Suppression of Ralstonia solanacearum in soil following colonization by other strains of R-solanacearum

The effect of prior colonization of a sterile loam soil and a sterile clay loam soil by individual soil bacteria on the subsequent growth of a bacteri al wilt pathogen Ralstonia solanacearum YU1Rif43 (tRNA type III: Seal et al . 1992: Appl. Environ. Microbiol., 58, 3759-3761) was investigated. Various strains, belonging to the same type, the same species, the same genus, Gra m-negative, Grampositive, or fungi, were used, The degree of suppression of the growth of R. solanacearum YU1Rif43 was markedly different depending on the species that had previously colonized the soil, hereafter referred to as priorcolonists. All the strains belonging to R, solanacearum type III su ppressed the growth of R. solanacearum YU1Rif43 markedly, while strains of R. solanacearum type I and type II showed a moderate suppressive effect on R. solanacearum YU1Rif43. The suppressive effect of the strains belonging t o species other than R. solanacearum, including fungal strains, was relativ ely limited, or some strains did not show any suppressive effect, The produ ction' of bacteriocin did not appear to be related to the strong suppressiv e effect of the R. solanacearum type III strains. Possible mechanisms for t he suppressive effect of priorcolonists on R. solanacearum YU1Rif43 are dis cussed in relation to nutrients and physical sites in soil available for gr owth.