Sardiniella urbana gen. et sp nov., a new member of the Botryosphaeriaceae isolated from declining Celtis australis trees in Sardinian streetscapes

During a survey carried out in 2013 throughout the streets of Sassari (Sardinia, Italy) aimed at clarifying the causes of a decline affecting European hackberry, a collection of a Botryosphaeriaceous taxon was isolated from 14 trees showing sunken cankers with wedge-shaped necrotic sectors and a progressive dieback of shoots and branches as well as collar rot and stem exudates. Although morphologically similar to Diplodia and Dothiorella, these strains differed from all known species of Botryosphaeriaceae in their colony appearance and conidial shapes. A phylogenetic analysis based on combined LSU, ITS and tef1-alpha sequence data showed that these strains form a distinct lineage within the Botryosphaeriaceae. Based on molecular phylogeny and morphology, a new genus named Sardiniella is herein introduced to accommodate the new taxon Sardiniella urbana. Pathogenicity was verified by wound inoculation of 3 year-old seedlings of European hackberry using four different strains. All strains caused sunken cankers and necrotic lesions on inner bark and sap wood tissues in the stems of inoculated seedlings and in all cases the fungus was successfully re-isolated, fulfilling Koch's postulates. Results from the pathogenicity test suggest that this new species is directly involved in the aetiology of the observed decline in European hackberry trees as well as representing a potential risk to public safety in urban environments.