Situation and perspectives of European ash (Fraxinus spp.) in Ukraine: focus on eastern border

The health condition of European ash (Fraxinus excelsior) stands in Ukraine has become worse since 2006. Firstly, in 2011 an alien invasive pathogenic fungus Hymenoscyphus fraxineus was identified in the eastern part of the country and, subsequently, its presence was confirmed in the western and central parts. The aims of our research were to evaluate the health of ash trees and identify the main causes of ash decline in different regions of Ukraine with emphasis on ash dieback and its association with collar rots. Results showed that since 2013 the number of trees with ash dieback symptoms has been gradually increasing, reaching up to 92 % in 2018. Total mortality due to ash dieback was up to 9 % in 2018. Disease intensity remains high in northern and central Ukraine comparing with the east. Branch dieback, collar rots, epicormic shoots and bacterial disease of ash occurred more often in the eastern region, some symptoms were observed simultaneously. Ash bark beetle galleries, as well as foliage browsing insects, were found mostly in weakened and/or dying trees. It was indicated that collar rots significantly increase the mortality of ash trees. Armillaria spp. fungi were found to be frequently associated with ash dieback on living stems and fallen trees in 2017, causing high rates of mortality in the northern and central regions. For further ash conservation and breeding programmes, resistant trees in severely damaged regions should be selected to preserve genetic diversity in ash populations. Keywords: Fraxinus excelsior, ash dieback, collar rot, bacterial disease, epicormic shoots, Hymenoscyphus fraxineus, Armillaria spp.

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Decline of Fraxinus excelsior L. in parks of Saint Petersburg: Who is to blame – Hymenoscyphus fraxineus or Diplodia spp.?

Forestry Studies / Metsanduslikud Uurimused ◽

10.2478/fsmu-2020-0013 ◽

2020 ◽

Vol 73 (1) ◽

pp. 43-51

Author(s):

Dmitrii A. Shabunin ◽

Andrey V. Selikhovkin ◽

Elena Yu. Varentsova ◽

Dmitry L. Musolin

Keyword(s):

Light Microscopy ◽

Fraxinus Excelsior ◽

Ash Dieback ◽

Saint Petersburg ◽

Hymenoscyphus Fraxineus ◽

Ash Trees ◽

Fallen Leaves ◽

European Ash

Abstract The weakening and decline of European ash Fraxinus excelsior L. and other ash species have been recorded at different locations in the suburbs of Saint Petersburg, Russia. During the summer of 2019 and spring of 2020, samples from leaves, petioles, and shoots were collected from the weakened and declining ash trees in three parks in Pushkin and Gatchina and maintained in humid chambers to induce the fructification of fungi. In total, 30 taxa of micromycetes belonging to 23 genera were identified using methods of light microscopy. Hymenoscyphus fraxineus, a putative agent of ash dieback, was not recorded in the samples collected in the crowns of trees, but only on the petioles of the fallen leaves in spring. Out of all the micromycetes recorded, only coelomycetes from the genus Diplodia Fr. (in particular, D. mutila) can damage the branches of ash trees and, thus, be considered pathogenic. It is likely that H. fraxineus opens “the entry of infection” and Diplodia spp. cause the major weakening and decline of branches. The data obtained can significantly change our understanding of the causes of ash dieback and possible methods of ash stand preservation. The reason for the low pathogenicity and activity of H. fraxineus, as well as the possible role of ascomycetes Diplodia spp. in the dieback of ash stands requires further research.

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Transformation of European Ash (Fraxinus excelsior L.) Callus as a Starting Point for Understanding the Molecular Basis of Ash Dieback

Plants ◽

10.3390/plants10112524 ◽

2021 ◽

Vol 10 (11) ◽

pp. 2524

Author(s):

Anna Hebda ◽

Aleksandra Liszka ◽

Piotr Zgłobicki ◽

Katarzyna Nawrot-Chorabik ◽

Jan J. Lyczakowski

Keyword(s):

