Pathological and molecular studies on bacterial wilt disease of Potato, Solanum tuberosum,

This work aimed to elucidate variation in pathogenicity for different Ralstonia solanacearum isolates which collected from potato fields in Egypt, characterize Ralstonia solanacearum at biochemical and molecular level and to determine the possible role of avirulent isolates of Ralstonia solanacearum in disease control. A total of 108 isolates of Ralstonia solanacearum were isolated from different sources and identified, according to Physiological and bacteriological tests and confirmed using Immunofluorescent Antibody Staining (IF AS) test and Real time PCR, as R. solanacearum race 3 biovar II. Soil drench or stem inoculation methods were used in pathogenicity test on potato and tomato plants. All tuber isolates were highly virulence compared with soil and water isolates. Total isolates were divided into two groups according to disease incidence; the first group contained virulent isolates which isolated from tuber samples and the second group contained avirulent isolates which isolated from soil and water samples. Variability on colony phenotypic and cell morphology was observed between virulent and avirulent isolates. Virulent isolates showed high content of either lipopolysaccharide or total sugars in LPS compared with avirulent isolates. Total sugars in LPS were determined using gas liquid chromatography (GLC). The glucose was the major content of R. solanacearum lipopolysaccharide in all examined isolates. Lipopolysaccharide for virulent isolates of R. solanacearum showed high amount of arabinose, xylose, mannose and galactose compared with avirulent isolates, while the amount of mannitol was the highest in Lipopolysaccharide for avirulent isolates compared with virulent isolates. There is no significant difference between the amount of rhamnose, fructose and sorbitol in lipopolysaccharide in all isolates. Virulent and avirulent isolates were varied in their fatty acid content. High amount of pectin lyase and cellulase enzymes was observed in cultural filtrate of virulent isolates,while the amount of polygalacturonase was low. No significant difference was observed between different bacterial isolates in SDS- PAGE electrophoresis. Both phcA and hrpA genes were detected and expressed in inoculated potato either by virulent or avirulent isolates.Avirulent isolate of R. solanacearum (SM4) was effective as antagonistic bioagent against virulent one under laboratory and greenhouse conditions.