In vitro induction of minitubers in yam (<Emphasis Type="Italic">Dioscorea cayenensis</Emphasis>- <Emphasis Type="Italic">D. rotundata</Emphasis> complex)

Two methods were used to produce yam minitubers from two different yam cultivars (cv. Krengle and cv. Kponan) using in vitro culture techniques. Method 1: Yam microtubers were first initiated in vitro and then transplanted to soil to generate plants from which minitubers were produced. Yam plants were obtained either by directly planting the microtubers to soil, or by inducing the germination of the microtubers using various chemical and physical treatments, before their transfer to soil. Method 2: Yam plantlets were first produced in vitro and then transplanted to soil for further development and tuber production. In both methods, the presence of jasmonic acid (JA) in the culture medium was found to be essential for yam tuberization, as well as for the germination of yam microtubers. In vitro production of yam microtubers was variety dependant. Compared to cv. Krengle, cv. Kponan responded better to microtuberization, and 2.5 μM JA was the optimum concentration resulting in 70 and 90% explants producing microtubers in the MS medium and the Tuberization medium (T-medium), respectively. Germination of the microtubers required treatment of JA at concentrations ranging from 1.0 to 2.5 μM. The overall length of the process to produce minitubers from microtubers took 32 weeks. In contrast, minitubers were obtained within 20 weeks when plantlets were directly transferred to soil. In this case, plantlets were first grown for 8 weeks on medium containing JA (0.1–1.0 μM) and 8% sucrose to initiate plant growth and rooting.