Molecular Basis ◽

Selection Process ◽

Pathogenic Fungus ◽

Fraxinus Excelsior ◽

Reporter System ◽

Ash Dieback ◽

Gus Reporter ◽

Hymenoscyphus Fraxineus ◽

Starting Point ◽

European Ash

The population of European ash (Fraxinus excelsior L.) is currently facing the risk of collapse, mainly due to ash dieback, a disease caused by a pathogenic fungus, Hymenoscyphus fraxineus. To facilitate studies into the molecular basis of ash dieback and design breeding strategies for a generation of resistant trees, it is necessary to develop tools enabling the study of gene function in F. excelsior. Despite this, a method for the genetic engineering of F. excelsior is still missing. Here, we report the first successful genetic transformation of F. excelsior callus and a selection process enabling the formation of stable transgenic callus lines. The protocol relies on the use of Agrobacterium tumefaciens to transform callus tissue derived from embryos of F. excelsior. In our experiments, we used the β-glucuronidase (GUS) reporter system to demonstrate the transformation of callus cells and performed RT-PCR experiments to confirm the stable expression of the transgene. Since ash dieback threatens the long-term stability of many native F. excelsior populations, we hope that the transformation techniques described in this manuscript will facilitate rapid progress in uncovering the molecular basis of the disease and the validation of gene targets previously proposed to be linked to the resistance of trees to H. fraxineus pathogenicity.

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Mycobiome of Fraxinus excelsior With Different Phenotypic Susceptibility to Ash Dieback

Frontiers in Forests and Global Change ◽

10.3389/ffgc.2021.580514 ◽

2021 ◽

Vol 4 ◽

Author(s):

Marta Agostinelli ◽

Diem Nguyen ◽

Johanna Witzell ◽

Michelle Cleary

Keyword(s):

Large Scale ◽

Population Decline ◽

Keystone Species ◽

Fungal Species ◽

Fraxinus Excelsior ◽

Fungal Communities ◽

Ash Dieback ◽

Hymenoscyphus Fraxineus ◽

Ash Trees ◽

European Ash

For the last two decades, large-scale population decline of European ash (Fraxinus excelsior) has occurred in Europe because of the introduction of the alien fungal pathogen, Hymenoscyphus fraxineus, from East Asia. Since European ash is a keystone species having critical importance for biodiversity, and only a small percentage of the ash population appears to show some tolerance against the pathogen, the loss of ash trees means that other associated organisms, especially those with high or obligate associations to ash, are at risk of further species declines. In this study, we used high throughput DNA sequencing and multivariate analysis to characterize: (i) the mycobiome in aerial tissues (i.e., leaf, bark, and xylem) of ash trees showing different phenotypic response to ash dieback, (ii) the temporal variation in fungal communities across the growing season, and (iii) the similarity in fungal community structure between ash and other common trees species that may serve as an ecological niche substitute for ash microfungi. Results showed that fungal communities differed among the three tissue types, susceptibility classes, in time and between sites. Trophic analysis of functional groups using the FUNGuild tool indicated a higher presence of pathotrophic fungi in leaves than in bark and xylem. The share of pathotrophic fungi increased along a gradient of low to high disease susceptibility in both bark and xylem tissue, while the proportion of symbiotrophic fungi correspondingly decreased in both tissue types. Neighboring, alternative host trees did not share all the fungal species found in ash, however, most microfungi uniquely associated to ash in this study are generalists and not strictly host specific. The progressive disappearance of ash trees on the landscape imposes a high risk for extinction of Red-listed macrofungal species, and breeding for resistance against ash dieback should help sustain important biodiversity associated to ash. Microfungal diversity though may be less prone to such demise since most ash-associated endophytes appear to occur on a broad range of host species.

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Estimating mortality rates of European ash ( Fraxinus excelsior ) under the ash dieback ( Hymenoscyphus fraxineus ) epidemic

Plants People Planet ◽

10.1002/ppp3.11 ◽

2018 ◽

Vol 1 (1) ◽

pp. 48-58 ◽

Cited By ~ 27

Author(s):

Tim L. R. Coker ◽

Jiří Rozsypálek ◽

Anne Edwards ◽

Tony P. Harwood ◽

Louise Butfoy ◽

...

