Photodynamic inactivation to control Xanthomonas gardneri in tomato seeds

Tomato bacterial spot caused by Xanthomonas spp. is one of the most important diseases that cause losses in yield and quality of tomatoes. One of the most effective ways to currently control the disease is the use of pathogen-free seeds. In this study, the photodynamic activity of methylene blue, toluidine blue, and a combination of both dyes on a bacterial suspension of Xanthomonas gardneri was evaluated, and in treating inoculated tomato seeds, for bacterial control. In the photodynamic inactivation of the bacterial suspension, the methylene blue, toluidine blue, and a mixture of both dyes at 25, 50, and 100 μmol/L were used, in the dark and the presence of light. Tomato seeds inoculated with bacterial suspension were treated with different dye solutions at 50 μmol/L. Under irradiation conditions, all the dye solutions tested at all concentrations were capable of effectively inhibiting bacterial growth. The amount of bacteria detected in the seeds treated with different dyes was significantly reduced, and the dyes did not interfere in the seed germination and in the seedling emergence, thus configuring a new technique of seed treatment, to control Xanthomonas gardneri in tomato seeds.