Combination effects of temperature and photoperiod on the development of flowering spikes and tubers in Chinese yams (Dioscorea opposita cv. Ichoimo)

Combination effects of 17/12 degrees C, 24/19 degrees C, 30/25 degrees C an d 35/30 degrees C and constant light vs 8-hr photoperiod on the development of flowering spikes and tubers in Chinese yams (Dioscorea opposita Thunb. cv. Ichoimo) were investigated. 1. Growth of the main shoot was promoted excessively by constant light in c ombination with 24/19 degrees C and 30/25 degrees C (day/night), but signif icantly inhibited by an 8-hr photoperiod at the same temperatures. Critical high temperature for shoot growth under constant light lies between 30/25 degrees C and 35/30 degrees C. Shoot growth ceased in all treatments except for 17/12 degrees C and 8-hr photoperiod. Shoot dieback occurred about 80 days after shoot elongation ceased. 2. Flowering spikes were initiated only on plants grown under 8-hr photoper iod at 35/30 degrees C,30/25 degrees C and 24/19 degrees C. At 30/25 degree s C, 5 out of 8 plants developed spikes, whereas at 24/19 degrees C and 35/ 30 degrees C, only 3 out of 8 plants did. 3. Early development of aerial and new tubers was similarly promoted by sho rt days under all temperatures treatments. The highest yield of tubers was attained in the 8-hr photoperiod with 24/19 degrees C; yield was moderate u nder 8-hr photoperiod in combination with 30/25 degrees C and 35/30 degrees C, and the lowest at 8-hr photoperiod and 17/12 degrees C. At the onset of shoot dieback, the highest yields of aerial and new tubers occurred under an 8-hr photoperiod and 30/25 degrees C and 24/19 degrees C as well as unde r constant light and 24/19 degrees C. These data indicate that the development of aerial and new tubers was promo ted under short days in combination with a moderate temperature, although t heir final weight was heaviest under constant light and 24/19 degrees C.