Reduction of grain yield in rice shaded during the early grain fillingperiod is not the result of inhibition of potential grain dry-matterincrease [Japanese]

摘要

A shortage of carbon assimilate supply to rice grain during the first ten days after heading (DAY(0-10)) has been considered to reduce the potential grain dry-matter increase(Delta GP). It was, however, uncertain whether assimilate supply after the shading period was sufficient to support Delta GP when the reduction of grain dry-matter increase (DeltaG) was observed. Our objective was to demonstrate that DeltaG after the shading treatments was reduced not through the decrease in Delta GP but through a lack of assimilate supply, based on our model analysis. In our model, DeltaG is determined by assimilate supply (current dry-matter production (DeltaW) plus reserved assimilate in straw (SP)) and the DeltaG has an upper limitation defined by Delta GP. In this study Delta GP was estimated under a sufficient supply of assimilates which were provided by periodical thinning of the plants. By the shading during DAY(0-10), DeltaG as well as DeltaW were reduced even after the end of the shading treatment. Observed DeltaW and SP at the heading were input to the model to calculate DeltaG and straw dry-matter increase (DeltaS). The calculated dry weight of the grain and straw coincided closely with the actual observed data. We herewith suggest that the grain dry-matter increase by shading during DAY(0-10) was not suppressed by inevitable reduction of Delta GP but rather by a lack of assimilate supply during the active DeltaG period.