Effects of photoperiod and temperature on the development of spikes and new tubers in Chinese yam (Dioscorea opposita Thunb. cv. Ichoimo)

The effects of photoperiod, air temperature, and root zone temperature (RZT ) on the development of spikes and new tubers in Chinese yam (Dioscorea opp osita Thunb. cv. Ichoimo) were investigated. The development of the main shoot and spikes was promoted by both 16-hr and 24-hr photoperiods, 24/19 degrees C: and 30/25 degrees C (day/night), and an RZT of 25 degrees C. Shoot and spikes development was severely inhibited by an 8-hr photoperiod, 17/12 degrees C, and an RZT of 10 degrees C. These data indicate that the development of main shoot and spikes is promoted by the long-day photoperiods, 24/19 degrees C and 30/25 degrees C, and the 25 degrees C RZT. Under these environmental conditions, spikes emerged relati vely early. Development of new tubers was significantly promoted by an 8-hr photoperiod , 24/19 degrees C, and the 25 degrees C RZT. Moderate development occured a t 30/25 degrees C, and the 17 degrees C RZT. In contrast, new tubers were s everely inhibited by both 16-hr and 24-hr photoperiods, and 10 degrees C RZ T.