Hazelnut (Corylus avellana L.) 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. This new and highly destructive powdery mildew agent has been identified as Erysiphe corylacearum U. Braun & S. Takam. based on its morphological characteristics and DNA sequence of the internal transcribed spacer (ITS) and 28S regions of the ribosomal DNA. Its pathogenicity to this species has been examined in an infection test and proven for the first time. To our knowledge, this is the first report of E. corylacearum parasitization of Corylus avellana worldwide.

Colletotrichum acutatum J.H. Simmonds was identified from fruit clusters of hazelnut (Corylus avellana L.) in Turkey. Pathogenicity tests were conducted under laboratory, greenhouse and field conditions. Necrotic, sunken lesions and rot were observed on leaves, fruit clusters and pedicels. This is the first report of C. acutatum as a pathogen of hazelnut.

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Apple mosaic virus (ApMV) is one of the most important diseases limiting the production of hazelnut and apple in Turkey and the objectives of this research were to determine the convenient and reliable method for RNA isolation and also to determine primer pair for real time polymerase chain reaction (RT-PCR) detection of coat protein gene for Turkish ApMV isolates. Apple mosaic virus isolates were collected in 2007 to 2010 and the presence of the pathogen was detected by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and RT-PCR tests. Six different RNA extraction protocols and three primer pairs were applied in RT-PCR amplifications and 44 hazelnut and 15 apple ApMV isolates were obtained. All of the amplicons were subjected to enzymatic digestion with restriction endonuclease enzymes and phylogenetic analysis were performed according to the digestion profiles.