Streptomyces species associated with common scab lesions of potatoes in South Africa

Streptomyces scabiei is largely accepted as the causal organism of common scab on potato in South Africa, and other Streptomyces species associated with common scab are not often considered. This study therefore aims to determine the diversity and prevalence of Streptomycetes associated with common scab on potatoes in South Africa. Isolates from 11 of the 16 potato producing regions in South Africa were characterized morphologically, physiologically and genetically. Most isolates resembled S. scabiei based on morphology and physiology. Most pathogenic isolates were S. scabiei and S. stelliscabiei, and no S. acidiscabies or S. turgidiscabies isolates were found. All three pathogenicity/virulence genes (txtAB, nec1, tomA) were found in South African isolates. Pathogenicity could not be linked to the presence of a single one or any combination of two of the three genes. These results represent the most comprehensive published survey of Streptomycetes isolated from common scab lesions on potatoes in South Africa.