Testing for potato viruses is globally very important to prevent a critical shortage of potato supply. In most countries, testing is obligated by law. In Germany, seed potatoes are monitored for six viruses: PLRV, PVY, PVM, PVA, PVX and PVS. They can cause up to 90% loss of potato tubers in the field. Common methods currently used for testing are ELISA and conventional real-time PCR, but both are very time-consuming, and the former needs a high capacity of green houses and human resources, the latter elaborate RNA extraction steps. Recently, we proposed a new method called real-time DiRT-PCR which enables us to test for PLRV, PVY and PVS along with an internal control in three duplex real-time PCR reactions directly on diluted tuber sap. In this study, we describe the first TaqMan® assay for PVM published so far and embed it into a multiplex system to detect the remaining viruses. We are now able to sensitively test for the presence of six viruses in two multiplex reactions using the real-time DiRT-PCR without RNA purification.

Potato viruses PLRV, PVY, PVM, PVA, PVX and PVS can cause up to 90% loss of potato harvest. Therefore, they are monitored by law in many countries using DAS-ELISA or conventional real-time RT-qPCR. Previously, we developed a multiplex real-time DiRT-PCR (Direct reverse transcript – polymerase chain reaction), which works directly on diluted tuber sap and thus saves time and chemical processing for RNA extraction or time and space in the glasshouse. So far, this method only ran on sap of single tubers which is not practical for routine testing. We are now able to sensitively test for the presence of six viruses in two multiplex reactions using the real-time DiRT-PCR on pooled samples of ten tubers. Here we show that there is an “almost perfect” agreement (Gwet’s AC1 index) comparing this multiplex real-time DiRT-PCR on pooled samples with DAS-ELISA and a commercial RT-qPCR kit with a rapid extraction method. The multiplex real-time DiRT-PCR is now ready to be used for routine testing.