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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.

The American hazelnut (Corylus americana) is native to a broad range of the eastern United States and southern Canada. It is the endemic host of the fungus Anisogramma anomala, which causes eastern filbert blight (EFB) disease and limits European hazelnut (C. avellana) production in eastern North America. While C. americana has thick-shelled, tiny nuts not suited for commercial production, it is cold hardy, highly tolerant of EFB, and phenotypically diverse. Previous studies with simple sequence repeat markers show that it is also genetically diverse. Further, the species is cross-compatible with C. avellana and is thus a valuable donor of EFB resistance and climate adaptability traits. However, only a narrow set of C. americana parents has been used in interspecific hybridizations, and current germplasm availability likely does not fully represent the species’ genetic diversity, given its vast range. A new collection of open-pollinated C. americana seed was assembled at Rutgers University to broaden available genetic resources. Here, we study the genetic diversity and population structure of 272 of these individuals, which represent 55 seedlots from across 15 states of the species’ native range. We use multivariate analyses to examine the distribution of genetic variation within the collection and to support the identification of a core set. A genotyping-by-sequencing (GBS) approach yielded 2653 single nucleotide polymorphisms and subsequent analyses revealed a collection with high estimates of heterozygosity (HE = 0.276, HO = 0.280), moderate differentiation (FST = 0.108) and low inbreeding (FIS = −0.136). Bayesian model-based and neighbor-joining (NJ) clustering corroborate an uppermost grouping of K = 3, with the NJ dendrogram depicting many small subgroups equally distant from common ancestry. Discriminant analysis of principal components (DAPC) reveals between-subgroup variation (K = 15) within the NJ dendrogram and allows the identification of 19 consensus subgroups. In general, our results support the assembly of a genetically diverse collection where a majority of the variation is explained at the genotype and subgroup levels, which aligns with previous studies of C. americana. Fifty-one accessions were identified that represent 95% of the observed allelic variation. These genotypes are suggested for inclusion in a core collection, which, when coupled to concurrent phenotypic evaluations, will aid in genetic resource assembly that preserves unique phenotypes and retains genetic variation.

Corylus americana is native to a wide area of land in eastern North America, bounded by the Rocky Mountains in the west and the Atlantic Ocean in the east, and ranging from southern Canada to the southeastern US. The species has been shown to be highly genetically diverse and is adapted to a variety of climates and soils. It is also resistant to the disease eastern filbert blight (EFB) caused by the fungus Anisogramma anomala. Unfortunately, C. americana has thick-shelled, tiny nuts that make it unsuitable for commercial production. However, it is cross-compatible with the commercial hazelnut C. avellana and can serve as a donor for genes for disease resistance, early nut maturity, cold tolerance, etc. As part of the Hybrid Hazelnut Consortium consisting of Rutgers University, Oregon State University, the University of Nebraska-Lincoln, and the Arbor Day Foundation, we have been successfully collecting C. americana germplasm since 2009 with the help of partners, colleagues, and the interested public around the USA. Today, we have a planting established in the field at Rutgers University in New Jersey that holds 1,899 seedlings obtained from 128 individual seed lots that span 23 states and one Canadian province. These bushes are being evaluated for EFB response, other diseases and insects, flowering and vegetative bud break phenology, cold hardiness, nut yield, and nut and kernel characteristics. The genetic diversity and population structure of the new collection is also being evaluated using several approaches, including genotyping by sequencing and subsequent SNP analysis, SSR allelic variation, and chloroplast haplotype determination across the large population. Using this multi-faceted approach, we hope that superior, diverse selections can be identified for use in systematic breeding efforts to develop new cultivars adapted to the eastern USA, especially in respect to consistent cropping in regions with highly variable year-to-year climates.

Eastern filbert blight (EFB) is a hazelnut disease caused by Anisogramma anomala, a fungus endemic to North America where it can be found associated with the wild hazelnut Corylus americana. While C. americana is resistant to EFB, the commercial hazelnut C. avellana is highly susceptible and typically dies within 5 years from exposure. A hazelnut breeding program was initiated in 1996 at Rutgers University in New Brunswick, New Jersey. The early objective was to identify sources of resistance to EFB for use in breeding regionally adapted, EFB-resistant plants to support the establishment of a hazelnut industry in eastern USA. By working with Oregon State University (OSU) and international colleagues, germplasm collections were made in Russia, Ukraine, Poland, Georgia, Latvia, Lithuania, Estonia, Italy, and Turkey. Over 5,000 seedlings were grown and evaluated for response to EFB. While most plants succumbed to EFB, about three percent were found to be resistant. Interestingly, the resistant plants spanned nearly all collection locations and molecular markers have shown them to be highly diverse. Today, we have access to over 100 EFB-resistant accessions selected from more than 60 locations, which represents a significant pool of germplasm to support breeding. Recent studies have shown that most resistance seems to be controlled by only one or a few major genes; R-gene mapping projects are underway at Rutgers as well as Oregon State University. We continue to study new sources of resistance for use in a focused cultivar improvement program.

