INVASIVENESS OF AVIRULENT STRAINS OF PSEUDOMONAS-SOLANACEARUM IN TOMATO CULTIVARS, RESISTANT OR SUSCEPTIBLE TO BACTERIAL WILT

Tomato plant colonization by avirulent strains of Pseudomonas solanace arum was studied. The strain 8217R a spontaneous rough mutant was able to penetrate into the roots by natural openings and colonize plants a t high levels. The strain 8173, a hrp- engineered fluidal mutant, colo nized the plants to a lesser extent than 8217R. There was no differenc e in colonization observed at taproots and hypocotyls between resistan t and susceptible cultivars with the avirulent strains 8217R and 8173, contrary to the plant-virulent strain interaction. Results indicated that the bacterial spread was limited in the two cultivars regardless of their resistance or susceptibility and suggested the existence of a host defence mechanism, limiting the bacterial spread.