RHIZOBIUM-LEGUMINOSARUM AS A PLANT GROWTH-PROMOTING RHIZOBACTERIUM - DIRECT GROWTH PROMOTION OF CANOLA AND LETTUCE

Early seedling root growth of the nonlegumes canola (Brassica campestr is is cv. Tobin, Brassica napus cv. Westar) and lettuce (Lactuca sativ a cv. Grand Rapids) was significantly promoted by inoculation of seeds with certain strains of Rhizobium leguminosarum, including nitrogen- and nonnitrogen-fixing derivatives under gnotobiotic conditions. The g rowth-promotive effect appears to be direct, with possible involvement of the plant growth regulators indole-3-acetic acid and cytokinin. Au xotrophic Rhizobium mutants requiring tryptophan or adenosine (precurs ors for indole-3-acetic acid and cytokinin synthesis, respectively) di d not promote growth to the extent of the parent strain. The findings of this study demonstrate a new facet of the Rhizobium-plant relations hip and that Rhizobium leguminosarum? can be considered a plant growth -promoting rhizobacterium (PGPR).