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Ash dieback (ADB) has been causing the progressive decline of Fraxinus excelsior trees throughout Europe, urging research and forest management to develop strategies to combat ADB. A genetically heritable component in susceptibility to this fungal disease was reported in common gardens. Thus, exploring the molecular basis of ADB susceptibility will further support breeding initiatives in the future. We performed transcriptional profiling of infected and uninfected leaves from two ash genotypes with different susceptibility to Hymenoscyphus fraxineus. Leaf rachises were sampled one week following inoculation. Differential gene expression analysis was performed to compare between treatments in each genotype (individual response) or in genotypes and treatments combined (common response). Due to the heterogeneity in the response, only DEGs were discussed that passed stringent assessment. Our results revealed that UW1, the most susceptible genotype, showed a total of 515 differentially expressed genes (DEGs), some of them possibly suggesting a self-control mechanism, hindering an effective immune response and causing increased susceptibility. On the other hand, FAR3, the least susceptible genotype with 230 DEGs, seemed to induce a contained but more efficient response, hinting toward a salicylic acid-mediated process and activating pathogen-related (like) proteins as thaumatin-like, peroxidases, and chitinases. In the common response, 512 DEGs were modulated and transcripts from the phenylpropanoid pathway were commonly altered in both genotypes. Altogether, this work comprised an initial transcriptional exploration including two selected genotypes with distinct susceptibility to ADB, however, the heterogenous response indicated the need to further improve the experimental inoculation approach. Exploring gene expression patterns in ADB susceptibility holds promise to reveal early response mechanisms, and new markers related to susceptibility, as well as to contribute to developing strategies that may help contain ADB. [ABSTRACT FROM AUTHOR]

Across various European countries, Fraxinus excelsior L. is facing a decline caused by Hymenoscyphus fraxineus. The underlying mechanisms of the disease are still insufficiently understood in detail. Observations suggest that, in addition to the main pathogen, viral infections may also contribute to the decline of ash trees. We described homologues in the F. excelsior genome of formerly annotated virus resistance genes in model species and tested the applicability of primers on these gene fragments. Further, a prediction of cis-acting regulatory elements and transcription factor binding sites was accomplished, to determine the exact location of the promoters of these genes in the ash genome. After annotation and filtering the low-complexity regions, primers for use with genomic DNA were designed on sequences that showed a high degree of similarity and equality in length to translated regions and promoters of these regions. From the newly designed primers, those with the most favourable primer selection parameters were selected and tested on eight virus infected—four symptomatic and four asymptomatic—samples. The amplified products were analysed by agarose gel electrophoresis. From all producing one-band amplicons, 36 primer pairs amplifying translated, and 36 primers amplifying promoter regions were selected. Our study is the first step of a SNP discovery and marker development test. The further marker development on these sequences could be useful for the selection of ash individuals with various resistance to viral infections, providing a route for a more thorough understanding of the ash dieback–virus resistance interaction. [ABSTRACT FROM AUTHOR]

Common ash (Fraxinus excelsior L.) has been considered an important candidate species for climate-resilient forest management in Germany. The occurrence of ash dieback, caused by the invasive fungus Hymenoscyphus fraxineus, severely limits its use. However, less damaged ash trees in heavily infested stands are observed. This suggests a tree-specific and genetically determined susceptibility to ash dieback. The potential of individual trees for selection and conservation programs has been investigated on 35 clones in a clonal trial and 30 families in a progeny trial since 2014. Ash dieback-related mortality, crown damage, and height growth were examined. Resistance to ash dieback was evaluated based on multi-year observations. Mortality of ramets occurred rapidly and crown damage of clones stabilized, whereas steadily increasing in progeny during the study period. About 34 percent of all offspring (0–56 percent per family) showed high resistance to ash dieback and 10 percent showed also good height growth. Broad-sense heritability and narrow-sense heritability were moderate and comparable to previous studies. We assume that at least some individuals from specific progenies will resist the disease in forest stands. In situ and ex situ conservation strategies should be promoted. Seed orchards with more resistant genotypes could provide less susceptible reproductive material, and breeding programs could help to accelerate the fixation of favorable alleles. [ABSTRACT FROM AUTHOR]

Hymenoscyphus fraxineus is an introduced ascomycete fungus which causes ash dieback and has resulted in widespread mortality of ash throughout Europe. Although H. fraxineus has been present on the continent for at least four decades, it was not identified until 2006. The first record of the pathogen in Britain came in 2012 although it was probably present a decade earlier. The most common host European ash (Fraxinus excelsior L.) is economically and ecologically important to Britain where the cost of ash dieback is estimated at billions of pounds. The impact of ash dieback has stimulated a major research response which we review with the aim of providing up-to-date information relevant to Britain and identifying knowledge gaps where research would contribute to improved disease mitigation. Hymenoscyphus fraxineus is an outcrossing fungus with high genotypic diversity; ascospores produced via sexual reproduction are critical to aerial dispersal and infection. Temperature, moisture, and ground cover influence pathogen fruit body development, the timing of ascospore release, and extent of ascospore germination; they also interact together to affect the likelihood of infection. In addition, stand characteristics, including tree density, tree height, and landscape fragmentation, affect disease dynamics with increased disease severity on moist sites with high ash density. Efforts at finding natural resistance in ash have identified genetic markers associated with disease tolerance, and gene expression analysis is providing insights into the basis of that resistance. Mainland European findings indicate that ash dieback makes trees more vulnerable to other pathogens, whilst endophytes in the ash phyllosphere can suppress infection by H. fraxineus. Possible tools for long-term control of ash dieback include (1) deployment of resistant ash, (2) quantitatively informed management practices based on microclimate models and better understanding of the pathogen life cycle, and (3) manipulation of biocontrol agents from the ash microbiome or pathogen mycoviruses. [ABSTRACT FROM AUTHOR]

Ash dieback is a tree disease caused by the fungal pathogen Hymenoscyphus fraxineus. Since its introduction into Europe, it has caused widespread and significant losses of the European ash, Fraxinus excelsior. Inoculations of F. excelsior with a low virulent H. fraxineus isolate were assessed as a promising method for reducing symptoms associated with ash dieback, presumably by triggering systemic induced resistance. Two strains of H. fraxineus were chosen based on observations of high and low in planta virulence. Crude extracts obtained from cultures of the highly virulent strain were more phytotoxic in a leaf puncture assay than ones obtained from the low virulent strain. UHPLC-DAD-MS/MS data identified the phytotoxin viridiol and the potential phytotoxin hyfraxin A in both cultures. However, the production of these compounds in vitro did not correspond with virulence in planta. To test the effects of priming, saplings of F. excelsior were first inoculated with the low virulent strain and subsequently with the highly virulent strain. On average, necrosis expansion on the stems was reduced by 53% in primed saplings at the end of the 14-week monitoring period, thus providing proof of the priming concept. These results contribute to our understanding of a possible integrated biological disease control approach for increasing resistance in saplings and reducing potential damages associated with pathogens, particularly during nursery propagation, out-planting and through the establishment phase. We discuss results in the context of relevant literature and summarise the limited availability of literature on priming and underlying principles in trees. [ABSTRACT FROM AUTHOR]

While assessing the filamentous fungi associated with woody tissues of stem collar rots, necroses, and lesions of European ash trees (Fraxinus excelsior) presenting symptoms of ash dieback in Germany, Cryptostroma corticale was recovered from three different ash trees. These isolated strains were the first report of C. corticale on ash and the first proof of an association of this plant pathogen with woody tissues of other tree species than Acer spp. in Germany. To test the pathogenicity of C. corticale against F. excelsior and to fulfil Koch's postulates, inoculation tests in planta with strains isolated from Acer pseudoplatanus and F. excelsior were conducted according to Henle–Koch's postulates in a greenhouse located in Göttingen. The pathogenicity tests were performed with apparently healthy ash saplings from June 2021 until January 2022. After three and seven months, neither necroses or lesions due to C. corticale nor disease symptoms were observed. Mostly, the inoculation wounds healed over, and C. corticale could not be re-isolated from the ash woody tissue. In an attempt to re-isolate the inoculated strains, the filamentous fungal endophytes of the ash woody tissues were isolated and identified. A total of 32 taxa of the Ascomycota were found, where the most common species was Boeremia exigua. Most frequently observed orders were Pleosporales (58.4%), followed by Sordariales (13.5%), Hypocreales (9.4%), and Diaporthales (8.7%). On average, 3.7 endophytic species were recorded on each sapling. [ABSTRACT FROM AUTHOR]

