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  • Author or Editor: Shawn A. Mehlenbacher x
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European hazelnut (Corylus avellana L.) is a significant crop in Oregon, where 99% of United States hazelnuts are produced. Eastern filbert blight (EFB) caused by Anisogramma anomala (Peck) E. Müller is an important disease that infects the trees, reduces yield, and causes premature death. Managing the disease through cultural methods and fungicide applications is laborious and expensive, and genetic host resistance is considered the most viable option for control. Genetic resistance from ‘Gasaway’ has been used to develop resistant cultivars including Yamhill and Jefferson, but concern about the durability of this single resistance gene stimulated a search for additional sources of resistance. This study used three recently identified sources of EFB resistance: ‘Culplà’ from Spain, ‘Crvenje’ from Serbia, and OSU 495.072 from southern Russia. RAPD markers linked to resistance from ‘Gasaway’ were absent in all three accessions. Disease response was noted in segregating progenies following greenhouse or structure inoculation, and the resistance loci were mapped using microsatellite markers. In only four of the nine progenies did segregation for disease response fit the ratio of 1 resistant:1 susceptible expected for a single locus, a heterozygous resistant parent, and a dominant allele for resistance. Three progenies showed an excess of resistant seedlings while two showed a deficiency of resistant seedlings. The reciprocal translocations reported in several leading hazelnut cultivars may be present in the parents of the studied progenies, and affecting the segregation ratios. Microsatellite marker A614, previously mapped to linkage group (LG) 6, was closely linked to resistance from all three sources. Maps were constructed for LG6 for each resistant parent using microsatellite markers. The three resistance loci mapped to the same region on LG6 where resistance from ‘Gasaway’ and OSU 408.040 are located. The resistance alleles in all five accessions may be the same, or more likely are a cluster of different resistance genes in the same region. Markers LG628, LG610, and LG696 will be useful to breed new hazelnut cultivars with resistance from Culplà, Crvenje, and OSU 495.072.

Free access

Eastern filbert blight (EFB), caused by Anisogramma anomala, is a fungal disease threatening the european hazelnut (Corylus avellana) industry in the Willamette Valley of Oregon. The pathogen is endemic to the eastern United States where it causes little damage to the wild Corylus americana but causes severe cankers on most cultivars of the commercially important european hazelnut. The host genetic resistance in ‘Gasaway’ is conferred by a dominant allele at a single locus on linkage group 6 (LG6), and resistance from several other sources has been mapped to the same region. Some fungal isolates can overcome ‘Gasaway’ resistance, prompting a search for other sources of resistance. Resistance from other sources has been mapped to LG2 and LG7, for which additional simple sequence repeat (SSR) markers would facilitate marker-assisted selection (MAS). In this study, an in silico approach was used to develop new polymorphic SSR markers in the EFB resistance regions on LG2 and LG7. Starting with a search of 17 contigs of the ‘Jefferson’ genome sequence, 45 new polymorphic SSR markers were developed, characterized, and placed on the linkage map. The new SSR markers had an average of 10.18 alleles per locus, and average values for expected heterozygosity, observed heterozygosity, polymorphism information content, and frequency of null alleles of 0.72, 0.65, 0.68, and 0.068, respectively. Of the 42 new polymorphic SSRs segregating in the mapping population, 24 were on LG2, 12 were on LG7, and six were placed on other LGs. The new and previously developed SSR markers were used to study six new sources of EFB resistance, four from Russia and two from Crimea. Six resistant selections were crossed with susceptible selections, resulting in 7 progenies. Phenotyping for disease response revealed that segregation in progenies of the two Moscow selections (#2 and #27), one Russian selection (OSU 1187.101), and one Crimean selection (H3R12P62) fit the 1:1 segregation ratio expected for control of resistance by a dominant allele at a single locus; but in progenies of the other Russian selection (OSU 1166.123) and the other Crimean selection (H3R07P11), there was an excess of resistant seedlings. Correlation of disease scores and alleles at SSR loci indicated that resistance from three Russian selections (Moscow selections #2 and #27 and OSU 1166.123) and the Crimean selection H3R12P62 was on LG7, while resistance from Russian selection OSU 1187.101 was on LG2. Resistance from Crimean selection H3R07P11 was not correlated with markers on LG6, or LG2, or LG7. These sources and new SSR markers will be useful in MAS and the pyramiding of resistance genes in the breeding of new EFB-resistant cultivars.

Open Access

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.

