First report of canker and dieback caused by Neofusicoccum parvum and Diplodia olivarum on oleaster in Italy

Abstract

Oleaster (Olea europaea subsp. europaea var. sylvestris) is a sclerophyllous forest tree occurring in the Mediterranean region including Sardinia (Italy). Oleaster suffers from few major diseases, but since 2017 a new and unusual disease leading to the death of both young and old trees has been observed in several woodlands of high ecological value in north-eastern Sardinia. Declining trees showed a variety of symptoms including leaf chlorosis, dieback and sunken canker on trunk and branches. The cankers often exuded a white to orange sap, giving them the appearance of bleeding, which gradually dried to a whitish gluey mass on the bark. Symptomatic wood samples yielded fungal isolates belonging to five fungal species: Diplodia olivarum, Dothiorella sarmentorum, Neofusicoccum parvum, Rosellinia corticium and unidentified Pestalotiopsis sp. In pathogenicity trials Neofusicoccum parvum proved to be the most aggressive species. Our results provide the first evidence for a combined involvement of different Botryosphaeriaceae species in the aetiology of a new oleaster disease.