Defining the twig fungal communities of Fraxinus species and Fraxinus excelsior genotypes with differences in susceptibility to ash dieback

Ash dieback disease (caused by Hymenoscyphus fraxineus) has affected European ash species (Fraxinus spp.) in recent decades. However, some Asian and American species of Fraxinus and certain genotypes of Fraxinus excelsior are less affected by the disease. We used ITS1-metabacoding to explore the drivers influencing diversity and composition of the twig fungal communities of Fraxinus species and F. excelsior genotypes. Our results revealed that fungi in the classes Eurotiomycetes and Dothideomycetes were among the most prevalent taxa in both Fraxinus species and F. excelsior genotypes. The diversity of the fungal communities differed significantly among Fraxinus species and could be explained by seed origin. Neither host genotype nor season had a significant effect on the community diversity of F. excelsior genotypes. On the other hand, the composition of twig fungal communities differed significantly among host species and among F. excelsior genotypes, and in F. excelsior there was also a significant effect of season on the composition of the fungal community. We did not find a clear effect of ash dieback susceptibility on either diversity or composition of fungal communities in twigs of Fraxinus species, although the effect was significant on the composition of fungal communities among F. excelsior genotypes. Our results demonstrated differences in fungal communities among species of Fraxinus and of F. excelsior genotypes, suggesting specific relationship between individual host genotypes and endophytic fungi.