The disease eastern filbert blight (EFB), caused by Anisogramma anomala, severely limits hazelnut (Corylus avellana) production in North America. In the 1970s, ‘Gasaway’, a late-flowering pollenizer, was found to be resistant to EFB in the Pacific northwestern U.S., and to transmit its resistance in a predictable Mendelian pattern. Its subsequent use in breeding at Oregon State University led to the release of a number of EFB-resistant cultivars, including Jefferson, Yamhill, Dorris, Wepster, and McDonald, which are now being widely planted across the Willamette Valley of Oregon. However, some cultivars carrying the ‘Gasaway’ R-gene develop EFB in New Jersey. Thus, the utility of this resistance source for breeding plants adapted to the eastern U.S has not been fully evaluated. In this study, we examined the EFB response of seedlings from 31 different full-sib progenies expected to segregate for the ‘Gasaway’ R-gene. Trees were exposed to the disease over at least 5 years and evaluated on a scale of 0 to 5 (0 = resistant, 5 = highly susceptible). In general, we found the number of seedlings free of EFB (class 0) to be less than expected based on prior work in Oregon, but resistant individuals were identified in each progeny, indicating the presence of heritable resistance. When disease response classes 0, 1, and 2 were combined (resistant through highly tolerant) and considered as “resistant”, the expected ratio of resistant to susceptible trees was recovered, signifying that the single dominant allele alone continues to provide a predictable level of at least tolerance. Modifying genes/factors appear to play a role in the final disease response of the individual seedling. It is thus hypothesized that some cultivars selected as resistant in Oregon that develop cankers in New Jersey may lack the necessary modifying genetic factors for full protection in the east. Until these modifying genes are elucidated, long-term field evaluation remains necessary to identify selections that carry the ‘Gasaway’ R-gene and express a high level of resistance to EFB in the eastern U.S.

Molnar, T. J., Walsh, E., Capik, J. M., Sathuvalli, V., Mehlenbacher, S. A., Rossman, A. Y., and Zhang, N. 2013. A real-time PCR assay for early detection of eastern filbert blight. Plant Dis. 97:813-818. Eastern filbert blight (EFB) is a devastating disease of European hazelnut, Corylus avellana, which causes economic losses in Oregon, where 99% of the U.S. crop is produced. The causal fungus, Anisogramma anomala, is native to eastern North America, where it is found associated with the American hazelnut (C. americana). Although C. americana is tolerant, EFB causes cankers, branch dieback, and death of C. avellana. Detection and identification of A. anomala is time consuming using conventional methods because the fungus can only be cultured from sporulating perithecia and the disease symptoms and signs only show 12 to 16 months after infection. In this study, a TaqMan real-time polymerase chain reaction (PCR) assay based on a ribosomal DNA internal transcribed spacer was developed for A. anomala. The assay was validated with multiple isolates of A. anomala, closely related species, common environmental microorganisms, and over 100 C. avellana samples. The real-time PCR assay detected as low as 0.12 pg of A. anomala genomic DNA, and positively diagnosed EFB on 82% of asymptomatic plants as early as 15 weeks from infection. The real-time PCR assay is more sensitive and faster than traditional diagnostic methods. It can facilitate hazelnut breeding and disease management by early and accurate diagnosis of EFB.

