title: Fungal diversity and seasonal succession in ash leaves infected by the invasive ascomycete Hymenoscyphus fraxineus.
abstract: High biodiversity is regarded as a barrier against biological invasions. We hypothesized that the invasion success of the pathogenic ascomycete Hymenoscyphus fraxineus threatening common ash in Europe relates to differences in dispersal and colonization success between the invader and the diverse native competitors. Ash leaf mycobiome was monitored by high-throughput sequencing of the fungal internal transcribed spacer region (ITS) and quantitative PCR profiling of H. fraxineus DNA. Initiation of ascospore production by H. fraxineus after overwintering was followed by pathogen accumulation in asymptomatic leaves. The induction of necrotic leaf lesions coincided with escalation of H. fraxineus DNA levels and changes in proportion of biotrophs, followed by an increase of ubiquitous endophytes with pathogenic potential. H. fraxineus uses high propagule pressure to establish in leaves as quiescent thalli that switch to pathogenic mode once these thalli reach a certain threshold - the massive feedback from the saprophytic phase enables this fungus to challenge host defenses and the resident competitors in mid-season when their density in host tissues is still low. Despite the general correspondence between the ITS-1 and ITS-2 datasets, marker biases were observed, which suggests that multiple barcodes provide better overall representation of mycobiomes.
authors.affiliation: Norwegian Institute of Bioeconomy Research, Pb. 115, Ås, NO-1431, Norway.
authors.forename: Hugh
authors.initials: H
authors.lastname: Cross
authors.affiliation: Norwegian Institute of Bioeconomy Research, Pb. 115, Ås, NO-1431, Norway.
authors.forename: Jørn Henrik
authors.initials: JH
authors.lastname: Sønstebø
authors.affiliation: Norwegian Institute of Bioeconomy Research, Pb. 115, Ås, NO-1431, Norway.
authors.forename: Nina E
authors.initials: NE
authors.lastname: Nagy
authors.affiliation: Norwegian Institute of Bioeconomy Research, Pb. 115, Ås, NO-1431, Norway.
authors.forename: Volkmar
authors.initials: V
authors.lastname: Timmermann
authors.affiliation: Norwegian Institute of Bioeconomy Research, Pb. 115, Ås, NO-1431, Norway.
authors.forename: Halvor
authors.initials: H
authors.lastname: Solheim
authors.affiliation: Norwegian Institute of Bioeconomy Research, Pb. 115, Ås, NO-1431, Norway.
authors.forename: Isabella
authors.initials: I
authors.lastname: Børja
authors.affiliation: Department of Biosciences, Section for Genetics and Evolutionary Biology, University of Oslo, Pb. 1066 Blindern, Oslo, NO-0316, Norway.
authors.forename: Håvard
authors.initials: H
authors.lastname: Kauserud
authors.affiliation: Department of Biosciences, Section for Genetics and Evolutionary Biology, University of Oslo, Pb. 1066 Blindern, Oslo, NO-0316, Norway.
authors.forename: Tor
authors.initials: T
authors.lastname: Carlsen
authors.affiliation: Faculty of Chemistry UJ, Jagiellonian University, Ingardena 3, Kraków, 30-060, Poland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Rzepka
authors.affiliation: Department of Pedology and Soil Geography, Institute of Geography and Spatial Management, Jagiellonian University, Gronostajowa 7, Kraków, 30-387, Poland.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Wasak
authors.affiliation: Norwegian Institute of Bioeconomy Research, Pb. 115, Ås, NO-1431, Norway.
authors.forename: Adam
authors.initials: A
authors.lastname: Vivian-Smith
authors.affiliation: Norwegian Institute of Bioeconomy Research, Pb. 115, Ås, NO-1431, Norway.
authors.forename: Ari M
authors.initials: AM
authors.lastname: Hietala
mesh_terms: D001203:Ascomycota / Q000145:classification / Q000502:physiology*; D044822:Biodiversity; D021901:DNA, Intergenic; D031661:Fraxinus / Q000382:microbiology*; D058865:Introduced Species; D018515:Plant Leaves / Q000382:microbiology*; D025341:Principal Component Analysis; D012621:Seasons
chemical_list: D021901:DNA, Intergenic
keywords: 
  Hymenoscyphus fraxineus
  ; ash dieback; indigenous fungi; internal transcribed spacer (ITS); invasive pathogens; metabarcoding