Corylus Americana Research Articles

Identification of Compounds That Contribute to Consumer Aroma Liking of Roasted American-European Hybrid Hazelnuts.

New interspecific hybrid hazelnut crosses between American (Corylus americana) and European (Corylus avellana) hazelnuts are being developed to support a commercial industry in the Midwest region of the United States. In this study, volatile compounds that impact consumer aroma liking of roasted hybrid hazelnuts (C. americana × C. avellana) were investigated by targeted and nontargeted GC/MS flavoromics. Chemical profiles from 10 roasted hybrid hazelnut samples were modeled with consumer aroma liking scores by orthogonal partial least-squares with good fit and predictive performance (R2 ≥ 0.92, Q2 ≥ 0.82, RMSECV = 0.2). Top ranked predictors positively correlated with liking included 12 aroma compounds and 4 profiled volatiles for the targeted and nontargeted methods, respectively. Sensory recombination testing of hazelnut samples with addition of the 12 predictive odorants was preferred by consumers (p < 0.001, Δ aroma liking = 2.2 on 9-point scale) and perceived as more roasty, nutty, and sweet compared to the control (p < 0.05). Addition of the 4 predictive volatiles at subthreshold levels also was preferred (p = 0.02) and perceived as less earthy and mushroom like than the control (p < 0.05).

Characterization and Profiling of Key Odorants in Roasted Hybrid American-European Hazelnuts.

American-European hybrid hazelnuts (Corylus americana × Corylus avellana) are an emerging crop in the Upper Midwest of the United States that have been reported to have unique sensory characteristics compared to traditionally grown European hazelnuts. In this study, key odor-active compounds in a roasted hybrid hazelnut variety (C. americana × C. avellana) were identified and profiled across different hybrid hazelnut varietals to understand sensory differences. Gas chromatography/mass spectrometry/olfactometry analysis identified 33 odorants with high flavor dilution factors (FD ≥ 16) in the roasted hybrid hazelnut, including 2-acetylpyrazine and 2-aminoacetophenone as first reported hazelnut odorants. Descriptive sensory analysis profiles of the roasted hazelnut and an aroma recombination model consisting of 27 odorants quantified above their odor detection thresholds were not significantly different for the six evaluated attributes, confirming the aroma contribution of the identified odorants. Variation in all 33 aroma-active compounds across 12 hybrid and two European hazelnut varieties was visualized through principal component analysis and related to aroma profiles previously characterized by consumers.

Consumer acceptance and sensory perception of roasted American-European hybrid hazelnuts.

Interspecific American-European hazelnut (Corylus americana × C. avellana) hybrids are being developed for the Upper Midwest region of the United States, which have potential economic and ecological benefits. Currently, researchers are working on pre-commercialization initiatives to create a local hazelnut industry. However, a lack of knowledge on the sensory characteristics and consumer acceptability of the hybrid hazelnuts have been identified as potential limitations to production. This study investigated consumer responses to hybrid hazelnuts, employing hedonic ratings and check-all-that-apply (CATA) questions. Twelve roasted hazelnut hybrids were subjected to consumer evaluation for liking (aroma, color, flavor, texture, and overall) and aroma and flavor descriptors. Consumers also evaluated two European hazelnut varieties for comparative purposes. Liking scores were significantly different (p<0.05) across different hybrid varieties and when comparing specific hybrids with European varieties. CATA sensory profiles specific to different varieties were also observed and discriminating attributes were identified using multiple-response methodologies. Penalty analysis based on CATA further identified the attributes roasty, hazelnut-like, caramel-like, chocolate-like, sweet, and salty as primary drivers of aroma/flavor liking, while earthy, burnt, and bitter were identified as primary drivers of disliking. Overall, unique flavors that impacted liking were found in hybrid hazelnuts and, when compared with European hazelnuts, provided insights for breeding and post-processing strategies to optimize product quality.

