Possible Residual Effects of Gibberellic Acid and Gibberellin Biosynthesis Inhibitors on Sprouting, Early Bulbil Formation and Tuber Yield in Chinese Yam

The residual effect of gibberellic acid (GA) and plant growth retardants [mepiquat chloride (MC) and trinexapac-ethyl (TNE)], on Chinese yam plants was examined. Bulbil formation in MC and TNE-treated tubers was earlier than that of the control and GA treatment. Bulbils in GA-treated tubers increased the ratio of bulbil size (>4 mm) compared with the control. The highest GA treatment was fivefold more increased than that of the control. Bulbil yield per hectare was significantly increased by the elevated GA application compared with the control. The more MC concentration was elevated the more the ratio of bulbil size (>4 mm) increased. Bulbil yield was highest in the MC concentration (400 p.p.m.). The more TNE concentration was elevated the more the ratio of bulbil size (>4 mm) increased. Similar to MC treatment, TNE treatment showed the effect of bulbil enlargement in all the concentrations. This suggests that MC is the most effective growth retardant to induce bulbil enlargement and formation, and to increase bulbil and tuber yield in Chinese yams.