Azospirillum brasilense strains Ab-V5 and Ab-V6 have been broadly and successfully used in commercial inoculants in Brazil, for both non-legumes and legumes, contributing to increases in grain yields with reduced applications of chemical fertilizers. Azospirillum survival, however, may be very low in liquid inoculant formulations and strategies such as the enrichment with polyhydroxybutyrate (PHB) and biofilm may help both bacterial survival and agronomic performance. The production was quantified for both PHB and biofilm by strains Ab-V5 and Ab-V6 in liquid inoculant formulations. Differences were observed between formulations, strains, and strain x formulation. Cellular PHB concentrations ranged from 7.9 to 40.2% of the cell dry weight after 96 h, and considerable amounts of biofilm were synthesized by both Ab-V5 and Ab-V6. Maximum accumulation of PHB and biofilm occurred with A. brasilense strain Ab-V6 in the formulation FORM2+P3, indicating that it is possible to enrich the inoculants on PHB and biofilm by improving the culture media. Field experiments will now be performed to confirm the agronomic efficiency of the improved inoculant.
Key words: Polyhydroxybutyrate, inoculation, N2 fixation, plant-growth-promoting bacteria, plant-growth-promoting bacteria (PGPB).
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