Graduate Institute of Agricultural Biotechnology, National Chung Hsing University, Taichung, Taiwan 40227 Republic of China
Tomato bacterial wilt caused by Ralstonia solanacearum is a model system for studying plant-bacterial interactions, because it is genetically one of the best characterized plant diseases. We demonstrate here that four different strains of R. solanacearum, two from radishes (Rd4 and Rd15) and two from tomato (Ps21 and Ps95), can infect 27 different ecotypes of Arabidopsis thaliana, causing different responses. All ecotypes tested were highly susceptible to strain Rd15, which caused symptoms similar to those observed in tomato plants. For example, leaf drooping and discoloration developed just 3 days after inoculation, and plants completely wilted within 1 week. Strains Rd4 and Ps95 were less infectious than Rd15. With these two strains, a variety of disease responses were observed among different ecotypes at 2 weeks after inoculation; both susceptible and resistant ecotypes of A. thaliana were identified. Ps21 was the least infectious of the four strains and caused almost no symptoms in any of the ecotypes of Arabidopsis tested. Direct bacterial isolation and plant skeleton hybridization analysis from infected plants indicated that bacterial colonization was correlated with the severity of symptoms. Growth of bacteria was limited to the infection site in resistant plants, whereas the bacteria spread throughout susceptible plants by 1 week after inoculation.