Inactivated bacterial suspension to control tomato bacterial spot

Bacterial spot caused by Xanthomonas hortorum pv. gardneri may produce significant losses in tomato crops. Chemical control of the disease is not efficient; therefore, alternative control measures should be assessed and low-cost products should be developed. The objective of this work was to evaluate preventive and curative applications of X. hortorum pv. gardneri suspensions inactivated using ultraviolet radiation, sterilization, and aging, to control tomato bacterial spot. The inactivated bacterial suspensions (IBSs) were obtained by exposure to ultraviolet radiation (IBS-UV), autoclave sterilization (IBS-A), aging in culture medium (IBS-CM), and aging in suspension on the laboratory bench (IBS-S). In the first assay, in the preventive application, the plants were sprayed with the IBS products, copper, acibenzolar-S-methyl (ASM), and water (control); 2 days after spraying, they were inoculated with the pathogenic bacterial suspension (108 and 109 CFU/mL). In the curative application, the plants were inoculated with the pathogenic bacterial suspension, and 2 days later were sprayed with the products. After adjustments, in the second assay the plants were only preventively sprayed with IBS-UV (108 CFU/mL) and IBS-A (108 and 109 CFU/mL), copper, ASM, and water, and 2 days later inoculated with the pathogenic bacterial suspension (107 and 108 CFU/mL). Disease severity was assessed and the area under the disease progress curve was calculated. IBS-UV, IBS-A, and ASM significantly reduced disease severity in the preventive application, in both assays. No significant difference was detected between these products in the curative application, in the first assay. IBS-UV and IBS-A effectively controlled tomato bacterial spot in the preventive application. IBS-A is a promising technique to control plant disease.