Liquid formulations of Acetobacter diazotrophicus L1 and Herbaspirillum seropedicae J24 and their field trials on wheat

Viability of the plant growth promoting bacteria A. diazotrophicus L1 and H. seropedicae J24 stored as liquid formulation was evaluated by studying the effect of growth medium, preservation medium and temperature. They were grown in molasses medium with the addition of NH₄Cl (0.1% w/v). Cells were harvested at 10,000 rpm for 30 min and washed in phosphate buffer. They were then preserved at 4°C and 25°C with isotonic solutions of different substances. Efficacy of liquid formulations stored for different periods was tested on wheat crop by pot assay and field trials. The best growth medium was found to be 3% molasses supplemented with 0.1% (w/v) NH₄Cl. Trehalose, gum arabica and polyethylene glycol 300 (PEG 300) provided better protective effects than other protective substances. Addition of L-ascorbic acid (0.02% w/v) to preservation media would improve the effectiveness of protective substances. After 8–9 months of storage at 4°C, A. diazotrophicus L1 and H. seropedicae J24 cells preserved in gum arabica (5% w/v) and PEG 300 (5% w/v), respectively maintained their viability and efficacy of plant growth promotion. Bacterial cultures of different ages in these liquid formulations exhibited different plant growth promoting traits up to 240 days. Similarly, they significantly promoted the wheat plant growth compared to untreated control. There was significant difference in growth, grain yield and dry matter (straw yield) of wheat with these formulations. This ascertained the efficacy of A. diazotrophicus L1 and H. seropedicae J124 in liquid-based formulation. Thus, gum arabic and polyethylene glycol could be used to develop a stable liquid formulation of A. diazotrophicus L1 and H. seropedicae J24 as a commercial product.