Combined application of novel broad-spectrum bacteriophages and antagonistic bacterial strain: enhanced biocontrol efficacy against Streptomyces induced potato common scab.

Potato common scab (PCS), caused by pathogenic Streptomyces spp., is a globally significant disease leading to substantial economic losses in potato production. Conventional chemical control methods pose environmental risks and contribute to antibiotic resistance, necessitating sustainable alternatives. This study isolated three novel broad-spectrum bacteriophages (pSt2308, pSt2402, and pSs2407) from potato field soils, exhibiting lytic activity against multiple pathogenic Streptomyces strains while sparing non-pathogenic species. All three phages demonstrated exceptional environmental stability, tolerating temperatures (4-50 °C), pH (3-11), and UV exposure. Whole-genome sequencing revealed that the three phages belong to the class Caudoviricetes, with pSt2308 and pSt2402 identified as new species. Following phage cocktail treatment, in vitro assays demonstrated rapid pathogen lysis, while in vivo experiments on potato slices and radish seedlings showed significant reductions in disease severity and enhanced plant growth. Combined with the antagonistic strain Bacillus cereus BC-1, which exhibited strong inhibition against PCS pathogens, the phage cocktail synergistically enhanced biocontrol efficacy against mixed pathogenic Streptomyces spp. infected potato slices, radish seedlings or contaminated soil. Our findings highlight the synergistic potential of phage-antagonist combinations as an eco-friendly and effective strategy for managing PCS, offering a promising alternative to chemical pesticides.