Abstract: The objective of this project was to develop a polymerase chain reaction (PCR) method to identify powdery and common scab from potato lesions. The PCR method is composed of three steps: (1) Extraction of DNA from scab lesions; (2) DNA purification; and (3) Amplification of DNA by PCR. Several methods to extract DNA such as commercial beat-beating, home-made beat-beating and grinder were tested. The grinder method was found inadequate for DNA extraction since a larger portion of the tuber needed to be ground and the sample obtained is too diluted. Both the commercial and home-made beat-beating methods performed well. Different extraction buffers were also tested. DNA purification was done using commercial purification column and phenol-chloroform. Although both methods were effective, the phenol-chloroform purification step was chosen for economical reasons. Finally, the PCR reaction was performed by designing primers recognizing sequence of pathogenic strains of the causal agent of common scab. The primers amplifying the powdery causal agent were available from the literature. The two sets of primers were successful at amplifying each causal agent separately and also in combination. Currently, we are evaluating the adequate quantity of potato lesions that need to be used to obtain DNA and ensure a positive identification of the presence of causal agents. The distribution of causal agents might be found in pockets in some of the lesions found on a tuber. We will evaluate the distribution of causal agents in the lesions of tubers and evaluate if external signs could help us identify the presence of the powdery scab and/or common scab pathogens.