The Sixth International Workshop on the Genetics of Host-Parasite Interactions in Forestry-Tree R... more The Sixth International Workshop on the Genetics of Host-Parasite Interactions in Forestry-Tree Resistance to Insects and Diseases: Putting Promise into Practice was held the first week of August 2018 at Deer Creek State Park in Mt. Sterling, Ohio. The workshop provided a continuing forum for researchers, tree breeders, and forest managers to focus on perhaps the most salient action society can take to restore tree species imperiled by invasive pests and pathogens-developing and deploying resistant tree populations. The 95 presentations (oral and poster) covered a wide range of tree species and associated pathogens and pests from throughout the world. Ash species (genus Fraxinus) throughout Europe and North America face relatively new perils (ash dieback disease and emerald ash borer) and a special session was devoted to this genus. Screening for resistance is a fundamental component of resistance development and the topic of another full session. Additional presentations detailed efforts to develop genomics and biotechnology tools and resources that have the potential to increase the efficiencies of applied resistance programs. Other presentations provided inputs on collaborative breeding approaches, citizen science in forest health, the potential role of endophytes in managed forests, threats to agroforestry species, prioritization of species in need of resistance programs, considerations necessary for the use of new biotechnologies, and concepts for integrating genetic, phenotypic and environmental data across host-parasite systems. Several presentations provided updates on "the ultimate goal"-progress of applied resistance programs and actual restoration efforts-leading into discussions on key topics such as the durability, stability, and usability of resistance in forest tree species. Taken together the presentations and discussions provided ample evidence that developing resistant populations is a viable (and in some cases necessary) approach for society to use to ensure healthy forests for future generations. These proceedings document the presentations given as lightly reviewed full papers, extended abstracts, and standard abstracts. In concluding the workshop, the attendees approved Spain by acclamation as the host of the Seventh Tree Resistance Workshop to be held in 2020 1 .
Since emerald ash borer (EAB), Agrilus planipennis, was discovered in North America in 2002, it h... more Since emerald ash borer (EAB), Agrilus planipennis, was discovered in North America in 2002, it has killed many millions of ash trees in North America, and ash mortality now exceeds 99% near the epicenter of the invasion in southeast Michigan (Klooster et al. 2014). The development of EAB-resistant ash trees will be critical for restoration of ash in natural and urban forests. Goals of our collaboration are to identify, breed and screen ash germplasm for EAB resistance and silvicultural traits; and identify mechanisms of EAB resistance to facilitate breeding and screening.
The original version of this article unfortunately contained a mistake. The presentation of Figs.... more The original version of this article unfortunately contained a mistake. The presentation of Figs. 3, 4,5 and 6 was incorrect. The correct figures are given below. The original article has also been corrected.
The emerald ash borer (Agrilus planipennis, EAB) invasion in North America threatens most North A... more The emerald ash borer (Agrilus planipennis, EAB) invasion in North America threatens most North American Fraxinus species, including green ash (F. pennsylvanica), the mostly widely distributed species (1, 2). A small number of green ash (“lingering ash”, 0.1-1%) survive years of heavy EAB attack (3) and kill more EAB larvae when challenged in greenhouse studies than susceptible controls (4). We combined untargeted metabolomics with intensive phenotyping of segregating F1 progeny from susceptible or lingering ash parents to detect chemotypes associated with defensive responses to EAB. We examined three contrasting groups: low larval kill (0-25% of larvae killed), high larval kill (55-95% of larvae killed) and uninfested. Contrasting the chemotypes of these groups revealed evidence of an induced response to EAB. Infested trees deployed significantly higher levels of select secoiridoids than uninfested trees. Within the infested group, the low larval kill (LLK) individuals deployed sig...