The massive 340 megabase genome of Anisogramma anomala, a biotrophic ascomycete that causes eastern filbert blight of hazelnut

BackgroundThe ascomycete fungus Anisogramma anomala causes Eastern Filbert Blight (EFB) on hazelnut (Corylus spp.) trees. It is a minor disease on its native host, the American hazelnut (C. americana), but is highly destructive on the commercially important European hazelnut (C. avellana). In North America, EFB has historically limited commercial production of hazelnut to west of the Rocky Mountains. A. anomala is an obligately biotrophic fungus that has not been grown in continuous culture, rendering its study challenging. There is a 15-month latency before symptoms appear on infected hazelnut trees, and only a sexual reproductive stage has been observed. Here we report the sequencing, annotation, and characterization of its genome.ResultsThe genome of A. anomala was assembled into 108 scaffolds totaling 342,498,352 nt with a GC content of 34.46%. Scaffold N50 was 33.3 Mb and L50 was 5. Nineteen scaffolds with lengths over 1 Mb constituted 99% of the assembly. Telomere sequences were identified on both ends of two scaffolds and on one end of another 10 scaffolds. Flow cytometry estimated the genome size of A. anomala at 370 Mb. The genome exhibits two-speed evolution, with 93% of the assembly as AT-rich regions (32.9% GC) and the other 7% as GC-rich (57.1% GC). The AT-rich regions consist predominantly of repeats with low gene content, while 90% of predicted protein coding genes were identified in GC-rich regions. Copia-like retrotransposons accounted for more than half of the genome. Evidence of repeat-induced point mutation (RIP) was identified throughout the AT-rich regions, and two copies of the rid gene and one of dim-2, the key genes in the RIP mutation pathway, were identified in the genome. Consistent with its homothallic sexual reproduction cycle, both MAT1-1 and MAT1-2 idiomorphs were found. We identified a large suite of genes likely involved in pathogenicity, including 614 carbohydrate active enzymes, 762 secreted proteins and 165 effectors.ConclusionsThis study reveals the genomic structure, composition, and putative gene function of the important pathogen A. anomala. It provides insight into the molecular basis of the pathogen’s life cycle and a solid foundation for studying EFB.

Identification of Compounds That Impact Consumer Flavor Liking of American-European Hazelnut Hybrids Using Nontargeted LC/MS Analysis.

American-European (Corylus americana × Corylus avellana) hazelnut hybrids are being developed for the Midwest-growing region of the United States. However, an inadequate understanding of the compounds that impact the consumer acceptance of hazelnuts limits breeding programs. Nontargeted liquid chromatography/mass spectrometry (LC/MS) chemical profiles of 12 roasted hybrid hazelnut samples and the corresponding consumer flavor liking scores were modeled by orthogonal partial least squares with good fit and predictive ability (R2Y > 0.9, Q2 > 0.9) to identify compounds that impact nut liking. The five most predictive compounds (1-5) were negatively correlated to flavor liking, selected as putative markers, purified by multidimensional preparative LC/MS, structurally elucidated (nuclear magnetic resonance, MS), quantified, and validated for sensory relevance. Compound 1 was identified as 1″-O-3'-b-glucofuranosyl-1'-O-1-b-glucofuranosyl-(2,6-dihydroxyphenyl)-ethan-4-one. Compounds 2 and 4 were identified as rotamers of 2-(3-hydroxy-2-oxoindolin-3-yl) acetic acid 3-O-6'-galactopyranosyl-2″-(2″oxoindolin-3″yl) acetate, whereas compounds 3 and 5 were identified as rotamers of 1″-O-1'-b-glucofuranosyl-9-O-6'-b-glucopyranosyl-2″-(2″-oxoindolin-3″yl) acetate. Sensory evaluation determined that all compounds were characterized by bitterness and/or astringency. The sensory threshold values of compounds 1-5 were determined to be below the concentrations reported in 91, 83, 41, 25, and 41% of all 12 hybrid hazelnut samples, respectively, indicating they contributed to aversive flavor attributes.

Evaluation of nitrogen fertilization of hybrid hazelnuts (Corylus americana × Corylus avellana) based on leaf nitrogen sufficiency thresholds

Hybrids between Corylus avellana and Corylus americana are one of several new perennial and winter annual crops being developed as part of the Forever Green Initiative at the University of Minnesota. As a woody perennial shrub, hazelnuts in agroforestry systems can provide a new revenue source for rural landowners; continuous living cover to prevent soil erosion, sequester soil carbon, protect water quality, and provide wildlife habitat; and a delicious and healthful new local food. If hazelnuts are to fulfill their potential, better germplasm and better nitrogen fertilization recommendations are both needed. We modeled these trials after trials by R.E. Worley, who showed that yields of pecan trees fertilized only when leaf nitrogen (N) fell below critical thresholds were maintained with lower levels of applied N, benefitting both the environment and growers’ profits. Results of trials at three Minnesota sites, comparing N applied only when leaf N fell below 1.8%, 2.0%, or 2.2% with annual N applications and no N over 4 years, support using 2.2% leaf N as the critical threshold for N fertilization. Our results showed that whereas only 8% of N applied annually ended up in the harvested nuts and husks, N that was applied to plants that demonstrated hunger for it was more efficiently taken up. Our results suggest a need for more productive germplasm and further research to develop best management practices for N fertilization.

