ИСТИНА

The recently formed family Pectobacteriaceae includes numerous plant pathogens that cause rot and wilting of many plant hosts. In particular, the non-taxonomic group Soft Rot Pectobacteriaceae (SRP) is distinguished within this family, , which is the causative agent of soft rot of potato. SRP includes diverse species of Pectobacterium and Dickeya, listed as the harmful pathogens of potato. Soft rot can lead to significant crop losses (up to 50%) during storage and transportation of potatoes. The spread of SRP in Russia is difficult to control since, despite the losses incurred, these pathogens are not included in the quarantine lists. Thus, an urgent need to develop control measures exists. Treatment of potatoes with bacteriophage suspensions can be one of the decisions for preventing the spread of infection. This procedure is effective for surface application and reduces soft rot development. Thus, the search and study of bacteriophages exhibiting lytic activity concerning SRP, especially those with a wide host range, is a necessary and urgent task. This work aimed to study the Q50 phage isolated on the P. versatile F018. This phage has a typical Myoviral morphology with an isometric head of 78 nm and a contractile tail 110 nm in length. Analysis of the phage genome (91,660 bp) revealed its similarity with phages of the genus Felixo1virus of the Ounavirinae subfamily. Q50 forms clear sharp plaques with a diameter of about 2 mm on the bacterial lawn. Phage quickly binds to host cells; adsorption of 98% of phage particles is shown in 3 minutes. Analysis of one-step growth showed that the latent period of the phage is ~45 minutes, followed by the rapid lysis of the bacterial culture. To assess the host range of the phage, a set of 57 SRP strains from the laboratory collection, isolated in Russia, was used. Lytic activity was assessed by the presence of a lysis zone after application of a bacteriophage suspension on a double agar medium with phytopathogen cells. The bacteriophage demonstrates a broad host range and causes lysis of 39% of the strains used in the study, including P. carotovorum, P. versatile, P. atrosepticum, as well as some strains of P. brasiliense and P. polaris. Prominent lytic activity and wide host range make Q50 a promising candidate for the use in the purposes of phage control of potato soft rot.