Genetic diversity of Streptomyces species causing potato common scab in northern China.

Potato common scab (PCS) is caused by various Streptomyces spp., which seriously affect the quality and economic value of potatoes. Different species of pathogens may affect disease control strategies due to their biological characteristics. To determine pathogen composition in the major potato production area, northern China, potato tubers with various types of PCS symptoms were collected from 18 counties. From 57 collected samples, 159 bacterial isolates of Streptomyces spp. were obtained on oatmeal agar. Pathogenicity of these isolates was examined on tuber disks and potted plants of potato, resulting in 42 isolates being confirmed as pathogenic and causing typical scabby symptoms. To confirm pathogenicity determinants, the txtAB, tomA, and nec1 genes of these pathogens were detected using polymerase chain reaction (PCR). Pathogenic isolates were also identified by the combination of morphological, physiological, and biochemical characteristics, BOX-PCR, 16S rDNA, and multilocus sequence analysis. Among the 42 pathogenic Streptomyces isolates, 36 (85.7% of total isolates) were identified as Streptomyces galilaeus, and 6 (14.3%) as Streptomyces scabies. The genome of S. galilaeus isolates from the predominant group was resequenced, yielding six distinct genetic clusters. The Shangdu population exhibited the most complex genetic structure. The dominance and genetic diversity of S. galilaeus revealed in this study provide a critical foundation for breeding resistant potato varieties and developing targeted control measures tailored to the agroecological conditions of northern China.IMPORTANCEPotato common scab (PCS) caused by pathogenic Streptomyces seriously affects the quality and economic value of potato, especially in northern China. The species of Streptomyces were closely related to their geographical distribution. We determined that Streptomyces galilaeus is dominant in this area, rather than Streptomyces scabies, which is widely distributed. This finding emphasizes the importance of developing effective prevention and control strategies for the region. In addition, genome resequencing of S. galilaeus revealed significant genetic diversity, with the Shangdu population displaying the most complex structure. These results provide important information for further understanding the population structure and distribution of PCS pathogens.