Effect of conditioning, betaine, and sucrose on survival of rhizobacteria in powder formulations.

To assess the feasibility of simplified dry formulations of beneficial rhizobacteria with improved shelf life, strains of Pseudomonas and members of the family Enterobacteriaceae were conditioned by either aging, exposure to osmotica, or growth on media amended with sucrose or betaine. Strains thus treated were formulated in 1% methylcellulose and talc, and survival was assessed over 10 to 12 months. Survival of 24-h-old cultures of the same strains suspended in 20% xanthan gum and talc over the same interval was used as the standard of comparison. The survival of strains treated with sucrose, with or without betaine, and formulated in methylcellulose and talc was equal to or greater than that of 24-h-old cultures suspended in 20% xanthan gum and talc. Aging of strains on unamended King's medium B, growth of strains on KCl-amended media, and addition of betaine to KCl-amended King's medium B, whether or not strains were suspended in buffer or a diluent isosmotic to culture conditions, failed to improve survival of the strains tested. The practicality of specific amendments, such as sucrose or other disaccharides, for promoting survival of beneficial bacteria in simplified dry formulations was thus demonstrated.