First report of Stemphylium eturmiunum causing postharvest rot of sweet cherry in Italy

Abstract

Italy is the first producing country of sweet cherries in Europe. In June 2019, sweet cherry fruit showing rot symptoms were collected from retailers located in Apulia (Southern Italy). Marginal pieces of rotted tissue of surface-sterilized fruit were plated onto semi-selective PDA medium. Colonies were further purified and grown on Potato Carrot Agar (PCA), looking initially whitish and then turning pale olive green to light brown. Conidia were septate and broadly ovoid or ellipsoid. Based on its micro- and macro-morphological features, the pathogen was identified as Stemphylium eturmiunum E.G. Simmons. A multi-locus approach was applied to confirm the identification. ITS-rDNA region and portion of genes coding for the glyceraldehyde-3-phosphate dehydrogenase and the calmodulin were sequenced. Both nBLAST homology and phylogenetic analysis confirmed the pathogen as S. eturmiunum. To fulfil Koch's postulates, surface-sterilized sweet cherry fruit, cv. Ferrovia, were inoculated with the strain. Typical disease symptoms were recorded after 7 days and the pathogen's identity was confirmed by re-isolation and characterization. Because of the resemblance with the symptoms caused by Alternaria spp., reasonably the incidence of S. eturmiunum infections might have been underestimated. This is the first report of S. eturmiunum as causal agent of postharvest rot of sweet cherries in Italy.