Isolation of Dickeya dadantii strains from potato disease and biocontrol by their bacteriophages

Abstract

One of the most economically important bacterial pathogens of plants and plant products is Dickeya dadantii. This bacterium causes soft rot disease in tubers and other parts of the potato and other plants of the Solanaceae family. The application of restricted host range bacteriophages as biocontrol agents has recently gained widespread interest. This study purposed to isolate the infectious agent of the potato and evaluate its biocontrol by bacteriophages. Two phytopathogenic strains were isolated from infected potatoes, identified based on biochemical and 16S rRNA gene sequencing, and submitted to GenBank as D. dadantii strain pis3 (accession no. HQ423668) and D. dadantii strain sip4 (accession no. HQ423669). Their bacteriophages were isolated from Caspian Sea water by enriching the water filtrate with D. dadantii strains as hosts using spot or overlay methods. On the basis of morphotypes, the isolated bacteriophages were identified as members of the Myoviridae and Siphoviridae families and could inhibit the growth of antibiotic resistant D. dadantii strains in culture medium. Moreover, in Dickeya infected plants treated with bacteriophage, no disease progression was detected. No significant difference was seen between phage-treated and control plants. Thus, isolated bacteriophages can be suggested for the biocontrol of plant disease caused by Dickeya strains.

Keywords: Dickeya dadantii; antibiotic resistance; bacteriophage; biocontrol; soft rot.

Figure 1. Plaques formation in agar medium. The isolated Dickeyapropagated on soft nutrient yeast agar medium, and the phage suspension spread on the medium. A) plaques up to 4–5 millimeter diameter (Myoviridae phage), and B) plaque up to 2–3 millimeter diameter (Siphoviridaephage)

Figure 2. Growth curve of Dickeya dadantii

Figure 3. Electron micrograph of Dickeya dadantii phages: (a) Myoviridae family, (b) Siphoviridae family

Figure 4. Cranesbill (Geranium spp.) plants infected by 5 × 10⁸cells/mL of Dickeya dadantii sip4 and treated by 3 × 10⁹PFU/mL of Siphoviridae and Myoviridae related bacteriophages, plant in control group treated with DDW, and plants in bacteria group inoculated with 5 × 10⁸ cells/mL of Dickeya dadantiisip4