ABSTRACT
Canola (Brassica napus L. var. oleifera) crop was recently introduced in the regions of “Triângulo Mineiro” and “Alta Paranaíba”, Minas Gerais State, Brazil. Black rot, caused by the bacterium Xanthomonas campestris pv. campestris (Xcc), is one of the major diseases affecting this crop. The bacterium is disseminated via seeds and alternative control methods should be investigated. Therefore, the objective of this study was to evaluate the use of photodynamic therapy with the dyes Methylene Blue (MB) and Toluidine Blue (TB), under irradiation, on Xcc growth inhibition in vitro and on the treatment of canola seeds naturally contaminated with the bacterium. Xcc bacterial suspension was treated with MB, TB and their association (MB+TB) at the concentrations 25, 50 and 100 μmol L-1, irradiated or not, and cultivated on culture medium; then, the number of colony-forming units was assessed. Seeds of three canola genotypes were treated with 0.45% NaCl (Control), MB, TB and MB+TB, at the concentrations 100, 50 and 25 μmol L-1, respectively, irradiated or not. Seed germination percentage, emergence speed rate, seedling emergence percentage and control of bacteria in the seeds were evaluated. MB, TB and MB+TB, at 100, 50 and 25 μmol L-1, respectively, under irradiation, inhibited Xcc growth in vitro. The combination of dyes MB+TB, at 25 µmol L-1, can be used in the treatment of canola seeds. Control of the bacterium Xcc in naturally contaminated canola seeds could not be determined with the different dyes.
Keywords
Methylene blue; toluidine blue; Brassica napus L; var. oleifera; photosensitizer; microorganism inactivation