Relationships between the characters of hull, brown rice and paddy grain of different specific gravity among different cultivars

By categorizing the water selected ripened paddy grains into groups with di fferent specific gravity, we observed several characteristics of the paddy grain and brown rice in four cultivars. It was found that the grains of cul tivars with heavier grain were intensively distributed in higher specific g ravity, whereas those of cultivar with lighter grain were sparsely distribu ted around lower specific gravity. The coefficient of variation (CV) of the character in brown rice was always higher than that of the respective char acter in paddy grain. These results suggested that after the size of the hu ll was determined at flowering, the brown rice still had a wider variation. The brown rice volume was primarily determined by its thickness, and the i nfluences of its length and width varied among cultivars. With the increase s of brown rice volume, all characters of the paddy grain volume, the speci fic gravity of paddy grain, the paddy grain weight, and the brown rice-padd y grain ratio increased. These were found to be consistent in the four cult ivars. The hull weight and the paddy grain weight showed positive correlati on in two cultivars, but not in the others. It was concluded that the speci fic gravity closely related with the paddy grain weight, which was mainly d etermined by its brown rice volume. The brown rice volume was primarily sub ject to its thickness. The hull's role in regulating the growth of brown ri ce might be different among cultivars.