Identification of Pseudoperonospora cubensis using real-time PCR and high resolution melting (HRM) analysis

To develop a molecular method to identify Pseudoperonospora cubensis in cucumber leaves with signs of downy mildew, we compared the nucleotide sequences of ribosomal DNA-internal transcribed spacer, cytochrome oxidase II, and beta-tubulin genes of P. cubensis and P. humuli isolates. Seven single nucleotide polymorphisms (SNPs) distinguished P. cubensis and P. humuli based on variations in beta-tubulin sequences, and one specific primer set was designed for further analysis. Real-time PCR and high resolution melting analysis showed that the primer set can be used to specifically identify P. cubensis in cucumber leaves with downy mildew.