New tools for the biological control of Xanthomonas fragariae in orchard

The angular leaf spot (ALS) disease caused by Xanthomonas fragariae (Xf) in strawberry is present in all growing areas seriously damaging the fruit quality. The Xf control mainly relies on preventive treatments with chemicals, such as copper-based products. Biological agents could represent an effective alternative within integrated control strategies. The antibacterial activity of two essential oil-based products (OEBPs) - VitiBioSap Plus® 1R45 and VitiBioSap Plus® 458 - was evaluated in orchard, by treatment with OEBPs against ALS, comparing it to the standard chemical treatments (control, SCT). In an orchard severely contaminated by Xf, in Emilia Romagna region (North-Central Italy), from August to November 2019, the OEBPs- or SCT-treatments were performed 13 times on plants belonging to five different cultivars (Asia, Malga, Roxana, Olympia and Tea). From October to November, three phytopathometric assessments were carried out to determine the leaf spot number to evaluate the disease severity (DS) using disease classes. At the first assessment, the DS resulted low in all OEBPs-treated cultivars. In particular, on cv. Asia, the OEBPs-treated plants showed a reduced DS compared to those SCT-treated, whereas on cvs. Malga and Roxana, the DS was higher with respect to that detected on SCT-treated plants. At the second and third assessments, the DS greatly increased in the orchard, but the OEBPs-treated plants of cvs. Asia, Malga, Roxana and Olympia showed a significantly reduced ALS severity compared to that of SCT-treated plants. During all the assessments, on cv. Tea the DS was low compared to the other cvs. regardless of treatment.