Emergence and diversification of a highly invasive chestnut pathogen lineage across southeastern Europe

Abstract

Invasive microbial species constitute a major threat to biodiversity, agricultural production and human health. Invasions are often dominated by one or a small number of genotypes, yet the underlying factors driving invasions are poorly understood. The chestnut blight fungus Cryphonectria parasitica first decimated the North American chestnut, and a more recent outbreak threatens European chestnut stands. To unravel the chestnut blight invasion of southeastern Europe, we sequenced 230 genomes of predominantly European strains. Genotypes outside of the invasion zone showed high levels of diversity with evidence for frequent and ongoing recombination. The invasive lineage emerged from the highly diverse European genotype pool rather than a secondary introduction from Asia or North America. The expansion across southeastern Europe was mostly clonal and is dominated by a single mating type, suggesting a fitness advantage of asexual reproduction. Our findings show how an intermediary, highly diverse bridgehead population gave rise to an invasive, largely clonally expanding pathogen.

Contrasting demographic histories revealed in two invasive populations of the dry rot fungus Serpula lacrymans

“…Our study confirms that invasive species can establish through founder events involving a few individuals, and that limited genetic diversity does not restrict further expansion. A similar pattern has been observed for many invasive plant and animal pathogens (e.g., Fontaine et al, 2013; McMullan et al, 2018; O’Hanlon et al, 2018; Stauber et al, 2021; Wuest et al, 2017), as well as for the invasive ectomycorrhizal species Amanita phalloides (Pringle et al, 2009). Our results confirm that this also applies to invasive wood decay fungi, such as S .…”

Ecological Differentiation Among Globally Distributed Lineages of the Rice Blast Fungus Pyricularia oryzae

“…The pattern of population structure revealed in P. oryzae is seems to be intermediate between observations for invasive fungi with fully clonal population structures -such as the pathogens causing wheat brown rust [25], boxwood blight 25 [64] or verticillium wilt [65,66] -and invasive fungi with barriers maintaining invasive lineages that are permeable and allow hybridization and introgression to occur, such as the pathogens causing Dothistroma needle blight [67], Dutch elm disease [8], soybean anthracnose Colletotrichum truncatum [68], and coffee rust [69,70]. The global structure of P. oryzae is more reminiscent of that of the pathogens causing chestnut blight [71,72], wheat yellow rust [73,74], and hop powdery mildew [75], for which clonal invasive lineages coexist with recombining lineages, although the proximal causes for the loss of sexual reproduction may differ between these models and rice blast.…”

A New Double-Stranded RNA Mycovirus in Cryphonectria naterciae Is Able to Cross the Species Barrier and Is Deleterious to a New Host

“…To genetically discriminate each isolate of C. naterciae individually prior and subsequent to pairing experiments, a genotyping assay based on simple sequence repeats (SSRs) was developed, which has a firm place as a diagnostic tool for non-model organisms [50]. Unassembled reads of genomic sequencing data of C. naterciae, developed previously in our lab [38,51], were screened using msatcommander v1.0.8-beta [52] that searches for repetitive motifs and designs primers. The loci Cn-Msat6 and Cn-Msat10 were selected for genotyping, which exhibited three and four polymorphic alleles, respectively.…”