Varietal Characterisation and Taxonomic Evaluation of Sweet Potato (Ipomoea batatas) Using Macro- and Micromorphological Evidence

Taxonomic audit was carried out on three varieties of sweet potato (Ipomoea batata) in north central part of Nigeria. Ten (10) tubers of the representative samples of three varieties of sweet potato (Purple, Yellow and White varieties) were collected from different locations within the north central part of Nigeria and planted in the research farm of the University of Agriculture, Makurdi, Nigeria. At full maturity, they were characterized using gross macro- and micromorphological features. Mean values of all quantitative parameters were computed for each variety. Qualitative and quantitative data generated were analysed by using SPSS software 20.0 version. Box plots and charts were constructed to reveal level of variations at a glance. Dendrogram was generated using furthest neighbor method to reveal the phylogenetic relationships among the varieties. Statistical test of significance was performed on major variable characters. From the results, the three varieties varied significantly in their epidermal characters such as stomatal types, stomatal indices and number of epidermal cells. Stomata types were tetracytic, anisocytic, and paracytic in all but the Purple variety had an additional stomatal type (anomocytic). Macroscopically, variation was observed with respect to some qualitative characters (leaf apices, leaf shape, leaf margins, leaf bases, leaf colour, stem colour and root colour) and quantitative characters (leaf sizes, petiole length, stem diameter, root sizes and plant height) at significant levels (p < 0.05). As a result, dendrogram classified the three varieties where the yellow and purple types were widely divergent as two separate species under the Genus Ipomoea. The white type could be seen as a variety of the yellow type based on their close relationship. The synergistic information obtained from both morphological and anatomical sources of evidence in this report has yielded a reliable result that may call for appropriate nomenclatural assignments. Hence, the authors suggest the following nomenclatures: Ipomea batatas var makurdi (Yellow variety); Ipomoea batatas var lafia (White variety) and Ipomoea aguoru (Purple variety).