THE ISOLATION AND BIOLOGICAL CHARACTERIZATION OF BACTERIOPHAGES LYTIC TO GEORGIAN STRAINS OF RALSTONIA SOLANACEARUM RACE 3 BIOVAR 2

Ralstonia solanacearum is a soilborne bacterial pathogen, distributed in tropical, subtropical and some temperate regions, causing serious diseases of strategic crops, such as potato, tomato, banana etc. Control of plant infections caused by R.solanacearum is a challenging issue. Phage preparations can be considered as effective tool for prevention of infection spread in the environment and in the seed plant material. Since first report on detection of R. solanacearum in Georgia up to 60 strains have been collected, majority attributed to race 2 biovar 3. The presented work aimed at isolation of bacteriophages specific to Georgian strains of R. solanacearum and study their biological properties in order to select phages for strain subtyping and for infection control. During 2015-2017 enrichment of environmental samples with 40 selected isolates of R. solanacearum and subsequent processing of primary mixtures resulted in obtaining of 25 individual Rs phages. Initial grouping of phages was done based on negative colony morphology, lytic spectrum and virion ultrastructure. Transmission electron micrioscopy (TEM) revealed the prevalence of Myoviridae type morphology among Rs phages, although single phages were attributed to Podoviridae and Siphoviridae families. The Rs phages showed diverse host range. The phage - and antibiotic susceptibility profiles of R. solanacearum strains were compared and showed no correlation between these two characteristics.Ten bacteriophages with overlapping spectrum were characterized in more details, including lytic activity in liquid culture and stability in various natural and artificial solutions. The mixture of 4 selected phages was composed for use in in vivo challenge experiments.