Abstract
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.
Highlights
Ralstonia solanacearum causes a lethal bacterial wilt disease in 200 plant species of 53 botanical families including agronomically important crop plants such as tomato, potato, eggplant, olive, banana, peanut, ginger, etc. (Hayward 1991)
R. solanacearum F1C1 causes wilt disease at the cotyledon stage in eggplant seedlings inoculated by the leaf-clip method The R. solanacearum F1C1 pathogenicity assay at the cotyledon stage in eggplant seedlings (14–15 days old; Devgiri cultivar) was executed by the leaf-clip inoculation method (Fig. 1)
In this work we have demonstrated that the leaf-clip inoculation is a stable and consistent method to study R. solanacearum pathogenicity in the cotyledon stage of eggplant seedlings
Summary
Ralstonia solanacearum causes a lethal bacterial wilt disease in 200 plant species of 53 botanical families including agronomically important crop plants such as tomato, potato, eggplant, olive, banana, peanut, ginger, etc. (Hayward 1991). R. solanacearum is a soil borne bacterium. Under natural conditions, this pathogen infects the host plants through root, colonizes in the xylem vessels and spreads systemically till causing wilting in its hosts (Genin 2010). There are plants, referred to as distant hosts, where R. solanacearum colonizes but fails to cause any disease symptom (Guidot et al 2014). Recent studies of experimental evolution in this bacterium have given crucial insight into the role of transcription regulators in its host adaptation and colonization (Marchetti et al 2010; Guidot et al 2014)
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