Selection of effective non-pathogenic Ralstonia solanacearum as biocontrol agents against bacterial wilt in eggplant

Abstract

Ralstonia solanacearum is a soil-borne pathogen that causes bacterial wilt and has a wide range of hosts in numerous plant species. This pathogen undergoes phenotypic conversion (PC) from a wild-type strain pathogenic form to a non-pathogenic form in broth culture, soil, plant, and water extract of the plant. Pre-inoculation of PC mutants to Solanum plants has been shown to have a protective effect against bacterial wilt disease. To select effective PC mutants as biocontrol agents against bacterial wilt disease in eggplant, control effect was investigated using five eggplant cultivars and 10 PC mutants. Control effects differed depending on PC mutants and eggplant cultivars. Two PC mutants (8224PC and 8103PC) showed highly suppressive effects in many eggplant cultivars and are anticipated to be practicable biocontrol agents. Furthermore, the antibacterial activities of PC mutants against the wild-type pathogen were tested to elucidate the relation between antibacterial activity of PC mutant and protective effect against bacterial wilt by PC mutant. Even the PC mutants that did not indicate antibacterial activity showed high suppression of bacterial wilt, suggesting that there are factors other than antibacterial activity involved in the suppression of bacterial wilt by PC mutant.