First report of the recently introduced,destructive powdery mildew Erysiphe corylacearum on hazelnut in Turkey

Hazelnut (Corylus avellana) is Turkey’s most valuable agricultural export, and an essential source of income for many families in the Black Sea Region. In spring 2013, hazelnut leaves, fruit clusters and shoots showing powdery mildew infection symptoms different from those observed previously were discovered in Giresun, Ordu and Trabzon provinces of Turkey. The disease has become epidemic throughout all hazelnut production areas spreading from east to west of the Black Sea Region over the subsequent years. Erysiphe corylacearum was identified as the causal agent of this new and highly destructive powdery mildew based on its morphological characteristics and analyses of DNA sequences of the internal transcribed spacer (ITS) and 28S regions of the ribosomal DNA. Pathogenicity of this species was examined in an infection test and proven for the first time. To our knowledge, this is the first report of E. corylacearum on Corylus avellana worldwide.