Analysis of Factors Determining Grain Weight by Investigating Husk Size and Grain Growth according to the Position within the Panicle in Rice

Abstract

Field experiments using five rice varieties in a cold region, and those combining two rice varieties, three fertilization methods and two transplanting times in a warm region were conducted. Grains were classified into superior grain, medium grain and inferior grain according to the position within the panicle. Husk size, grain weight at 20 days after heading (early grain weight), and grain weight at maturity (grain weight) and their differences (late grain weight) were measured. Husk size clearly differed depending on variety and slightly differed depending on fertilization method, year and transplanting time. In most cases, the husk size was larger in the order of superior grain, medium grain and inferior grain. Grain growth differed depending on variety, fertilization method, year and transplanting time. In all cases, the early grain weight was larger in the order of superior grain, medium grain and inferior grain, and the late grain weight tended to be larger in medium and inferior grains than in superior grain. Grain weight was inferred to be determined by husk size in the superior and medium grains, although it seemed suppressed by insufficient grain growth in the inferior grain. The early grain weight of superior grain tended to be large in the extra-large grain variety ‘Bekoaoba’. On the contrary, the late grain weight of every grain was large in the slightly large grain variety ‘Niji-no-kirameki’.