Molecular Characterisation and Phylogenetic Relationships of Dioscorea Species in South East Nigeria Using ITS and matK Gene Sequences

The taxonomic boundaries and phylogenetic relationships among wild and cultivated Dioscorea species in South East Nigeria remain controversial, with morphological characters alone proving insufficient for reliable species delimitation, and molecular approaches are needed to resolve these ambiguities. This study characterised and determined phylogenetic relationships among 11 Dioscorea taxa collected from Imo, Enugu, Anambra, Ebonyi, and Abia States using nuclear ribosomal internal transcribed spacer (ITS) and chloroplast matK gene sequences. Leaf tissue was sampled from 5 individuals per taxon, DNA was extracted using the CTAB method, and target regions were amplified by polymerase chain reaction, sequenced bidirectionally, and edited using Geneious software. Multiple sequence alignments were performed using MAFFT. Phylogenetic analyses employed maximum likelihood (RAXML) and Bayesian inference (MrBayes) with appropriate substitution models selected by jModelTest. The maximum likelihood and Bayesian inference trees were largely congruent. Results confirmed that Dioscorea cayenensis and Dioscorea rotundata formed a supported species complex rather than distinct species, consistent with their interspecific hybridisation history. Dioscorea alata formed a strongly supported clade with all cultivated samples, while Dioscorea bulbifera sequences were monophyletic and distinct. Three wild accessions showed sequences intermediate between named species, suggesting potential hybrid origin. The ITS region provided greater phylogenetic resolution than matK for this group. The study provides molecular evidence for a revised taxonomic treatment of South East Nigerian Dioscorea and recommends formal molecular taxonomy revision for the genus in Nigeria.

Keywords: Dioscorea, molecular phylogenetics, ITS, matK, South East Nigeria