Evaluation of flusulfamide for the control of bacterial ring rot of potato

The potential of flusulfamide (2’, 4-dichloro- α, α, α, trifluoro-4’-nitro-m-toluenesulfonanilide) as a control agent for bacterial ring rot of potato was evaluated by testing the bactericidal activity of this compound against the causal agent,Clavibacter michiganensis subsp.sepedonicus inin vitro tests, followed by greenhouse and field trials involving treatment of inoculated seed tubers. In thein vitro tests, significant reduction in the size and number ofC. m. sepedonicus colonies was observed with complete inhibition of growth occurring at flusulfamide concentrations of 100 mg/1 or greater. In the greenhouse and field trials, tubers of potato cultivar Russet Burbank were inoculated with the causal organism of bacterial ring rot,C. m. sepedonicus, in one of three different ways (cutting, dipping, injection) and subsequently treated by dipping in an aqueous solution containing varying concentrations of flusulfamide. The “dip” and “cut” methods of inoculation were intended to simulate transmission that would occur during normal production practices, while the “inject” treatment was intended to assess the effect of flusulfamide on existing infections. In both the greenhouse and field experiments, foliar disease incidence and infection rates were reduced, but not eliminated, in plants that were inoculated by cutting or dipping and treated with flusulfamide, whereas plants that had been inoculated by injection showed little effect of treatment with flusulfamide. Based on the results of these experiments, flusulfamide appears to have protective rather than curative properties againstClavibacter michiganensis subsp.sepedonicus.