Test performance study for detection of Ralstonia solanacearum and Clavibacter sepedonicus in potato tubers with TaqMan PCR

Abstract

A test performance study (TPS) was organized in 2018 with ten official testing laboratories to evaluate the performance of different real‐time PCR tests for the detection of Clavibacter sepedonicus and/or Ralstonia solanacearum in potato tubers. Participants were sent spiked potato extracts with low (0.8–1.2 × 104 cfu mL‐1), medium (1.6–2.4 × 105 cfu mL‐1) and high (1.6–2.4 × 107 cfu mL‐1) bacterial loads, DNA extracts thereof and heel‐end cores from symptomatic potato tubers. The four real‐time PCR tests in this TPS for detection of C. sepedonicus were considered fit for purpose as principal screening methods. Two real‐time PCRs in this TPS were considered fit for purpose as principal screening methods for detection of R. solanacearum. A third real‐time PCR missed 23% of the DNA samples from low‐level R. solanacearum spikes and is considered not fit for purpose as a principal screening method. Correct identification of spiked samples was lower when DNA extraction from the spiked samples was performed by the participating laboratories, highlighting the importance of appropriate DNA extraction protocols.