Dutch Elm Disease Research Articles

Genotype-by-environment interaction in Dutch elm disease resistance

Dutch elm disease (DED) is a devastating forest disease. Recently, the deployment of native resistant cultivars has prompted initiatives of elm reintroduction in Europe and North America. It is known that DED resistance varies with the tree genotype and is influenced by climatic factors. However, genotype-by-environment interactions in DED resistance remain largely unexplored. In this work, we examined whether there is genetic variation in DED resistance plasticity and the roles of tree growth, phenology and anatomical traits in plastic responses. We established two experimental plots with 12 Ulmus minor genotypes in two environmentally contrasting locations in Spain: Madrid, under an inland continental climate, and Valencia, under a coastal Mediterranean climate. We monitored growth and phenology detecting high plasticity in both traits. In the inland plot, genotypes were taller and showed a more synchronized phenology than in the coast. A first DED-pathogen inoculation was carried out 45 days after the average flushing date in each location, after which trees exhibited more symptoms inland. A second inoculation was carried out by dividing the coastal plot trees into early and late flushing trees and inoculating each group at 45 days after its average flushing date. Therein, susceptibility rose to a level close to the inland plot. In both inoculations, we detected a significant genotype-by-location interaction in DED resistance. The xylem anatomy revealed high plasticity and a significant genotype-by-location interaction in most traits. In the coastal trial, trees formed narrower vessels and stored more starch before inoculation. The synchrony of leaf phenology, higher growth rate, lower starch reserves and higher structural vulnerability of earlywood to DED possibly favored susceptibility in the inland plot. The varying responses of genotypes in phenology, growth and anatomy at both locations were likely related to the differences in DED resistance, which can have important consequences for elm reintroduction.

Cold Tolerance Assay Reveals Evidence of Climate Adaptation Among American Elm (Ulmus americana L.) Genotypes

T he American elm (Ulmus americana L.), once a dominant species in North American floodplain forests, has suffered significant population declines due to Dutch elm disease (DED). Despite this, some elms persist, potentially exhibiting disease resistance and climate-adaptive traits that could facilitate restoration. Understanding these traits is crucial for selecting genotypes suited to current and future climatic conditions, particularly in colder regions. This study evaluated the mid-winter cold tolerance of American elm genotypes across a climatic gradient to ascertain evidence of local climate adaptation. We used relative electrolyte leakage (REL) to assess mid-winter cold tolerance of current-year shoots on eleven survivor genotypes from New England and one susceptible, control genotype from Ohio. The lethal temperature, at which 50% of cellular leakage occurs (LT50), was determined and compared with 30-year climate data to identify potential climate adaptation. Genotypes from colder regions exhibited greater cold hardiness, indicating local adaptation to climate. Observed mid-winter LT50 values (−42.8 °C to −37.7 °C) were in excess of the 30-year minimum air temperature, even at the coldest source location. This calls into question whether mid-winter cold tolerance is the critical period for injury to American elm and more attention should be given to environmental conditions that cause de-acclimation to cold. By understanding the adaptive capacity of American elm, managers can better select mother trees for regional seed orchards, ensuring the long-term success of restoration initiatives.

Breeding site segregation and Dutch elm disease fungi carriage percentage of three bark beetle species (Scolytus esuriens, S. chikisanii, and S. japonicus) in a Japanese elm tree in Hokkaido, Japan

ABSTRACT In Japan, three bark beetle species, namely Scolytus esuriens, S. chikisanii, and S. japonicus, have been recently identified as new vectors of Dutch elm disease (DED), although their detailed breeding sites and relation to DED fungi acquisition have not been revealed. We investigated the diameter of branches and a trunk (branch – trunk) at the location of the maternal tunnel (Ømt) and the pupal chamber (Øpc), the distance from the pupal chamber to the bark surface i.e. depth of the pupal chamber (Dpc) on a single Japanese elm tree, and the percentages of bark beetles carrying DED fungi (%bcDED) among those collected from the chamber for three species. The Ømt was 11.0–25.6 cm for S. esuriens, 8.3–23.3 cm for S. chikisanii, and 1.3–3.2 cm for S. japonicus. Therefore, three species were found to exhibit breeding site segregation based on the branch – trunk diameter. The %bcDED were 90.2%, 66.7%, and 40.0% for S. esuriens, S. chikisanii, and S. japonicus, respectively. %bcDED showed an increasing trend with increase in Øpc and Dpc. For DED control, it is necessary to monitor and remove small branches that were previously overlooked to prevent an increase in the population of vector beetles, although %bcDED of bark beetles emerging from small branches tends to be low.