In North America, the native hazelnut Corylus americana harbors an endemic fungus, Anisogramma anomala, which causes the disease eastern filbert blight (EFB). Although C. americana is tolerant of EFB, the economically important European hazelnut, C. avellana, is highly susceptible to the disease. This susceptibility greatly limits commercial European hazelnut production in North America. The breeding and subsequent utilization of resistant plants are considered the most effective means of control and efforts are underway to identify diverse sources of genetic resistance. In this study, 1374 C. avellana seedlings, spanning 47 seed lots collected in the Republic of Georgia and 3 in Azerbaijan, were inoculated with the EFB pathogen and evaluated for disease response in New Jersey, USA. After 5 years, plant responses were rated on a scale of 0–5, in which 0 represents no signs or symptoms of EFB and 5 represents all stems showing cankers. Cankers were found on over 94% of the seedlings, with the large majority being highly susceptible (91.4% = rating 4 and 5). However, 79 plants from 34 seed lots remained free of signs or symptoms of EFB (rating 0). In most cases, only one or two resistant seedlings were in each of these seed lots, making it difficult to infer any genetic control of resistance. In contrast, seed lots from ‘Gulshishvela’ and ‘Kharistvala’ yielded significant numbers of resistant plants, which may indicate that dominant genes for resistance are present. Overall, these new plants will add to the genetic resources available for breeding new EFB-resistant cultivars.

The development of new cultivars resistant to the disease eastern filbert blight (EFB), caused by Anisogramma anomala, is of primary importance to hazelnut (Corylus sp.) breeders in North America. Recently, a large number of EFB-resistant cultivars, grower selections, and seedlings from foreign germplasm collections were identified. However, for a significant number of these, little is known of their origin, relationships, or genetic background. In this study, 17 microsatellite markers were used to investigate the genetic diversity and population structure of 323 unique accessions, including EFB-resistant and tolerant germplasm of uncertain origins, in comparison with a panel of known reference accessions representing a wide diversity of Corylus cultivars, breeding selections, and interspecific hybrids. The resulting allelic data were used to construct an unweighted pair group method using arithmetic averages (UPGMA) dendrogram and STRUCTURE diagram to elucidate relationships among the accessions. Results showed 11 consensus groups with EFB-resistant or tolerant accessions in all, providing strong evidence that EFB resistance is relatively widespread across the genus Corylus. Furthermore, open-pollinated seedlings tended to group together with reference accessions of similar geographic origins, providing insight into their genetic backgrounds. The results of this study add to the growing body of knowledge of hazelnut genetic resources and highlight recently introduced EFB-resistant seedling germplasm as new, unrelated genetic pools of resistance.

Hazelnuts (Corylus sp.) are monoecious and wind-pollinated with reproduction limited by a sporophytic self-incompatibility system. They flower during the winter and are dichogamous with the dates of flowering ranging from December to March in New Jersey depending on the genotype, geographic location, and year. Successful, consistent nut production depends on both genetic compatibility and the appropriate timing of flowering between pollinizing and nut-producing cultivars. While the disease eastern filbert blight (EFB), caused by Anisogramma anomala, has severely limited past hazelnut production in the eastern United States, resistant and tolerant genotypes are now available for testing. However, little is known of their flowering phenology in this region. In this study, the flower and budbreak phenology of 19 different EFB-resistant and EFB-tolerant hazelnut accessions was evaluated over 4 years, and the results compared with air temperature data collected during bloom. Results showed that the accessions followed a similar progression of bloom each year (both staminate and pistillate flowers), which allowed their placement into early-, mid-, and late-flowering groups. However, the date of bloom and duration of bloom, especially for pollen shed, differed each year, largely corresponding to average air temperature trends. Confirming previous reports from other cold regions, it was shown that consistently colder average temperatures delayed bloom until later in the winter, which then led to a compressed period of flowering once temperatures warmed. In contrast, relatively warm temperatures over the season led to earlier flowering as well as a significant lengthening of the duration of bloom, similar to responses reported in Mediterranean climates. Our study documents hazelnut flowering phenology under New Jersey’s variable winter climate, and the results provide a benchmark for selecting suitable pollenizers and breeding parents for future nut production, flowering research, and/or genetic improvement in this region.

Central Asia is a center of diversity for many important fruit and nut tree species, including wild and cultivated apricots (Prunus armeniaca L.). A wealth of apricot germplasm that expresses novel and valuable characteristics such as fruits with high soluble solids, edible kernels, glabrous skin, and diverse colors and flavors, as well as later-blooming flowers, late-maturing fruit, and drought, cold, and salt tolerance, can be found growing across this region. Since the dissolution of the Soviet Union, Central Asia has become more accessible for reciprocal germplasm exchange and scientific collaborations. Thus, opportunities now exist to obtain, study, and use a much wider diversity of Central Asian apricot germplasm in breeding efforts, which can lead to improved crop traits and ultimately an expansion of the regions where this high-value crop can be grown. To bring attention to the valuable P. armeniaca genetic resources found in Central Asia and to promote its better use, management, and preservation, a description and history of the species from a Central Asian perspective, along with recent and ongoing activities, are discussed in this article.

