Shelf life enhancement of plant growth promoting rhizobacteria using a simple formulation screening method

Plant growth promoting rhizobacteria (PGPR) are a specific group of bacteria interacting beneficially with plants. Among the known PGPRs, the species Pseudomonas fluorescens and Burkholderia pyrrocinia have been highlighted in both growth promotion and control of rice diseases. Ensuring the stability of the microorganism during production, formulation, distribution and storage has been a challenge for these species. In this context, the objective of this work was to develop liquid formulations, through a simplified process, that allows increase in the shelf life of these rhizobacteria for commercial application. Both bacteria were tested in 32 formulations under two storage temperature conditions: 8 and 28°C, resulting in 64 treatments for each species, which were evaluated for 180 days. Combinations of the adjuvants: molasses, glycerol, NaCl, PVP, MgSO4, K2HPO4 and yeast extract were evaluated. Formulations containing molasses, stored at 8°C, were considered the most efficient in maintaining microbial viability. The method used was considered efficient to select three formulations that allowed maintenance of the concentration of viable cells of P. fluorescens and B. pyrrocinia in 108 cfu.mL-1, for at least 90 and 150 days, respectively, not interfering with bacterial action potential.