Dieback of European ash (Fraxinus excelsior), caused by the ascomycete Hymenoscyphus pseudoalbidus (anamorph Chalara fraxinea), started around 1992 in Poland and has since then spread over large ...geographical areas. By November 2010, the disease had been recorded in 22 European countries. The gradual expansion and high intensity of the ash dieback epidemic in Europe may suggest that H. pseudoalbidus is an invasive alien organism. In Norway, ash dieback was first reported in spring 2008, and a survey in early summer of the same year revealed that the disease had spread over large parts of the southern and eastern regions of the country. The distance from the southernmost to the northernmost infected stands was, at that time, about 400 km. Some old necrotic lesions were also observed, indicating that the ash dieback pathogen is likely to have been present in Norway since at least 2006. In 2009, a spore sampler was installed in a diseased ash stand at Ås, South‐Eastern Norway. Sampling started in late July and continued until late September. Large numbers of ascospores resembling those of H. pseudoalbidus were observed, with the maximum number of spores occurring from the end of July to mid‐August. The deposition of ascospores occurred mainly between 6 and 8 a.m. Ascospores are most likely to be the primary source initiating host infections and responsible for the rapid recent spread of H. pseudoalbidus in Europe.
•Present species are established in areas more vulnerable to climate change impacts.•The impact of this process on species can predict the possible changes in the future.•Despite the potential loss ...of some species, forest continuity will be maintained.•Some areas are forecasted to have better conditions for these species in the future.•Smart planning should be done in order to ensure the continuity of forests.
Climate change is expected to have various impacts on forest ecosystems through drought, heat stress, insect invasions and forest fires. Therefore, lack of taking the necessary measures in time will lead to the extinction or endangerment of valuable species. The entropy method was used in order to estimate the geographic distribution of Fraxinus excelsior L. available in Turkey under present and future climate conditions. 19 bioclimatic variables obtained from the monthly data within 30 provinces, where Fraxinus excelsior L. was found in Turkey, as well as the topographic variable of elevation were used in the modelling process. The results show that Fraxinus excelsior L. is largely affected by precipitation in the driest month, the driest quarter and the hottest quarter. According to the response curve of Fraxinus excelsior L. in Turkey, it is observed that it prefers the habitats with average precipitation of 22 mm in the driest month, average precipitation of 100 mm in the driest quarter and the precipitation over 70 mm in the hottest quarter. The SSPs 245 and SSPs 585 climate scenarios, respectively, show that the geographic distribution of Fraxinus excelsior L. will narrow by 7.58% and 6.28% in 2100. All of these results show that species response to the individual and communal impacts as well as the impacts at ecosystem scale dictated by climate change by changing their climatic niches. Most of the plant species that lack an effective and rapid migration ability will have difficulty in finding suitable habitat areas. Thus, the ecological consequences of the narrowing experienced in the foreseen borders may have serious consequences for both the management and protection of forests.
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.
At present, the distribution area of
L. in the forest ecosystems of the Volga Region is rather low and ranges from 0.01% to 2.5%. In the Middle Volga Region, using the example of the Penza region, ...five types of deciduous forests were identified in the composition with
L.: oak forest aegopodium, oak forest nettle, oak forest hazel-linden, oak forest aegopodium-motley grass, oak forest carex-motley grass. In the forest phytocenoses of the Moksha River basin, the quality of
L. is 1.5-1.7. In the forest phytocenoses of the Khoper River basin, the average quality value reaches 2.4-2.8, and in the forest tracts of the Sura river basin it is 2.8-3.2. In the western part of the study area, individuals of age class II-III (21-40, 41-60 years) predominate, in the central part-age class I (1-20 years), in the eastern part-age class V (81-100 years). This circumstance allows us to conclude that its populations in the western regions are represented by stands of different ages; the presence of young stands and middle-aged stands indicates the presence of conditions for reproduction and distribution. At the border of its range,
L. grows in a stable population; in the western part of the Middle Volga Region, the number of species in forest stands with a predominance of
L. is 26-30% higher than this indicator in more eastern regions. In the direction from east to west, the number of species in the composition of forest stands increases (up to 8.4), with a predominance of
L. The number of plant associations increases in the direction from east to west. If in the east of the Penza region
L. occurs in 6-7 plant associations, then in the west of the region-in 18-25 associations. The maximum timber stock for 100 years of
L. stands reaches 380 m
/ha. Such a natural bioresource potential is of importance for the conduct of the national economy. Forest management in phytocenoses with the participation of this tree species is a strategic branch direction. It is expedient to restore populations of
L. everywhere and to cultivate them in the territory of the East European Plain and especially in its south-eastern part. This is fully consistent with the principles of sustainable ecological and economic development against the background of local natural, climatic and geographical conditions. This type is necessary when solving environmental, resource-saving and economic problems in the territory under consideration.
