Phenotypic Conversion of Ralstonia solanacearum in Susceptible and Resistant Solanum Plants

Ralstonia solanacearum undergoes spontaneous phenotypic conversion (PC) from a wild-type pathogenic to non-pathogenic form in plant. Little is known about the dependence of bacterial PC on the strength of plant resistance to bacterial wilt. Furthermore, bacterial PC conditions in plants have not been elucidated. We inoculated R. solanacearum into resistant Solanum plants and susceptible eggplants grown in aseptic and non-aseptic culture, and investigated bacterial proliferation and PC in stems at various wilting stages. PC mutants were detected among all susceptible and resistant Solanum species. The pathogen underwent PC in 47–78% of plants that recovered from wilting and those that were in the final stages of wilting (bacteria lived stems for a long period with high density). On the other hand, only 0–22% of plants that were in the initial stage of wilting (bacteria existed stems for a short period with high density) and those that did not wilt (bacteria inhabited stems for a long period with low density) were isolated PC mutants. These results suggest that R. solanacearum spontaneously undergoes PC in plants regardless of the plants' resistance to bacterial wilt, and this mutation occurs after it had infected the host plants for a certain period at a high density.