The first two chromosome-scale genome assemblies of American hazelnut enable comparative genomic analysis of the genus Corylus.

The native, perennial shrub American hazelnut (Corylus americana) is cultivated in the Midwestern United States for its significant ecological benefits, as well as its high-value nut crop. Implementation of modern breeding methods and quantitative genetic analyses of C. americana requires high-quality reference genomes, a resource that is currently lacking. We therefore developed the first chromosome-scale assemblies for this species using the accessions 'Rush' and 'Winkler'. Genomes were assembled using HiFi PacBio reads and Arima Hi-C data, and Oxford Nanopore reads and a high-density genetic map were used to perform error correction. N50 scores are 31.9 Mb and 35.3 Mb, with 90.2% and 97.1% of the total genome assembled into the 11 pseudomolecules, for 'Rush' and 'Winkler', respectively. Gene prediction was performed using custom RNAseq libraries and protein homology data. 'Rush' has a BUSCO score of 99.0 for its assembly and 99.0 for its annotation, while 'Winkler' had corresponding scores of 96.9 and 96.5, indicating high-quality assemblies. These two independent assemblies enable unbiased assessment of structural variation within C. americana, as well as patterns of syntenic relationships across the Corylus genus. Furthermore, we identified high-density SNP marker sets from genotyping-by-sequencing data using 1343 C. americana, C. avellana and C. americana × C. avellana hybrids, in order to assess population structure in natural and breeding populations. Finally, the transcriptomes of these assemblies, as well as several other recently published Corylus genomes, were utilized to perform phylogenetic analysis of sporophytic self-incompatibility (SSI) in hazelnut, providing evidence of unique molecular pathways governing self-incompatibility in Corylus.

The Hazel Stem Borer, Agrilus pseudocoryli (Coleoptera: Buprestidae), as a Pest of Hybrid Hazelnuts.

Nuts from hybrid hazels (Corylus americana Walter × Corylus avellana L.) are a burgeoning, novel industry for the Great Lakes region of the United States. As such, scant information exists about the pest complex, although stem-boring beetles in the genus Agrilus Curtis (Coleoptera: Buprestidae) have been noted by growers as potential pests. Here, we report results of a comprehensive survey of 186 plants in a hybrid hazel planting consisting of nine cultivars in southeastern Minnesota affected by stem borers. Sixteen percent of the hybrid hazel plants exhibited between 25 and 100% buprestid associated dieback. Morphological and molecular identification of the adult and larval buprestids colonizing hybrid hazel plants revealed that the hazel stem borer, Agrilus pseudocoryli Fisher, was the only species present. Adult A. pseudocoryli were observed on plants between 8 June and 13 July 2021. Plants with higher damage ratings from the hazel stem borer were more likely to exhibit signs of eastern filbert blight (Anisogramma anomala Peck), a fungal pathogen virulent to C. avellana. Some hazel cultivars were more susceptible to damage from stem borers than others. Taken together, our findings suggest that the hazel stem borer has the potential to impact hybrid hazelnut yield. We speculate that a regional drought may have promoted increased populations of the hazel stem borer, as native Agrilus species are often secondary pests that become problematic when environmental stresses decrease host resistance. More research is needed to elucidate interactions between hazels, buprestid pests, and environmental conditions to predict impacts on crop yields.

A disjunct population of American Hazelnut (&lt;i&gt;Corylus americana&lt;/i&gt;): a new plant species for the Ottawa district

A previously unknown population of American Hazelnut (Corylus americana), a native shrub species, has been discovered in the Ottawa district. This location is disjunct from the species’ nearest known populations. Although American Hazelnut is not a particularly conspicuous species, it was found in a relatively well documented area. The location includes remnant vegetation from the Constance Bay Sandhills, a former savannah habitat, including other species whose occurrence in the region is disjunct. American Hazelnut is strongly affiliated with savannahs and related habitats across Ontario and the upper midwest of the United States.

