Studies on Matter Production of Rape Plants : VII. Dependence of seed yield on sink capacity and matter supply from the source in individual pods

Abstract

Dependence of seed yield on sink capacity and matter supply from the source was examined in individual pods of rape plants (Brassica napus L., cv. Norin No. 16) grown in a field. The effects of matter supply from the source were examined grading light intensity by shading treatments in the ripening period. The effects of sink capacity were analyzed based on the individual variation of seed number that occurred naturaly in a pod. Seed yield and sink capacity were expressed as those based on unit surface area of pod and termed "relative seed yield" and "relative sink capacity" respectively. Aspects of variation in relative sink capacity in the "pod layer" were also examined. The results obtained are summarized as follows: 1. Under natural light (no shading), relative seed yield increased linearly with relative sink capacity, suggesting that seed yield was determined by sink capacity of pod. Under lower light intensities (72% and 44% of natural light), relative seed yield increased with relative sink capacity only in the case where the latter was small. Above a critical point, the increase in relative sink capacity did not result in an increase of relative seed yield any more, showing that seed yield was determined by matter supply from the source in this situation. The critical point of the relative sink capacity lowered with decreasing light intensity (Fig. 1). 2. Relative seed yield increased with light intensity, the rate of increment was larger at the larger relative sink capacity (Fig. 2). 3. Since pods located at higher levels of the pod layer are exposed to strong light, it is desirable that the relative sink capacities of those pods are large. However, the acutual vertical distribution of relative sink capacity in a pod layer wes just the opposite to this (Figs. 3 and 4). 4. There was a fairly close positive correlation between percentage of seed-setting and relative sink capacity. Thus, improving seed-setting in pods at higher levels of the pod layer was considered to be effective for increasing seed yield (Fig. 5).