Abstract
An attempt was made to clarify the relationship between the formation and growth of tubers and the photosynthetic rate during the early growth stage in sweet potato by using the grafts of several cultivars differing in sink potential. The tuber formation largely depended on the characteristics of stock cultivar. Both of the stock and scion effects on tuber thickening were observed at the stage after its formation. A positive correlation with tuber dry weight was found in the dry weight of petioles, leaf blades or leaf area, and a negative one was observed in the ratio of number of dead leaves to total leaves. There was no relation between the photosynthetic rate and the root dry weight at the stage before tuber formation. However the photosynthetic rate in a scion correlated with tuber dry weight at the stage after the tuber dry weight amounted to about 10g/plant. Thus the results suggested that the tuber becomes dominant sink of assimilate and the source activity was influenced by tuber sink activity quantitatively after this stage.
