Pathogenicity, molecular characterization and mycotoxigenic potential of Alternaria spp. agents of black spots on fruit and leaves of Pyrus communis in Italy

Brown and black spots, caused by Stemphylium and Alternaria species, are important fungal diseases affecting European pear (Pyrus communis L.) in orchards. Both fungal genera cause similar symptoms, which could favour misidentification, but Alternaria spp. are increasingly reported due to the changing climatic conditions. In this study, Alternaria spp. were isolated from symptomatic leaves and fruits of European pear, and their pathogenicity was evaluated on pear fruits from cultivar 'Abate Fétel' and molecular and chemical characterization were performed. Based on Maximum likelihood phylogenetic analysis, 15 out of 46 isolates were identified as A. arborescens species complex (AASC), 27 as A. alternata and four were named Alternaria sp. Both species were isolated from mature fruits and leaves. In pathogenicity assays on pear fruits all isolates reproduced the symptoms observed in the field, both by wound inoculation and direct penetration. All but one isolates were produced Alternaria-toxins on European pears, including tenuazonic acid and alternariol (89.1% of the isolates), alternariol monomethyl ether (89.1%), altertoxin I (80.4%), altenuene (50.0%) and tentoxin (2.2%). These isolates also produced at least two mycotoxins and 43.5% produced four mycotoxins, with an average total concentration of the Alternaria-toxins exceeding 7.58×106 ng/kg. Our data underline the potential risks for human health related to the high mycotoxin content found on fruits affected by black spot. This study represents also the first report of AASC as agent of black spot on European pear in Italy.