Occurrence of Streptomyces stelliscabiei Causing Potato Common Scab in China and Resistance Evaluation of Potato Germplasm Resources

Potato common scab is a widespread soil-borne disease that severely reduces tuber quality and market value. However, the diversity of common scab pathogens and the availability of resistance resources in major potato-producing regions of China remain poorly understood. In this study, potato common scab pathogens were isolated from diseased tubers collected in Heilongjiang Province, China, and identified based on morphological characteristics, 16S rRNA gene sequencing, and pathogenicity-related gene detection. Two pathogenic <i>Streptomyces</i> species, <i>Streptomyces scabiei</i> and <i>Streptomyces stelliscabiei</i>, were identified. Notably, <i>S. stelliscabiei</i> was identified in potato common scab samples collected in Heilongjiang Province for the first time, suggesting that it may represent an emerging causal agent of potato common scab in China. Molecular analysis revealed two pathogenicity-related gene profiles among the isolates-namely, <i>txtAB</i>⁺/<i>tomA</i>⁺/<i>nec1</i>⁺ and <i>txtAB</i>^-/tomA⁺/nec1⁺-indicating diversity in virulence-associated gene composition. Resistance to potato common scab caused by <i>S. stelliscabiei</i> was further evaluated in 132 potato germplasm accessions, including domestic and introduced materials, local landraces, and widely cultivated cultivars. Significant variation in resistance levels was observed. Only two accessions were classified as highly resistant, six as resistant, and eighteen as moderately resistant, whereas the majority of accessions were susceptible or highly susceptible. Overall, this study provides the first evidence of <i>S. stelliscabiei</i> causing potato common scab in China, reveals pathogenicity-related gene diversity among common scab pathogens, and identifies valuable resistance resources for potato breeding. These findings contribute to a better understanding of potato common scab epidemiology and support the development of resistant cultivars.