Keyword(s):

Mortality Rates ◽

Fraxinus Excelsior ◽

Ash Dieback ◽

Hymenoscyphus Fraxineus ◽

European Ash

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Canditate metabolites for ash dieback tolerance in Fraxinus excelsior

Journal of Experimental Botany ◽

10.1093/jxb/eraa306 ◽

2020 ◽

Vol 71 (19) ◽

pp. 6074-6083 ◽

Cited By ~ 3

Author(s):

Miguel Nemesio-Gorriz ◽

Riya C Menezes ◽

Christian Paetz ◽

Almuth Hammerbacher ◽

Marijke Steenackers ◽

...

Keyword(s):

Fungal Growth ◽

Fraxinus Excelsior ◽

Bark Extract ◽

High Susceptibility ◽

Ash Dieback ◽

Hymenoscyphus Fraxineus ◽

Ash Trees ◽

Fungal Growth Inhibition ◽

Increased Susceptibility

Abstract Ash dieback, a forest epidemic caused by the invasive fungus Hymenoscyphus fraxineus, threatens ash trees throughout Europe. Within Fraxinus excelsior populations, a small proportion of genotypes show a low susceptibility to the pathogen. We compared the metabolomes from a cohort of low-susceptibility ash genotypes with a cohort of high-susceptibility ash genotypes. This revealed two significantly different chemotypes. A total of 64 candidate metabolites associated with reduced or increased susceptibility in the chemical families secoiridoids, coumarins, flavonoids, phenylethanoids, and lignans. Increased levels of two coumarins, fraxetin and esculetin, were strongly associated with reduced susceptibility to ash dieback. Both coumarins inhibited the growth of H. fraxineus in vitro when supplied at physiological concentrations, thereby validating their role as markers for low susceptibility to ash dieback. Similarly, fungal growth inhibition was observed when the methanolic bark extract of low-susceptibility ash genotypes was supplied. Our findings indicate the presence of constitutive chemical defense barriers against ash dieback in ash.

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Fungi isolated from shoots showing ash dieback in the Wolica Nature Reserve in Poland and artificially inoculated seedlings with Hymenoscyphus fraxineus

Folia Forestalia Polonica ◽

10.2478/ffp-2019-0004 ◽

2019 ◽

Vol 61 (1) ◽

pp. 42-50 ◽

Cited By ~ 2

Author(s):

Anna Żółciak ◽

Justyna Anna Nowakowska ◽

Artur Pacia ◽

Nenad Keča ◽

Tomasz Oszako

Keyword(s):

Nature Reserve ◽

Pathogenic Fungus ◽

Internal Transcribed Spacer Region ◽

Ash Dieback ◽

Hymenoscyphus Fraxineus ◽

Ash Trees ◽

Serious Disease ◽

One Year ◽

In The Beginning ◽

Qualitative Changes

Abstract Ash dieback caused by an alien, invasive fungus Hymenoscyphus fraxineus is a serious disease of European ash species in many parts in Europe. In Poland, the disease was recorded in the beginning of the 1990s. This study was performed in 2016–2017 with the aim to identify fungi isolated from ash shoots showing dieback symptoms in the Wolica Nature Reserve in Poland, as well as from shoots of two years-old ash seedlings inoculated with H. fraxineus in the greenhouse. The most frequently isolated fungi from shoots of common ash (associated with the pathogenic fungus H. fraxineus) were identified on the basis of sequencing of the internal transcribed spacer region (ITS1) of fungal rDNA. In total, 19 fungal taxa were identified for ash shoots as follows: H. fraxineus, Fusarium avenaceum, Alternaria spp., Phomopsis oblonga, Diplodia mutila and other Phomopsis spp. The pathogen H. fraxineus was not found for all the shoots samples; one year after inoculation the aforementioned fungi and other species as: Alternaria alternata, Bionectria ochroleuca, Epicoccum nigrum, F. acuminatum, F. avenaceum, and Paraphaesphaeria neglecta were identified in inoculation point, as well as H. fraxineus. The same quantitative and qualitative changes of organisms were observed in the case of artificially colonised ash seedlings in the greenhouse, as well as in the shoots of adult ash trees in the forest.

