irrespective of geographical origin. They will aid in fingerprinting genotypes of the european hazelnut and other Corylus species, genome mapping, and genetic diversity assessments.