Since 2002, ash dieback caused by the invasive fungus Hymenoscyphus fraxineus has been observed in Germany. The pathogen and its associated symptoms have fatal consequences for the vitality and survival of European ash (Fraxinus excelsior L.), an economically and ecologically important tree species. This study analyses the ash monitoring results of eleven intensive monitoring plots of the FraxForFuture research network distributed across Germany and focuses on within-stand differences of symptoms in dependence of small-scale site and tree properties. A cohort of 1365 ash trees was surveyed six times over three years, testing and applying a summer and a winter version of a nationally standardised ash dieback assessment key. The main disease symptoms (crown dieback and basal lesions) were more pronounced in areas with higher ash density, in edaphically moist areas (hydromorphic soils), on younger/smaller ash trees, and generally increased over time. However, the trend over time differed between single plots. In case of considering only the surviving part of the ash populations, crown condition even improved in 6/11 plots, indicating a selection process. Large basal lesions at the beginning of the observation period were a very good predictor for deadfall probability, especially on trees with lower stem diameter. Generally, ash dieback related symptoms at stem and crown were highly correlated. Silvicultural management practice in the past that actively pushed ash towards the moister end of its water demand spectrum has to be questioned in the light of ash dieback. Cost-intensive ash re-cultivation in the future—possibly with less dieback-susceptible progenies—should avoid pure ash stands and hydromorphic soil conditions. [ABSTRACT FROM AUTHOR]

European ash populations face a significant threat from the invasive fungus Hymenoscyphus fraxineus, leading to ash dieback disease. The absence of resistant individuals and restrictions on biotechnological solutions hinder the ability to combat this widespread illness in the near term. Priming strategies offer an alternative approach to boost stress tolerance not only in this scenario but also in other endangered tree species by triggering plant defense mechanisms. The non-proteinogenic amino acid β-aminobutyric acid (BABA) has demonstrated potential in enhancing resistance to diverse stressors in plants. Despite limited research on forest tree species, the current study evaluated BABA's effectiveness in mitigating ash dieback disease severity and explored potential correlations between priming treatments and epigenetic modifications. The results indicated that BABA enhanced stress tolerance in ash seedlings following inoculation with Hymenoscyphus fraxineus. BABA effectively decreased the development of necrosis associated with ash dieback disease in seedlings five months post-inoculation. Additionally, treatments involving BABA were linked to observed epigenetic alterations. Elevated levels of the non-canonical deoxynucleosides 5-(hydroxymethyl)-2'-deoxycytidine (5-hmdC) and 5-(hydroxymethyl)-2'-deoxyuridine (5-hmdU) were confirmed subsequent to the treatments. This study highlights the potential of BABA and other priming strategies in enhancing disease tolerance in forest tree species like European ash. Short-term improved stress tolerance and epigenetic changes were confirmed. Yet, the exact priming conditions for inducing long-term effects in plants, including long-living forest trees, remain unknown, posing a challenge for applying priming strategies to manage ash dieback and protect many other endangered tree species. [ABSTRACT FROM AUTHOR]

The decline of European ash by dieback caused by Hymenoscyphus fraxineus together with stem collar necroses and rots caused by various fungi has been investigated intensively during the last years. Nevertheless, hitherto nearly nothing is known about the species diversity of the fungal rhizobiome of ash trees. Here we investigated the fine roots of affected ash trees on 15 sampling sites in 6 federal countries of Germany. Fine-root samples have been treated in three different sample regimes each as root-adhering soil, unsterilized fine roots and sterilized fine roots. The samples of trees in sampling sites were pooled to get an overview of the species-richness in the area. The next-generation sequencing platform Oxford Nanopore MinION was used to sequence the entire ITS of pooled probes. Most abundant phyla in all samples were the Basidiomycota and Ascomycota. Species richness in sterilized roots was significantly different from unsterilized roots and root-adhering soil. Surprisingly most abundant genera in sterilized roots were the genera Mycena, Mycenella and Delicatula, all of them agaricoids with saprophytic lifestyle. Eleven genera of Glomeromycota have been detected in various abundances, whereas the detection of H. fraxineus was neglectable. [ABSTRACT FROM AUTHOR]

Over the past decades, European ash trees in Germany have been affected by ash dieback, reducing their vigour and mechanical resistance. Those trees that also have stem collar necroses and the resulting stem rot are particularly affected. In this study, multilocus genotypes (MLGs) of Hymenoscyphus fraxineus and their interactions with other fungi from stem collar necroses were analysed. Ten ash trees from three different adjacent forest stands in central Germany were sampled. A total number of 716 isolates were obtained from stem collar necroses from these ten trees. Microsatellite analysis was successfully performed on 274 isolates identified as H. fraxineus and 26 MLGs were revealed. The number of MLGs varied from one to seven per tree and did not correspond to the number or severity of necroses. A striking result was that five of the MLGs occurred in two trees. All other MLGs occurred independently in only one tree, as expected. Our data show that when multiple MLGs were observed in a tree, one of the MLGs outnumbered the others, indicating that H. fraxineus is a primary coloniser of stem collar necroses. A total of 61 morphotypes, including H. fraxineus, were identified and discussed, comprising endophytic, saprotrophic and pathogenic fungi. Between five and 19 different fungi were found per stem collar necrosis. The majority of all isolated morphotypes were Ascomycota (82%), with the most common orders being Xylariales and Hypocreales. The most frequently isolated morphotypes, apart from H. fraxineus, were Armillaria sp. and Diplodia fraxini. Together they account for more than three quarters of all assigned isolations. Apart from H. fraxineus, only Diplodia fraxini was isolated from all ten trees. [ABSTRACT FROM AUTHOR]

The ongoing global climate change has aroused interest in the spring phenology of woody species in boreal and temperate regions that require cold temperatures to break bud dormancy. Most research on this topic has been concentrated on fruit species, rather than forest trees. We studied the effect of chilling duration in vitro and ex vitro on the timing of dormancy release in European ash plants. In vitro chilling (at 4–5ºC) of rooted ash plants delayed their subsequent growth when planted out in the greenhouse, and the length of delay correlated with chilling duration. The fastest growth was observed after 5–7 weeks of cold treatment, whereas 13 weeks reduced the plant viability. The impact of cold treatment for 300–3000 h was assessed on one-year-old ash plantlets. Subsequently, clonal micropropagation of European ash on a dihydroquercetin (taxifolin)-containing medium significantly reduced the requirement for chill temperatures: the plantlets came out of endodormancy after having accumulated 500 chill hours, whereas control (unchilled) plantlets required more than 1000 h. The budburst period was also significantly shorter in chilled plants. We suppose that the effect might have been due to the antioxidant activity of the flavonoid dihydroquercetin. The thermal time requirement for budburst in European ash was well described as an inverse exponential function of the number of chill hours at ≤ 5 °C. Late-flowering and photoperiod-insensitive European ash is a good object for studying the impact of external and internal factors on the mechanisms behind the induction and release of dormancy. [ABSTRACT FROM AUTHOR]

