Tuber formation and growth of Dioscorea cayenensis-D. rotundata complex. Interactions between exogenous and endogenous jasmonic acid and polyamines

Tubers can be initiated and developed in vitro from nodal cuttings of yam (Dioscorea cayenensis - D. rotundata complex). The effect of exogenous jasmonic acid, alone or in combination with putrescine, on these processes was investigated in relationship to endogenous jasmonic acid and polyamine levels.
Application of exogenous jasmonic acid at various concentrations positively affected microtuber formation and growth from yam nodal cuttings. In control conditions, three weeks were needed to obtain 100% of tuberisation. Jasmonic acid at low level (0.1 µM) accelerated tuber formation (46% after one week) as did putrescine (10 µM). But endogenous levels of jasmonic acid were not significantly affected by its exogenous presence in the medium. Jasmonic acid also interacted with other growth regulators as polyamines, but the decrease in time necessary to observe tuber formation could not be correlated with endogenous modifications of PUT content.
The presence of jasmonic acid (0.1 to 1 µM) as PUT (1 µM) induced also an increase of tuber length and weight. The combination of jasmonic acid (0.1 µM) and putrescine (1 µM) had no positive effect on tuber formation (precocity) but had an additive effect on further growth (length and weight).
In the future, these results could help the optimising in vitro conditions for mass production of larger yam microtubers.