Studies on application of growth substances to increase yield in sweet potatoes. II

Abstract

(1) In the previous report, the authors had proved that the number of sweet potato tubers per sprout were certainly increased by soaking the sprout in synthetic growth substance (pota-ssium α-naphthaleneacetate). The study reported here were successively carried out in 1945-47. (2) The growth hormone was significantly effective on increasing tuber numbers on the various sprouts, except on very small and tender ones, and these were especially remarkable for the hard ones. On the sprout having small leaf area, the effect was also observed. (3) In every case, the hormones-like effect (tuber increasing effect), can be observed by water soaking treatment, and because these effects were distinguished from those of hor-mone by shortening the time of the treatment, it seems that these were due to quick root deve-looment, by absorbing water. (4) The effect of the growth hormone treatment on increasing tuber numbers was also observed on the comparatively dried or high nitrogen level fields, but were not especially remarkable as compared with ordinary ones. (5) When the growth hormone or the watersoaking treatment was effective on increasing the tuber numbers, the length of the tuber necks were shortened and this fact was especially remarkable under the dry condition of the field. This fact seems to denote that by hormone or water treatments, root tuber formation was smoothly occured and cork formation of root tissues were delayed. (6) Why the numbers of the tuber were increased by hormone treatment? We consi-dered the following reasons, A. Acceleration of root formation. B. To increase the number of roots. C. Cork formation of root tissues were delayed. Above facts show from nutritional condition of sprout that the nutrient of sprout (stored and elaborated) might be translocated to roots predominantly. (7) The effect of the treated solution on the root numbers in the early stage of the tuber growth was tested with the seven varieties. The results show that 0.002% solution was most effective for four varieties, 0.005% was for two, 0.0005% was for one. (8) Effects of the hormone treatment on the tuber yield, were almost insigni fi cant, so we can not discuss statistically and it seems that the growth hormone treatment did not necessarily cause increasing of the root tuber yield.