Diversity and multifunctional potential for plant growth promotion in bacteria from soil and the rhizosphere

Beneficial microorganisms play essential roles in soil fertility, plant nutrition, and health. In this study, we examined the potential of a collection of 138 bacterial strains to promote plant growth. The strains were isolated from the rhizosphere of two monocotyledonous and two dicotyledonous plant species and from bare fallow soil, all from the same site. Our interest in this study was to investigate the diversity and the potential for growth promotion in this collection of culturable bacteria. The most common trait was phosphorus (P) solubilization from aluminium phosphate (in 66.7% of the strains), whereas solubilization of P from phytic acid (6.5%) and from iron phosphate (5.8%) was the least common and they were only detected in bacterial strains from faba bean and oilseed rape. All bacterial strains inhibited the growth of Fusarium graminearum (from 5.4% to 87.2%). In total, 10 genera were identified among the strains by 16S rRNA sequencing and Pseudomonas was the most common in monocotyledonous plants and in bulk soil, while Stenotrophomonas was dominant in the rhizosphere of the dicotyledonous plants. Combinations of bacterial strains improved the spectrum of in vitro activity in most cases, however, wheat growth was generally lower. These strains have potential to be used as biofertilizers and/or biocontrol agents and further studies should be pursued to develop them into practical solutions for a more sustainable agricultural production.