Elms (Ulmus L.) in the Branch “Myrhorod Forestry” of the State Specialized Forest Enterprise “Forests of Ukraine”

Introduction Elms are spread in forests, landscaping settlements, and protective forest belts. After several waves of elm mortality from Dutch elm disease (DED) in the 20th century, individual populations recovered or formed resistant hybrids. However, epiphytoties of bacterial and fungal diseases sometimes develop, particularly due to pathogen vectoring by bark beetles. In Ukraine, the spread of elms and their damage by different causes are relatively poorly investigated. This research aimed to discover the features of Ulmus sp. distribution by stand origin, age, and forest site condition in the forest fund of the Branch “Myrhorod Forestry”. Materials and Methods The data as of 2010 and 2017 on the forest fund of enterprises belonging to the Branch “Myrhorod Forestry” of the State Specialized Forest Enterprise “Forests of Ukraine” were selected from the database of Ukrainian State Forest Management Planning Association “Ukrderzhlisproekt” using SQL-query and converted to the *.xls files. Area distribution by types of forest site conditions was assessed following the Ukrainian school of forest typology. Such distributions for the entire area covered with forest vegetation, for subcompartments with elms in the stand composition, and with elms as the dominant species were compared for various elm species and stand origins, using c2-test. The percentages of stand areas of different origins and elm species in 2010 and 2017 were compared using z-test in the two proportions comparisons. The data for subcompartments with various elms as the dominant species and as a part of stands composition have been analyzed by 10-year age classes for different origins (natural and planted). The proportion of the stand area of each 10-year age class was assessed for each set of subcompartments. Then the proportion of the stands’ area, which survives up to a certain age, was evaluated. Results and Conclusions In the Branch “Myrhorod forestry”, an area of natural stands with Ulmus sp. as the dominant species for 2010–2017, and the proportion of U. minor has significantly increased. The most dramatic decrease in the survival rate of all elm species of natural stands occurred in the VI age class and planted stands in the V age class. Respective natural and planted stands were formed in the 1960s and 1970s when the peak of DED occurred in many regions. In the Branch “Myrhorod Forestry”, U. minor prefers moist fertile forest site conditions. U. laevis grows mainly in moist forest site conditions, U. pumila occurs in dry to wet habitats, U. glabra is present only in natural stands and absent in plantations. As part of stand composition, the same elm species grow in a wider range of forest site conditions than elms as the dominant species. 2 Figs., 8 Tables, 31 Refs.

Unraveling the transcriptional features and gene expression networks of pathogenic and saprotrophic Ophiostoma species during the infection of Ulmus americana.

American elm (Ulmus americana), highly prized for its ornamental value, has suffered two successive outbreaks of Dutch elm disease (DED) caused by ascomycete fungi belonging to the genus Ophiostoma. To identify the genes linked to the pathogenicity of different species and lineages of Ophiostoma, we inoculated 2-year-old U. americana saplings with six strains representing three species of DED fungi, and one strain of the saprotroph Ophiostoma quercus. Differential expression analyses were performed following RNA sequencing of fungal transcripts recovered at 3- and 10-days post-infection. Based on a total of 8,640 Ophiostoma genes, we observed a difference in fungal gene expression depending on the strain inoculated and the time of incubation in host tissue. Some genes overexpressed in the more virulent strains of Ophiostoma encode hydrolases that possibly act synergistically. A mutant of Ophiostoma novo-ulmi in which the gene encoding the ogf1 transcription factor had been deleted did not produce transcripts for the gene encoding the hydrophobin cerato-ulmin and was less virulent. Weighted gene correlation network analyses identified several candidate pathogenicity genes distributed among 13 modules of interconnected genes.IMPORTANCEOphiostoma is a genus of cosmopolitan fungi that belongs to the family Ophiostomataceae and includes the pathogens responsible for two devastating pandemics of Dutch elm disease (DED). As the mechanisms of action of DED agents remain unclear, we carried out the first comparative transcriptomic study including representative strains of the three Ophiostoma species causing DED, along with the phylogenetically close saprotrophic species Ophiostoma quercus. Statistical analyses of the fungal transcriptomes recovered at 3 and 10 days following infection of Ulmus americana saplings highlighted several candidate genes associated with virulence and host-pathogen interactions wherein each strain showed a distinct transcriptome. The results of this research underscore the importance of investigating the transcriptional behavior of different fungal taxa to understand their pathogenicity and virulence in relation to the timeline of infection.

