Development of a real-time PCR method for the detection of the dagger nematodes Xiphinema index, X. diversicaudatum, X. vuittenezi and X. italiae, and for the quantification of X. index numbers

The ectoparasitic dagger nematodes Xiphinema index and Xiphinema diversicaudatum, often at low numbers in the soil, are vectors of grapevine nepoviruses, which cause huge agronomical problems for the vineyard industry. This study reports a method, based on real-time PCR, for the specific detection of these species and of the closely related non-vector species Xiphinema vuittenezi and Xiphinema italiae. Specific primers and TaqMan probes were designed from the ribosomal DNA internal transcribed spacer 1 (ITS1), enabling the specific detection of single individuals of each of the X.index, X.diversicaudatum, X.italiae and X.vuittenezi species whatever the nematode population. The specificity of detection and absence of false positive reaction were confirmed in samples of each species mixed with the three other Xiphinema species or mixed with nematodes representative from other genera (non-plant-parasitic Dorylaimida, Longidorus sp., Meloidogyne spp., Globodera spp. and Pratylenchus sp.). The method was shown to be valid for the relative quantification of X.index numbers through its use, from crude nematode extracts of soil samples, in a greenhouse assay of grapevine accessions ranging from highly susceptible to resistant. As an alternative to time-consuming microscopic identification and counting, this real-time PCR method will provide a fast, sensitive and reliable diagnostic and relative quantification technique for X.index nematodes extracted from fields or controlled conditions.