Morphological, SSR and ploidy analysis of water yam (Dioscorea alata L.) accessions for utilization of aerial tubers as planting materials

The high cost and supply shortage of seed yam propagules for planting are major constraints in yam production. In the water yam (Dioscorea alata L.), aerial tubers have potential as alternative sources of planting material. In this study, we investigated morphological, molecular and ploidy variation across multiple aerial tuber producing accessions of Dioscorea alata. Initial screening of over 800 accessions from the International Institute of Tropical Agriculture germplasm collection for aerial tuber production identified a subset (15 %) of accessions, which produced aerial tubers. The aerial tuber producing accessions (along with 18 non-aerial tuber accessions) were further characterized for phenotypic and ploidy variation. In addition, using SSR markers we characterized the genetic diversity amongst all of the aerial tuber producing accessions, along with six non-aerial tuber producing accessions. Multiple Correspondence Analysis (MCA) using morphological data grouped the accessions according to their aerial tuber production. The aerial tuber production characteristics of accessions were associated with phenotypic variables and ploidy levels. The MCA analysis revealed three main groups consisting of; Group 1) all non aerial tuber producing accessions (n = 15), hastate leaf shape, less or no anthocyanin pigmentation and diploid (2n = 2x = 40), Group 2) group with some aerial tuber producing accessions, different extent of anthocyanin pigmentation, sagittate leaf shape, mainly diploid (n = 44) and three triploid (2n = 3x = 60) and 3) a group where all individuals bear aerial tuber, cordate leaf shape, intermediate anthocyanin pigmentation and majority (n = 74) tetraploid (2n = 4x = 80) and three triploid individuals. Aerial tuber production may be subject to a genome dosage effect as an increase in aerial tuber production was associated with increased ploidy level. For instance, tetraploid plants produce more aerial tubers per sprout than either triploids or diploids. Principal coordinate analysis based on SSR markers using Jaccard’s coefficient also revealed distinct groups associated with the pattern of aerial tuber formation, leaf shape and anthocyanin pigmentation. Overall our study indicates the usefulness of combining SSR markers, ploidy level and phenotypic data for identification and classification of Dioscorea alata accessions according to their extent of aerial tuber production.