Diaporthe decedens Is the Causal Agent of Canker of Hop Hornbeam (Ostrya carpinifolia) in Tuscany (Italy)

During 2018, extensive European hop-hornbeam (Ostrya carpinifolia L.) diebacks were observed in natural stands in the Apennines (central Italy). Cankers on the stems and branches and crown dieback were the more common symptoms observed, mainly at the beginning of the growing season. In 2023, similar symptoms were reported on the same host species in natural stands in the province of Lucca. Three species were most frequently isolated from the tissues of symptomatic plants: Diaporthe decedens, Dothiorella parva and Pezicula sporulosa. The identity of these species was confirmed through phylogenetic analysis. Their pathogenicity was assessed with two trials performed on 2-year-old hop-hornbeam seedlings and cut shoots. Dothiorella parva and Pezicula sporulosa caused limited necrotic lesions only on cut shoots, while D. decedens showed the higher virulence and aggressiveness, being able to cause extensive cankers in both trials. To our knowledge, this is the first report of D. decedens causing cankers and dieback on O. carpinifolia in Italy or elsewhere. Considering the ecological importance of O. carpinifolia as a pioneer species, further investigations are needed to assess the spread of the disease and the extent of its impact in natural stands.