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Ralstonia solanacearum, the bacterium that causes bacterial wilt in many plant species, produces a number of extracellular plant cell wall-degrading enzymes that are thought to be virulence factors. Endopolygalacturonase (endo-PG), PehA, and two exo-PGs, pehB and pehC, are among them. R. solanacearum was isolated and identified from sick potato tubers, yielding five isolates (BR1, BR2, BR3, BR4, and BR5). The pathogenicity of the isolates was determined, results revealed that the isolates differed in their virulence. R. solanacearum isolates (BR3, BR2, and BR5) had different levels of virulence on the potato stems of the examined cultivar (strong, moderate, and weak) respectively, so these isolates were chosen to assess potato cultivars for susceptibility to R. solanacearum isolates. R. solanacearum susceptibility differed amongst potato varieties. Spunta cultivar was the most sensitive, whereas Nicola cultivar was the most resistant. Mondial was a fairly sensitive cultivar. The activity of the PG enzyme was measured in the five isolates. BR3, BR2 and BR5 isolates were high, moderate and low activity, respectively. The optimum PG activity was observed at pH 5 and 5.5 and PG activity reached the highest level at 2 and 2.5 from incubation time, the maximum activity of PG was observed at 30 ºC and 40 ºC of incubation temperature, the optimum PG activity was observed with NaCl followed by CaCl2, The optimum NaCl concentrations for PG activity were 0.1 and 0.

Three isolates of Streptomyces scabies (St.1, St.2, and St.3) were examined for virulence on potato mini tubers, necrosis initiation on potato slices, inhibition of radish seedling length, production of thaxtomin A, and the presence of thaxtomin A (txtA) and nec1 genes. The three isolates, St.1, St.2, and St.3, were classified as highly virulent, moderately virulent, and weakly virulent, respectively. The St.1 isolate showed the highest scab severity index on potato mini tubers and necrosis on potato slices, while the St.3 had the lowest, and St.2 had intermediate values. The St.1 reduced radish seedling length by 82.35% and produced the highest toxin level (3.1 mg/ml), while the St.3 isolate reduced seedling length by 63.5% and produced the lowest level of toxin (1.18 mg/ml). The three isolates were positive for the presence of thaxtomin A (txtA) gene and produced a specific gene band at 500bp. However, St.1 and St.2 isolates were able to create a particular band at 700bp associated with the necrosis gene (nec1), while the isolate St.3 lacked this band. Based on the total protein profile analysis, the three S. scabies isolates clustered into two groups which diverged at a similarity index of 0.78. The St.2 and St.3 virulent isolates were located in the same group with 0.86 similarity, while the highly virulent isolate St.1 was located in a separate group. Current findings highlight the correlation between the presence of thaxtomin A and necrosis virulence factors and S. scabies pathogenicity.