Tissue culture and cryopreservation in the utilization and conservation of genetic resources of Norway spruce (Picea abies) and elms (Ulmus glabra, U. laevis)

In this work, tissue culture techniques were developed for two purposes: the production of Norway spruce (Picea abies [L.] Karst.) forest regeneration material with somatic embryogenesis (I–III) and the conservation of genetic resources of European white elm (Ulmus laevis Pall.) and wych elm (Ulmus glabra Huds.) with cryopreservation and organogenesis (IV, V). In P. abies somatic embryogenesis, zygotic embryos are used as explants to produce embryogenic tissue, which can be matured into copies of the initial embryo for clonal propagation. In Paper I Plantform temporary immersion system bioreactors were tested for P. abies somatic embryogenesis. The production of cotyledonary embryos in bioreactors required adding steps to the protocol and the bioreactors were laborious to use. In Paper II growing embryogenic tissue in suspension culture was evaluated. Suspension culture is more scalable than propagation on a semi-solid media. However, it required rinsing the tissue before maturation and it could benefit from optimizing the media composition. Higher hydrogen peroxide content was observed in embryogenic tissue grown in suspension than on semi-solid media, but no conclusive evidence of higher oxidative stress in suspension culture was found. In Paper III, filter disc cultures grew faster than clumps on semi-solid media and produced slightly more embryos. The storage compound profile of somatic embryos was most similar to the zygotic embryos at 4–8 weeks of cold storage. In organogenesis, plant organs and new plants are clonally propagated from meristematic tissues or through a callus phase. In Paper IV, a micropropagation protocol was developed to regenerate U. laevis and U. glabra dormant buds from cryostorage. Both elm species are endangered in Finland and globally threatened by Dutch elm disease. The main challenges were surface sterilization and poor regeneration of U. glabra from cryostorage. In Paper V, dehydration was successfully implemented to improve the regeneration rate.

Understory changes in mixed elm stands in response to canopy dieback in Latvia

In the eastern Baltic region, warming is favouring the advance of thermophilic tree species and the formation of mixed stands with a higher share of broadleaves, thus contributing to productivity and other ecosystem services of forests. However, the accelerating environmental changes often trigger the spread and intensification of biotic disturbances such as disease outbreaks at unprecedented rates, which might alter the course of stand development. Within the region, elms (Ulmus sp.), which are of low importance as a source of timber, yet highly important in terms of other ecosystem services, are suffering varying degree of dieback due to the Dutch elm disease, which can threaten the existence of species. Still, there are explicit local differences in the susceptibility of trees, which add uncertainties regarding the sustainability of elms. A permanent sampling plot network was established to monitor changes in mixed elms stands in response to the dieback caused by the disease; canopy and understory trees were accounted. Two surveys in 2016 and 2021 have been made. Canopy elms have suffered moderate dieback during the first wave already before the surveys, as ca. 17% of canopy elms were already dead. However, the susceptibility differed among the species (Ulmus glabra exceeded U. laevis), likely due to the preference of the vectors of the disease. In response to canopy openings, self-regeneration occurred, though the balance between the advance regeneration and undergrowth species was affected by the intensity of canopy dieback. The advanced growth of the former canopy species including elms was sufficient under moderate changes in the canopy, while low and high changes favoured undergrowth, suggesting the formation of shrubland. Accordingly, the additional mortality of elms due to Dutch elm disease tended to diverge the development course of the mixed broadleaved stands; hence further monitoring is advised. Keywords: Ulmus sp.; Ophiostoma sp.; advance growth; undergrowth; Dutch elm disease; succession

New vectors: Scolytus chikisanii and S. japonicus (Scolytidae) associated with Dutch elm disease in Hokkaido, Japan