In: Publication: Gen. Tech. Rep. SRS-252. Asheville, NC: U.S. Department of Agriculture Forest Service. Southern Research Station, 2020
Exotic pests and pathogens are causing widespread decline and possible extirpation of several of ... more Exotic pests and pathogens are causing widespread decline and possible extirpation of several of our foundational forest tree species. The decline of such species has large-scale effects on their associated ecosystems and services they provide. A steady barrage of new threats to important forest species is anticipated to continue as a by-product of increasing global trade. The Forest Health Initiative (FHI) was conceived in recognition of these issues and the challenges they present to biodiversity and ecosystem sustainability. The FHI concept is a new paradigm that engages social, regulatory, and biological science experts and various stakeholders in developing and evaluating options for solving our most critical forest health problems. Blight resistance in American chestnut was selected as a test case for FHI, and although not completely solved, significant progress is being made and the promise of effective resistance and chestnut restoration has been advanced. Clearly additional work remains for American chestnut as well as the many other severely threatened forest tree species. To address these additional species, we are building on the FHI experience and developing two complementary initiatives designed to improve the ability of the research community to identify, produce, and deploy effective tree resistance. A projectoriented initiative, Forest.Health, will prioritize the most seriously threatened species, bring researchers and stakeholders together to reach consensus on a science-based solution, and seek collaborators and funding to carry out the work. At the same time, a network-based participatory tree breeding consortium is proposed to ensure long-term development of publically available, genetically improved forest trees.
In: Publication: Gen. Tech. Rep. SRS-252. Asheville, NC: U.S. Department of Agriculture Forest Service. Southern Research Station, 2020
American beech (Fagus grandifolia Ehrh.) is an aesthetically, ecologically, and economically impo... more American beech (Fagus grandifolia Ehrh.) is an aesthetically, ecologically, and economically important native component of the North American eastern hardwood forest. American beech is susceptible to beech bark disease (BBD), however, and has suffered high rates of mortality as the disease complex spreads. The invasive sap-feeding woolly beech scale insect (Cryptococcus fagisuga) is the pre-disposing factor for infection by introducing either Neonectria faginata or N. ditissima fungus species that result in extensive cankering of American Beech trees. A small percentage of trees survive BBD attack, and many of these show signs of natural resistance to the insect vector in the egg-inoculation tests used to assay for resistance. We have developed and applied genomics resources to learn more about the molecular genetic basis of gene expression and gene sequence variation associated with cases of natural resistance to the insect. Initially, transcriptome resources were developed, and differential gene expression analyses conducted from which candidate genes were selected. From the transcriptome, an SNP chip assay was developed to genotype an association population of 506 individuals from across the American beech range, 249 of which were resistant and 257 susceptible to BBD. We also constructed a genetic linkage map based on SNPs with a full-sib family of 115 individuals to locate BBD-resistance QTL. The GWAS project revealed four highly significant SNPs on Linkage Group 5 for a single gene encoding a metallothioneinlike protein. Metallothioneins are cysteine-rich metal chelator proteins that can moderate oxidative stress by coordinating metal atoms, which may provide a resistance mechanism against the woolly beech scale insect.
Green ash (Fraxinus pennsylvanica) is the most widely distributed ash tree in North America. Once... more Green ash (Fraxinus pennsylvanica) is the most widely distributed ash tree in North America. Once common, it has experienced high mortality from the non‐native invasive emerald ash borer (EAB; Agrilus planipennis). A small percentage of native green ash trees that remain healthy in long‐infested areas, termed “lingering ash,” display partial resistance to the insect, indicating that breeding and propagating populations with higher resistance to EAB may be possible. To assist in ash breeding, ecology and evolution studies, we report the first chromosome‐level assembly from the genus Fraxinus for F. pennsylvanica with over 99% of bases anchored to 23 haploid chromosomes, spanning 757 Mb in total, composed of 49.43% repetitive DNA, and containing 35,470 high‐confidence gene models assigned to 22,976 Asterid orthogroups. We also present results of range‐wide genetic variation studies, the identification of candidate genes for important traits including potential EAB‐resistance genes, an...
4 We define iconic species as foundational or keystone species in the ecological sense indicating... more 4 We define iconic species as foundational or keystone species in the ecological sense indicating that they disproportionately affect the forest's flora and fauna and the succession of the forest itself.
