Detection of Hymenoscyphus fraxineus in Leaf Rachises from European Ash (Fraxinus excelsior) in Germany

The ash dieback disease caused by Hymenoscyphus fraxineus is widespread in Germany and is the subject of intensive research efforts. The fungus identification is based on the genomic internal transcribed spacer (ITS) region, which can also be the site of intragenomic variability. In Germany, despite intense research efforts, only a few numbers of H. fraxineus sequence data are recorded. Therefore, this study aims to characterize H. fraxineus isolates obtained from diseased ash leaves in Brandenburg (Germany). Fungal isolates from infected ash leaf tissue were analyzed molecularly using species-specific primers and based on sequencing the ITS region of rDNA. The analysis of the two identified sequences revealed two base substitutionscompared to the reference sequences. Thus, they show an identity of 98.8%–100% to the reference sequences and support the assumption that H. fraxineus has multiple copies of the ITS region. The phylogenetic grouping with reference sequences did not show a distinct cluster for the European, particularly the German, sequences. This indicates that the evolvement of the genetic variability of the ITS region is still an ongoing process.