ABSTRACT Scolytus esuriens is a vector of Dutch elm disease (DED) in Japan. However, small holes that were presumed to be irruption or flight holes of bark beetle species other than S. esuriens were observed at dead small branches of Japanese elms in Sapporo City, Hokkaido, Japan. In this study, bark beetles that use small branches of elm trees for breeding were surveyed as candidate DED vectors. It was determined if the causal fungi of DED, Ophiostoma ulmi and O. novo-ulmi, could be acquired from adult beetles. Two bark beetles were determined as new vectors: Scolytus chikisanii and S. japonicus. The morphology of feeding wounds on the crotches of living twigs by each vector species was investigated. Subsequently, the relative frequency of feeding wounds made by each bark beetle species was estimated based on the morphological type of feeding wounds on wilting twigs in the field. S. chikisanii and S. japonicus may have contributed more to the spread of infection than S. esuriens in the study area.

Comparative transcriptomes of four Elm species provide insights into the genetic features and adaptive evolution of Ulmus spp.

Ulmus spp. have a wide distribution, strong adaptability, and high application value. However, due to the outbreak of Dutch elm disease and a lack of nuclear genome data, studies on Ulmus spp. are lacking. In this study, we obtained full-length transcriptomes from four elm species, with an average of 64,529 transcripts per species. Among these transcripts, an average of 6410 long noncoding RNAs were obtained per species. We performed SSR site detection and primer design and obtained an average of 20,650 SSR primer pairs per elm species. Fisher’s exact test revealed a large difference in the enrichment of functional genes shared between Ulmus parvifolia and three other elms, which represented 31 Gene Ontology terms, four Kyoto Encyclopedia of Genes and Genomes pathways, and two transcription factors. Phylogenetic evolution and divergence time analyses indicated that U. parvifolia diverged from the three other elms ca. 13.98 Mya; the divergence time of Ulmus macrocarpa, Ulmus davidiana, and Ulmus pumila was ca. 10.84–7.25 Mya. Furthermore, we identified 22 genes that were positively selected, and transcriptional profiling analysis showed that the expression levels of those genes showed marked changes under high temperature. These positively selected genes are widely involved in the ubiquitin system, nucleotide excision repair, protein modification, circadian rhythm regulation, light stimulus response, abiotic stimulus response, MAPK signaling, and plant pathogenicity interactions; they may play an important role in the adaptation of elms to environmental changes. This study provides a basis for the study of adaptive evolution, genetic diversity and functional gene development in Ulmus spp.

The age structure of Ulmus L. stands in the eastern regions of Ukraine

The aim of the research was to determine the features of the age structure for natural and artificial elm stands depending on species, origin, and region. The proportion of the stand area of natural and artificial stands of each elm species by 10-year age classes was evaluated for the forest fund of the Donetsk, Kharkiv, and Sumy Regional Forest and Hunting Management Administrations (RFHMA). Four main forest-forming elm species are represented in the forest fund of the Donetsk and Kharkiv RFHMA (U. minor, U. laevis, U. glabra, and U. pumila). In the Sumy RFHMA, there are three forest-forming elm species: U. minor, U. laevis, and U. glabra. The maximum age of U. minor is 120, 117, and 91 years in the Donetsk, Kharkiv, and Sumy RFHMA, respectively. The mean and the maximum age of U. minor and U. glabra tends to decrease in the Donetsk – Kharkiv – Sumy RFHMA row. The proportion of U. laevis is larger in man-made plantations than in natural stands, however, in natural stands, it also increases in the Donetsk – Kharkiv – Sumy RFHMA row. U. glabra prevails in natural stands. U. pumila in the Donetsk RFHMA grows mainly in man-made plantations. A decrease in the area of newly formed U. minor stands in the Donetsk RFHMA occurred after the 1950s, and in the Kharkiv RFHMA after the 1960s in both artificial and natural stands. In the Sumy RFHMA, this also happened in the 1960s in man-made plantations. A decrease in the area of U. glabra natural and artificial stands occurred also after the 1960s. We suppose that an epiphytoty of the Dutch elm disease, well-known in Europe in the 1960s, could also be the cause of elm decline in the eastern part of Ukraine. The proportion of the stands’ area preserved up to a certain age, depends on particular elm species, region, and stand origin. However, in order to clarify the survival rate, it is necessary to consider the type of forest site conditions, the proportion of elms in the stand composition, and some other features that are to be analyzed in future research.