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Parastā oša Fraxinus Excelsior L. destrukcija Latvijā: audžu sukcesija un oša atjaunošanās = Dieback of common ash Fraxinus Excelsior L. in Latvia: species succession and ash regeneration

10.22616/lluthesis/2020.008 ◽

2020 ◽

Author(s):

◽

Ilze Matisone ◽

Keyword(s):

Western Europe ◽

Health Condition ◽

Fraxinus Excelsior ◽

Mixed Stands ◽

Ash Dieback ◽

Factors Affecting ◽

Stand Management ◽

Species Succession ◽

Hymenoscyphus Fraxineus ◽

Ash Trees

The area of common ash forest is only 1–2% of the total forest area in Europe and 0.3% in Latvia. Prior to dieback, ash was an economically and still is ecologically highly important tree species. In Eastern Europe since the beginning of the 1990s, and a decade later throughout Central and Western Europe, rapid dieback of ash stands caused by an unknown reason was observed. In 2006 the causal agent of ash dieback – an anamorphic fungus Hymenoscyphus fraxineus (species name later refined) was determined. In Latvia, intensive dieback of ash stands has been observed since 2000. The aim of the thesis was to assess the dieback dynamics of common ash Fraxinus excelsior L. stands and determine the main factors affecting susceptibility of the trees, as well as future succession and potential regeneration of the affected common ash stands in Latvia. In Latvia, The area of young ash stands decreased by 4.4 times during 2000–2015. The ten-year-inventory (2005–2015) revealed that the overall mortality of ash was 6.9% and standing volume of ash stands decreased by 171 m3 ha–1. The obtained results indicated that regeneration of ash saplings in ash young stands as well as in mature stands was lower than in in the pre-dieback times, but regeneration was still successful. Furthermore, survival and health condition of ash saplings was relatively poor, as only ca. ⅓ of individuals were healthy, and the health condition decreased with aging. Overgrowth of ash stands with shrub species has begun, suggesting formation of broadleaved stands with a small admixture of ash in the future. We found that, susceptibility to ash dieback is significantly affected by morphometric parameters of ash trees and stands, site conditions and meteorological factors. In Latvia, ash dieback was present in ash stands of all ages and composition, yet some individual and regional differences were observed. Lower susceptibility to ash dieback was observed for older/larger dimensions trees, mixed stands on well-drained and dry mineral soils, stands thinned more intensively, and in the eastern part of Latvia. The findings of the thesis are applicable for the planning of ash stand management, assessment of the existing situation, for the designation of additional genetic resource forests, as well as provide basic information for future studies.

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Host Range of Hymenoscyphus fraxineus in Slovak Arboreta

Forests ◽

10.3390/f11050596 ◽

2020 ◽

Vol 11 (5) ◽

pp. 596

Author(s):

Katarína Pastirčáková ◽

Katarína Adamčíková ◽

Marek Barta ◽

Jozef Pažitný ◽

Peter Hoťka ◽

...

Keyword(s):

Host Range ◽

Native Species ◽

Pathogenic Fungus ◽

Nuclear Ribosomal Dna ◽

New Host ◽

Ash Dieback ◽

Susceptible Host ◽

Hymenoscyphus Fraxineus ◽

Ash Trees ◽

Pcr Targeting

The health of 34 different Fraxinus taxa in association with the pathogenic fungus Hymenoscyphus fraxineus was assessed in four Slovak arboreta. Averaged across all arboreta, nearly one-quarter (24.9%) of all evaluated trees showed ash dieback symptoms. The damage was most serious on the common ash F. excelsior, a native species. The percentage of dead trees did not exceed 2% for all evaluated trees. Generally, ash trees of all ages were affected, though the intensity of the damage varied among the sites. The identity of H. fraxineus was confirmed by conventional PCR targeting the internal transcribed spacer (ITS) sequences of the nuclear ribosomal DNA, as well as the 18S gene/ITS-2 region of the rDNA operon. In Slovakia, the pathogen has expanded its host range from native species not only to their ornamental cultivars, but also to introduced North American (F. cinerea, F. latifolia, F. pennsylvanica, F. quadrangulata) and Asian (F. bungeana, F. chinensis ssp. rhynchophylla, F. mandshurica) ash species. H. fraxineus was also observed on the previous year’s leaf petioles of the native European species F. ornus, considered a weakly susceptible host. In Slovak arboreta, H. fraxineus was found on 23 Fraxinus taxa; 21 of them represent first records for the country. F. bungeana is recorded as a new host species of H. fraxineus.