Abstract Objective The endophytic mycobiome is present in all studied plant compartments, including fruits and seeds. Here, we studied the mycobiome of seed wings as they are transferred with seeds in common ash and tested whether the mycobiome differs among trees. To achieve this, we used ITS1-based amplicon sequencing and two genotypes of F. excelsior as a model to compare the mycobiome of mother trees and their wings. Results We compared the mycobiome of 57 seed wings to the seed stalks (57) collected from two genotypes of F. excelsior using three ramets of each genotype. Alpha diversity indices (ACE, Fisher and Observed OTUs) suggested a higher richness of the mycobiome associated with the seed wing than the seed stalk within each genotype. However, there were neither significant differences in Shannon diversity between the mycobiomes from the two tissue types nor the two genotypes. PERMANOVA revealed significant differences in the mycobiome composition between tissue types (P

Plant diseases are mostly multicausal with several factors influencing the health status of affected hosts. Common ash (Fraxinus excelsior), a significant tree species of European forests, is currently mostly endangered by ash dieback, caused by the invasive fungus Hymenoscyphus fraxineus. However, contributing factors, including pathogenic viruses, are poorly understood. Here, we report the results of a virus screening conducted on selected special stands of F. excelsior. Over three consecutive years, ash trees from different origins were tested, including leaf material from mature seed trees, young trees and ash seedlings from the natural regeneration. Using RT-PCR, we screened for five viruses, including the generalist species ArMV (Nepovirus arabis) and CLRV (Nepovirus avii), as well as newly discovered viruses in ash, including the emaravirus ASaV (Emaravirus fraxini), the idaeovirus PrLBaV (Idaeovirus ligustri), and cytorhabdoviruses. The results revealed a high virus diversity in common ash. An association of ASaV detection with specific leaf symptoms, including shoestring, chlorotic ringspots, and vein yellowing, was documented. An analyses of relevant gene products of cytorhabdoviruses obtained from ashes of different sites revealed sequence diversities and two distinct phylogenetic groups present in ash populations. Signatures of novel viruses from different families have been identified by high-throughput sequencing. Together, our results provide insights into the virus diversity and distribution of viruses in ash and expand our knowledge about the virome of this endangered tree species. [ABSTRACT FROM AUTHOR]

Objective: The endophytic mycobiome is present in all studied plant compartments, including fruits and seeds. Here, we studied the mycobiome of seed wings as they are transferred with seeds in common ash and tested whether the mycobiome differs among trees. To achieve this, we used ITS1-based amplicon sequencing and two genotypes of F. excelsior as a model to compare the mycobiome of mother trees and their wings. Results: We compared the mycobiome of 57 seed wings to the seed stalks (57) collected from two genotypes of F. excelsior using three ramets of each genotype. Alpha diversity indices (ACE, Fisher and Observed OTUs) suggested a higher richness of the mycobiome associated with the seed wing than the seed stalk within each genotype. However, there were neither significant differences in Shannon diversity between the mycobiomes from the two tissue types nor the two genotypes. PERMANOVA revealed significant differences in the mycobiome composition between tissue types (P < 0.001). It also showed a significant difference between seed wings (P = 0.04), but not between seed stalks of the two genotypes. Our results suggest that Fraxinus excelsior mother trees disperse different sets of mycobiomes with their seed wings, which may be important for germination and seedling establishment—especially in the light of ash dieback. [ABSTRACT FROM AUTHOR]

The photosynthesis and chlorophyll content are fundamental to understanding ecological processes in forest ecosystems, providing valuable clues to the health and functioning of these complex systems. The study of photosynthetic rates and chlorophyll content in five different tree species (Carpinus betulus, Fraxinus excelsior, Robinia pseudoacacia, Acer campestre and Acer pseudoplatanus) conducted in two different locations, namely in the Iron Gates Natural Park in Moldova Nouă (PNPF) and in Timișoara, brings to the fore a detailed analysis of the adaptations and responses of vegetation to environmental variability. Across the whole study, Acer pseudoplatanus revealed a significantly higher value of chlorophyll content, followed by Robinia pseudoacacia and Carpinus betulus with similar values and Acer campestre and Fraxinus excelsior with the lowest values, respectively. Acer campestre had a significantly higher photosynthesis rate than the other species, while Acer pseudoplatanus had the lowest values in both locations. [ABSTRACT FROM AUTHOR]

The increase in introduced insect pests and pathogens due to anthropogenic environmental changes has become a major concern for tree species worldwide. Common ash (Fraxinus excelsior L.) is one of such species facing a significant threat from the invasive fungal pathogen Hymenoscyphus fraxineus. Some studies have indicated that the susceptibility of ash to the pathogen is genetically determined, providing some hope for accelerated breeding programs that are aimed at increasing the resistance of ash populations. To address this challenge, we used a genomic selection strategy to identify potential genetic markers that are associated with resistance to the pathogen causing ash dieback. Through genome‐wide association studies (GWAS) of 300 common ash individuals from 30 populations across Poland (ddRAD, dataset A), we identified six significant SNP loci with a p‐value ≤1 × 10−4 associated with health status. To further evaluate the effectiveness of GWAS markers in predicting health status, we considered two genomic prediction scenarios. Firstly, we conducted cross‐validation on dataset A. Secondly, we trained markers on dataset A and tested them on dataset B, which involved whole‐genome sequencing of 20 individuals from two populations. Genomic prediction analysis revealed that the top SNPs identified via GWAS exhibited notably higher prediction accuracies compared to randomly selected SNPs, particularly with a larger number of SNPs. Cross‐validation analyses using dataset A showcased high genomic prediction accuracy, predicting tree health status with over 90% accuracy across the top SNP sets ranging from 500 to 10,000 SNPs from the GWAS datasets. However, no significant results emerged for health status when the model trained on dataset A was tested on dataset B. Our findings illuminate potential genetic markers associated with resistance to ash dieback, offering support for future breeding programs in Poland aimed at combating ash dieback and bolstering conservation efforts for this invaluable tree species. [ABSTRACT FROM AUTHOR]

Fraxinus excelsior L. (ash) is a key forest tree species challenged by Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz, Hosoya, the causal agent of ash dieback. The goals of this study were (I) to assess the presence, spatial distribution, and incidence of H. fraxineus in the inner-alpine valleys of northwestern Italy, along with the severity of ash dieback; (II) to model the probability of infection by H. fraxineus based on environmental variables; (III) to reconstruct the direction of provenance of the front of invasion of the pathogen; and (IV) to test whether H. fraxineus has replaced the native relative Hymenoscyphus albidus (Gillet) W. Phillips, a saprobe of ash litter. By combining phytosanitary monitoring and samplings in 20 forest stands, laboratory analyses, and statistical modelling, this study showed that H. fraxineus was present in 65% of stands with an average incidence of 27%, reaching peaks of 80%. Rainfalls were the most relevant drivers of the probability of infection by H. fraxineus, rising up to 80% with the increased precipitation in April and July. Other drivers included elevation, maximal temperatures, latitude, and longitude. The front of invasion likely moved from Italy and/or Switzerland, rather than from France, while the replacement of H. albidus is uncertain. [ABSTRACT FROM AUTHOR]

In this work, the total content of phenolics, flavonoids, and phenolic acids in the leaves and bark extracts of Fraxinus ornus L. and Fraxinus excelsior L. was determined. In addition, the identification and quantification of phenolic acids was performed using the HPLC-DAD technique. Samples were tested for antioxidant activity using the ABTS and DPPH methods. Eight extract samples were prepared by Soxhlet and ultrasound extraction using 70 % ethanol as solvent. The content of phenolic compounds ranged from 7.59 for F. ornus to 88.93 mg GAE/g for F. excelsior in the bark extracts obtained by Soxhlet extraction. The highest content of total flavonoids in F. ornus and F. excelsior was found in the leaves extracts obtained by ultrasound extraction, which was 5.68 and 1.74 mg GAE/g extract, respectively. The results also showed that the highest content of total phenolic acids was found in F. ornus (105.33 mg CAE/g) and F. excelsior (97.97 mg CAE/g) in the bark extract obtained by Soxhlet extraction. The highest content of gallic acid (112.96 ± 1.32 mg g–1 extracts) and chlorogenic acid (246.94 ± 0.82 mg g–1 extracts) was found in the F. ornus bark extract obtained by ultrasound extraction. As for antioxidant activity, the bark extract obtained by Soxhlet extraction of F. ornus showed the best antioxidant activity by ABTS method with IC50 value of 0.062 mg ml–1. The results of the DPPH method show that the leaves extract obtained by Soxhlet extraction had the best antioxidant activity for the F. ornus sample, with an IC50 value of 0.23 mg ml–1.

