Morphogenesis of the Tuberization of Two Varieties of Yam (D. cayenensis-rotundata): Attempt to Understand the Precocity of Var. Kponan

Yams exhibit variations in dormancy break, which could be responsible for the early maturity of certain varieties. The present study aimed to understand the origin of the early maturity of the Kponan yam variety. This was studied through morphological observation of tuberization during the first month and monitoring until tuber maturity. Two varieties, Kangba and Kponan, belonging to the species Dioscorea cayenensis-rotundata, were used. An experimental field was set up in 20 cm x 20 cm nursery bags. For monitoring purposes, the mass and length of the tuber were determined. Early emergence was sometimes observed 10 days ± 1 after planting. Most emergence ranged from 22 days ± 2 to 35 days ± 5 for the Kponan variety. For the Kangba variety, seeds without buds on the day of planting showed emergence 34 days ± 3 to 45 days ± 2 after being placed in bags. Early emergence was observed at 27 days in two plants. From the date of emergence in the field, the first visible sign of tuberization in the Kponan variety appears between 48 ± 4 and 57 ± 3 days. For Kangba, this period ranges from 48 ± 2 days to 71 ± 4 days after emergence in the field. The earliness of the Kponan variety is due to the dual earliness of field emergence and tuber initiation. The Kponan yam tuber is morphologically shorter and has a larger diameter than the Kangba tuber, which would explain, on the one hand, the higher position of the Kangba variety on the length growth curve and, on the other hand, the higher mass of the Kponan variety tubers.