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Marker-Trait Associations for Tolerance to Ash Dieback in Common Ash (Fraxinus excelsior L.)

Forests ◽

10.3390/f11101083 ◽

2020 ◽

Vol 11 (10) ◽

pp. 1083

Author(s):

Rajiv Chaudhary ◽

Tilman Rönneburg ◽

Matilda Stein Åslund ◽

Karl Lundén ◽

Mikael Brandström Durling ◽

...

Keyword(s):

Disease Severity ◽

Genotypic Variation ◽

Tree Breeding ◽

Mixed Linear Model ◽

Snp Markers ◽

Fraxinus Excelsior ◽

Single Nucleotide ◽

Ash Dieback ◽

Hymenoscyphus Fraxineus ◽

Ash Trees

Common ash (Fraxinus excelsior L.) is a tree species of significant ecological and economic importance that has suffered a devastating decline since the 1990s in Europe. Native ash species are being threatened by the alien invasive fungus Hymenoscyphus fraxineus, which causes ash dieback. The main goal of the study was to develop markers for traits related to tolerance to ash dieback and to investigate whether genotypes selected for tolerance were genetically different from susceptible wild populations. We phenotyped 326 ash trees from Sweden for disease severity and genotyped them using 63 amplicon-derived single-nucleotide polymorphism (SNP) markers derived from genes in 40 scaffolds spanning 8 MB in total, which represents approximately 1% of the ash genome. We used a mixed linear model to test for an association between genotypic variation at these loci and disease severity of ash. In total, two SNPs were found to have significant associations. One non-synonymous SNP associated with the disease severity of ash was found in a gene predicted to encode a subtilisin-related peptidase S8/S53 domain. A second marginally significant marker was associated with an LRR gene. Our results demonstrate an inexpensive time-effective method for generating genomic data that could have potential for use in future tree breeding programs and provide information for marker-assisted selection. Our study also showed a low differentiation between genotypes selected for disease tolerance and the wild population of ash representing a range of susceptibilities to ash dieback, indicating opportunities for further selection without significantly losing genetic diversity in the ash population.

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Genomic basis of European ash tree resistance to ash dieback fungus

10.1101/626234 ◽

2019 ◽

Author(s):

Jonathan J. Stocks ◽

Carey L. Metheringham ◽

William Plumb ◽

Steve J. Lee ◽

Laura J. Kelly ◽

...

Keyword(s):

Sequence Data ◽

Seed Source ◽

Source Zone ◽

Whole Genome Sequence ◽

Ash Dieback ◽

Hymenoscyphus Fraxineus ◽

A Genome ◽

Ash Trees ◽

Gp Model ◽

European Ash

SummaryPopulations of European ash trees (Fraxinus excelsior) are being devastated by the invasive alien fungus Hymenoscyphus fraxineus, which causes ash dieback (ADB). We sequenced whole genomic DNA from 1250 ash trees in 31 DNA pools, each pool containing trees with the same ADB damage status in a screening trial and from the same seed-source zone. A genome-wide association study (GWAS) identified 3,149 single nucleotide polymorphisms (SNPs) associated with low versus high ADB damage. Sixty-one of the 203 most significant SNPs were in, or close to, genes with putative homologs already known to be involved in pathogen responses in other plant species. We also used the pooled sequence data to train a genomic prediction (GP) model, cross-validated using individual whole genome sequence data generated for 75 healthy and 75 damaged trees from a single seed source. Using the top 30% of our genomic estimated breeding values from 200 SNPs, we could predict tree health with over 90% accuracy. We infer that ash dieback resistance in F. excelsior is a polygenic trait that should respond well to both natural selection and breeding, which could be accelerated using GP.

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