Elm trees ( Ulmus sp.) occurring naturally or planted as ornamentals in Europe are
susceptible to powdery mildew (PM). In the past, the causal agent of the powdery mildew
symptoms on the adaxial side of leaves of Ulmus trees was Erysiphe ulmi in Hungary.
However, we identified E. kenjiana on Ulmus pumila leaves sampled from the urban area
of Budapest. Identification was based on morphological characteristics and molecular
phylogenetic analysis. Numerous spherical chasmothecia, which were 58–94 µm in diameter,
were found on the samples. The apices of the appendages were characteristically spirally
twisted and flattened. Anamorphs were found only on one sample, characterized by conidiophores
developing ellipsoid–cylindrical conidia singly. The mycelium was epiphytic with lobed
to multilobed hyphal appressoria, mostly in opposite pairs. The internal transcribed
spacer region (ITS) of the nrDNA was amplified, and the BLAST search showed 100% similarity
with E. kenjiana sequences in GenBank. In the maximum likelihood phylogenetic analysis,
the sequences of the Hungarian samples grouped in one clade with the sequences of
other E. kenjiana specimens collected in Europe and Asia. This is the first report
of the non-native E. kenjiana causing powdery mildew on Ulmus pumila in Hungary.
