Development of a multiplex TaqMan qPCR targeting unique genomic regions for the specific and sensitive detection of Pectobacterium species and P. parmentieri

Aim: The newly defined species Pectobacterium parmentieri has emerged as an aggressive pathogen that causes soft rot and blackleg diseases on potato and has been widely disseminated across the globe, jeopardizing the productivity and potato food safety. The implementation of a fast and accurate detection tool is imperative to control, monitor and prevent further spread of these pathogens. The objective of this work was to develop a specific and sensitive multiplex TaqMan qPCR to detect P. parmentieri and distinguish it from all known Pectobacterium species. A universal internal control was included to enhance the reliability of the assay.

Methods and results: A comparative genomics approach was used to identify O-acetyltransferase and the XRE family transcriptional regulator as specific targets for primers/probe design for the detection of the Pectobacterium genus and P. parmentieri, respectively. Specificity was assessed with 35 and 25 strains included in the inclusivity and exclusivity panels, respectively, isolated from different geographical locations and sources. The assay specifically detected all 35 strains of Pectobacterium sp. and all 15 P. parmentieri strains. No cross-reactivity was detected during assay validation. Our assay detected up to 10 fg genomic DNA and 1 CFU ml^-1 bacterial culture. No change in the detection threshold (1 CFU ml^-1 ) was observed in spiked assays after adding host tissue to the reactions. The assay was validated with naturally and artificially infected host tissues and soil rhizosphere samples. All infected plant samples containing the target pathogens were accurately amplified.

Conclusion: The presented multiplex TaqMan qPCR diagnostic assay is highly specific, sensitive, reliable for the detection of Pectobacterium species and P. parmentieri with no false positives or false negatives.

Significance and impact of the study: The developed assay can be adopted for multiple purposes such as seed certification programmes, surveillance, biosecurity, microbial forensics, quarantine, border protection, inspections and epidemiology.