Machine learning-based spectral and spatial analysis of hyper- and multi-spectral leaf images for Dutch elm disease detection and resistance screening

Diseases caused by invasive pathogens are an increasing threat to forest health, and early and accurate disease detection is essential for timely and precision forest management. The recent technological advancements in spectral imaging and artificial intelligence have opened up new possibilities for plant disease detection in both crops and trees. In this study, Dutch elm disease (DED; caused by Ophiostoma novo-ulmi,) and American elm (Ulmus americana) was used as example pathosystem to evaluate the accuracy of two in-house developed high-precision portable hyper- and multi-spectral leaf imagers combined with machine learning as new tools for forest disease detection. Hyper- and multi-spectral images were collected from leaves of American elm genotypes with varied disease susceptibilities after mock-inoculation and inoculation with O. novo-ulmi under greenhouse conditions. Both traditional machine learning and state-of-art deep learning models were built upon derived spectra and directly upon spectral image cubes. Deep learning models that incorporate both spectral and spatial features of high-resolution spectral leaf images have better performance than traditional machine learning models built upon spectral features alone in detecting DED. Edges and symptomatic spots on the leaves were highlighted in the deep learning model as important spatial features to distinguish leaves from inoculated and mock-inoculated trees. In addition, spectral and spatial feature patterns identified in the machine learning-based models were found relative to the DED susceptibility of elm genotypes. Though further studies are needed to assess applications in other pathosystems, hyper- and multi-spectral leaf imagers combined with machine learning show potential as new tools for disease phenotyping in trees.

Vegetation responses to pathogen-induced tree loss: Swedish elm and ash forests revisited after 32 years

Invasive fungal pathogens are an increasing problem globally and can cause strong effects on forest ecosystems. In this study, we contrast vegetation surveys in eutrophic elm (Ulmus glabra) and ash (Fraxinus excelsior) forests in southern Sweden, conducted just prior to the arrival of Dutch elm disease (DED) in 1989, and then again in 2021, several years after ash dieback (ADB) began. At the sample plot scale, species richness (α–diversity) of the upper tree layer strongly decreased from 1989 to 2021, and the mean cover of elm decreased from 27 to 1% and of ash from 29 to 13%. In the lower tree and shrub layers, elm and ash were replaced by other, mainly shade-tolerant, tree species. The cover and richness of the shrub layer increased in previously elm-dominated stands but not in ash-dominated stands. The extensive loss of canopy cover in elm stands caused a larger change in upper tree layer species composition and increased compositional variability (β-diversity) between plots when compared to the ash stands. The direction of the changes in tree layer composition between the surveys varied with soil moisture and nutrient availability. While beech increased in less eutrophic plots, more nutrient-rich plots changed toward hornbeam or small-leaved lime, and wetter plots turned toward alder and bird cherry. Hence, our results indicate increased compositional diversity and alternative successional pathways for community reorganization following DED and ADB. Future research will reveal if these pathways will later merge or further split.

ECONOMIC AND SOCIAL CONSEQUENCES OF INVASIONS OF PESTS AND PATHOGENS OF TREES IN ST. PETERSBURG

An economic assessment of the damage caused by invasive tree insect pests and pathogens in urban plantings of St. Petersburg is given. Between 2001 and 2020, the invasion of elm bark beetles Scolytus multistriatus (Marsham), S. scolytus (Fabricius) and S. pygmaeus (Fabricius) and the concomitant spread of Dutch elm disease caused by the fungi Ophiostoma ulmi (Buisman) Nannfeldt and O. novo-ulmi (Brasier) (Ascomycota: Ophiostomataceae) resulted in the death of at least 37 000 elms in the city. The total damage exceeded 50 billion rubles. Compulsory sanitary cutting of the infected elms raised significant public concern. Plantations of common use, especially historical parks and gardens, lost most important landscape compositions, in which exactly elm trees had a key role. In two years, 2022-2022, the economic losses associated with the invasion and spread of Emerald ash borer Agrilus planipennis , reached 270 million rubles. Detection of infested ash trees and their timely felling was effective. However, not all infested trees were spotted and removed and the pest reproduction continued. Urgent measures are needed to prevent further spread of Emerald ash borer and other invasive pests and pathogens in St. Petersburg and adjacent territories.