In light of the increase of environmental pollution, we tested the effect of cadmium (Cd) and lead (Pb) soil contamination on ash dieback. The experiment included the inoculation of Hymenoscyphus fraxineus on Fraxinus excelsior and Fraxinus angustifolia seedlings growing on unpolluted soil, soil contaminated with cadmium (Cd), and soil contaminated with lead (Pb). At the end of the experiment, 173 days after soil contamination and 50 days since inoculation, all F. excelsior and F. angustifolia seedlings inoculated with H. fraxineus showed ash dieback symptoms in comparison to their control groups. However, both F. excelsior and F. angustifolia seedlings grown on contaminated soil had significantly increased necrotic lesions in comparison to the seedlings grown on uncontaminated soil. Our results showed for the first time that cadmium (Cd) and lead (Pb) soil contamination can significantly contribute to ash dieback and increase damage to F. excelsior and F. angustifolia seedlings.

Infestation with the emerald ash borer Agrilus planipennis Fairmaire, 1888 (Coleoptera: Buprestidae) was detected in September 2024 in roadside stands along the Debaltsevo–Lugansk–Rovenki highway in the Donbass region. A similar pest focus was found in the Sea of Azov region along the Rostov-on-Don–Novoazovsk highway, approximately 40 km west of Taganrog. Judging by the extent of spreading and the signs of tree decline, the species must have appeared in the Donbass region no later than 2021 or 2022. Adult parasitoid wasps Spathius polonicus Niezabitowski, 1910 were reared from the emerald ash borer larvae found in the infested trees. The invasion of A. planipennis in Donbass appears to depend on dispersal along roadside forest belts. It is notable that the species was not recorded in natural ravine forests of the Donetsk Ridge during forest pathology surveys in 2019–2024. [ABSTRACT FROM AUTHOR]

Leaf litter decomposition is a major component of nutrient cycling which depends on the quality and quantity of the leaf material. Ash trees (Fraxinus excelsior, decay time ∼ 0.4 years) are declining throughout Europe due to a fungal pathogen (Hymenoscyphus fraxineus), which is likely to alter biochemical cycling across the continent. The ecological impact of losing species with fast decomposing leaves is not well quantified. In this study we examine how decomposition of three leaf species with varying decomposition rates including ash, sycamore (Acer pseudoplatanus, decay time ∼ 1.4 years), and beech (Fagus sylvatica, decay time ∼ 6.8 years) differ in habitats with and without ash as the dominant overstorey species. Ten plots (40 m × 40 m) were set up in five locations representing ash dominated and non-ash dominated habitats. In each plot mesh bags (30 cm × 30 cm, 0.5 mm aperture) with a single leaf species (5 g) were used to include (large holes added) and exclude macrofauna invertebrates (with a focus on decomposer organisms such as earthworms, millipedes, and woodlice). The mesh bags were installed in October 2020 and retrieved without replacement at exponential intervals after 6, 12, 24 and 48 weeks. Total leaf mass loss was highest in the ash dominated habitat (ash dominated: 88.5%, non-ash dominated: 66.5%) where macrofauna were the main contributor (macrofauna: 96%, microorganisms/mesofauna: 4%). The difference between macrofauna vs microorganisms and mesofauna was less pronounced in the non-ash dominated habitat (macrofauna: 68%, microorganisms/mesofauna: 31%). Our results suggest that if ash dominated habitats are replaced by species such as sycamore, beech, and oak, the role of macrofauna decomposers will be reduced and leaf litter decomposition rates will decrease by 25%. These results provide important insights for future ash dieback management decisions.

This study describes the seasonal changes in cell-to-cell transport in three selected angiosperm tree species, Acer pseudoplatanus (maple), Fraxinus excelsior (ash), and Populus tremula × tremuloides (poplar), with an emphasis on the living wood component, xylem parenchyma cells (XPCs). We performed anatomical studies, dye loading through the vascular system, measurements of non-structural carbohydrate content, immunocytochemistry, inhibitory assays and quantitative real-time PCR to analyse the transport mechanisms and seasonal variations in wood. The abundance of membrane dye in wood varied seasonally along with seasonally changing tree phenology, cambial activity, and non-structural carbohydrate content. Moreover, dyes internalized in vessel-associated cells and 'trapped' in the endomembrane system are transported farther between other XPCs via plasmodesmata. Finally, various transport mechanisms based on clathrin-mediated and clathrin-independent endocytosis, and membrane transporters, operate in wood, and their involvement is species and/or season dependent. Our study highlights the importance of XPCs in seasonally changing cell-to-cell transport in both ring-porous (ash) and diffuse-porous (maple, poplar) tree species, and demonstrates the involvement of both endocytosis and plasmodesmata in intercellular communication in angiosperm wood. [ABSTRACT FROM AUTHOR]

Plants are especially useful as biological indicators to assess air pollution and the effects of urbanisation. The aim of this study was to investigate tree species' sensitivity to air pollution using the Air Pollution Tolerance Index (APTI), the dust content (PM10) of leaves, and the heavy metal concentration of leaves. Sampling sites were in a city park (urban area), a location on the edge of the city (suburban area), and a forested location (rural area) along an urbanisation gradient in the city of Vienna in Austria. Leaf samples were collected from Acer platanoides, Fraxinus excelsior, and Quercus robur tree species. The APTI was determined by measuring the content of relative water ascorbic acid and chlorophyll, and the pH of leaf extracts. We found significant difference among species in their relative water content, pH, and content of ascorbic acid and chlorophyll Additionally, we found significant differences in chlorophyll content and pH based on sampling site. The highest chlorophyll content was found in A. platanoides. There was a significant difference among species in Al, Ba, Cr, Ni, and Zn concentrations in each stage of urbanisation. Based on APTI values, the studied species were sensitive indicators of air pollution; thus, they are useful bioindicator species, and they are suitable for air pollution monitoring. We demonstrated the effects of urbanisation with these bioindicator species with elevated PM10, Al, Ba, Cu, Fe, Sr, and Zn concentrations in urban area samples. [ABSTRACT FROM AUTHOR]

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In recent decades the vitality and physical stability of European ash trees in Germany have been reduced by European ash dieback, especially when associated with stem collar necroses and rots. This study was carried out to investigate the composition of the fungal communities associated with stem collar necroses. Filamentous fungi were isolated from 58 ash trees out of nine forest stands in northern, eastern, and central Germany. Obtained isolates were identified to a genus or species level by means of morphological and molecular analyses. In total 162 morphotypes including endophytic, saprotrophic, and pathogenic fungi were isolated. For 33 species found no prior reports from Fraxinus excelsior were recognised, including Cryptostroma corticale and Diplodia sapinea. None of the identified species were found at all studied sites, though Diplodia fraxini was the most common fungus with regard to frequency within all isolates, occurring at seven sample sites. This species is followed by Hymenoscyphus fraxineus, Armillaria spp., Neonectria punicea, Diaporthe cf. eres, Fusarium cf. lateritium, and Paracucurbitaria sp. in order of frequency within all isolates. The aforementioned species are characterised and analysed in respect to their occurrence in stem collar necroses and at sample sites. The influence of site conditions on the fungal composition was described for five intensively sampled sites with a minimum of five studied trees (Schwansee, Rhüden, Berggießhübel, Satrup, and Schlangen). The sampling site of Schlangen was further subdivided into four subplots with different positions in the terrain. In the remaining four extensive sample sites, either one or two trees, respectively, were sampled and analysed (Oranienbaumer Heide, Woltershausen, Wolfenbüttel, and Neuhege). Over all sample sites, fungal communities of symptomatic stem tissue are similar concerning the most frequent fungi, but vary greatly according to singularly isolated fungi. [ABSTRACT FROM AUTHOR]

