Ralstonia solanacearum virulence in eggplant seedlings by the leaf-clip inoculation

Ralstonia solanacearum causes a lethal bacterial wilt disease in numerous plants including important vegetable crops such as eggplant and tomato. One of the difficulties in studying virulence of this bacterium in different host plants is the development of an easy and stable pathogenicity assay. Recently we described a leaf-clip inoculation method to study its pathogenicity at the cotyledon stage of tomato seedlings. Hereafter, we demonstrated the leaf-clip inoculation method to be equally efficient for studying R. solanacearum pathogenicity in the cotyledon stage of eggplant seedlings. Our study revealed eggplant seedlings to be highly susceptible to R. solanacearum as compared to tomato seedlings, illustrated by appearance of disease symptoms in significantly higher number of seedlings. We also tested the virulence of several global transcription regulator mutants of R. solanacearum including hrpB , hrpG and phcA in eggplant seedlings. The phcA mutant was found to be only moderately virulence deficient in eggplant seedlings but was significantly reduced in virulence in tomato. This is indicative of some host specific responses towards certain pathogenicity functions of R. solanacearum , which are markedly different in tomato and eggplant seedlings. Apart from being economical in requiring less labor, time and space, this simple gnotobiotic leaf-clip inoculation method is anticipated to be helpful in further exploring the interaction between R. solanacearum and eggplant seedlings at the cotyledon stage.