Characterization of fungal pathogens associated with fungal trunk diseases of hazelnut in Northern Italy

Hazelnut (Corylus avellana) represents one of the most economically important nut crops across the world. Italy is the second largest hazelnut producer worldwide with 84,526 ha cultivated and 98,666 tonnes of fruit harvested in 2022. The regions with the highest productivity are Piedmont, Latium, Campania and Sicily. In Piedmont, an expansion of hazelnut cultivation and production was registered during the last decade. However, the changing climatic condition characterized by water deficiency, late-spring frosts, and hot summer temperatures, along with the high incidence of Cytospora cankers, known also as ‘Mal dello stacco’, and twig blight represent a serious threat to this crop. Considering the severe impact of fungal trunk diseases (FTD) on this crop and lack of studies conducted so far to investigate the respective causal agents in Piedmont, surveys were conducted in seven hazelnut orchards during 2021-2022. Eight fungal species were identified: Anthostoma decipiens, Botryosphaeria dothidea, Diaporthe eres, Diaporthe rudis, Diplodia seriata, Diplodia subglobosa, Dothiorella parva and Nothophoma brennandiae. Species identification was achieved through morphology assessment and multilocus phylogeny. The fungal species were confirmed as pathogenic when inoculated on healthy hazelnut plants of the cv. ‘Tonda Gentile’. The present study is the first report of B. dothidea, Dia. eres, Dia. rudis, Dip. subglobosa and N. brennandiae as causal agents of FTD on hazelnut in Italy. Moreover, the provided clarification of the fungal pathogens associated with FTD on this crop in Piedmont is crucial for further investigations on disease epidemiology and management strategies.