Tuber formation and development of Dioscorea cayenensis-D. rotundata complex in vitro. Effect of polyamines.

Tuberisation was obtained in vitro on yam (Dioscorea cayenensis-D.rotundata complex). The effect of exogenous polyamines on tuber formation and development (length and weight of microtubers) were investigated and discussed in relation with changes in endogenous polyamines. Application of exogenous polyamines, inhibitors of their metabolism and polyamines precursors in various concentrations positively affected microtuber formation by yam nodal cuttings and their further development. In control conditions, three weeks are needed to obtain 100% of tuberisation. With low concentrations of putrescine (10 5 or 10 6 M), tuber formation occurred earlier. Polyamine endogenous level and metabolism can be significantly affected by exogenous polyamines but modifications of endogenous free polyamines could not be directly correlated to the tuber formation process. Increases in endogenous putrescine and auxins were observed in tubers showing a better development in the presence of putrescine. These results can be used for optimising in vitro conditions for mass production of larger microtubers of the Dioscorea cayenensis-D. rotundata complex