Duplex real-time PCR assay for the simultaneous detection of Ophiostoma novo-ulmi and Geosmithia spp. in elm wood and insect vectors

Dutch elm disease (DED) is a destructive tracheomycosis caused by Ophiostoma novo-ulmi, an ascomycete probably originating in East-Asia that is devastating natural elm populations throughout Europe, North America and Asia. The fungus is mainly spread by elm bark beetles that complete their life cycle between healthy and diseased elms. Recently, it has been highlighted that some fungi of the genus Geosmithia, which are similarly well associated with bark beetles, seem to also play a role in the DED pathosystem acting as mycoparasites of O. novo-ulmi. Although some relationship between the fungi is clear, the biological cycle of Geosmithia spp. within the DED cycle is still partly unclear, as is the role of Geosmithia spp. in association with the bark beetles. In this work, we tried to clarify these aspects by developing a qPCR duplex TaqMan assay to detect and quantify DNA of both fungi. The assay is extremely sensitive showing a limit of detection as low as 2 fg μl–1 for both fungi. We collected woody samples from healthy and infected elm trees throughout the beetle life cycle. All healthy elm samples were negative for both Geosmithia spp. and O. novo-ulmi DNA. Geosmithia spp. are never present in infected, but living trees, while they are present in frass of elm bark beetles (EBB – Scolytus spp.) and at each stage of the EBB life cycle in much higher quantities than O. novo-ulmi. This work provides a better understanding of the role and interactions occurring amongst the main players of the DED pathosystem.

Ecological factors related to seed germination and early seedling establishment inUlmus minorMill., an endangered riparian tree species

AbstractNatural populations of Ulmus minor Mill., an outstanding component of European riparian forests, are endangered due to Dutch elm disease, which has led to the development of several breeding programs throughout Europe. However, the reproductive ecology of this species is scarcely known even though sexual regeneration is an essential factor that must be understood before implementing elm stand restoration. In this paper, the main ecological factors affecting seed germination and early seedling establishment in U. minor are studied through a factorial design with five different factors: Light (levels: Full-sun, Shade), Initial water (levels: Initially-flooded, Initially-irrigated), Subsequent water (levels: Semi-submerged, Later-irrigated), Soil cover (levels: Bare-soil, Litter) and Substrate (levels: Silty-clay, Sandy-loam). Seed germination and seedling survival were monitored for 7 weeks. All factors except Initial water and Substrate turned out to be highly significant. Shade increased seed germination and seedling survival. Response to Initial water fluctuated, with an early higher percentage of germinated seeds in Initially-flooded but a higher seedling survival in Initially-irrigated. Subsequent water did not affect seedling establishment and survival, but Semi-submerged treatments increased seed germination. Bare-soilincreased seed germination too, whereas, in the medium term, Litter affected positively seedling survival. Sandy-loam substrates favoured seed germination, but Silty-claysubstrates favoured seedling survival. Together, these results suggest that the most favourable scenario for U. minor sexual regeneration may be a combination of a not-too-severe late-winter or early-spring flood followed by a wet spring and summer, probably with a higher establishment in heavy-textured substrates located in small gaps and forest edges where the overstorey provides some protection against strong sunlight.

Core endophytic mycobiome in Ulmus minor and its relation to Dutch elm disease resistance.

The core microbiota of plants exerts key effects on plant performance and resilience to stress. The aim of this study was to identify the core endophytic mycobiome in U. minor stems and disentangle associations between its composition and the resistance to Dutch elm disease (DED). We also defined its spatial variation within the tree and among distant tree populations. Stem samples were taken i) from different heights of the crown of a 168-year-old elm tree, ii) from adult elm trees growing in a common garden and representing a gradient of resistance to DED, and iii) from trees growing in two distant natural populations, one of them with varying degrees of vitality. Endophyte composition was profiled by high throughput sequencing of the first internal transcribed spacer region (ITS1) of the ribosomal DNA. Three families of yeasts (Buckleyzymaceae, Trichomeriaceae and Bulleraceae) were associated to DED-resistant hosts. A small proportion (10%) of endophytic OTUs was almost ubiquitous throughout the crown while tree colonization by most fungal taxa followed stochastic patterns. A clear distinction in endophyte composition was found between geographical locations. By combining all surveys, we found evidence of a U. minor core mycobiome, pervasive within the tree and ubiquitous across locations, genotypes and health status.