Inflammation is the first physiological defence mechanism against external and internal stimuli. The prolonged or inappropriate response of the immune system may lead to the persistent inflammatory response that can potentially become a basis for chronic diseases e.g., asthma, type II diabetes or cancer. An important role in the alleviation of inflammatory processes, as an adjunct to traditional pharmacological therapy, is attributed to phytotherapy, especially to raw materials with a long tradition of use, e.g., ash leaves. Despite their long-term use in phytotherapy, the specific mechanisms of action have not been confirmed in a sufficient number of biological or clinical studies. The aim of the study is a detailed phytochemical analysis of infusion and its fractions, isolation of pure compounds from the leaves of Fraxinus excelsior and evaluation of their effect on the secretion of anti-inflammatory cytokines (TNF-α, IL-6) and IL-10 receptor expression in an in vitro model of monocyte/macrophage cells isolated from peripheral blood. Methods: Phytochemical analysis was carried out by the UHPLC-DAD-ESI-MS/MS method. Monocytes/macrophages were isolated from human peripheral blood using density gradient centrifugation on Pancoll. After 24 h incubation with tested fractions/subfractions and pure compounds, cells or their supernatants were studied, respectively, on IL-10 receptor expression by flow cytometry and IL-6, TNF-α, IL-1β secretion by the ELISA test. Results were presented with respect to Lipopolysaccharide (LPS) control and positive control with dexamethasone. Results: The infusion, 20% and 50% methanolic fractions and their subfractions, as well as their dominating compounds, e.g., ligstroside, formoside and oleoacteoside isolated from the leaves, show the ability to increase the IL-10 receptor expression on the surface of monocyte/macrophage cells, stimulated by LPS, and to decrease the secretion of pro-inflammatory cytokines, e.g., TNF-α, IL-6. [ABSTRACT FROM AUTHOR]

Objectives: Fraxinus excelsior L. (FE) is traditionally used to treat inflammatory and pain disorders. This study aimed to identify the constituents of FE leaves and evaluate the effects of its n-hexane (FEH), ethyl acetate (FEE), methanol (FEM) extracts and constituents on the viability of THP-1 cells and their ability to release pro-inflammatory cytokines. Methods: THP-1 cell viability was assessed using an MTT assay. The immunomodulatory activity was evaluated by measuring tumour necrosis factor-alpha (TNF-α) and interleukin 12 (IL-12) released by lipopolysaccharide-stimulated THP-1 cells using enzyme-linked immunosorbent assays. Key findings: Triterpenes, tyrosol esters, alkanes, phytyl and steryl esters, pinocembrin and bis(2-ethylhexyl)phthalate were isolated from FE. The tyrosol esters showed no significant effect on THP-1 cell viability. FEH, FEE, FEM, and pinocembrin, ursolic acid, oleanolic acid had IC50 values of 56.9, 39.9, 124.7 µg/ml and 178.6, 61.5 and 199.8 µM, respectively. FE extracts, ursolic acid, oleanolic acid and pinocembrin significantly reduced TNF-α/IL-12 levels. The tyrosol esters did not significantly affect TNF-α/IL-12 production. Conclusions: FE was able to reduce pro-inflammatory cytokine production indicating a mechanistic focus in its use for inflammation and pain. Further investigations are warranted to unravel the mode of action of the tested constituents and discover other potentially active compounds in FE extracts. [ABSTRACT FROM AUTHOR]

Pollen are an important food source for numerous insects and may be used as natural markers in ecological studies. However, to make inferences about the movement rates of insects based on their gut contents, information on pollen digestion rates is needed. Here, we assessed how the consumption and digestion rates of pollen ingested by Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) adults are influenced by plant species, temperature, and sex. We offered pollen of two insect‐pollinated plants – Acer pseudoplatanus L. (Sapindaceae) and Helianthus annuus L. (Asteraceae) – and two wind‐pollinated plants – Fraxinus excelsior L. (Oleaceae) and Quercus rubra L. (Fagaceae) – differing in size and protein content, to adult lacewings at two temperatures, 20 and 25 °C. After feeding, lacewings were allowed to digest pollen for up to 14 days, sampled at 10 time intervals. At each of these intervals, lacewings were frozen and the internal pollen were obtained through acetolysis and quantified under a light microscope. The number of pollen grains decreased exponentially over time and declined faster for Acer than for the other three plant species. The half‐life and the time at which 95% of the pollen grains were digested were lower for Acer than for the other plant species. Lacewings consumed more pollen grains from Acer and Quercus than from Fraxinus and Helianthus. Male lacewings consumed 30% fewer pollen grains than females, but without differences in their digestion rates. Our results show that lacewings consumed higher amounts of high‐protein pollen (Acer and Quercus) and that digestion rates differed among plant species, which could be linked to their structural characteristics. The variable digestion rates of pollen grains may influence the study of lacewing diet composition. Studies that make inferences about the pollen diet or movement ecology of lacewings by analysing their gut contents should account for species‐specific pollen digestion rates. [ABSTRACT FROM AUTHOR]

European ash dieback caused by the alien, invasive ascomycete species Hymenoscyphus fraxineus currently represents, along with its side effects, the greatest threat to common ash (Fraxinus excelsior) trees in Europe. The disease is widely distributed in Germany and present in all regions where common ash is growing. In order to study European ash dieback in Germany and to develop management strategies to conserve common ash as a forest tree species, the concerted, interdisciplinary research project FraxForFuture was initiated. FraxForFuture consist of an association of five sub-networks: FraxConnect, FraxMon, FraxGen, FraxPath, and FraxSilva. In total, 27 individual projects conduct research on the epidemiology of the disease, the pathogen and the preservation of ash, including various control, breeding, and silvicultural strategies. The main goals of the FraxForFuture network and the sub-networks as well as essential information about the network of common research plots are provided. [ABSTRACT FROM AUTHOR]

Ash dieback caused by the invasive fungus Hymenoscyphus fraxineus leads to massive mortality among common ash (Fraxinus excelsior) in Europe. To select tolerant genotypes, inoculation experiments are frequently conducted with isolates of the fungus. The aim of this study was to improve the inoculation methodology for evaluating susceptibility of ash genotypes to ash dieback through (i) testing the virulence of different isolates of Hymenoscyphus fraxineus and (ii) investigating temporal lesion development using three widely applied cultivars: Altena, Atlas and Westhof's Glorie. First, an experiment was conducted with a repeated measure design in which virulence of five different isolates was tested. Second, a subset of two isolates that induced the longest downward lesion length in experiment one was used in combination with a slightly adjusted inoculum protocol. Significant differences were found between isolates for downward lesion length, but a significant interaction effect of isolates and cultivars was absent. Also, the inoculation position within the stem affected lesion length; the largest lesions were found on the highest inoculation position within the stem. Furthermore, we found that cryopreserved isolates can remain virulent over years. The timing of inoculation at the end of the growing season was effective as large lesions already occurred during winter dormancy. For future inoculation studies, we propose to use: (i) isolates that induce large lesions, as less virulent isolates induced not only shorter but also fewer lesions; (ii) a similar inoculation position to better compare inoculations within and between experiments; (iii) cryopreserved isolates for testing over years; (iv) mycelial suspensions for inoculum preparation to cover wood chips more evenly; (v) reference clone—like the studied cultivars—to standardize research outcomes between years and research groups. [ABSTRACT FROM AUTHOR]

