Hymenoscyphus fraxineus and two new Hymenoscyphus species identified in Korea

Hymenoscyphus fraxineus is an invasive fungal pathogen that causes ash dieback in Europe. Recent investigations have identified H. fraxineus on herbarium specimens in Korea. In this paper, these specimens, plus five additional collections, were studied by internal transcribed spacer (ITS) screening and subsequent phylogenetic analysis using three additional sequence markers (actin, calmodulin, EF1-α). Using the concept of genealogical concordance phylogenetic species recognition (GCPSR), H. fraxineus was confirmed in five of the collections on petioles of Fraxinus mandshurica and F. chinensis subsp. rhynchophylla. The remaining collections revealed two novel species, both occurring on petioles of F. chinensis subsp. rhynchophylla. They are described as Hymenoscyphus occultus sp. nov. and Hymenoscyphus koreanus sp. nov., based on morphological and molecular data. Both develop a Chalara-like anamorph similar to that of H. fraxineus. Together with the newly described H. albidoides from China and H. linearis from Japan, the clade containing H. fraxineus now consists of six species. Within this clade, H. koreanus forms a sister species to H. albidus and both share highly similar morphological and molecular features. Hymenoscyphus occultus is more distantly related to H. fraxineus and shows proximity to H. linearis. Ascocarp production on ash leaf malt-extract agar could be shown for the two new species, and for H. linearis and H. albidus. The experiment demonstrated these species’ ability to self-fertilize. Our findings suggest the diversity of Hymenoscyphus species on Fraxinus sp. might be higher than currently known, calling for further investigations on petioles of other Fraxinus species.ISSN:1617-416XISSN:1861-895

Data from: Population structure of the invasive forest pathogen Hymenoscyphus pseudoalbidus

Understanding the genetic diversity and structure of invasive pathogens in source and introduced areas is crucial to reveal hidden biological aspects of an organism, to reconstruct the course of invasions and to establish effective control measures. Hymenoscyphus pseudoalbidus (anamorph: Chalara fraxinea) is an invasive and highly destructive fungal pathogen on common ash Fraxinus excelsior in Europe and occurs natively in east Asia. To get insights into the dispersal mechanism and the history of invasion, we used microsatellite markers and characterized the genetic structure and diversity of H. pseudoalbidus populations at three spatial levels: (i) in Europe; (ii) at the epidemic front and (iii) between Europe and Japan. The 1208 European strains form one large population as no evident structure was detected using Bayesian and multivariate clustering analysis. Only the distribution of genetic diversity in space, pairwise population differentiation (GST) and the spatial analysis of principal components revealed a faint geographic pattern around Europe. A significant allele deficiency in most European populations pointed to a recent genetic bottleneck whereas no pattern of isolation by distance was found. Populations from Japan harbored a higher genetic diversity and were genetically differentiated from European ones. Nevertheless, phylogenetic and network analysis clearly demonstrated that individuals from both regions are conspecific. Our data suggest that H. pseudoalbidus was introduced only once by a minimum of two individuals. The potential source region of H. pseudoalbidus is huge and further investigations are required for a more accurate localization of the source population

Detection of a Conspecific Mycovirus in Two Closely Related Native and Introduced Fungal Hosts and Evidence for Interspecific Virus Transmission

Hymenoscyphus albidus is a native fungus in Europe where it behaves as a harmless decomposer of leaves of common ash. Its close relative Hymenoscyphus fraxineus was introduced into Europe from Asia and currently threatens ash (Fraxinus sp.) stands all across the continent causing ash dieback. H. fraxineus isolates from Europe were previously shown to harbor a mycovirus named Hymenoscyphus fraxineus Mitovirus 1 (HfMV1). In the present study, we describe a conspecific mycovirus that we detected in H. albidus. HfMV1 was consistently identified in H. albidus isolates (mean prevalence: 49.3%) which were collected in the sampling areas before the arrival of ash dieback. HfMV1 strains in both fungal hosts contain a single ORF of identical length (717 AA) for which a mean pairwise identity of 94.5% was revealed. The occurrence of a conspecific mitovirus in H. albidus and H. fraxineus is most likely the result of parallel virus evolution in the two fungal hosts. HfMV1 sequences from H. albidus showed a higher nucleotide diversity and a higher number of mutations compared to those from H. fraxineus, probably due to a bottleneck caused by the introduction of H. fraxineus in Europe. Our data also points to multiple interspecific virus transfers from H. albidus to H. fraxineus, which could have contributed to the intraspecific virus diversity found in H. fraxineus

Microsatellite dataset

This data file contains all microsatellite data, mating type data and relevant population information

