The cultivative properties of yacon strawberry for producing the fructooligosaccaride have been studied in Shikoku National Agricultural Experiment Station. At the beginning of June in 1992, wilted plants were found in the field. The vascular bundles of the plants were dameged whose color turned to brown. The disease incidence was increased rapidly in the first ten days of July. However, the development of the symptoms and the increase of the disease incidence halted in mid-summer. Small amount of bacterial exudation was found in the lesions. Bacterial isolates showing white color, round with entire margin, smooth surface, and dented center were isolated from the lesions. The bacteria caused the rotting of the potato tuber slice and had pathogenicities to the stems of yacon strawberry by the needle prick inoculation. They were Gram-negative, farmentative and methyl red test-negative. They reduced nitrate, produced indole, acetoin, lecithinase, and L-arginine decarboxylase. They produced acid from melibiose, raffinose and inulin and utilized L-tartrate and malonate. No isolates produced acid from maltose, trehalose or D-arabinose. They grew under 37°C, but did not under 38°C. On the basis of pathogenicity test and bacteriological characteristics, these isolates were identified as Erwinia chrysanthemi. According to the subdivision of E. chrysanthemi proposed by R. S. Dickey, they were classified in subdivision V. Bacterial wilt of yacon strawberry was proposed as the name of the disease.