A large proportion of the western marginal range for common ash (Fraxinus excelsior L.) is located on the island of Ireland. However, the molecular diversity of common ash in Ireland has only been studied in a limited number of populations and using mainly non-standard chloroplast and nuclear simple sequence repeat (SSR) markers. This has prevented direct comparisons with studies on the rest of the species' range across Europe. Here, four chloroplast and six nuclear SSR markers were used to infer the genetic diversity from 347 trees sampled across 20 populations. Results confirmed that, like Britain, Ireland is dominated by one main haplotype (H04) which originates from an Iberian glacial refugium. The occurrence of a second, rarer haplotype (H13) that also occurs as a rare haplotype in Britain but nowhere else, suggests at least some post-glacial recolonisation from the east. Chloroplast allelic richness was similar to Norway, which constitutes the species' northern marginal range, but lower than in Britain and the European average. Nuclear allelic richness was also comparable with Norway, but Irish common ash differed in a complete absence of sub-population structure and geographic variability at both the chloroplast and nuclear level. Analysis of nuclear genetic structure indicated that common ash in Ireland mainly comprises one genetic group which is likely part of a single, western European meta-population. However, a less frequent genetic cluster is hypothesised to represent a mix of non-native alleles from imported plantation ash. Finally, conservation recommendations and the consequences of a uniform and low genetic diversity are discussed in the context of ash dieback disease, which was present in all populations sampled here. [ABSTRACT FROM AUTHOR]

Abstract Background The dieback epidemic decimating common ash (Fraxinus excelsior) in Europe is caused by the invasive fungus Hymenoscyphus fraxineus. In this study we analyzed the genomes of H. fraxineus and H. albidus, its native but, now essentially displaced, non-pathogenic sister species, and compared them with several other members of Helotiales. The focus of the analyses was to identify signals in the genome that may explain the rapid establishment of H. fraxineus and displacement of H. albidus. Results The genomes of H. fraxineus and H. albidus showed a high level of synteny and identity. The assembly of H. fraxineus is 13 Mb longer than that of H. albidus’, most of this difference can be attributed to higher dispersed repeat content (i.e. transposable elements [TEs]) in H. fraxineus. In general, TE families in H. fraxineus showed more signals of repeat-induced point mutations (RIP) than in H. albidus, especially in Long-terminal repeat (LTR)/Copia and LTR/Gypsy elements. Comparing gene family expansions and 1:1 orthologs, relatively few genes show signs of positive selection between species. However, several of those did appeared to be associated with secondary metabolite genes families, including gene families containing two of the genes in the H. fraxineus-specific, hymenosetin biosynthetic gene cluster (BGC). Conclusion The genomes of H. fraxineus and H. albidus show a high degree of synteny, and are rich in both TEs and BGCs, but the genomic signatures also indicated that H. albidus may be less well equipped to adapt and maintain its ecological niche in a rapidly changing environment.

Societal Impact Statement Emerald ash borer (EAB) is thought to have arrived in North America and European Russia at least 10 years prior to detection. Despite heightened awareness that EAB could invade Great Britain (GB), detection in the early stages of establishment is difficult, and initial symptoms might be mistaken for Chalara ash dieback. Our results suggest that if partial resistance to EAB in Fraxinus excelsior does not significantly dampen EAB population dynamics, then EAB could establish and spread across large parts of southern England within a relatively short time period; however, further northern spread may be limited by the relatively cool climate. Summary The accidental introduction of emerald ash borer (EAB) to North America and European Russia in the 1990s has resulted in an ongoing crisis with millions of ash trees damaged and killed at immense economic and social cost. Improving our understanding of how rapidly the pest might spread should it enter Great Britain (GB) plays an essential part in planning for a potential outbreak. Two metrics are used to investigate the potential dynamics of EAB in GB: the observed rate of spread in the North American and Russian regions; and the relationship between degree days and emergence that may determine environmental suitability and whether the life cycle is univoltine or semivoltine. The pest is still spreading in North America and European Russia with an overall average rate of spread between 2002 and 2018 of approximately 50 km a year. Early detection of the pest is difficult, but a similar delay in detection to that in North America would result in a costly and hard to control outbreak. Comparison of degree days between regions suggests that a semivoltine life cycle is most likely in most areas of GB but spread maybe limited by the relatively cool climate in parts of GB. There are several potentially important differences in the biophysical environment in GB compared with North America and European Russia. However, the speed with which it has invaded these areas highlights the need for early surveillance and mitigations to minimise human‐mediated spread of this highly destructive pest.

The aim of this study was to evaluate the health condition of Fraxinus excelsior L. in provenance tests, with special focus on ash dieback (ADB), but taking into account also other causes of its decline. The research was carried out in the provenance tests of F. excelsior in the forest-steppe part of the Sumy region. ADB symptoms were revealed in all provenance tests. For 2012–2019 the health condition index, ADB incidence and severity increased for all provenances except the Steppe. Collar rot was present in all ash provenances. Fungi species were isolated from the stem parts of ash at all provenances. Hymenoscyphus fraxineus induced longest necrotic lesions following wound inoculation of stems of 7–10-years-old plants of European ash in the forest while inoculation with both Cytospora sp. and Diplodia sp. resulted in smaller necroses. The conclusion from other regions about the coincidence the damage of European ash by ADB and collar rots as well as the coincidence the damage of European ash by collar rot and tree colonization by Hylesinus crenatus (Fabricius, 1787) is supported.

Climate change and human activities have accelerated the spread of non-native species, including forest pests and pathogens, significantly contributing to global biodiversity loss. Pathogens pose a significant threat to forest ecosystems due to a lack of coevolution with native hosts, resulting in ineffective defence mechanisms and severe consequences for the affected tree species. Ash dieback, caused by the fungus Hymenoscyphus fraxineus , is a relatively new invasive forest pathogen threatening ash (Fraxinus excelsior) with mortality rates in northern Europe reaching up to 80 %. The loss of ash due to dieback has severe ecological implications, potentially leading to an extinction cascade as ash provides crucial habitats and resources for many organisms. Despite this, the consequences of ash dieback on associated communities are largely unknown. To address this, we analysed changes in species richness, vegetation structure, and composition in 82 permanent vegetation plots across 23 Norwegian woodlands. We compared data collected before and 10–14 years after the emergence of ash dieback. In these woodlands, ash significantly declined in cover, leading to changes in tree species composition and facilitating the establishment of other woody tree species like hazel (Corylus avellana) and the invasive species sycamore (Acer pseudoplatanus). Despite these changes in the tree species composition, no significant alterations were observed in the understory plant community, indicating a degree of ecosystem resilience or a lagging community response. At this point, and with our focus on the vascular plants, we do not find support for cascading effects due to ash dieback. However, our findings demonstrate that one invasive species is facilitating the expansion of another, raising concerns about potential ecological imbalance and cascading effects in the future. • Ash dieback significantly alters tree composition in Norwegian woodlands. • Decline of ash trees facilitates growth of hazel and invasive sycamore. • No significant change in understory plant community richness or diversity. • Resilience observed in ash seedlings and juveniles, indicating regenerative potential. • Potential future ecological imbalance due to invasive species expansion. [ABSTRACT FROM AUTHOR]

