Severe trunk and branch diseases of hazelnut trees have recently been observed in several groves in Sardinia (Italy). Since there is little information about the aetiology of these diseases and given the high ecological and economic importance of these agro-systems, an in-depth study was carried out. From autumn 2012 to spring 2014, sixty samples of twigs and branches of hazelnut trees showing exudates and different types of canker (sunken with wedge-shaped necrotic sector, open canker and Cytospora canker) were collected in the main hazelnut growing area in the centre of the island. Based on morphology, colony appearance and DNA sequence data, seven species belonging to four genera and three families were isolated and identified. These included Diplodia sapinea, D. seriata, Dothiorella iberica, Do. parva and Do. symphoricarposicola (Botryosphaeriaceae), Gnomoniopsis smithogilvyi (Gnomoniaceae) and Anthostoma decipiens (Diatrypaceae). In addition, two new species namely Diaporthella cryptica sp. nov. and Dothiorella omnivora sp. nov. are described. Pathogenicity trials carried out on wounded hazelnut branches showed that three species, Anthostoma decipiens, Diaporthella cryptica and Diplodia seriata are aggressive pathogens on hazelnut. Results obtained have allowed us to clarify, almost a century after its first description, the aetiology of the disease known as Cytospora canker of hazelnut and to reveal the existence of three evolutionarily distinct lineages for its causal agent A. decipiens. Finally, the diversity of fungal pathogens associated with twig and branch cankers of hazelnut is greater than previously recognised and further studies are necessary to determine the exact role played by each species and their possible synergistic interaction.
