Morphological and Molecular Characterization of Cultivated Dioscorea l. (Dioscoreaceae) from Selected Counties in Kenya
MetadataShow full item record
Yam (Dioscorea species) is one of the underutilized and neglected tuber crops in the country. Earlier studies indicated the need for further research to establish the phylogeny of Kenyan yams through molecular methods. This study aimed to characterise Dioscorea spp. using morphological and molecular methods. Twenty-four specimens from five growing areas; Meru, Embu, Taita-Taveta, Busia and Bungoma counties were collected directly from farmer’s fields. Herbarium voucher specimens were collected and deposited at the Kenyatta University Herbarium. Morphological data were recorded in the field using characters stated in the IPGRI’s descriptor of Yams. The collected Dioscorea spp. specimens were identified into; D. minutiflora Engl., D. alata L., D. bulbifera L. and D. cayenensis Lam by twining direction, flesh colour, tuber shape, presence and absence of wings, presence and absence of spines and flowering or non-flowering. Spine density was significant in characterising D. minutiflora Engl. which had spines on the stem bases. D. alata L. was distinguished based on its four-angled stem and petioles that were all purplish-green with a purple base, elongate tuber shape and white tuber flesh colour. Dioscorea cayenensis Lam. was distinguished based on its yellow tuber flesh colour and cylindrical tuber shape. All the other species twined to the right in an anticlockwise direction except D. bulbifera L. which twined to the left in a clockwise direction and produced aerial tubers that were irregular in shape. Based on cluster analysis, all 24 specimens were grouped into three clusters. Cluster 1 had D. minutiflora Engl. Cluster 2 contained three sub-cluster groups of D. alata L., D. bulbifera L. and D. cayenensis Lam. Cluster 3 grouped a few D. minutiflora Engl. Principal Component Analysis showed the correlation between the different morphological characters, and most of the correlation was between PC-1 and PC-2. The distribution of species based on PC-1 and PC-2 showed the distantly related species in each quarter; D. alata L. (1st quarter), D. bulbifera L. (2nd quarter), D. cayenensis Lam. (3rd quarter) and D. minutiflora Engl. (4th quarter). Seventeen leaf specimens were selected for DNA extraction and observation made using rbcL marker. The genotypes were grouped to two main clusters. Dioscorea minutiflora Engl. and D. burkilliana J. Miege clustered together as one genetic group. However not all D. minutiflora Engl. species were in one specific cluster hence showing that there may be variation within the species. Dioscorea alata L. and D. bulbifera were seen to be potentially related. Generally, the rbcL marker demonstrated the phylogeny of Kenyan Dioscorea spp. Comparison of morphological and molecular data analysis gave similar results. The phylogenetic relationships of Kenyan Dioscorea spp. was established and morphological and molecular characterisation was efficient in establishing species relatedness among Dioscorea spp. Further study can be done with an emphasis on the use of more than one molecular marker.