Stable genetic resistance to the fungal disease eastern filbert blight (EFB), caused by Anisogramma anomala, is vital for sustainable production of European hazelnut (Corylus avellana) in eastern North America. In this study, new hazelnut germplasm from the Russian Federation, Ukraine, and Poland (a total of 1844 trees from 66 seed lots) was subjected to A. anomala under field conditions over at least five years in New Jersey. Plants were then rated for the presence of EFB using an index of 0 (no disease) through 5 (all stems containing cankers). Nuts of the resistant trees were evaluated to identify plants with improved kernel characteristics. Genomic DNA of these trees was also screened with sequence-characterized amplified region (SCAR) markers generated by the primers BE-03, BE-33, and BE-68, which are closely linked to the single dominant R-gene of ‘Gasaway’, to assess the resistant seedlings for the presence of this well-known source of resistance. At final evaluation, 76 trees remained free of disease with nine expressing only minor symptoms (rating 1 or 2). The resistant trees spanned 24 different seed lots representing all three countries. The remaining trees ranged from moderately to severely infected with 81% of the total collection rating 5. Several of the resistant trees were found to produce commercial-sized (≈12 mm diameter), round kernels that blanched well. Although the results of the ‘Gasaway’ SCAR primers were inconclusive, the diverse collection origins and disease phenotypes provide evidence that novel sources of resistance were likely identified in this study. These new plants should broaden the genetic base of EFB-resistant C. avellana hazelnut germplasm available for breeding.

Eastern filbert blight (EFB), caused by Anisogramma anomala, is a devastating disease of Corylus avellana, the European hazelnut of commerce, and is considered the primary limiting factor of production in eastern North America. Conversely, C. americana, the wild American hazelnut, is generally highly tolerant of EFB, although it lacks many horticultural attributes necessary for commercial nut production. Hybrids of C. americana and C. avellana combine the EFB resistance of the wild species with the improved nut quality of the European species. However, inheritance of EFB resistance from C. americana remains unclear with existing hybrids derived from a very limited selection of parents. To investigate this topic, C. americana and advanced-generation C. americana × C. avellana hybrids were crossed with susceptible C. avellana and the resulting seedlings exposed to EFB through field inoculations and natural disease spread. In the winter after their fifth growing season, plants were rated for the presence of EFB using an index of 0 (no disease) through 5 (all stems containing cankers). The three progeny related to C. americana ‘Rush’ segregated for resistance in a ratio of one resistant to one susceptible, suggesting the presence of a single dominant R gene. A wide array of disease responses was observed for the other progenies with some expressing little EFB resistance or tolerance and others showing a distribution of disease phenotypes typical of control by multiple genes. Overall, the results indicate that both qualitative and quantitative resistance is present in C. americana. They also suggest that the choice of C. americana parent as well as the C. avellana parent will play a significant role in obtaining useful levels of EFB resistance in hybrid offspring, although the degree of disease expression in the parents may not be a useful predictor of progeny performance. Thus, more research is needed to understand inheritance of resistance, especially in advanced-generation backcrosses to susceptible C. avellana.

One hundred ninety clonal accessions of Corylus, including species and various interspecific hybrids of C. avellana, C. americana, C. heterophylla, C. colurna, and C. fargesii, were assessed for their response to field exposure to the eastern filbert blight (EFB) pathogen, Anisogramma anomala, in New Jersey, where the fungus is native. Plants were obtained from the U.S. Department of Agriculture Agricultural Research Service National Clonal Germplasm Repository and Oregon State University, the University of Nebraska, Lincoln, and the National Arbor Day Foundation. Additional plant material was acquired from the Morris and Holden Arboreta and from private nurseries in Amherst, NY, and Niagara-on-the-Lake, Ontario, Canada. The accessions were chosen based on their resistance to EFB in Oregon, a region where A. anomala is not native, or anecdotal reports and grower observations of tolerance or resistance to the disease. Trees were planted in the field from 2002 through 2009 in New Jersey where they were exposed to EFB yearly through field inoculations and natural spread. In Jan. 2012, they were visually evaluated for the presence of EFB. The cankers were measured, and the proportion of diseased wood was calculated for susceptible trees. Nearly all accessions reported to be resistant to EFB in Oregon maintained at least a useful level of tolerance in New Jersey with a number remaining free of cankers. However, several accessions developed small to medium-sized cankers and showed branch dieback, including offspring of C. avellana ‘Gasaway’. Most C. americana and C. heterophylla accessions remained free of EFB, although variation in EFB response was found in hybrids of these species with C. avellana, ranging from no signs or symptoms to severe EFB. Nearly half of the C. colurna × C. avellana hybrids developed cankers, whereas each of the C. fargesii accessions and most grower selections developed in eastern North America remained free of EFB. The results document the existence of a wide diversity of Corylus germplasm that expresses resistance or a high level of tolerance to EFB in New Jersey and confirms previous reports that C. americana is highly resistant to the disease. Interestingly, most C. heterophylla and the C. fargesii were also found to be resistant despite originating in Asia where A. anomala has not been found. The various interspecific hybrids show the potential for incorporating EFB resistance from wild species through breeding. The results provide further evidence of differences in disease expression in Oregon and New Jersey, where isolates differ and disease pressure may be higher.