Improvements for the Micropropagation of Hybrid Hazelnut (C. americana × C. avellana)

The micropropagation of hybrid hazelnut (Corylus americana × Corylus avellana) has been limited in its agricultural application due to the lack of efficient procedures for tissue culture and root organogenesis. We established an efficient sterilization protocol for hazelnut micropropagation suitable for in vitro root induction that permitted us to approach the poor root organogenesis experienced with the micropropagation of hazelnut hybrids in vitro. Typically, with standard protocols, root organogenesis had yields of well under 20%. We found that cuttings grown in vitro to the four-leaf stage can be successfully rooted using a combination of indole-3-butyric acid (IBA) pretreatment, followed by a one-week growth period in absolute darkness. The dark period was then followed by a transition to continuous light. In many cases, prolific visible roots formed between 12 and 14 days.

First rhyncaphytoptine mite (Eriophyoidea, Diptilomiopidae) parasitizing American hazelnut (Corylus americana): molecular identification, confocal microscopy, and phylogenetic position.

The plant genus Corylus is an economically important crop, valued especially for its nuts. Numerous pathogens and harmful phytophagous arthropods are known to damage hazelnuts. We report on a new eriophyoid mite, Rhyncaphytoptus corylivagrans n. sp., and the first record of Coptophylla lamimani both collected from leaves of American hazelnut (Corylus americana) in North Carolina, USA. Including our new data, the complex of eriophyoids from Corylus comprises 15 species from three families: Phytoptidae (2 spp.), Eriophyidae (11 spp.), and Diptilomiopidae (2 spp.). We obtained sequences of three genes (Cox1, D1-D5 28S, and ITS1-5.8S-ITS2), applied BLAST and tree-based approaches for identification of R. corylivagrans n. sp., and performed the first molecular phylogenetic analysis focused on Rhyncaphytoptinae. Among the three genes, Cox1 showed better power when used for BLAST searches. Combined molecular phylogenetic analyses inferred R. corylivagrans n. sp. as sister to R. betulae, determined several moderately supported host-specific lineages of rhyncaphytoptines, and indicated a close relationship of the new species with members of the genus Rhinotergum. In two Rhinotergum spp. from Rosaceae, confocal microscopy revealed a new structure, the needle-like anterior process of the prodorsal shield, which is absent in R. corylivagrans n. sp. Additionally, the elements of the anal secretory apparatus presumably associated with silk-production and hypothesized as a synapomorphy of Eriophyoidea, were detected in the new species, providing the first documented report of this structure in Diptilomiopidae. Our study contributes to knowledge on the biodiversity of phytoparasites associated with hazelnuts and calls for future comparative phylogenetics of Diptilomiopidae.

Using plants to control buckthorn (Rhamnus cathartica): Improved biotic resistance of forests through revegetation

Woody invaders of temperate forest understories reduce native diversity worldwide. Common buckthorn Rhamnus cathartica, is among the most widespread of such invaders in North America. Invaded communities often have seedbanks largely comprised of the dominant invader - with few native species remaining - and therefore lack the capacity to build biotic resistance against re-invasion following invader removal. Consequently, invaders, including buckthorn, often quickly re-establish in the absence of continued management. We investigated the capacity of native plant revegetation to inhibit buckthorn re-establishment from seedbanks in the understories of three forests of Minnesota, USA. Specifically, we established experimental plots subjected to seeding of 35 native species, planting of Pennsylvania sedge (Carex pensylvanica) plugs, or bare-root plantings of either mixed shrubs (Sambucus canadensis, Sambucus racemosa, Corylus americana, and Cornus racemosa) or mixed trees (Abies balsamea and Acer saccharum). We then measured buckthorn germinant establishment, growth, and survival for the following four growing seasons. We observed consistent impacts of revegetation on ground-level light availability and associated buckthorn performance. Compared to unplanted understory controls beneath the mature tree canopy, shrub plantings were the most impactful. Shrubs reduced light availability to buckthorn seedlings by 67% relative to unplanted controls (to <2% total light by the third year) and led to 51% lower year-over-year survival of buckthorn by the end of the experiment. Revegetation also suppressed buckthorn seedling growth. After four years, shrub plantings resulted in buckthorn that were 53% shorter and had 38% fewer leaves than buckthorn grown in unplanted controls. Considering the combined impacts on survival and growth, planted shrubs, trees, and sedges reduced buckthorn invasion by 89%, 81%, and 66%, respectively; and seeding alone reduced invasion by 51%. Our findings indicate that revegetating forests, particularly with shrubs and trees, can greatly reduce invasion by buckthorn and potentially other species. Greater adoption of revegetation by land managers may therefore increase native biodiversity, reduce herbicide applications, and improve the overall health and value of forests.

