Abstract
The effects of irrigation at the early growth period on the thickening and shape of the tuberous roots in sweet potato were examined. The number and length of the tuberous roots were determined by 70 days after the planting(70 DAP). There was high positive correlation between the length and width of the tuberous roots, which indicated that the rate of lateral growth was higher in the long tuberous roots than in the short ones. The rate was higher in the irrigated plot than in the non-irrigated plot. Width/length ratio of the tuberous roots, which were diversed at the early growth period, tended to converge as the growth progressed. At the final growth period, it was larger in the irrigated plot than in the non-irrigated. The number of spindle-type and long spindle-type tuberous roots occupied 35% and 65%, respectively, of the total number at 70 DAP. At the final growth period, however, most of the tuberous roots were of the spindle-type in the irrigated plot, although many of them were still of the long spindle-type in the non-irrigated plot. These results indicate that the irrigation at the early growth period greatly affects the shape of the tuberous roots.