The emerald ash borer (EAB, Agrilus planipennis) continues to kill ash trees in North America at ... more The emerald ash borer (EAB, Agrilus planipennis) continues to kill ash trees in North America at an alarmingly fast pace. Although EAB is a threat to all species of ash (Fraxinus) in the United States, green ash (F. pennsylvanica) is among the most susceptible. Among the most commonly planted landscape trees in the United States, green ash is also an important species in riparian forests, rural agricultural systems and urban woodlands. Within 4 to 6 years from the time of first detection, the damage caused by EAB larval feeding can kill 100 percent of the green ash trees in a stand. Green ash is genetically incompatible with EAB-resistant Asian ash species, ruling out a simple backcrossing program to transfer resistance from species. However, a small number of green ash trees (~0.05 percent) have survived long term EAB attack. Careful testing of grafted clones of these “lingering ash” selections provides compelling evidence of a defensive response against EAB. The defenses lingering...
Ashes (Fraxinus spp.) are important hardwood tree species in rural, suburban, and urban forests o... more Ashes (Fraxinus spp.) are important hardwood tree species in rural, suburban, and urban forests of the eastern USA. Unfortunately, emerald ash borer (EAB,Agrilus planipennis) an invasive insect pest that was accidentally imported from Asia in the late 1980s–early 1990s is destroying them at an alarming rate. All North American ashes are highly susceptible to EAB, although blue ash (F. quadrangulata) may have some inherent attributes that provide it some protection. In contrast Manchurian ash (F. mandshurica) is relatively resistant to EAB having coevolved with the insect pest in its native range in Asia. Given its level of resistance, Manchurian ash has been considered for use in interspecies breeding programs designed to transfer resistance to susceptible North American ash species. One prerequisite for successful interspecies breeding is consistency in chromosome ploidy level and number between the candidate species. In the current study, we cytologically determined that both Manc...
Emerald ash borer (Agrilus planipennis; EAB) has devastated populations of ash (Fraxinus spp.) tr... more Emerald ash borer (Agrilus planipennis; EAB) has devastated populations of ash (Fraxinus spp.) trees in dozens of U.S. states and Canada over the past few decades. The continued survival of scattered ash trees known as "lingering ash" in heavily infested natural stands, however, offers evidence of genetic resistance or tolerance to EAB. These surviving or "lingering" ash individuals may form the basis for reforestation programs in EAB-impacted areas, and clonal mass-propagation of these genotypes can help accelerate these efforts. Between 2013 and 2018, we initiated embryogenic cultures by culturing immature zygotic embryos from open-pollinated (OP) seeds collected from several surviving white ash and green ash trees in Michigan and Pennsylvania. In addition, in 2018, we initiated cultures from crosses made between lingering green ash parents from the USDA Forest Service ash breeding program in Ohio. Somatic embryos were produced by growing cultures in liquid suspension, followed by fractionation and plating on semisolid medium to produce developmentally synchronous populations of somatic embryos. Somatic embryo germination and conversion were enhanced by a combination of pre-germination cold treatment and inclusion of activated charcoal and gibberellic acid in the germination medium. Ash somatic seedlings derived from OP explants grew rapidly following transfer to potting mix and somatic seedlings representing nine ash clones were acclimatized, grown in the greenhouse and planted in a preliminary field test, along with EAB-resistant Manchurian ash (F. mandshurica) and EAB-susceptible control seedlings. Somatic seedlings have now been produced from cultures that originated from seeds derived from the progeny of lingering green ash parents and an ex vitro germination protocol has shown some promise for accelerating early somatic seedling growth. Results of this research could provide the basis for scaled-up production of EAB-resistant ash varieties for seed orchard production for forest restoration and cultivar development for urban tree restoration. Keywords Clonal propagation • Fraxinus americana • Fraxinus pennsylvanica • Insect pest resistance • In vitro culture • Lingering ash Key message New Forests 2 1 3 Somatic embryogenesis provides a promising, scalable approach for clonal propagation of green ash and white ash genotypes derived from lingering ash parents with potential genetic resistance to emerald ash borer for reforestation.
Invasive Species in Forests and Rangelands of the United States, 2021
Preventing invasions of aquatic and terrestrial habitats is the preferred and most cost-effective... more Preventing invasions of aquatic and terrestrial habitats is the preferred and most cost-effective approach to address the invasive species threat (see Chap. 6). However, when prevention efforts fail, invasive species can become widespread and deeply embedded in native ecosystems, causing severe impacts (see Chaps. 2, 3, and 4). In such cases, invader control (see Chap. 7) accompanied by restoration facilitates recovery of native species and prevents reinvasion (e.g., Pearson et al. 2016). Here, we summarize the current state of restoration science and highlight critical information gaps that must be overcome to advance ecosystem restoration in terrestrial and aquatic systems affected by invasive plants, insects, diseases, and vertebrates.
