Molecular Characterization of Diaporthe Species Associated With Hazelnut Defects

Fungi of the genusDiaporthehave been reported as the main causative agent of hazelnut defects in the Caucasus area. This study aimed to define which fungal species are present in defective hazelnuts grown in Turkey and confirm the role ofDiaporthespp. Seven hazelnut orchards were selected, with each one located in a different Turkish Province (Düzce, Giresun, Ordu, Samsun, Sakarya, Trabzon, and Zonguldak), and hazelnuts were collected at early and full ripening. Fungal isolation and identification were performed at the genus level based on morphological characteristics. Several genera were isolated, withDiaporthespp. being among the prevalent. This was the only genus with increasing incidence from early to full ripening, and incidence at full ripening was positively correlated both with internal (ρ = 0.86) and visible defects (ρ = 0.81), which confirmed its role as the key causative agent of hazelnut defects. The correlation of defect occurrence with rainfall, reported in previous study, was not confirmed, possibly due to the low defect incidence. A total of 86Diaporthemonosporic strains isolated from Turkish hazelnut samples, together with 33 strains collected in the Caucasus region and 6 from Italy, were analyzed with a multi-locus phylogeny based on three genomic loci (ITS,EF1-α, andtub). The results showed thatDiaporthestrains can be grouped into 7 distinct clades, with a majority of Turkish strains (95%) being placed into a single clade related withD. eres. These samples were organized into several sub-clades, which indicates the existence of genetically diverse sub-populations.