Method for aseptically regenerating ginger plants and studying infection by Ralstonia solanacearum using hrp mutants

Ralstonia solanacearum causes a bacterial wilt of ginger (Zingiber officinale) that hampers ginger production. Because pathogenicity tests using rhizomes are laborious and time-consuming, here we developed a new test using ginger plants that were aseptically regenerated in vitro from shoot tips using 6-benzyl adenine and 1-naphthalene acid (NAA) in Murashige-Skoog (MS) agar. The regenerated plants were then cultured in MS broth with NAA to evaluate pathogenicity after the roots were dipped into a bacterial solution. The wild-type strain (MAFF 211479) caused wilt symptoms such as leaf yellowing within 15 days after inoculation (dpi), and plants had died by 28 dpi. MAFF 301069, an avirulent strain of ginger, did not cause any symptoms. Because method was suitable for assessing virulence of R. solanacearum, we then used to test the pathogenicity of MAFF 211479 mutants that we constructed and were defective in the type III secretion system. None of the mutants were pathogenic in the regenerated ginger plants or in eggplant. The mutant cells proliferated less efficiently than the wild type in the inoculated ginger plants. We thus conclude that aseptically regenerated ginger plants can be used to elucidate the infection mechanism of R. solanacearum in ginger.

Automated summary

In this study, a new method for evaluating the pathogenicity of Ralstonia solanacearum in ginger using aseptically regenerated plants was developed. It was found that the type III secretion system of the pathogenic strain is crucial for its virulence. These findings contribute to a better understanding of the infection mechanism of Ralstonia solanacearum in ginger.