Growth of tuberous root as affected by the ambient humidity in sweetpotato (Ipomoea batatas Lam.)

摘要

In solution culture os sweetpotato (Ipomoea batatas Lam.), tuberous root can grow in the air. Then the tuberous root growth was analyzed to examine the effect of air humidity around the tuberous root. Sweetpotato (cv. Koganesengan) was planted in the hydroponic system, and the tuberous root was kept in the air space separated from the shoot and the fibrous root environments. The tuberous root was grown under 50, 70 or 90 percent RH, and the volume change was measured on-line. Quantitative analysis of water balance in the growing tuberous root was also carried out for each humidity. Volume increments of the tuberous root during four days were about 0.6 cm-3 at 50 percent RH, 1.5 cm-3 at 70 percent RH and 0.2 cm-3 at 90 percent RH, indicating that the tuberous root growth was enhanced most at 70 percent RH and depressed most at 90 percent RH. Diurnal pattern of the growth rate revealed that the humidity effect was brought during the nighttime. At 50 percent RH, water influx into the tuberous root through vascular bundle was almost similar to that at 70 percent RH, whereas the largest evaporative water loss depressed the water accumulation for growth. On the other hand, the smallest water influx into the tuberous root was found at 90 percent RH, which resulted in the smallest water accumulation in spite of the least evaporative water loss. Responses of the tuberous root to step changes in the ambient humidity suggested that 90 percent RH induced quick and strong inhibition on the growth.