Toxicity of free riboflavin and methionine–riboflavin solutions to Phytophthora infestans and the reduction of potato late blight disease

Abstract

Treatments of sporangia and zoospores of Phytophthora infestans race 1.2.3.4 with methionine or riboflavin for durations of up to 8 h under fluorescent light did not affect its colonization of rye-seed agar. In contrast, exposure of sporangia and zoospores to methionine-riboflavin mixture for 2 h or more resulted in the failure of race 1.2.3.4 to grow when transferred to rye-seed agar medium. Hyphal growth of races 1.2.3.4 and 0, when incubated in liquid synthetic medium, was inhibited by free riboflavin. Potato plants, Solanum tuberosum cv. Kennebec, when pretreated with a methionine–riboflavin mixture and then spray inoculated with race 1.2.3.4 developed fewer diseased leaves per plant than plants pretreated with water, methionine, or riboflavin. Key words: Solanum tuberosum, hydroxyl radical, superoxide anion.