Bacterial spot management on tomatoes

Abstract

Bacterial spot of tomato, incited by Xanthomonas campestris pv. vesicatoria, is a perennial problem in commercial fields in Florida. Various strategies have been used to control this disease including applying copper bactericides, antibiotics and various other chemicals. Although copper compounds and streptomycin were initially effective in disease control, the presence of strains resistant to these compounds has reduced the efficacy of these compounds. Systemic acquired resistance (SAR) compounds have become a popular alternative to conventional bactericides. One that has shown promise for bacterial spot control is acibenzolar-S-methyl (ASM). Other SAR compounds tested have had variable results. A second strategy which has excellent promise is the application of bacteriophages specific to the bacterial spot pathogen. Following the development of an application strategy, which included a modification in formulation and the timing of bacteriophage applications, bacteriophages were improved in efficacy. We have conducted studies using various combinations of bacteriophages and SAR compounds. In three consecutive seasons, ASM applied in combination with bacteriophage significantly reduced bacterial spot compared to the other treatments. Application of host-specific bacteriophages was effective against the bacterial spot pathogen in all experiments, providing better disease control than copper-mancozeb or untreated control. When results of the disease severity assessments or harvested yield from the bacteriophage-treated plots were grouped and compared to the results of the corresponding non-bacteriophage group, the former provided significantly better disease control and yield of total marketable fruits. Although ASM applications controlled bacterial spot,yield was not significantly improved compared to plots receiving no ASM applications. Bacteriophages offer an excellent alternative to conventional disease control strategies and combining it with ASM shows promise.