Anatomical observation on release of tuber dormancy in water yam (Dioscorea alata L.)

The effects of gibberellin (GA) and a gibberellin inhibitor were investigated on bud growth of two water yam (Dioscorea alata L.) varities. The tubers were harvested after plants senescenced and were subsequently treated with GA and the gibberellin inhibitor uniconazole-P (UP). Tuber dormancy was radically prolonged by GA, but not influenced by UP. The bud germination was observed 90 days after harvesting in both varieties. However, the differentiated shoot meristem was found under microscope observation on top of tuber (corm) at harvesting. It was thought that the shoot meristem development started before harvesting. The observed dormancy period of 90 days was not actual dormancy period, and the true plant dormancy released before or with plant senescence. GA treatment after plant senescence inhibited the shoot meristem development.   Key words: Dioscorea alata, dormancy, gibberellin, shoot meristem development, yams.