Abstract
“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.
Highlights
Pectinolytic Soft Rot Pectobacteriaceae (SRP: Pectobacterium spp. and Dickeya spp.; former pectinolytic Erwinia spp.) infect a number of plant species worldwide including agriculturally relevant crops (Toth et al 2003)
We aimed to develop a formulation of the Great Five” (GF) consortium that could be applied to the surface of potato tubers prior to storage and/or before planting to protect them against SRP
The SRP pathogens and the biological control strains of the Great Five consortium (GF): S. plymuthica strain A294 (Polish Collection of Microorganisms, Wroclaw, Poland (PCM) B/00143), E. amnigenus strain A167 (PCM B/00145), R. aquatilis strain H145 (PCM B/00144), S. rubidaea strain H440 (PCM B/00141), and S. rubidaea strain H469 (PCM B/00142) were grown for 24–48 h at 28 °C on Tryptone Soy Agar (TSA; Oxoid, Basingstoke, UK) or in Tryptone Soy Broth (TSB)
Summary
Pectinolytic Soft Rot Pectobacteriaceae (SRP: Pectobacterium spp. and Dickeya spp.; former pectinolytic Erwinia spp.) infect a number of plant species worldwide including agriculturally relevant crops (Toth et al 2003). SRP are recognized among the top 10 most important bacterial pathogens in agriculture (Mansfield et al 2012) In potato, these pathogens cause a variety of disease symptoms including preemergence decay of tubers, aerial stem rot, and blackleg under field conditions, as well as soft rot of progeny tubers in storage (Pérombelon 2002). In Europe, the high losses in (seed) potato production are predominantly associated with declassification and rejection of lots Infected tubers can carry a relatively high SRP inoculum reaching after storage period even 102–104 viable cell per gram of tuber tissue. This inoculum is enough to cause soft rot symptoms in the growing season (Czajkowski et al 2009). The production of pathogen-free seed material and/or application of protective measures against contamination with Pectobacterium spp. and Dickeya spp. remain of utmost importance (Pérombelon 1992)
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