Effects of the Shading and Rachis-Branch Clipping on the Grain-Filling Process of Rice Cultivar Differing in the Grain Size

Abstract

Using 6 rice cultivars, this study elucidated the responses of the grain-filling process (increasing process of grain weight) to the treatments of shading and rachis-branch clipping, particularly in the cultivars having different grain size. In this study, the grain-filling process was represented by the following 3 parameters, the rate and the duration of grain-filling and the final grain weight, based on the linear-plateau model. In all cultivars, the grain-filling process was affected by the clipping treatment being increased in therate and decreased in the duration. The decreasing effect on the duration was more slight in the large grained cultivars, BG 1 and Arborio Jl, than the other cultivars with smaller grain size. Thus, the large grained cultivars showed an increase in the final grain weight more significantly than the others. The shading treatment decreased the final grain weight in all cultivars. The decrease in the grain weight was attributed to both or either the decreased rate and duration of the grain-filling process depending on the cultivar. In the cultivars with smaller grain size, the effect of shading on the final grain weight was more intensified in the grains on secondary branches and/or proximal part of a panicle. On the other hand, in the large grained cultivars the final grain weight in every grain position was decreased with a similar intensity. These results strongly suggest that the grain-filling process of the large grained cultivars showed different responses to the excess and limited assimilates compared with that of the cultivars with smaller grain size. This study also indicated a contrast in the grain-filling process between early and late heading cultivars through the analysis on the year-difference of this process. © 1986, CROP SCIENCE SOCIETY OF JAPAN. All rights reserved.