Graduate Institute of Agricultural Biotechnology, National Chung Hsing University, Taichung, Taiwan 40227 ROC
Strains of Ralstonia solanacearum have been shown to cause bacterial wilt in some, but not all, ecotypes of Arabidopsis thaliana. We demonstrate here that after inoculation of the leaves of resistant ecotype S96 with R. solanacearum strain Ps95 necrosis around the inoculation site rapidly appeared and no further symptoms developed in the plant. Leaves of susceptible ecotype N913 completely wilted 7 days after inoculation with Ps95, and symptoms spread systemically throughout the whole plant within 2 weeks after inoculation. These results suggest that the resistance of Arabidopsis S96 to R. solanacearum is due to a response similar to the hypersensitive response (HR) observed in other plant diseases. Northern blot analysis of the expression of defense-related genes, known to be differentially induced during the HR in Arabidopsis, indicated that pathogenesis-related protein PR-1, glutathione S-transferase (GST1), and Cu, Zn superoxide dismutase (SOD) mRNAs increased significantly in S96 leaves between 3 to 12 h after infiltration with Ps95. The induction of these genes in susceptible ecotype N913 by Ps95 was clearly delayed. Genetic analysis of crosses between resistant ecotype S96 and susceptible ecotype N913 indicated that resistance to Ps95 is due to a single dominant locus.