"The Great Five" (GF) is an artificial bacterial consortium developed to protect potato tubers from soft rot caused by Pectobacterium spp. and Dickeya spp. To investigate the commercialization potential of the GF, we developed liquid and powder formulations of the consortium and of each of the comprising strains (Serratia plymuthica strain A294, Enterobacter amnigenus strain A167, Rahnella aquatilis strain H145, Serratia rubidaea strain H440, and S. rubidaea strain H469). To form powders, the cells were lyophilized using a newly developed lyoprotectant: Reagent PS. The shelf life of the formulations stored at 8 and 22 °C was monitored for a period of 12 months. The longest shelf life was obtained for formulations stored at 8 °C; however, the viability of all formulations was negatively affected at 22 °C. For the consortium, a 2.5 log10 cfu (colony forming units) drop in cell number was recorded for the liquid formulation after 6 months, while in case of powders, the drop remained below 1 log10 cfu following 12 months. The ability of the powder formulations to preserve biocontrol activity of the consortium was tested on potato tubers treated with the formulations and a mixture of the soft rot pathogens. The inoculated tubers were stored for 6 months at 8 °C to mimic commercial storage conditions. Soft rot severity and incidence on potato tubers treated with formulations were significantly reduced (62-75% and 48-61%, respectively) in comparison to positive control with pathogens alone. The potential use of the newly developed formulations of "The Great Five" for the biocontrol of soft rot is discussed. KEY POINTS : • An innovative reagent to protect bacterial cells during lyophilization was developed. • Powder formulations of "The Great Five" prolonged its shelf life. • The powder-formulated "The Great Five" was active against soft rot bacteria on potato tubers.
Keywords: Antagonism; Biological control; Blackleg; Pectinolytic Erwinia; Potato.