Vaccination of Elms against Dutch Elm Disease-Are the Associated Epiphytes and Endophytes Affected?

Dutch elm disease (DED) is causing extensive mortality of ecologically and culturally valuable elm trees (Ulmus spp.). Treatment of elms with the biological vaccine Dutch Trig® has been found to provide effective protection against DED by stimulating the defensive mechanisms of the trees. We hypothesized that the same mechanisms could also affect non-target organisms associated with elms. We explored the possible effects of vaccination on epiphytes (mainly lichens) and fungal endophytes living in the bark and young xylem of treated elms. Epiphyte cover percentage was assessed visually using a grid placed on the trunks, and a culture-based approach was used to study endophytes. Epiphyte cover was lower on the trunks of vaccinated trees as compared with unvaccinated trees, but the difference was not statistically significant. The presence of slow-growing and uncommon endophytes seemed to be reduced in continuously vaccinated elms; however, the highest endophyte diversity was found in elms four years after cessation of the vaccination treatments. Our findings suggest that although vaccination may shape epiphyte and endophyte communities in elms, its impacts are not straightforward. More detailed studies are, therefore, needed to inform the sustainable application of the vaccine as a part of the integrated management of DED.

The varved succession of Crawford Lake, Milton, Ontario, Canada as a candidate Global boundary Stratotype Section and Point for the Anthropocene series.

An annually laminated succession in Crawford Lake, Ontario, Canada is proposed for the Global boundary Stratotype Section and Point (GSSP) to define the Anthropocene as a series/epoch with a base dated at 1950 CE. Varve couplets of organic matter capped by calcite precipitated each summer in alkaline surface waters reflect environmental change at global to local scales. Spheroidal carbonaceous particles and nitrogen isotopes record an increase in fossil fuel combustion in the early 1950s, coinciding with early fallout from nuclear and thermonuclear testing - 239+240Pu and 14C:12C, the latter more than compensating for the effects of old carbon in this dolomitic basin. Rapid industrial expansion in the North American Great Lakes region led to enhanced leaching of terrigenous elements by acid precipitation during the Great Acceleration, and calcite precipitation was reduced, producing thin calcite laminae around the GSSP that is marked by a sharp decline in elm pollen (Dutch Elm disease). The lack of bioturbation in well-oxygenated bottom waters, supported by the absence of fossil pigments from obligately anaerobic purple sulfur bacteria, is attributed to elevated salinities and high alkalinity below the chemocline. This aerobic depositional environment, highly unusual in a meromictic lake, inhibits the mobilization of Pu, the proposed primary stratigraphic guide for the Anthropocene.

One Health Solution to Dutch Elm Disease in Renfrew Country

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Independent Evolution Has Led to Distinct Genomic Signatures in Dutch Elm Disease-Causing Fungi and Other Vascular Wilts-Causing Fungal Pathogens.

Vascular wilts are important diseases caused by plant pathogenic fungi that result in the rapid death of their plant hosts. This is due to a systemic defense mechanism whereby the plant induces the compartmentalization of the infected vascular system in order to reduce the propagation of the fungus. The ascomycete class Sordariomycetes contains several species that cause vascular wilts in diverse plant hosts, and they can be classified into four taxonomic orders. The genetic mechanisms of pathogenesis have already been investigated in Fusarium and Verticillium species, but they have not yet been compared with other well-known wilt-causing species, especially fungi causing oak wilt or Dutch elm disease (DED). Here we analyzed 20 whole genome assemblies of wilt-causing fungi together with 56 other species using phylogenetic approaches to trace expansions and contractions of orthologous gene families and gene classes related to pathogenicity. We found that the wilt-causing pathogens evolved seven times, experiencing the largest fold changes in different classes of genes almost every time. However, some similarities exist across groups of wilt pathogens, particularly in Microascales and Ophiostomatales, and these include the common gains and losses of genes that make up secondary metabolite clusters (SMC). DED pathogens do not experience large-scale gene expansions, with most of the gene classes, except for some SMC families, reducing in number. We also found that gene family expansions in the most recent common ancestors of wilt pathogen groups are enriched for carbohydrate metabolic processes. Our study shows that wilt-causing species evolve primarily through distinct changes in their repertoires of pathogenicity-related genes and that there is the potential importance of carbohydrate metabolism genes for regulating osmosis in those pathogens that penetrate the plant vascular system.