The Role of Thaxtomin A and Necrosis Protein in Virulence of Streptomyces scabies that Cause Potato Common Scab Disease

Abstract

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.