Eastern filbert blight (EFB) is a serious disease of European hazelnut, Corylus avellana L., which causes economic losses in Oregon (OR) where 99% of the U.S. crop is produced. The causal organism, Anisogramma anomala (Peck) E. Müller, is native east of the Rocky Mountains where it is found in association with C. americana Marshall. While C. americana is tolerant, EFB causes cankering, branch dieback, and death of C. avellana (3). EFB was first discovered in Washington State in the late 1960s (1). Since then, it has spread throughout the Willamette Valley of OR. In OR, ‘Gasaway’, an obsolete pollinizer, shows complete resistance to EFB, conferred by a dominant allele at a single locus (4). ‘Gasaway’ has been widely used in breeding at Oregon State University (OSU) to develop resistant cultivars that are used in most new orchards. In January 2008, cankers containing rows of dark brown elliptical stroma, characteristic of EFB, were first observed on more than 25 trees of ‘Gasaway’ growing at the Rutgers University research farms in Adelphia and North Brunswick, NJ. At that time, cankers were also found on 18 trees of ‘VR20-11’ growing on the research farms. ‘VR20-11,’ an offspring of ‘Gasaway’ that carries the same resistance gene, was released by OSU for use as a pollinizer for ‘Barcelona’, an EFB-susceptible but widely grown cultivar in OR. Additional cankers were observed on the New Jersey trees in January 2009 and 2010. To our knowledge, this is the first report of EFB on either cultivar under field conditions. The cankers are smaller than those on susceptible cultivars. Of 61 cankers on 10 trees of ‘Gasaway’, the average length was 11 cm with a range of 4 to 42 cm. Canker lengths on susceptible trees are typically 20 to 100 cm. The cankers appear otherwise alike with stromata, 2 to 4 × 2 mm, up to 2 mm high; perithecia upright, in the lower part of stroma; asci ellipsoid, 35 to 45 × 9 to 12 μm; and ascospores 8 to 11 × 4 to 5.5 μm, hyaline, smooth, ellipsoid, 2-celled, with the lower cell very short (1 to 1.5 μm long and wide). Genomic DNA was isolated from ascospores excised from cankers of ‘Gasaway’ and ‘VR20-11’. ITS1F and ITS2 primers were used to amplify and sequence the internal transcribed spacer 1 region (ITS1) of the rRNA genes (GenBank Accession Nos. HM565133 and HM565132). BLAST analysis of the 238-bp segments showed 99% homology with a sequence of A. anomala (EU683064). Phylogenetic analysis also confirmed that the two isolates are A. anomala. To test viability, ‘Gasaway’ cankers were excised and ascospore suspensions (1 × 106 spores ml–1) were applied to 15 trees of susceptible ‘Barcelona’ in March 2008 following the protocol of Johnson et al. (2). In December 2009, 12 of 15 inoculated trees expressed EFB. ‘Gasaway’ has shown no signs or symptoms of infection by A. anomala over several decades of exposure in OR, which is believed to have a limited diversity of the fungus due to a single-point introduction. Our findings suggest quarantine efforts must be bolstered to prevent further introductions of A. anomala into the Pacific Northwest to protect the viability of the U.S hazelnut industry. References: (1) A. D. Davison and R. M. Davidson, Jr. Plant Dis. Rep. 57:522, 1973. (2) K. B. Johnson et al. Phytopathology 84:1465, 1994. (3) K. B. Johnson and J. N. Pinkerton. Eastern filbert blight. Page 44 in: Compendium of Nut Crop Diseases in Temperate Zones. B. L. Teviotdale et al., eds. The American Phytopathological Society. St. Paul, MN. 2002. (4) S. A. Mehlenbacher et al. HortScience 26:410, 1991.