Biological and molecular characterization of Italian isolates of Valsa ceratosperma on pear

The Ascomycete Valsa ceratosperma (Tode ex Fr.) Maire [anamorph Cytospora sacculus (Schwein.) Gvritischvili = C. vitis] is the causal agent of a bark canker also known as Valsa canker, one of the most important disease of apple trees in East Asia. In 2001 it was reported on pear in the Emilia Romagna (Northern Italy) for the first time and since then reports of the disease have increased. Valsa cankers can be confused with other cankers caused by Nectria galligena, Phomopsis mali and Erwinia amylovora. Symptoms are elongated cankers on trunks and branches where dark picnidia are formed, which release conidia when the humidity is high. Thirty-two isolates from Emilia Romagna, Lombardia and Veneto and 14 Japanese strains of V. ceratosperma were morphologically described and genetically characterized by sequencing the ITS1-5.8S-ITS2 regions. Pathogenicity assays were also performed on apple and pear fruits. The morphology of Italian isolates was similar, i.e. white or pale yellow mycelium with patchy margins and forming numerous black picnidia. In contrast, the Japanese isolates showed a white or black mycelium and only five of them produced picnidia. Three different ITS types were found among Italian isolates and specific primers were developed for a rapid detection of the pathogen. The Italian isolate sequences were monophyletic with Valsa spp. GenBank accessions from China, Iran and Spain and they were phylogenetically separated from the Japanese isolates. All the Italian isolates were pathogenic to pear fruits whereas only two Japanese strains infected pear. None of the isolates infected apple fruits.