Seedling Petri-dish inoculation method: a robust, easy-to-use and reliable assay for studying plant-Ralstonia solanacearum interactions1

Ralstonia solanacearum causes a lethal bacterial wilt disease in many crops, leading to huge losses in crop production every year. Understanding of plant-R. solanacearum interactions will aid to develop efficient strategies to control the disease. As a soilborne pathogen, R. solanacearum naturally infects plants via roots. A huge limitation in studying plant-R. solanacearum interactions is the large variation of R. solanacearum infection assay due to the variable soil conditions and uneven inoculum exposure. Here, we developed a robust and reliable Petri-dish inoculation method which allows consistent and stable infection in young plant seedlings. This method is easy to use, takes about only 10 days from seed germination to the completion of inoculation assay, and requires less inoculum of bacteria as well as growth chamber space. We proved the efficacy of the seedling Petri-dish inoculation method by analyzing plant defense primed by molecular patterns, resistance of defense-related plant mutants, and virulence of R. solanacearum mutants. Furthermore, we demonstrated that the seedling Petri-dish inoculation method can be applied to other host plant such as tobacco and has great potential for high-throughput screening of resistant plant germplasm to bacterial wilt in the future.