Inoculants of Azospirillum brasilense: Biomass production, survival and growth promotion of Setaria italica and Zea mays

We grew Azospirillum brasilense biomass in fed-batch culture for 28 h using succinic acid as a C source and liquid NH3 as N source. Viable cell concentration reached 1–3 × 1010 CFU ml−1 after 28 h. Ground or granular peat, serving as carriers for the bacteria, maintained the highest number of A. brasilense compared to vermiculite, talcum powder, basalt granules or bentonite. A. brasilense viable counts declined from about 1010 CFU g−1 peat to 105–106 CFU g−1 peat after 6 months. A pot system for evaluating the effect of A. brasilense inoculants on plant growth in greenhouses demonstrated that application of peat-carrier containing 108 CFU g−1 peat, significantly increased panicle length and dry weight of Setaria italica and ear and kernel weight of maize (Zea mays L). Highest growth promotion effects on maize were observed when using A. brasilense cells containing 40% polyhydroxybutyrate (PHB) and by applying the peat inoculant 2 cm below the maize seed.