THE EFFECTS OF GIBBERELLIN CONCENTRATION, TREATMENT INTERVAL AND COMMENCEMENT TIMING ON THE DEVELOPMENT OF TUBERS AND INFLORESCENCES IN CHINESE YAM (DIOSCOREA OPPOSITIFOLIA L.) 'ICHOIMO' PLANT

The effects of gibberellic acid (GA₃) concentration, treatment interval, and treatment commencement timing on the development of the main vegetative shoots, aerial and new tubers, and inflorescences (spikes) were investigated in Chinese yam (Dioscorea oppositifolia L.) ‘Ichoimo’. Foliar applications of 25, 50, 100, and 200 mg L^-1 of GA₃ (GA₃ 25, GA₃ 50, GA₃ 100, and GA₃ 200) was carried out at 1-week intervals after shoot emergence, and the subsequent foliar applications of GA₃ (100 mg L^-1) were carried out at 1-, 2-, and 4-week (GA₃ E1W, GA₃ E2W, and GA₃ E4W) intervals after shoot emergence. The last foliar application of GA₃ (100 mg L^-1) was carried out at 1, 2, 4, and 8 weeks (GA₃ A1W, GA₃ A2W, GA₃ A4W, and GA₃ A8W) after emergence. Following the above applications, the final fresh weight of the aerial tubers was observed to be higher in the control plants than in both the GA₃ 25- to GA₃ 200- and GA₃ E1W- to GA₃ E4W-treated plants. However, the GA₃ 25- to GA₃ 100- and GA₃ E1W- to GA₃ E4W-treated plants produced new tubers with the highest final fresh weight. Similarly, aerial tubers with the highest final fresh weight were harvested from the control plants. These were followed by the GA₃ A8W-treated plants; the GA₃ A1W- to GA₃ A4W-treated plants produced aerial tubers with the lowest final fresh weight. However, the GA₃ A1W- to GA₃ A4W-treated plants produced new tubers with the highest final fresh weight. The ratio of the development of spikes in every GA₃-treated plant was slightly lower than that in the control plants.