First evidence of Pantoea ananatis infections on strawberry in Italy

Recently, symptoms resembling fire blight such as brownish lesions, necrosis, and production of exudates were observed on a new cold-resistant strawberry variety (Ania®). Thus, the aim of this study was to isolate, identify and characterize the causative agents. Bacterial isolation was carried out from symptomatic plant tissues (leaves and stems) collected from four strawberry plants. Tissues were surface-sterilized, homogenized in 0.85% (w/v) NaCl and serially diluted onto Nutrient Agar. One hundred twenty bacterial isolates were tested for the induction of the hypersensitive response (HR) in tobacco leaves. Bacterial isolates with yellow colonies able to induce HR were identified as Pantoea ananatis by 16S rDNA gene sequencing. PCRs using the primer pair PANA_1080 specific for P. ananatis species validated these results. Subsequently, pathogenicity tests were carried out by wounding detached ripe pseudo-fruits from strawberry plants (Ania®) and inoculating five µL of bacterial cell suspension (∼1×108 CFU/mL) of a selected P. ananatis strain. Distilled water and Escherichia coli DH5were used as control treatments. Strawberries were incubated in the dark at 27°C and 90% RH and appearance of symptoms was monitored daily. No symptoms were observed on the control treatments. On P. ananatis inoculated strawberries, symptoms appeared after five days and the bacterial strain was re-isolated from the sympotmatic pseudo-frutits. Furthermore, P. ananatis strains were evaluated for the production of plant cell wall degrading enzymes (i.e. cellulases). To the best of our knowledge, this is the first report of P. ananatis on strawberry in Italy.