First report of Erysiphe salmonii causing powdery mildew on Fraxinus excelsior in Romania

In October 2020, Fraxinus excelsior saplings showing powdery mildew symptoms on both sides of the leaves were found in Southern Romanian Carpathians. Morphological examination revealed that the pathogen agent is Erysiphe salmonii, an Asian fungus that recently arrived in Europe. Species identity was confirmed by the phylogenetic analysis of two internal transcribed spacer (ITS) sequences from Romanian samples and a few other E. salmonii sequences available from GenBank. On the phylogenetic tree, they are all recovered as a highly supported clade of very similar sequences. A description and illustrations of the specimens collected in Romania are provided. To our knowledge, this is the first report of E. salmonii in Romania and the third in Europe, after Ukraine and Switzerland. Due to the invasive potential of the powdery mildew fungi, this record is important in the context of the range extension of E. salmonii in Europe.