Trenton Berrian1, Christopher Clarke2, Aymeric Goyer1 1Department of Botany and Plant Pathology, Oregon State University, OR 2USDA Agricultural Research Service, Genetic Improvement for Fruits and Vegetables Laboratory, Beltsville, MD Soil-borne Streptomyces species are the causal agents of potato common scab, a disease that causes cork-like lesions on the surface of tubers that can make tubers unmarketable. Current cultural control methods are limited and inefficient, and cultivar resistance is highly dependent on the specific Streptomyces species and isolates present in a certain field. New control methods are therefore needed. Thiamin, also known as vitamin B1, can prime plants when externally applied to foliage, enabling plants to respond more rapidly and/or more robustly to pathogens and thus annihilating or limiting disease. However, the priming effect of thiamin to control bacterial diseases of potato has never been tested, nor has it against any pathogen in any crop in a field setting. Therefore, in this project, we will test the effectiveness of thiamin priming application to control potato common scab in an organic field that has shown high incidence of the disease in the past several years. To confirm the pathogen, we purified four Streptomyces isolates from symptomatic tubers harvested from the infested field in 2021. Three isolates contained the thaxtomin biosynthesis locus and are therefore likely pathogenic. Genomic sequencing and phylogenomic analysis indicated that pathogenic isolates belong to the Streptomyces scabiei species, the primary species known to be present in Oregon. In 2022 and 2023, we will plant two purple-skinned potato varieties that are susceptible to common scab, Purple Viking and Huckleberry Gold. Two treatments, mock and thiamin at 50 mM, will be applied on foliage every other week starting at time of tuberization. Four blocks will be arranged in a randomized complete block design. At harvest, tubers will be scored for type and coverage of lesions and statistical differences will be determined by Student t-test. If successful, application of thiamin would provide a useful tool for common scab management in potato.