Distribution and Multiplication of Ralstonia solanacearum in Stem-inoculatedTomato Rootstock Cultivar LS-89 Resistant to Bacterial Wilt.

Bacterial wilt, caused by Ralstonia solanacearum (Syn onym Pseudomonas solanacearum), is a serious disease of solanaceous crops in tropical, subtropical, and some warm temperate regions of the world3). The most preva lent method for control of bacterial wilt is the use of resistant cultivars8). In Japan, many resistant rootstock cultivars have been developed to manage bacterial wilt4,10). Seedlings of the resistant rootstock cultivar LS-89 (Lycopersicum esuculentum) inoculated with R. solanacearum at their roots had latent infections, while inoculated seedlings of the susceptible cultivar Ponderosa (L. esuculentum) wilted5,6). In inoculated LS-89 seedlings, bacteria were located in the primary xylem tissues, whereas in Ponderosa, bacteria were found in both primary and secondary xylem tissues, indicating a limitation in bacterial movement in LS-89 tissues6). When grown at temperatures over 30•Ž after inoculation5,11) or when inoculated on their stems11), LS-89 plants often wilted. The relationship between disease severity and distribution of bacteria in such wilting plants, however, needs to be clarified. In this study, LS-89 seedlings inoculated with R. solanacearum at 106 and 109cfu/ml through injury on their stems were latently infected and partially wilted, respectively. We examined precisely the distribution of bacteria in tissues of these seedlings to clarify the mechanism of bacterial wilt resistance in LS-89. R. solanacearum strain 8107S6) which is resistant to 200ƒÊg/ml streptomycin sulfate was used in this study. Prior to inoculation, the stock culture6) was defrosted and streaked on the selective agar medium of Hara and Ono2) amended with the antibiotic. After incubation at 30•Ž for 48hr, bacteria were collected using a plastic spatula and suspended in distilled water to give 109 or 106cfu/ml by means of a colorimeter (OD660=0.54:1•~ 109cfu/ml). LS-89 seedlings were raised individually in