Segregation of Eastern Filbert Blight Disease Response and Single Nucleotide Polymorphism Markers in Three European–American Interspecific Hybrid Hazelnut Populations

The perennial stem canker disease eastern filbert blight (EFB), caused by Anisogramma anomala, is devastating to most trees of European hazelnut (Corylus avellana), as genetic resistance is rare in the species. The pathogen is harbored by the wild American hazelnut (Corylus americana) found throughout much of eastern North America. Wild American hazelnut is generally resistant or tolerant to EFB, and is fully cross compatible with C. avellana, the species grown commercially for its nuts, making it a valuable resource for disease resistance breeding. The objective of this study was to identify quantitative trait loci (QTLs) associated with EFB resistance and tolerance in these two species. Three unrelated EFB-resistant C. americana selections [Oregon State University (OSU) 533.069 from Pennsylvania, OSU 403.040 from Nebraska, and OSU 557.122 from Wisconsin] were crossed with C. avellana ‘Tonda di Giffoni’ (TdG), a cultivar from Italy known to be tolerant of EFB. Their progenies, each containing 124 trees, were exposed to A. anomala through field inoculations and natural spread over 7 years, then each tree was evaluated for cumulative disease response. Results showed that disease response of all three populations exhibited a roughly normal distribution, indicating that resistance/tolerance was under multigenic control. An average of 2869 total markers were used to construct each population’s linkage map following genotyping, which included an average of 121 published simple sequence repeat markers to anchor linkage groups (LGs) to those of previous studies. Linkage maps were constructed for each parent of each population and used to map QTLs associated with EFB response. The subsequent analysis resolved five EFB-related QTLs across the three populations, highlighting three genic regions. Unexpectedly, only one QTL was identified from one of the three resistant C. americana parents, located on LG11 of the map of OSU 403.040, whereas three QTLs were found in a similar region on LG10 across the three maps of TdG, and a fifth QTL was found on LG6 of one TdG map. The lack of strong QTLs identified from the three EFB-resistant C. americana parents suggests that their resistance may be highly quantitative and not resolved within the constraints of this study. In contrast, tolerance from TdG appears to be conferred by a limited number of genes with relatively strong effects. Based on prior mapping work in European and American hazelnut where R genes have been located on LG2, LG6, and LG7, the QTLs associated with resistance/tolerance on LG10 and LG11 represent novel resistance regions. These QTLs present new targets for marker aided breeding, especially when pyramiding EFB resistance genes is a goal.

Phenological niche overlap between invasive buckthorn (Rhamnus cathartica) and native woody species

Common buckthorn (Rhamnus cathartica L.) is a prolific invader of forest understories throughout eastern North America. Its ability to invade is partially attributable to its relatively high shade tolerance and ability to capture light both early and late in the growing season because of its phenological differences from native species. Competitors that mitigate this phenological advantage by casting shade early and late in the growing season may therefore increase biotic resistance against invasion. However, controlled comparisons between buckthorn and other woody understory species are scarce and to what extent buckthorn’s phenology is truly exceptional is incompletely known. Here, we compare the spring and autumn phenologies of five shade tolerant, native woody species (Sambucus canadensis, Sambucus racemosa, Corylus americana, Cornus racemosa, and Acer saccharum) to those of buckthorn in two common garden experiments. Spring phenology of buckthorn was often comparable to the five native species considered. All native species broke bud no later than 7 days after buckthorn, with S. racemosa reaching spring phenophases consistently earlier than buckthorn. In contrast to spring, buckthorn fall phenology was distinct in comparison to some natives but not all. Native species started to senesce up to 20 days earlier than buckthorn, but both Sambucus species senesced slowly and held their leaves equally long as buckthorn. These findings illustrate that buckthorn does not possess unique phenology amongst understory species. Forest communities rich in deciduous shrubs or trees that are phenologically similar to buckthorn (particularly S. racemosa) likely limit buckthorn's critical spring and fall carbon gains and exert greater biotic resistance to invasion by buckthorn.