Free access

Eastern filbert blight (EFB), caused by the fungus Anisogramma anomala, is a primary limitation to european hazelnut (Corylus avellana) cultivation in eastern North America. American hazelnut (Corylus americana) is the endemic host of A. anomala and, despite its tiny, thick-shelled nuts, is a potentially valuable source of EFB resistance and climatic adaptation. Interspecific hybrids (Corylus americana × C. avellana) have been explored for nearly a century as a means to combine EFB resistance with wider adaptability and larger nuts. Although significant progress was made in the past, the genetic diversity of the starting material was limited and additional improvements are needed for expansion of hazelnut (Corylus sp.) production outside of Oregon, where 99% of the U.S. crop is currently produced. Our objective was to determine if C. americana can be a donor of EFB resistance. We crossed 29 diverse EFB-resistant C. americana accessions to EFB-susceptible C. avellana selections (31 total progenies) to produce 2031 F1 plants. In addition, new C. americana germplasm was procured from across the native range of the species. The new collection of 1335 plants from 122 seed lots represents 72 counties and 22 states. The interspecific hybrid progenies and a subset of the American collection (616 trees from 62 seed lots) were field planted and evaluated for EFB response following field inoculations and natural disease spread over seven growing seasons. EFB was rated on a scale of 0 (no EFB) to 5 (all stems containing cankers). Results showed that progeny means of the interspecific hybrids ranged from 0.96 to 4.72. Fourteen of the 31 progenies were composed of at least one-third EFB-free or highly tolerant offspring (i.e., ratings 0–2), transmitting a significant level of resistance/tolerance. Several corresponding C. americana accessions that imparted a greater degree of resistance to their hybrid offspring were also identified. In addition, results showed that 587 (95.3%) of the 616 C. americana plants evaluated remained completely free of EFB. These findings confirm reports that the species rarely expresses signs or symptoms of the disease and should be robustly studied and exploited in breeding.

Open Access

European hazelnut (Corylus avellana L.) is an economically important edible nut producing species, which ranked sixth in world tree nut production in 2016. European hazelnut production in the United States is primarily limited to the Willamette Valley of Oregon, and currently nonexistent in the eastern United States because of the presence of a devastating endemic disease, eastern filbert blight (EFB) caused by Anisogramma anomala (Peck) E. Muller. The primary commercial means of control of EFB to date is through the development and planting of genetically resistant european hazelnut cultivars, with an R-gene introduced from the obsolete, late-shedding pollinizer ‘Gasaway’. Although the ‘Gasaway’ resistance source provides protection against EFB in the Pacific northwestern United States (PNW), recent reports have shown that it is not effective in parts of the eastern United States. This may be in part because the identification and selection of ‘Gasaway’ and ‘Gasaway’-derived cultivars occurred in an environment (PNW) with limited genetic diversity of A. anomala. The objectives of the current research were to develop a genetic linkage map using double digestion restriction site associated DNA sequencing (ddRADseq) and identify quantitative trait loci (QTL) markers associated with EFB resistance from the resistant selection Rutgers H3R07P25 from southern Russia. A mapping population composed of 119 seedling trees was evaluated in a geographic location (New Jersey) where the EFB fungus is endemic, exhibits high disease pressure, and has a high level of genetic diversity. The completed genetic linkage map included a total of 2217 markers and spanned a total genetic distance of 1383.4 cM, with an average marker spacing of 0.65 cM. A single QTL region associated with EFB resistance from H3R07P25 was located on european hazelnut linkage group (LG) 2 and was responsible for 72.8% of the phenotypic variation observed in the study. Based on its LG placement, origin, and disease response in the field, this resistance source is different from the ‘Gasaway’ source located on LG6. The current results, in combination with results from previous research, indicate that the H3R07P25 source is likely exhibiting resistance to a broader range of naturally occurring A. anomala isolates. As such, H3R07P25 will be important for the development of new european hazelnut germplasm that combines EFB resistance from multiple sources in a gene pyramiding approach. Identification of EFB resistance in high disease pressure environments representing a diversity of A. anomala populations is likely a requirement for identifying plants expressing durable EFB resistance, which is a precursor to the development of a commercially viable european hazelnut industry in the eastern United States.

Free access

Abstract

‘McShay’ is an attractive, excellent quality apple (Malus × domestica Borkh.) with field immunity to apple scab. The fruit is similar in color, flavor, and texture to ‘McIntosh’. ‘McShay’ is named in honor of the late J. Ralph Shay and is a late fall dessert apple well-adapted to Oregon's Willamette Valley. ‘McShay’ is the ninth cultivar to be released by the cooperative apple breeding program of Indiana, Illinois, and New Jersey Agricultural Experiment Stations.

Open Access