Influence of shading treatment on the growth of leaf and root, and sugar accumulation in sugar beet varieties

Abstract

In order to evaluate the influence of light intensity on the growth of leaf and root in sugar beet varieties, six varieties grown in the field were subjected to shading treatment by cheesecloth at three growing stages (early, middle, and late) as shown in Fig. 1. The results obtained were as follows : 1) The shading at early and middle growing stages brought about the increase in length of leaf, blade and petiole, but the decrease in blade width. These facts suggested that the shading caused the elongation of leaf, which was quite similar to the phenomenon as was often the case with the dense planting. 2) Since root length expressed the length of the noticeable thickened part of the tap root, the larger root length was regarded as the prosperous thickening growth of the lower part of root. The root diameter in individual beet representing the largest diameter of a root will be the yardstick of the thickening growth of the upper part of root. The shading treatments at early and middle growing stages suppressed the thickening growth of the whole root, and the influences of shading were more conspicuous at the lower part of root. However, the interruption of the treatments promoted the thickening growth of this part, and consequently at the end of season the root shape of the treated plant did not show any marked difference as compared with the control. 3) The shading treatment at the early growing stage caused the suppression of the increase in weight of root and leaf, and especially root weight decreased remarkably. After the interruption of the shading, leaf weight was promptly recovered at middle growing stage and it became larger than that of control. These inclinations were marked in varieties such as AJ 4 and Tsukisappu (errect plant type). The shading at middle growing stage caused the increase in leaf weight, but the differences of the increase due to the plant types were not oflserved. 4) The yield type varieties in which leaf weight showed the marked increase by the shading treatment had the lower sugar content at the end of season than that of control. 5) The shading at the late growing stage caused the decrease in sugar content. But the influences on the sugar type varieties (Hon-Iku No. 401 and AJ 4) were not so conspicuous. 6) It was pointed out that the residual effects of the shading such as over-luxuriant growth of leaf and the decline in photosynthetic capacity in shade leaf produced by shading hindered the growth of root.