Effects of gibberellin on the development of aerial tubers in node culture of Chinese yam (Dioscorea oppositifolia 'Nagaimo')

The effects of gibberellin A₃ (GA₃) treatment on the development of aerial tubers (ATs) on single nodes of Chinese yam (Dioscorea oppositifolia 'Nagaimo') cultured in medium with varying concentrations of sucrose medium (SM) were investigated in order to clarify the mechanism by which GA₃ treatment inhibits AT development in Chinese yam. Stem cuttings for single-node culture were taken from shoots treated with GA₃ (100 ppm) weekly for 2 weeks (GA EW2W) or just before culture (GA JBC). After 10 days of single-node culture, ATs had developed from axillary buds on the stem cuttings. At the same SM concentration, control and GA JBC nodes produced the highest total number of leaves, followed by GA EW2W nodes. The control stem nodes produced the highest number of ATs, followed by GA JBC and then GA EW2W nodes. The number of ATs produced by GA EW2W nodes increased with increasing SM concentration. ATs produced by control and GA EW2W nodes had the highest fresh weight at the same SM concentration. The average ATs produced by GA EW2W nodes had the highest fresh weight, whereas the corresponding values for the control and GA JBC nodes were low at the same level. With control and GA JBC treatments, ATs developed from both the axillary buds on the stem cuttings and from lateral shoots arising from the stem cuttings. Fewer ATs developed from the axillary buds on the lateral shoots of GA EW2W nodes owing to poor lateral shoot growth. Therefore, we conclude that AT which has been growing was not inhibited (or promoted) by GA₃ treatment, but AT was inhibited by the differentiation of axillary buds, from which ATs develop, was inhibited by GA₃ treatment.