In vitro evaluation of the virulence of Japanese strains of Ralstonia solanacearum species complex in potato at two temperatures

Twenty-six Japanese strains of potato pathogen Ralstonia solanacearum species complex (phylotypes I and IV) were evaluated in vitro for virulence on potato lines Saikai 35 (resistant) and Aiyutaka (susceptible) at 24 °C and 28 °C. Numerous strains resulted in significantly lower disease indices for Saikai 35 than Aiyutaka. Responses to temperature were highly diverse, and virulence varied greatly among strains. Hierarchical and nonhierarchical clustering classified the strains into five pathotypes, which did not correspond to any previous classification schemes including phylotypes. Cultivar selections for breeding stably resistant varieties in target geographic areas should thus be based on pathotypes.