Powdery mildew of ash trees caused by the non-native Erysiphe salmonii in Hungary

Abstract

Fraxinus ornus and F. excelsior are naturally occurring woodland trees and widely cultivated ornamental plants in Hungary. Leaves with powdery mildew symptoms observed unusually on adaxial side of leaves of F. ornus and F. excelsior were collected from two locations in Hungary. We identified the causing fungi based on their morphological characteristics and molecular phylogenetic analysis. Numerous chasmothecia were found on a part of the samples, which were spherical, 83–120 µm in diameter, and the apices of the appendages uncinated or spirally curved. Anamorphs were characterized by conidiophores developing conidia singly, and by hyphae with lobed appressoria, characteristic of Erysiphe spp. The internal transcribed spacer region of the nrDNA was amplified, and the BLAST searches showed 100% similarity with Erysiphe salmonii sequences in GenBank. In the phylogenetic analysis the sequences of the Hungarian samples grouped in one clade with the sequences of other E. salmonii specimens collected in Central and Eastern Europe and Asia. This is the first report of the non-native E. salmonii causing powdery mildew on Fraxinus sp. in Hungary.