Abstract
By categorizing the water selected ripened paddy grains into groups with different specific gravity, we observed several characteristics of the paddy grain and brown rice in four cultivars. It was found that the grains of cultivars with heavier grain were intensively distributed in higher specific gravity, whereas those of cultivar with lighter grain were sparsely distributed around lower specific gravity. The coefficient of variation (CV) of the character in brown rice was always higher than that of the respective character in paddy grain. These results suggested that after the size of the hull was determined at flowering, the brown rice still had a wider variation. The brown rice volume was primarily determined by its thickness, and the influences of its length and width varied among cultivars. With the increases of brown rice volume, all characters of the paddy grain volume, the specific gravity of paddy grain, the paddy grain weight, and the brown rice-paddy grain ratio increased. These were found to be consistent in the four cultivars. The hull weight and the paddy grain weight showed positive correlation in two cultivars, but not in the others. It was concluded that the specific gravity closely related with the paddy grain weight, which was mainly determined by its brown rice volume. The brown rice volume was primarily subject to its thickness. The hull's role in regulating the growth of brown rice might be different among cultivars.
