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Hazelnut or filbert is the fruit of plants in the genus Corylus L., which are members of the family Betulaceae. European hazelnuts ( C. avellana ) are deciduous shrubs or small trees native to the northern temperate zone. Major producers of

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) identification (ID) number, consensus ID number, and eastern filbert blight (EFB) response of 323 Corylus accessions examined using simple sequence repeat markers. z The 142 seed-derived C. avellana accessions include 86 EFB-resistant and 33 EFB

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Hazelnut, also known as filbert, is the fruit of plants in the genus Corylus L., a member of the family Betulaceae. The european hazelnut is a deciduous shrub or small tree native to most of Europe and adjacent areas in the Caucasus Mountains and

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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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`Gasaway' hazelnut (Corylus avellana L.) is highly resistant to eastern filbert blight caused by Anisogramma anomala (Peck) E. Muller. Progeny produced from controlled crosses of `Gasaway' with five susceptible genotypes and open pollination in a `DuChilly' orchard were planted in a diseased orchard and rated for symptom expression for 9 to 10 years. All progeny were found to segregate 50% resistant: 50% susceptible, indicating that `Gasaway' is heterozygous for a single dominant resistance gene.

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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.

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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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In the plant world, where oddity is commonplace, the filbert, Corylus, stands out because it has so many unusual traits:

  • The filbert blooms in midwinter in the areas where it is commercially produced.

  • Six months can elapse between pollination and fertilization.

  • At the time of pollination, the rudimentary flower has no ovary.

  • When the filbert nut has completed its development, its apex is over a year older than its base.

  • Commercial filbert production is restricted to limited areas of Turkey, Italy, Spain, and the Pacific Northwest, yet members of the genus Corylus are widely distributed throughout the northern hemisphere.

  • The plant is thought never to go dormant because in mild climatic areas it exhibits some type of growth the year around.

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Eastern filbert blight, caused by the ascomycete fungus Anisogramma anomala , is an endemic disease of the wild American hazelnut, Corylus americana . This pathogen is associated with C. americana throughout its native range, which spans much of

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made since colonial times to produce hazelnuts in the eastern United States with little recorded success. It was eventually understood that the fungal disease eastern filbert blight (EFB), caused by Anisogramma anomala , an obligate biotrophic

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