New Simple Sequence Repeat Markers on Linkage Groups 2 and 7, and Investigation of New Sources of Eastern Filbert Blight Resistance in Hazelnut

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.

Using genotyping-by-sequencing derived SNPs to examine the genetic structure and identify a core set of Corylus americana germplasm

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.

Eastern Filbert Blight Resistance in American and Interspecific Hybrid Hazelnuts

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.

Field Pretreatment of Crown Suckers for Propagating Hybrid Hazelnuts

Abstract Hybrid hazelnuts [Corylus americana (Walter) x C. avellana (L.)] are being developed for their ecological and economic value as a new crop for the Upper Midwest, but lack of economically viable propagation methods is a significant bottleneck to their wide scale adoption. Thus far, mound layering has been the primary propagation method, but layering cannot produce the numbers of plants needed for large-scale production. Rooting hardwood stem cuttings is a possible alternative. In a factorial experiment, we evaluated two pretreatments, blanching with sawdust and application of IBA, applied to rapidly growing first year collar suckers in the field five months ahead of collection for rooting. These treatments simulated mound layering, but without girdling. Sawdust by itself significantly increased both quantity and quality of subsequent rooting, but IBA pretreatment in combination with sawdust produced even better results. Stem cuttings were rooted in a growth chamber, set at 22 C (72 F) and 60% relative humidity, with PAR of 320 umol.m−2 s−1 for 16 hours per day. The lack of heat stress in the growth chamber likely also contributed to relatively high rooting relative to the humidity tents used in previous trials. Index words: Propagation, Corylus americana (Walter), Corylus avellana (L.), rooting, etiolation. Chemicals used in this study: indole-3-butyric acid (IBA). Species used in this study: hybrid hazelnuts [Corylus americana (Walter) x Corylus avellana (L.)].

Timing of Collection and Preparation of Hardwood Stem Cuttings for Propagating Hybrid Hazelnuts 1

AbstractIn previous trials we had found that dormant hybrid hazelnuts crown suckers collected in the fall after leaf drop can be successfully rooted if they are chilled at least until January before being placed in low-cost humidity tents in a greenhouse. The first objective of this experiment was to determine if cuttings could be rooted if started earlier, so as to avoid the heat stress found in the greenhouse in late spring and early summer. The second objective was to see if rooting rates could be improved by collecting non-dormant crown suckers in September and October, before leaf drop. We hypothesized that by collecting stems at a time in the fall when woody plants are translocating resources from leaves to their root systems, we could direct those resources towards growth of adventitious roots. This hypothesis proved to be wrong: stems collected in full leaf died, even with measures to avoid moisture loss from leaves. However, we found that stems collected soon after leaf abscission, in early November, could be rooted if placed in the humidity tents in late November, after only three weeks of artificial chilling at 2 C (36 F). That is much less chilling than we previously thought was needed.Index words: propagation, Corylus americana (Walter), Corylus avellana (L.), rooting, chilling requirement.Chemicals used in this study: indole-3-butyric acid (IBA).Species used in this study: hybrid hazelnuts [Corylus americana (Walter) x Corylus avellana (L.)].

Optimizing Temperature and Humidity for Rooting Hybrid Hazelnuts from Hardwood Stem Cuttings1

Abstract Hybrid hazelnuts are being developed as a new crop for the Upper Midwest for their ecological and economic value, but lack of economically viable propagation methods is a significant bottleneck to their wide scale adoption. In previous trials we found that hardwood stem cuttings could be propagated in low cost humidity tents constructed of molded plastic tubs covered with white 70% shade plastic. When the plastic was sealed tightly at the sides, these tubs maintained relative humidity near saturation, but also tended to overheat. This trial experimented with the use of ordinary household humidifiers as an alternative way of maintaining humidity while avoiding overheating. We found that it is not necessary to maintain RH near 100% as we had been doing when we kept the humidity tents tightly sealed. Stem survival and, as a consequence, rooting were improved in vented tents in which humidity was maintained with humidifiers, though these required much more management than the sealed tents. Index words: Propagation, Corylus americana (Walter), Corylus avellana (L.), rooting, indole-3-butyric acid Chemicals used in this study: indole-3-butyric acid (IBA) Species used in this study: hybrid hazelnuts [Corylus americana (Walter) x Corylus avellana (L.)]