EVALUATION OF FLUSULFAMIDE FOR THE CONTROL OF BACTERIAL RING ROT OF POTATO

The potential of flusulfamide (2', 4-dichloro- alpha, alpha, alpha, tr ifluoro-4'-nitro-m-toluenesulfonanilide) as a control agent for bacter ial ring rot of potato was evaluated by testing the bactericidal activ ity of this compound against the causal agent, Clavibacter michiganens is subsp. sepedonicus in in vitro tests, followed by greenhouse and fi eld trials involving treatment of inoculated seed tubers. In the in vi tro tests, significant reduction in the size and number of C. m. seped onicus colonies was observed with complete inhibition of growth occurr ing at flusulfamide concentrations of 100 mg/l or greater. In the gree nhouse and field trials, tubers of potato cultivar Russet Burbank were inoculated with the causal organism of bacterial ring rot, C. m. sepe donicus, 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'' method s of inoculation were intended to simulate transmission that would occ ur during normal production practices, while the ''inject'' treatment was intended to assess the effect of flusulfamide on existing infectio ns. In both the greenhouse and field experiments, foliar disease incid ence and infection rates were reduced, but not eliminated, in plants t hat were inoculated by cutting or dipping and treated with flusulfamid e, whereas plants that had been inoculated by injection showed little effect of treatment with flusulfamide. Based on the results of these e xperiments, flusulfamide appears to have protective rather than curati ve properties against Clavibacter michiganensis subsp. sepedonicus.