الفهرس 
Virulence of ralstonia solanacearum the causal agent of potato brown rot
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Abstract
The present work was performed to characterize the phenotypic variations between virulent and avirulent isolates of Ralstonia solanacearum race 3 biovar 2, The causal agent of potato brown rot. Twelve isolates of Ralstonia solanacearum (Six virulent and six a virulent isolates) were recoverd from different habitats. All isolates were identified based on morphological, cultural, physiological and biochemical characteristics and proved to be Ralstonia solanacearum race 3 biovar 2 equvialent to phylotype II sequevar I. Serological test by means of Immunofluorescence antibody staining (IFAS) didn’t show any variation between virulent and avirulent isolates either in cell morphology or degree of fluorescence, Conventional PCR showed similarity of the bands in Agarose gel electrophoresis and Tag- man Real time PCR showed typical curve over the threshold in virulent and avirulent isolates.Dendrogram clustering analysis show genetic diversity based on broadly the phenotypic form of the used isolates and does not show any trend according to the source of the isolates or geographical region. Differences between the two forms of R. solanacearum can be observed on semi selective media of South Africa (SMSA), Triphenyl teterazolium chloride (TZC) and king’s B media (KB). Virulent and avirulent isolates were tested for their pathogenic potentials on two potato cultivars in terms of pathogenicity