Urbanization impacts plant-herbivore interactions, which are crucial for ecosystem functions such as carbon sequestration and nutrient cycling. While some studies have reported reductions in insect herbivory in urban areas (relative to rural or natural forests), this trend is not consistent and the underlying causes for such variation remain unclear. We conducted a continental-scale study on insect herbivory along urbanization gradients for three European tree species: Quercus robur, Tilia cordata, and Fraxinus excelsior, and further investigated their biotic and abiotic correlates to get at mechanisms. To this end, we quantified insect leaf herbivory and foliar secondary metabolites (phenolics, terpenoids, alkaloids) for 176 trees across eight European cities. Additionally, we collected data on microclimate (air temperature) and soil characteristics (pH, carbon, nutrients) to test for abiotic correlates of urbanization effects directly or indirectly (through changes in plant secondary chemistry) linked to herbivory. Our results showed that urbanization was negatively associated with herbivory for Q. robur and F. excelsior , but not for T. cordata. In addition, urbanization was positively associated with secondary metabolite concentrations, but only for Q. robur. Urbanization was positively associated with air temperature for Q. robur and F. excelsior , and negatively with soil nutrients (magnesium) in the case of F. excelsior , but these abiotic variables were not associated with herbivory. Contrary to expectations, we found no evidence for indirect effects of abiotic factors via plant defences on herbivory for either Q. robur or F. excelsior. Additional biotic or abiotic drivers must therefore be accounted for to explain observed urbanization gradients in herbivory and their interspecific variation. In more urbanized areas, insect leaf herbivory was lower for Quercus robur and Fraxinus excelsior but not for Tilia cordata , while leaf secondary metabolites were higher for Q. robur but not for F. excelsior and T. cordata. [Display omitted] • The association between the urbanization degree and herbivory varied among the tree species. • Urbanization is positively associated with leaf secondary metabolite concentrations in Q. robur. • Abiotic proxies of urbanization showed no direct or indirect association with herbivory in either species. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of seed maturation on germination, growth and seedling quality index of common ash (Fraxinus excelsior L.) in Kelardasht forest nursery. In 2017, the seeds of immature in late August and the seeds of mature in late November were collected and following stratification in moist sand were sown in nursery bed in mid-Feberaury each with three 100-replications . From the mature seeds, some of them germinated in 2nd year (April 2018) and the seed germination, biomass and quality indices of their seedlings were statistically (paired t-test) compared with the results of immature seeds germinated in spring 2017. The highest percentage of cumulative germination allocated to the immature seeds, followed by mature seeds germinated in 2nd year. Due to the lack of germination of most of the mature seeds in spring 2017, showed the seed dormancy, their germination traits were not considered in the statistical test. Germination percentage, mean germination time and germination speed and also, dry biomass, root biomass, root length and seedling quality index in immature seeds were greater than those in mature seeds germinated in second year. Generally, it is best to collect the seedlings of immature seed in order to achieve the optimum germination and growth, because the mature seeds are often dormant and unable to germinate during the first growing season. If mature seeds are supplied, it is advisable that these seeds to be stratified until spring of the second year.

Elimination of hazardous chemicals in the process of synthesis, which guarantees the safety of the nanoparticles (NPs) for therapeutic utilization, could be obtained by using the phyto-synthesis method. The present project is a multidimensional survey that aimed to optimize the phyto-synthesis conditions of copper nanoparticles (Cu NPs) using the microwave and ultrasound-assisted methods and facilitate approaching the dilemma of choosing between these two methods by characterizing the final products of each method. Based on the transmission electron microscopy (TEM), the obtained NPs were sub 10 nm in both methods. The optimized NPs were achieved in 5 min using 6 mL of phytoextract at 95 ℃ in a microwave oven, and amplitude 100% and cycle 0.8 in an ultrasonic processor. In addition to the antibacterial property and molecular wound healing stimulation of Cu NPs, these amorphous nanoscale particles could provide desirable absorption and distribution over the wounds to be suggested as an effective transdermal drug delivery system. The ultrasound-assisted method was the most appropriate way to obtain an amorphous mixture of Cu NPs with a majority of copper oxide while the microwave-assisted method was more suitable for synthesis procedures using plant extracts with heat-sensitive and volatile components.

Agrilus planipennis (Coleoptera: Buprestidae) is the most serious invasive pest of ash trees (Fraxinus spp., Oleaceae) in the world. It has not yet reached the range of olive tree plantations, however it has been shown to complete its life cycle in this host tree. This pest native to East Asia was first found in Europe in Moscow in 2003 and has been spreading ever since. The aims of this study were to determine if the southern border of the range has already reached the Caucasus and to assess the potential range in this region based on host availability and heat availability. In 2021, we surveyed ash trees south to the known range in Russia. We did not find the pest in six cities in the North Caucasus region but found it in the city of Azov close to the Caucasus. Analysis of information about 550 localities of ash trees in the Caucasus showed that Fraxinus spp. is common throughout the region. The calculation of annual growing degree days base 10 °C indicated that the places where Fraxinus spp. grow above 1500 m are too cold for A. planipennis and therefore could potentially become a refuge for ash trees. The spread of A. planipennis to the Caucasus is of concern. First, the forest ecosystems of this region are endangered, since European ash Fraxinus excelsior is much more common there than in the currently infested regions in Russia. Second, the Russian Caucasus can become the gateway to Georgia, Armenia, Azerbaijan, Turkey and other countries of the Middle East and Southern Europe. We propose using Fraxinus angustifolia, F. ornus and Olea europaea growing in the Caucasus and adjacent regions as sentinel trees for the monitoring and pest risk assessment of these tree species. [ABSTRACT FROM AUTHOR]

Abstract Background With the expanding ash dieback epidemic that has spread across the European continent, an improved functional understanding of the disease development in afflicted hosts is needed. The study investigated whether differences in necrosis extension between common ash (Fraxinus excelsior) trees with different levels of susceptibility to the fungus Hymenoscyphus fraxineus are associated with, and can be explained by, the differences in gene expression patterns. We inoculated seemingly healthy branches of each of two resistant and susceptible ash genotypes with H. fraxineus grown in a common garden. Results Ten months after the inoculation, the length of necrosis on the resistant genotypes were shorter than on the susceptible genotypes. RNA sequencing of bark samples collected at the border of necrotic lesions and from healthy tissues distal to the lesion revealed relatively limited differences in gene expression patterns between susceptible and resistant genotypes. At the necrosis front, only 138 transcripts were differentially expressed between the genotype categories while 1082 were differentially expressed in distal, non-symptomatic tissues. Among these differentially expressed genes, several genes in the mevalonate (MVA) and iridoid pathways were found to be co-regulated, possibly indicating increased fluxes through these pathways in response to H. fraxineus. Comparison of transcriptional responses of symptomatic and non-symptomatic ash in a controlled greenhouse experiment revealed a relatively small set of genes that were differentially and concordantly expressed in both studies. This gene-set included the rate-limiting enzyme in the MVA pathway and a number of transcription factors. Furthermore, several of the concordantly expressed candidate genes show significant similarity to genes encoding players in the abscisic acid- or Jasmonate-signalling pathways. Conclusions A set of candidate genes, concordantly expressed between field and greenhouse experiments, was identified. The candidates are associated with hormone signalling and specialized metabolite biosynthesis pathways indicating the involvement of these pathways in the response of the host to infection by H. fraxineus.

European ash (Fraxinus excelsior) is highly affected by the pathogenic fungus Hymenoscyphus fraxineus in all of Europe. Increases in plant’s secondary metabolite (SM) production is often linked tol enhanced resistance to stress, both biotic and abiotic. Moreover, plant-associated bacteria have been shown to enhance SM production in inoculated plants. Thus, our hypothesis is that bacteria may boost ash SM production, hence priming the tree’s metabolism and facilitating higher levels of resilience to H. fraxineus. We tested three different ash genotypes and used Paenibacillus sp. and Pseudomonas sp. for inoculation in vitro. Total phenol (TPC), total flavonoid (TFC) and carotenoid contents were measured, as well as the chlorophyll a/b ratio and morphometric growth parameters, in a two-stage trial, whereby seedlings were inoculated with the bacteria during the first stage and with H. fraxineus during the second stage. While the tested bacteria did not positively affect the morphometric growth parameters of ash seedlings, they had a statistically significant effect on TPC, TFC, the chlorophyll a/b ratio and carotenoid content in both stages, thus confirming our hypothesis. Specifically, in ash genotype 64, both bacteria elicited an increase in carotenoid content, TPC and TFC during both stages. Additionally, Pseudomonas sp. inoculated seedlings demonstrated an increase in phenolics after infection with the fungus in both genotypes 64 and 87. Our results indicate that next to genetic selection of the most resilient planting material for ash reforestation, plant-associated bacteria could also be used to boost ash SM production. [ABSTRACT FROM AUTHOR]

