Strawberry angular leafspot: efficacy of biocontrol agents and acibenzolar-S-methyl towards Xanthomonas fragariae

The angular leafspot of strawberry (ALS) is present in all areas where strawberry is cultivated, and in nurseries it represents a significant problem for the production of pathogen-free plant material. The control of Xanthomonas fragariae (Xf) is mainly achieved through preventive treatments based on copper compounds or antibiotics, where they are allowed. The efficacy of three bacterial antagonists (Bacillus sp.; D747 and QST713; Pseudomonas fluorescens: BB20), two essential oil (EO)-based products (Vitibiosap Plus® 458 and Vitibiosap Plus® 1R45) and the resistance inducer Bion® was tested against the growth of Xf both in vitro and in vivo. All the biocontrol agents were able to directly reduce the pathogen growth in vitro, whereas Bion®, as expected, resulted ineffective. Under climatic chamber conditions, the three antagonists and the resistance inducer reduced the ALS severity and provided approx. 50% and 38% relative protection, respectively; besides, the two EO-based products provided approx. 40% relative protection. In addition, during the two years field trial, the EO-based products were able to significantly reduce ALS severity with a relative protection equal to 60 to 80%, compared to the conventional treatments with copper compounds. Indeed, biological agents, such as bacterial antagonists or EO, and resistance inducers could represent an effective alternative in the framework of integrated control strategies.