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Bull's eye rot, caused by Phlyctema vagabunda and Neofabraea species, is one of the most important postharvest diseases of apple. South Tyrol (northern Italy) holds the largest continuous apple producing… Click to show full abstract
Bull's eye rot, caused by Phlyctema vagabunda and Neofabraea species, is one of the most important postharvest diseases of apple. South Tyrol (northern Italy) holds the largest continuous apple producing area in Europe with approximately 1 million tons being produced yearly and conserved in technologically advanced storage facilities for several months. Still, studies on the pathogen species causing postharvest bull's eye rot of apple as well as their diversity and biology are lacking for this region. Therefore, the main purpose of the present work was to identify and characterize fungal isolates obtained from decayed apple fruit with symptoms of bull's eye rot that were collected in 2018 and 2019 in different packinghouses of South Tyrol. Among more than 1,000 fungal isolates that were obtained, 419 could be assigned to the genera Phlyctema and/or Neofabraea based on rot symptoms on apple fruit and colony morphology on Potato Dextrose Agar (PDA). A smaller subset of 101 representative isolates was further analyzed by DNA sequencing of the internal transcribed spacer region (ITS). Furthermore, partial segments of the β-tubulin gene (TUB2), the translation elongation factor 1α gene (EF-1α) and the 16S mitochondrial rRNA gene (mtSSU) were studied. The phylogenetic analyses, including sequences of reference species, showed that P. vagabunda is the dominant species associated with bull's eye rot of apple in the study area, while N. kienholzii was found only on a small number of apple fruit samples. The combination of multi-locus sequence data revealed eleven unique genotypes that belonged to P. vagabunda and four to N. kienholzii. To the best of our knowledge, this study is the first to report N. kienholzii as a postharvest pathogen of apple in Italy. Finally, a pathogenicity test demonstrated different degrees of virulence among selected isolates of P. vagabunda and N. kienholzii on the cultivar 'Golden Delicious'. The present study emphasizes the importance of accurate species identification, as different species may vary in in their biological and pathogenic characteristics, and consequently require distinct disease management strategies, both in the field and during the postharvest stages.