A foliar nematode, Litylenchus crenatae ssp. mccannii, is associated with beech leaf disease (BLD... more A foliar nematode, Litylenchus crenatae ssp. mccannii, is associated with beech leaf disease (BLD) symptoms. Information about the types of tissues parasitized and how nematode populations fluctuate in these tissues over time is needed to improve surveys as well as understand the nematodes role in BLD. During this study, the nematode was detected throughout the known range of BLD by researchers at both Canadian and US institutions using a modified pan method to extract nematodes. Monthly collections of symptomatic and asymptomatic leaves during the growing season (May-October), and leaves and buds between growing seasons (November-March), revealed that nematodes were present in all tissue types. Progressively larger numbers of nematodes were detected in symptomatic leaves from Ohio and Ontario, with the greatest detections at the end of the growing season. Smaller numbers of nematodes were detected in asymptomatic leaves from BLD-infected trees, typically at the end of the growing season. The nematode was detected overwintering in buds and detached leaves. The discovery of small numbers of nematodes in detached leaves at one location before BLD was detected indicates that nematodes may have been present before disease symptoms were expressed. Other nematodes, Plectus and Aphelenchoides spp., were infrequently detected in small numbers. Our findings support the involvement of the nematode in BLD and indicate that symptoms develop only when certain requirements, such as infection of buds, are met. We also found that the nematode can be reliably detected in buds and leaves using the modified pan extraction method.
Fraxinus pennsylvanica genome assembly and annotation
We report the first chromosome-level assembly for green ash (<em>Fraxinus pennsylvanica<... more We report the first chromosome-level assembly for green ash (<em>Fraxinus pennsylvanica</em>) to assist in ash breeding efforts to propagate resistance to the emerald ash borer. The final haploid assembly consists of 23 chromosomes and 87 unplaced scaffolds of 10 kb or more. Over 99% of the bases anchored to the chromosomes. The assembly spans 757 Mb and consists of 49.43% repetitive DNA. Gene annotation yielded 35,470 high-confidence gene models, all located on the chromosomes and assigned to 22,976 Asterid Orthogroups.
Reference-Guided Scaffolding of Worldwide Fraxinus Species, Set 1
Following the recent assembly of the chromosome-level <em>Fraxinus pennsylvanica </em>... more Following the recent assembly of the chromosome-level <em>Fraxinus pennsylvanica </em>genome, we used the assembly to construct reference-guided assemblies of 27 previously sequenced <em>Fraxinus </em>taxa, including <em>Fraxinus excelsior</em>. Thus we present a significant step forward in genomic resources for research and protection of <em>Fraxinus </em>species.
Additional file 7: of Genome-wide association study identifies a major gene for beech bark disease resistance in American beech (Fagus grandifolia Ehrh.)
The statistics for Fisher exact test and Logistic regression test. (XLSX 4534Â kb)
Additional file 6: of Genome-wide association study identifies a major gene for beech bark disease resistance in American beech (Fagus grandifolia Ehrh.)
(A) DAPC analysis revealed three main genetic clusters where the individuals shown as dots and th... more (A) DAPC analysis revealed three main genetic clusters where the individuals shown as dots and the groups as inertia ellipses. Eigenvalues of the analyses are displayed inset. (B) Quantile-quantile (QQ) plot of GWA p-values where on x-axis, are expected –log10 P values and on y-axis observed –log10 P values. The plot is showing large deviation from the null distribution where the inflation factor was higher than the threshold of 1, indicating a high genomic inflation in Beech association data and an existence of the population stratification. (PDF 90 kb)
Additional file 4: of Genome-wide association study identifies a major gene for beech bark disease resistance in American beech (Fagus grandifolia Ehrh.)
The sequences and statistics for the high quality and most informative SNPs used in the GWAS. (XL... more The sequences and statistics for the high quality and most informative SNPs used in the GWAS. (XLSX 1080Â kb)
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