Cytokinins and Tuber Initiation in the Potato Solanum tuberosum L

SEVERAL experiments have implicated the presence of a specific stimulus responsible for the initiation of tuber formation 1 , but there are few reports of the effect of cytokinins on the process 2,3 . Courduroux 2 suggested that the specific tuber forming substance may be related to cytokinins but he did not demonstrate a requirement for cytokinins in tuber induction. The interplay of gibberellins and endogenous growth inhibitors in the regulation of tuber initiation is suggested by the extraction of gibberellin-like substances from plants and stolons in non-inductive conditions 4 . The disappearance of these substances and the appearance of inhibitors during the early stages of tuberization have also been demonstrated 4,5 . It has been claimed that tuber formation is initiated by high concentrations of soluble sugars at the stolon tip 6 , but Lovell and Booth found no correlation between sugar level in stolons and tuberization 7 . Exogenous applications of hormones have been confined mostly to foliar sprays or application of paste to stems. There is very little information on the influence of growth regulators on the stolons themselves. We have now demonstrated a requirement for cytokinins in the tuberization of isolated stolons in vitro .