Using in silico analysis to investigate the false positive potential of qPCR systems for potato disease diagnosis

Potato (Solanum tuberosum) is one of the most important crops facing threats from different diseases. Rapid and accurate diagnosis is essential to control disease development and spread. Quantitative real-time PCR (qRT-PCR) has been widely used in potato disease diagnosis. In this study, we evaluated the specificity of 19 probe-based and four SYBR Green-based qPCR protocols for 17 potato diseases using in silico analysis. Primers and probes of those protocols were subjected to BLASTn analysis against the nucleotide collection (nr/nt) database and the whole-genome shotgun contigs (wgs) database of NCBI for the presence of primer/probe sequences in non-target species. Results showed that 12 of 23 qPCR protocols were not specific to the target pathogens. A qPCR experiment indicated that even nine single nucleotide polymorphisms (SNPs) are present on the sequences of the primer/probe binding sites between the potato silver scurf pathogen Helminthosporium solani and its close-related species H. velutinum, the primers/probe specific to the former could amplify signals from the latter. These findings highlight the need for additional methods to enhance the diagnostic accuracy and new sequencing technologies such as next generation sequencing could provide useful information to develop specific diagnostic protocols for these pathogens.