Distribution and Multiplication of Ralstonia solanacearum (Synonym Pseudomonas solanacearum) in Tomato Plants of Resistant Rootstock Cultivar LS-89 and Susceptible Ponderosa.

Abstract

We examined the distribution and multiplication of Ralstonia solanacearum (Synonym Pseudomonas solanacearum) in roots and stems of tomato plants of resistant rootstock cultivar LS-89 and susceptible cultivar Ponderosa. In a growth chamber at 30°C, 30-day-old seedlings were inoculated with R. solanacearum strain 8107S after trimming lateral roots and immersing the root ball in a bacterial suspension of 107 cfu/ml. In inoculated Ponderosa plants, bacteria were recovered from all taproot and stem samples tested. Pathogen density increased in root and stem tissues to 108 or 109 cfu/g fresh matter in 10 days. Inoculated LS-89 plants were latently infected with the pathogen. Recovery of the pathogen in these LS-89 plants at 14 days after inoculation was about 90% in taproots and the upper hypocotyls, and about 80% in the first internodes, but the percentage decreased higher in the stem (30% recovery at the fifth internode). Pathogen density increased to 106 cfu/g fresh matter in taproots, upper hypocotyls and the first internodes in the first 4 days, but it was steady afterwards. Transverse sections of the upper hypocotyls of infected plants showed bacterial masses in the primary and secondary xylem tissues in Ponderosa, but only in a portion of the primary xylem tissues in LS-89. These results indicate that the bacteria are localized in the primary xylem tissues and their movement is limited in resistant LS-89 plants.