Characterization of root-nodule bacteria isolated from Vicia faba and selection of plant growth promoting isolates

A collection of 104 isolates from root-nodules of Vicia faba was submitted to 16S rRNA PCR-RFLP typing. A representative sample was further submitted to sequence analysis of 16S rRNA. Isolates were assigned to 12 genera. All the nodulating isolates (45 %) were closely related to Rhizobium leguminosarum USDA2370(T) (99.34 %). The remaining isolates, including potential human pathogens, failed to nodulate their original host. They were checked for presence of symbiotic genes, P-solubilization, phytohormone and siderophore production, and then tested for their growth promoting abilities. Results indicated that 9 strains could induce significant increase (41-71 %) in shoot dry yield of faba bean. A Pseudomonas strain was further assessed in on-farm trial in combination with a selected rhizobial strain. This work indicated that nodule-associated bacteria could be a valuable pool for selection of effective plant growth promoting isolates. Nevertheless, the possible involvement of nodules in increasing risks related to pathogenic bacteria should not be neglected and needs to be investigated further.