Twig black pitting and cankers of pomegranate (Punica granatum) caused by Pseudomonas syringae pv. syringae in Central Italy

In May 2019, a two-year-old pomegranate orchard cultivar "Wonderful", located in Central Italy, showed extensive black pitting and longitudinal cankers on twigs as well as apical leaf wilting. Bacterial isolates were identified by applying biochemical, molecular and pathogenicity assays. All isolates showed identical biochemical characteristics typical of Pseudomonas syringae. In addition, upon artificial inoculations, the isolates caused symptoms in pomegranate twigs and leaves similar to those observed in the field, and in lemon fruit and pear leaves. The isolates possess the syrB gene. An ERIC-PCR fingerprinting analysis revealed an identical pattern for the strains isolated from pomegranate and other strains previously obtained from lemon and chickpea, in Tunisia and Italy, respectively, as well as a similarity with other strains obtained from different host plants. The 16S rRNA gene analysis showed a very high similarity with other P. s. pv. syringae strains. The study allowed to conclude that the disease was caused by P. s. pv. syringae, reported for the first time as a pathogen for pomegranate. Frost and high humidity could have favoured the outbreak. The year after the outbreak, a formulate that contains zinc, copper, manganese, chitosan and garlic powder, effectively reduced the severity of the disease in the field.