Variability of the ITS rDNA and identification of Nacobbus aberrans (Thorne, 1935) Thorne & Allen, 1944 (Nematoda: Pratylenchidae) by rDNA amplification

Abstract

Abstract In order to identify the false root-knot nematode, Nacobbus aberrans, a nematode of quarantine importance, investigations were undertaken at the molecular level. Study of the ITS rDNA region among six South American populations showed an extremely high polymorphism. This polymorphism is due to point mutation insertions-deletions, the importance of which is increased by the presence of a degenerate microsatellite in this region. The usefulness of the ITS rDNA is therefore questionable when designing a species-specific identification tool. A study based on partial sequences of the 18S gene was carried out. A conserved part of the 18S gene, with a low level of variation when compared to Pratylenchus spp. and Meloidogyne spp., was found in all the N. aberrans populations tested. The primer set designed for this part of the 18S gene allows the amplification of a 295 bp fragment in all the N. aberrans populations tested. No amplification was obtained with other species belonging to Pratylenchidae, Heteroderidae or Hoplolaimidae. This PCR-based identification tool is effective on all N. aberrans migratory stages. From this study it is concluded that this N. aberrans specific primer set may provide a very useful tool for the identification of South American N. aberrans populations and thereby assist diagnosticians in implementing N. aberrans quarantine regulations.