Hymenoscyphus linearis sp nov: another close relative of the ash dieback pathogen H. fraxineus

Hymenoscyphus is a large fungal genus containing a single known severe pathogen (H. fraxineus) causing ash dieback in Europe. Here, the closely related species Hymenoscyphus linears sp. nov. is described from Japan. Apothecia of this fungus emerge from linear, black pseudosclerotia on rachises and petioles of Fraxinus platypoda. In culture, the species forms a Chalara anamorph similar to that of H. fraxineus. In addition, a Sporotrichum-like synanamorph is produced. Spores of neither anamorphic forms germinate on malt extract agar and might act solely as spermatia. After prolonged incubation, ascocarps are produced directly on agar plates, indicating the ability to self-fertilize. Phylogenetic investigations using four sequence markers placed the species alongside H. albidus, H. albidoides, and H. fraxineus. Eight fungal strains, co-occurring with H. linearis on petioles of F. platypoda, were isolated and identified by sequencing the ITS region of the rDNA. Seven different species were revealed, showing that there is no other dominant fungus on petioles of F. platypoda. Pathogenicity tests on Fraxinus excelsior and its native host F. platypoda revealed that the fungus is avirulent. The close phylogenetic relationship with H. fraxineus and the avirulence of H. linearis offer an opportunity to study the evolution of pathogenicity of H. fraxineus in further detail in the future.ISSN:1617-416XISSN:1861-895

Hidden invasion and niche contraction revealed by herbaria specimens in the fungal complex causing oak powdery mildew in Europe

Deciphering the dynamics involved in past microbial invasions has proven difficult due to the inconspicuous nature of microbes and their still poorly known diversity and biogeography. Here we focus on powdery mildew, a common disease of oaks which emerged in Europe at the beginning of the twentieth century and for which three closely related Erysiphe species are mainly involved. The study of herbaria samples combined with an experimental approach of interactions between Erysiphe species led us to revisit the history of this multiple invasion. Contrary to what was previously thought, herbaria sample analyses very strongly suggested that the currently dominant species, E. alphitoides, was not the species which caused the first outbreaks and was described as a new species at that time. Instead, E. quercicola was shown to be present since the early dates of disease reports and to be widespread all over Europe in the beginning of the twentieth century. E. alphitoides spread and became progressively dominant during the second half of the twentieth century while E. quercicola was constrained to the southern part of its initial range, corresponding to its current distribution. A competition experiment provided a potential explanation of this over-invasion by demonstrating that E. alphitoides had a slight advantage over E. quercicola by its ability to infect leaves during a longer period during shoot development. Our study is exemplary of invasions with complexes of functionally similar species, emphasizing that subtle differences in the biology of the species, rather than strong competitive effects may explain patterns of over-invasion and niche contraction

From leaf to continent: The multi-scale distribution of an invasive cryptic pathogen complex on oak

The spatial distribution and niche differentiation of three closely related species (Erysiphe alphitoides, Erysiphe quercicola and Erysiphe hypophylla) causing oak powdery mildew was studied at scales ranging from the European continent, where they are invasive, to a single leaf. While E. alphitoides was dominant at all scales, E. quercicola and E. hypophylla had restricted geographic, stand and leaf distributions. The large-scale distributions were likely explained by climatic factors and species environmental tolerances, with E. quercicola being more frequent in warmer climates and E. hypophylla in colder climates. The extensive sampling and molecular analyses revealed the cryptic invasion of E. quercicola in nine countries from which it had not previously been recorded. The presence of the three species was also strongly affected by host factors, such as oak species and developmental stage. Segregation patterns between Erysiphe species were observed at the leaf scale, between and within leaf surfaces, suggesting competitive effects

Global Spore Sampling Project: A global, standardized dataset of airborne fungal DNA.

Novel methods for sampling and characterizing biodiversity hold great promise for re-evaluating patterns of life across the planet. The sampling of airborne spores with a cyclone sampler, and the sequencing of their DNA, have been suggested as an efficient and well-calibrated tool for surveying fungal diversity across various environments. Here we present data originating from the Global Spore Sampling Project, comprising 2,768 samples collected during two years at 47 outdoor locations across the world. Each sample represents fungal DNA extracted from 24 m3 of air. We applied a conservative bioinformatics pipeline that filtered out sequences that did not show strong evidence of representing a fungal species. The pipeline yielded 27,954 species-level operational taxonomic units (OTUs). Each OTU is accompanied by a probabilistic taxonomic classification, validated through comparison with expert evaluations. To examine the potential of the data for ecological analyses, we partitioned the variation in species distributions into spatial and seasonal components, showing a strong effect of the annual mean temperature on community composition