Yam (Dioscorea spp.) is an important food and cash crop in the Guinea-Sudan zone of Benin. The genetic diversity of about 70 cultivars of Dioscorea cayenensis/Dioscorea rotundata (Guinea yam) andabout 20 cultivars of Dioscorea alata (water yam) was analysed using random amplified polymorphic DNA (RAPD). The amplified bands revealed high polymorphism. These polymorphic DNA fragmentswere used to construct dendrograms, clustering all accessions into 18 groups: 12 for D. cayenensis/D. rotundata and six for D. alata. The analysis of molecular variance revealed highly significant variationamong species, among groups within species, and among cultivars within groups. The study showed that the genetic diversity changed along a spatial gradient. In general, there was a tendency that mostof the varieties from the north-east and north-west of the zone investigated appeared to be distinctive from the ones of the centre. However, few varieties were distributed randomly and did not reflect anyspecific relation to their zone of collection. The current study suggests that the Guinea-Sudan zone of Benin has a large gene pool of yam varieties. Yam farmers may have played a significant role in theenrichment and the maintenance of the genetic diversity of yam
