Bacterial soft rot disease is one of the most important and widespread bacterial diseases that cause destructive losses to the crop in a matter of days. The disease causes severe many vegetable crops including potato. In this study, four isolates of Pectobacterium carotovorum the main causal of the soft rot disease were isolated from naturally rotted tubers. Then, the isolates were subjected to a new set of primer pairs designed to amplify the pel gene which distinguish the P. carotovorum  strains. The results confirmed that four isolates belong to P. carotovorum  by having the pel gene. Then, a pathogenicity test was performed on potato tubers which showed variability between the isolates in pathogenicity and diseases severity. Finally, a quantitative reverse transcriptase PCR (qRT-PCR) techniquewas used to investigate the effect of the presence of the potatoes tissues on stimulating the expression of the pathogenicity genes. The gene expression of five pathogenicity genes was studied included: polygalacturonase (Peh), pectate lyase (Pel), xylanase (Xy), protease (Prt), and cellulase (Cel). The results confirmed that the presence of potatoes tissues stimulates the expression of pathogenicity genes in both strong and weak P. carotovorum  isolates.