Interactive effects between photoperiod and seed tuber weight on the development of flowering spikes and tubers in Chinese yams (Dioscorea opposita) cv. Ichoimo

Interaction between photoperiod and seed tuber weight on the development of the main shoot, spikes, and new tubers in Chinese yam (Dioscorea opposita Thunb. cv. Ichoimo) plants were investigated. Growth of the main shoot was promoted by a 24-hr photoperiod (continuous li ght) in combination :vith a large seed tuber weight, but inhibited by an 8- hr photoperiod in combination with a small seed tuber weight. Cessation of shoot elongation was advanced by the short photoperiod in combination with light seed tubers. Flowering spikes were initiated on plants with seed tube r weighing 25 g or more under both 8- and 24-hr photoperiods. The proportio n of plants developing spikes increased with tubers weighing in excess of 2 5 g. The node positon of the first spike was shorter under the 8-hr photope riod than that under the 24-hr photoperiod. The date of flower bud emergenc e under the 8- hr photoperiod was earlier than that in the 24-hr photoperio d. The large tubers produced more spikes under a 24-hr photoperiod than wit h an 8- hr photoperiod. Early development of aerial and new tubers was prom oted by an 8-hr photoperiod when the tubers weighed between 10 and 50 g, bu t they were inhibited under both 8- and 24-hr photoperiods if the tuber wei ghed 100g. The large final fresh weights of aerial and new tubers under the 24-hr photoperiod is attributed to the extensive shoot growth. However, dr y weight ratios of total tubers to leaves were high in plants derived from small seed tubers under 8- and 24-hr photoperiods. These results indicate t hat the early development of aerial and new tubers is promoted by a small s eed tuber weight.