Cryptic speciation in Hymenoscyphus albidus Queloz, V.; Grünig, C. R.; Berndt, R. ...
Forest pathology = Journal de pathologie forestière = Zeitschrift für Forstpathologie,
04/2011, Letnik:
41, Številka:
2
Journal Article
Recenzirano
Summary
Ash dieback caused by the mitosporic ascomycete Chalara fraxinea is a novel disease of major concern affecting Fraxinus excelsior and Fraxinus angustifolia in large parts of Europe. Recently, ...its teleomorph was detected and assigned to Hymenoscyphus albidus, which has been known from Europe since 1851. In this study, we present molecular evidence for the existence of two morphologically very similar taxa, H. albidus, which is lectotypified and Hymenoscyphus pseudoalbidus sp. nov. Differences were found between the species in the loci calmodulin, translation elongation factor 1‐α and the internal transcribed spacers of the rDNA genes, and strong differentiation was obtained with ISSR markers. It is likely that H. albidus is a non‐pathogenic species, whereas H. pseudoalbidus is a virulent species causing ash dieback. Genotyping herbarium specimens showed that H. pseudoalbidus has been present in Switzerland for at least 30 years prior to the outbreak of the epidemic.
•Tree-ring chronologies of four temperate broad-leaved tree species were studied.•Growth always responded negatively to high summer temperatures and climatic aridity.•Climate sensitivity of growth ...decreased in the period 1967–2016.•Larger growth reduction during severe drought in diffuse- than ring-porous species.•Minor timber species deserve broader consideration in silvicultural concepts.
Climate warming and a rise in evaporative demand expose forests to increasing stress, challenging silvicultural planning in many temperate forest regions. As some major timber species are drought susceptible, the choice of native broadleaf minor timbers with assumed higher drought tolerance is a promising alternative option. However, their growth performance and vitality in a warmer and drier climate are not well known. We studied tree-ring chronologies of the Central European minor timbers Acer platanoides L., Fraxinus excelsior L., and Tilia cordata Mill. in comparison to the widely planted Quercus petraea Matt. Liebl in different mixed stands along a precipitation gradient in Central Germany and analyzed the sensitivity of radial growth to climatic drivers and severe drought events with the aim to compare the species’ drought tolerance. While growth responded in all four species positively to summer (or spring) precipitation and negatively to higher summer temperature and climatic aridity, climate sensitivity of growth decreased in the period 1967–2016, proving non-stationarity. Superposed epoch analysis revealed larger growth reduction during severe drought in the diffuse-porous species (A. platanoides, T. cordata) than the ring-porous species (Q. petraea, F. excelsior), but resilience was high in all species. Moreover, none of the species showed negative growth trends with recent climate warming, and drought sensitivity was not higher at drier sites, suggesting a considerable acclimation and adaptation potential to increasing drought stress. As all four species proved to be fairly drought tolerant, they deserve broader consideration in silvicultural concepts targeted at adapting production forests to climate warming.
In the last few years, the alarming spread of
Hymenoscyphus fraxineus
, the causal agent of ash dieback, has resulted in a substantial threat to native ash stands in central and northern Europe. ...Since leaves and leaf petioles are the primary infection sites, phyllosphere microorganisms are presumed to interact with the pathogen and are discussed as a source of biocontrol agents. We studied compound leaves from susceptible and visible infection-free trees in four ash stands with a high likelihood of infection to assess a possible variation in the bacterial microbiota, depending on the health status of the trees. The bacterial community was analyzed by culture-independent 16S rRNA gene amplicon sequencing and through the isolation and taxonomic classification of 2,589 isolates using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The bacterial community structure did not show significant differences. However, a set of amplicon sequence variants (ASVs) and MALDI groups belonging to
Luteimonas
,
Aureimonas
,
Pseudomonas
,
Bacillus
, and
Paenibacillus
were distinctly increased in tolerant trees, which may be associated with the ability of the tree to resist the pathogen. The most obvious differences were observed for
Luteimonas
, a genus that is also exclusively present in the healthy core microbiome. In a first
in vitro
screen of antagonists, approximately 11% of total isolates suppressed the growth of
H. fraxineus
, but a statistical test with two different
H. fraxineus
strains confirmed only the antagonistic activity of 8% of these isolates. The antagonistic isolates were assigned to
Bacillus velezensis
,
Pantoea vagans
, and
Pseudomonas caspiana.