Background and Aims Quantifying the Earth's forest above-ground biomass (AGB) is indispensable for effective climate action and developing forest policy. Yet, current allometric scaling models (ASMs) to estimate AGB suffer several drawbacks related to model selection and uncertainties about calibration data traceability. Terrestrial laser scanning (TLS) offers a promising non-destructive alternative. Tree volume is reconstructed from TLS point clouds with quantitative structure models (QSMs) and converted to AGB with wood basic density. Earlier studies have found overall TLS-derived forest volume estimates to be accurate, but highlighted problems for reconstructing finer branches. Our objective was to evaluate TLS for estimating tree volumes by comparison with reference volumes and volumes from ASMs. Methods We quantified the woody volume of 65 trees in Belgium (from 77 to 2800 L; Pinus sylvestris , Fagus sylvatica , Larix decidua , and Fraxinus excelsior) with QSMs and destructive reference measurements. We tested a volume expansion factor (VEF) approach by multiplying the solid and merchantable volume from QSMs by literature VEF values. Key Results Stem volume was reliably estimated with TLS. Total volume was overestimated by +21 % using original QSMs, by +9 % and –12 % using two sets of VEF-augmented QSMs, and by –7.3 % using best-available ASMs. The most accurate method differed per site, and the prediction errors for each method varied considerably between sites. Conclusions VEF-augmented QSMs were only slightly better than original QSMs for estimating tree volume for common species in temperate forests. Despite satisfying estimates with ASMs, the model choice was a large source of uncertainty, and species-specific models did not always exist. Therefore, we advocate for further improving tree volume reconstructions with QSMs, especially for fine branches, instead of collecting more ground-truth data to calibrate VEF and allometric models. Promising developments such as improved co-registration and smarter filtering approaches are ongoing to further constrain volumetric errors in TLS-derived estimates. [ABSTRACT FROM AUTHOR]

The tolerance of ash trees against the pathogen Hymenoscyphus fraxineus seems to be associated with the occurrence of specific microbial taxa on leaves. A group of bacterial isolates, primarily identified on tolerant trees, was investigated with regard to their taxonomic classification and their potential to suppress the ash dieback pathogen. Examination of OGRI values revealed a separate species position. A phylogenomic analysis, based on orthologous and marker genes, indicated a separate genus position along with the species Achromobacter aestuarii. Furthermore, analysis of the ratio of average nucleotide identities and genome alignment fractions demonstrated genomic dissimilarities typically observed for inter-genera comparisons within this family. As a result of these investigations, the strains are considered to represent a separate species within a new genus, for which the name Schauerella fraxinea gen. nov., sp. nov. is proposed, with the type strain B3P038T (=LMG 33092 T = DSM 115926 T). Additionally, a reclassification of the species Achromobacter aestuarii as Schauerella aestuarii comb. nov. is proposed. In a co-cultivation assay, the strains were able to inhibit the growth of a H. fraxineus strain. Accordingly, a functional analysis of the genome of S. fraxinea B3P038T revealed genes mediating the production of antifungal substances. This potential, combined with the prevalent presence in the phyllosphere of tolerant ash trees, makes this group interesting for an inoculation experiment with the aim of controlling the pathogen in an integrative approach. For future field trials, a strain-specific qPCR system was developed to establish an efficient method for monitoring the inoculation success. [ABSTRACT FROM AUTHOR]

Gypsy moth, Lymantria dispar L. (Lepidoptera: Erebidae) feeds on a large number of tree species, while ash, Fraxinus spp. (Lamiales: Oleaceae) species are considered resistant and are only sporadically eaten. To assess the conditions under which late instar gypsy moth larvae (GML) can temporarily use non-host common ash (CA) (F. excelsior L.), and to evaluate their ability to recover from ingestion of this toxic food, we determined the relative growth rate, the relative consumption rate and the amount of produced feces in different laboratory feeding trials. Our report is the first to show that under specific circumstances, the resources acquired after short-term consumption of CA leaves can be utilized for larval growth. We varied the intensity of density and starvation stress prior to feeding on CA leaves. We observed that after moderate stress a group of GML was temporarily capable of coping with CA leaves. Although observed growth and consumption were much lower on CA than on the optimal host oak, Quercus cerris L. (Fagales: Fagaceae), CA-oak-switched larvae showed the ability to recover from short-term use of a toxic non-host foliage. This suggests that feeding on CA might enable GML to survive under conditions of food shortage. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 43007: Studying climate change and its influence on the environment: impacts, adaptation and mitigation]

With ongoing climate change, episodes of severe flooding are predicted to become more frequent despite a general trend towards increasing summer drought. We investigated how wood growth of adult trees of two species characteristic of floodplain forests in Central Germany (Fraxinus excelsior L., Quercus robur L.) and two less-typical species (Acer pseudoplatanus L., Carpinus betulus L.) responded to both maximum stream water level and climate, with a special focus on the effects of the extraordinary flood of the Saale River in June 2013 and the extreme drought in summer 1976. Tree-ring widths were measured on wood cores, and standardized ARSTAN tree-ring chronologies were produced. Using variance partitioning as well as linear mixed-effects models, we compared the effects of monthly values for maximum water level, temperature and precipitation sum on tree-ring width. Further, we calculated resistance, resilience and recovery of the tree species to the extreme events of flooding in 2013 and drought in 1976. Wood growth of all species studied, and particularly of F. excelsior, responded positively to the extraordinary flooding in June 2013. However, in the best models for the characteristic floodplain forest species (F. excelsior and Q. robur), mainly precipitation (F. excelsior) or a combination of precipitation and wood growth of the previous year (Q. robur) acted as drivers of wood growth of the current year. In contrast, growth of the less habitat-specific species (A. pseudoplatanus) mainly showed a significant response to the combination of temperature and wood growth of the previous year. C. betulus was the only species studied that benefited from the extreme drought in 1976. However, two years afterwards, only the wood growth of A. pseudoplatanus was still reduced, while F. excelsior and Q. robur fully recovered. In comparison to other regions in Central Europe, the moderate flood regime of the Saale River seems to have the potential to mitigate effects of summer drought in this region, which is one of the driest in Germany. Thus, increased flooding frequency might, to some degree, reduce drought effects brought about by climate change as well.

Fraxinus excelsior populations are in decline due to the ash dieback disease Hymenoscyphus fraxineus. It is important to understand genotypic and environmental effects on its fungal microbiome to develop disease management strategies. To do this, we used culture dependent and culture independent approaches to characterize endophyte material from contrasting ash provenances, environments, and tissues (leaves, roots, seeds). Endophytes were isolated and identified using nrITS, LSU, or tef DNA loci in the culture dependent assessments, which were mostly Ascomycota and assigned to 37 families. Few taxa were shared between roots and leaves. The culture independent approach used high throughput sequencing (HTS) of nrITS amplicons directly from plant DNA and detected 35 families. Large differences were found in OTU diversity and community composition estimated by the contrasting approaches and these data need to be combined for estimations of the core endophyte communities. Species richness and Shannon index values were highest for the leaf material and the French population. Few species were shared between seed and leaf tissue. PCoA and NMDS of the HTS data showed that seed and leaf microbiome communities were highly distinct and that there was a strong influence of Fraxinus species identity on their fungal community composition. The results will facilitate a better understanding of ash fungal ecology and are a step toward identifying microbial biocontrol systems to minimize the impact of the disease. [ABSTRACT FROM AUTHOR]

The aim of the presented research was to study and assess Total Suspended Particle mitigation capacity of Fraxinus excelsior and Platanus orientalis - the two most widespread tree species in Yerevan. It turned out that in the conditions of Yerevan, both tree species show high efficiency of TSP mitigation. In this regard, we recommend using P. orientalis and F. excelsior in Yerevan green infrastructure as wide as possible, especially along the highways, in the industrial areas of the city, and in areas with intensive construction. [ABSTRACT FROM AUTHOR]