Interactive Effects of Photoperiods and Plant Growth Regulators on the Development of Tubers and Flowering Spikes in Chinese Yam (Dioscorea opposita) cv. Nagaimo.

Abstract

The interaction between an 8- and 24-hr photoperiods and plant growth regulators (PGR) [gibberellin A3 100ppm (GA) and uniconazole-P 25ppm (Uni)] on the development of the main shoots, aerial and new tubers, and spikes (inflorescences) in Chinese yam (Dioscorea opposita Thunb. cv. Nagaimo) plants was examined. The GA-treated plants yielded main shoots that were the same size as the shoots in the untreated (control) plants. However, the Uni-treated plants yielded shoots that were much shorter than those in the control plants. The GA treatment, irrespective of the photoperiod, severely inhibited the formation of aerial tubers, but significantly promoted the growth of new tubers compared with the control plants. The GA treatment in combination with the 24-hr photoperiod (constant light, LD) increased new tubers growth. The Uni treatment suppressed the development of new tubers, as compared with those in the control and GA-treated plants. Within the same treatments, the total fresh weight of the aerial and new tubers in the control and PGR-treated plants grown under the 8-hr photoperiod (SD) and harvested early were heavier than those grown under LD, but by final harvest in December, those tubers grown under LD were equally heavy as those exposed to SD. A small percentage of plants grown under both photoperiods developed spikes, especially when treated with GA. The interactive effects of the photoperiods and PGR on the nodal position of the first spike and on the number of spikes per plant were inconclusive.