Overall, our study provides a set of isolates or phylogenetic groups that might be involved in the process that prevents the penetration and spread of
H. fraxineus.
In the next step,
in planta
experiments are required with a longer period of exposure to
H. fraxineus
to evaluate effective isolates or consortia of isolates acting through direct antagonism or competition or indirectly by inducing resistance.
Positive relationships between biodiversity and ecosystem functioning are reported in many studies. The underlying mechanisms are, however, only little understood, likely due to the focus on the ...aboveground system and neglecting species-specific traits. We used different clusters of tree species composition to investigate how tree species diversity and tree species identity affect belowground nematode communities. Since soil nematodes comprise different trophic groups and are strongly linked to the microbial community, results can provide insight on how soil food webs are structured. In addition, data on leaf litter and fine root biomass were included to account for different effects of aboveground and belowground resources. Clusters of three trees of one, two and three species were identified within a temperate deciduous forest. Target tree species were European beech (Fagus sylvatica), common ash (Fraxinus excelsior) and lime (Tilia cordata, T. platyphyllos) differing in physiology, leaf litter quality and type of mycorrhiza. Tree species identity strongly affected nematode trophic structure, whereas tree species diversity had no impact. Ash beneficially affected bacterial-feeding nematodes, whereas fungal feeders were suppressed, likely caused by ash litter increasing soil pH. Fostering of the bacterial food chain by ash additionally could be related to rhizodeposition gaining importance after disappearance of high quality ash litter in spring, highlighting seasonal shifts in root and leaf litter-derived resources. The negative effect of ash on fungal-feeding nematodes is suggested to be due to the lack of ectomycorrhizal fungi as ash roots only form arbuscular mycorrhiza. In contrast, beech benefited fungal feeders and detrimentally affected bacterial feeders due to more acidic soil conditions that increase the competitive strength of fungi. Lime tended to negatively impact total nematode density but positively influenced plant-feeding nematodes. Generally, beech and ash strongly but opposingly influenced the trophic structure of nematode communities suggesting that changes in tree species identity result in major shifts in the channeling of energy through decomposer food webs. The results indicate that the structure of soil food webs varies markedly with tree species and point to the importance of basal resources, i.e., leaf litter and rhizodeposits. This suggests bottom-up forces mediated by individual tree species to control major decomposition pathways rather than tree diversity.
► Tree species identity is more important than diversity in structuring soil food webs. ► Beech fostered the fungal energy channel and ash the bacterial energy channel. ► Root and litter-derived resources differently affect soil food webs.
Summary
The ascomycete Hymenoscyphus pseudoalbidus (anamorph Chalara fraxinea) causes a lethal disease known as ash dieback on Fraxinus excelsior and Fraxinus angustifolia in Europe. The pathogen was ...probably introduced from East Asia and the disease emerged in Poland in the early 1990s; the subsequent epidemic is spreading to the entire native distribution range of the host trees. This pathogen profile represents a comprehensive review of the state of research from the discovery of the pathogen and points out knowledge gaps and research needs.
Taxonomy
Members of the genus Hymenoscyphus (Helotiales, Leotiomycetidae, Leotiomycetes, Ascomycota) are small discomycetes which form their ascomata on dead plant material. A phylogeny based on the internal transcribed spacers (ITSs) of the rDNA indicated the avirulent Hymenoscyphus albidus, a species native to Europe, as the closest relative of H. pseudoalbidus.
Symptoms
Hymenoscyphus pseudoalbidus causes necrotic lesions on leaves, twigs and stems, eventually leading to wilting and dieback of girdled shoots. Bark lesions are characterized by a typical dark‐ to cinnamon‐brown discoloration.
Life cycle
Hymenoscyphus pseudoalbidus is heterothallic and reproduces sexually on ash petioles in the litter once a year. Ascospores are wind dispersed and infect ash leaves during the summer. The asexual spores only serve as spermatia.
Tools and techniques
The most important techniques for fungal handling, such as detection, isolation, culturing, storage, crossing and ascocarp production, are briefly described.
Management
Once the disease is established, management is hardly possible. The occurrence of a small fraction of partially tolerant trees constitutes hope for resistance breeding in the future. Healthy‐looking trees should be preserved.
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