2007 Volume 76 Issue 3 Pages 230-236
The effect of seed tuber (ST) weight on the development of main shoots, aerial tubers (bulbils, AT), new tubers (below ground, NT), and flowering spikes (inflorescences) was examined in Japanese yam plants (Dioscorea japonica) grown under different photoperiods and with plant growth regulators (PGRs). Within the same PGR and ST-weight group, the main shoot lengths of plants grown under a 24-h photoperiod (constant light, LD) were found to be longer than those grown under an 8-h photoperiod (SD) in all seasons. Furthermore, within the same photoperiod and ST-weight group, except for the plants grown from 25 g of ST (25gST plants) under SD conditions, the main shoot lengths of control and gibberellic acid (GA3)-treated plants were found to be longer than those of uniconazole-P (Uni)-treated plants. These tendencies were stronger in the 50gST plants than in the 25gST plants. In the 25gST plants, the final fresh weight (FW) of NT and the combined FW of AT and NT were greater in plants grown under LD conditions (LD plants) than those of SD plants; however, this was not observed in the case of the 50gST plants. This is because AT and NT development commenced earlier in the 25gST plants than in the 50gST plants. Furthermore, in the case of the 25gST-LD plants, the control plants also produced a few AT. Hence, we could confirm that the yield of NT was slightly increased by the inhibition of AT in the GA3-treated plants. The 25gST or 50gST-SD plants had only one peak of spike development from June through July, whereas the 25gST or 50gST-LD plants had two peaks of spike development, that is, in June and July and then again from September through October. In the season (June to July) of early spike development, the number of spikes per LD plant was greater than that in the SD plants, and the total number of spikes per plant was inhibited by GA3 treatment. These tendencies were stronger in the 50gST plants than in the 25gST plants.