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Phytophthora blight caused by Phytophthora capsici is a serious disease affecting pepper production and other important vegetable crop. This study developed a species-specific PCR assay for the rapid and accurate detection of P. capsici in infected plant tissues, soil, and water. The PCR primers were designed based on Ras-related protein (Ypt1) gene, and 236 isolates representing 12 species of Phytophthora and 26 fungal species of plant pathogens were used to test the specificity of the primers. PCR amplification with the species-specific primer pair resulted in products of 364 bp solely from all isolates of P. capsici that was not amplified from any other isolates tested. The detection sensitivity of the species-specific primer pair Pc1F/Pc1R was 10 pg of genomic DNA. This sensitivity increased 1000-fold to 10 fg by developing a nested PCR procedure that uses Pc1F/Pc1R as first-round primers combined with Pc1F/Pc2R as a second round primers. The PCR assay can also be used to detect P. capsici in naturally infected plant tissues, soil, and water. The PCR-based methods developed here could simplify both plant disease diagnosis and pathogen monitoring and aid in plant disease management.