Tatum Miklasevics

Streptomyces spp. are soilborne gram positive filamentous bacteria from phylum actinobacteria (Flores-González, 2007). While the distribution of Streptomyces spp. is across the world, a small number are phytopathogenic, some of which cause common scab of potato including S. scabies. Streptomyces produce antibiotics and biologically active secondary metabolites that contribute to both disease and stress resistance (Zhang, 2020). This study concentrated on 19 nonpathogenic Streptomyces isolates that were previously isolated in 2021 and 2022 from the Sand plain research farm in Becker, Minnesota and subsequently screened for pathogenicity through potato tuber and radish seedling assays and using PCR based determination of pathogenicity island genes. The nonpathogenic isolates were tested for antagonistic activity against Sclerotinia sclerotiorum, Fusarium subglutinans, and Pythium ultimum. Antagonistic activity was quantified by performing a dual plate assay on PDA and calculating percentage inhibition between the fungal plug and 100µl of the Streptomyces STR broth culture at 5 days post inoculation (dpi) and 10 dpi. Antagonistic activity was observed in three of the isolates: Sc7.1.10 significantly inhibited Pythium ultimum and Sclerotinia sclerotiorium., SIA.27 significantly inhibited Pythium ultimum, and Sc3.2.10 significantly inhibited all three pathogens. These Streptomyces strains show promising biocontrol agent properties that could be used as a preventative control method against common scab of potato. Further studies include a dual plate assay against Rhizoctonia solani and Fusarium graminearum following with a filtrate study to determine if these isolates secrete beneficial antibiotics and metabolites.