Contribution of the Symbiotic Plasmid to the Competitiveness of Rhizobium leguminosarum

Abstract

Four different symbiotic plasmids from Rhizobium leguminosarum were introduced into three different recipient strains that lacked plasmid-linked symbiotic determinants. The twelve synthetic strains so constructed were each tested for competitiveness against a standard reference strain. The recipient strain and the introduced symbiotic plasmid contributed about equally to competitiveness in forming root nodules on pea plants: there was also significant interaction between strain and plasmid, although this was much less important than the main effects. Competitiveness for growth on the legume root surface (the rhizosphere) was attributable entirely to the recipient strain; the introduced plasmid had no significant effect.