Diversity of plant growth-promoting rhizobacteria communities associated with the stages of canola growth

Plant growth-promoting rhizobacteria (PGPR) stimulate the growth of their host plant and the presence of the plant clearly has a significant effect on rhizospheric bacterial community structure. In this study, cultivable bacteria associated with soil, rhizosphere and the roots of canola (Brassica napus) were isolated and identified by amplifying the V6–V8 region on the 16S rDNA sequence, in order to verify if possible changes in the microbial communities were associated with some stages of crop rotation and canola growth. Several PGP activities of all isolates were also evaluated. The bacterial richness associated to the rhizospheric soil of canola at the rosette stage was more than 20% larger than the other stages indicating that the microbial community structure was influenced by seasonal variation. There was also a relationship between bacterial diversity and monthly rainfall. Agrobacterium, Burkholderia, Enterobacter, and Pseudomonas were the most abundant among all the bacterial genera identified. Several of those bacteria could produce indolic compounds and siderophores, to solubilize phosphate, and some could also fix nitrogen. Some of the isolates tested for growth-promoting effects of bacterial treatment in canola were able to promote plant growth. The presence of specific PGP traits suggests that these particular organisms can promote plant growth by more than one mechanism and that some of these strains should be tested in further field inoculation experiments.