Studies on Thickening of Mother Tubers in Directly Planted Sweet Potato by Cutting Piece of Seed Tubers

Abstract

This experiment was carried out to find out that the thickening ratio of mother tubers was influenced by several conditions in cutting piece of seed tubers. The results obtained were as follows; (1) The correlation between the weight of mother tubers and the weight of fresh tubers was negative about some varieties. (2) The thickening ratio difference for the seed tubers weight was not so much, even if seed tubers were divided between 8 and 16, but the difference of the thickening ratio for the yield was remarkable, and the smaller of cutting piece, the lower thickening ratio of mother tubers for the yield. (3) The seed tubers was chosen in the three weight grades such as large, medium and small, and they were divided into 8 parts, respectivlp. The small seed tubers thickened most in the harvest time. In case of the same weight of cutting piece of their three weight grades tubers, the thickening ratio of the small tuber was larger, too. And the head and tail part showed a tendency to thicken more than the center part. (4) The thickening ratio of mother tubers varied according to the difference of characters of seed tubers. Namely, in case of cutting piece of seed tubers, the young seed tubers caused high thickening ratio of mother tubers. On the other hand, old tubers caused low. Here, the former was produced in late transplanting of sprouts in previous year, and the latter in early transplanting. (5) Physiological changes in mother tubers from planting time to early thickening period were studied. The activity of some enzyme of thickening tubers increased in early stage, and then the starch accumulated gradually, but they decreased in the non-thickening tubers.