Species delimiting of the genus Pratylenchus (Nematoda: Pratylenchidae) plant-parasitic nematodes

Root-lesion nematodes of the Pratylenchus are an important pest parasitizing a wide range of vascular plants, including several economically important crops. However, morphological diagnosis of more than 100 species is problematic due to the low number of diagnostic features, high morphological plasticity, and incomplete taxonomic descriptions. In order to employ bar-coding-based diagnostics, we analyzed the most important species of Pratylenchus based on COI sequences. In this study, we reconstructed the species delimitation of the Penetrans group using mitochondrial gene sequences. A combination of different methods for species delimitation allowed us to establish the species boundaries within the Pratylenchus group and, as such, clarify long-standing controversies about the taxonomic status of Pratylenchus. Therefore, in 2024, a study was undertaken at the University of Limpopo to compare species delimitation analyses within the Pratylenchus genus based on the cytochrome c oxidase I (COI) region. In this study, Assemble Species by Automatic Partitioning (ASAP) and Automatic Barcode Gap Discovery (ABGD) species delimitation approaches were employed. A total of 73 sequences GenBank were utilized, representing 13 species (Pratylenchus sp., P. zeae, P. parazeae, P. vulnus, P. scribneri, P. brachyurus, P. speijeri, P. coffeae, P. loosi, P. horti, P. hippeastri, P. penetrans, P. neglectus, and P. thornei). The phylogenetic analyses grouped all the species into 14 clades, which separated all species clearly. The ASAP and ABGD analysis reveal a remarkable amount of cryptic biodiversity within the genus Pratylenchus, confirming that identification based on COI marker alone can be inconclusive in this taxonomically confusing genus. The phylogenetic tree supported these analyses. In conclusion, our analyses indicate COI to be a good barcode gene, as all Operational Taxonomic Units (OTUs) do not only form monophyletic groupings in the COI phylogeny.