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A Multiplex Real-Time Polymerase Chain Reaction (TaqMan) Assay for the Simultaneous Detection of Meloidogyne chitwoodi and M. fallax

This study describes a multiplex real-time polymerase chain reaction (PCR) approach for the simultaneous detection of Meloidogyne chitwoodi and M. fallax in a single assay. The approach uses three fluorogenic minor groove binding (MGB) TaqMan probes: one FAM-labeled to detect M. chitwoodi, one VIC-labeled to detect M. fallax, and one NED-labeled to detect the internal amplification control (IAC) to monitor false negative results. One common primer set is used for the amplification of part of the internal transcribed spacer (ITS) region of M. chitwoodi and M. fallax and one primer set for the amplification of the IAC. The test enabled detection of M. chitwoodi and/or M. fallax in DNA samples extracted from batches of juveniles, from single juveniles, and from infected plant material. Compared with current assays to detect M. chitwoodi and M. fallax, the multiplex real-time PCR offers the following advantages: it is faster because the test can simultaneously detect both quarantine species without the need for post-PCR processing; and it is at least 10 times more sensitive than a comparable regular PCR also targeting the ITS sequence. Inclusion of the IAC facilitates the interpretation of the FAM and VIC cycle threshold (Ct) values and can prevent the scoring of false negative results when FAM, VIC, and NED Ct values are high. The test allows precise quantification when only one of the two species is present in the sample. However, experiments with mixtures of genomic DNA of M. chitwoodi and M. fallax revealed that the ability of the multiplex real-time PCR assay to detect small quantities of DNA of one species is reduced when large quantities of DNA of the other species are present.