Abstract
A new method of root-system analysis was designed based on root diameter. Using this method the formation of the root system in the rice cultivar, Hinohikari, was examined and the root system of 40 cultivars at the full heading stage compared. The morphology of the root system was visualized and analyzed based on the pipe model theory. Next, a distribution chart of the root volume was drawn for each the root-diameter classes based on the ideal pipe theory, and the "mean root-diameter index" which is the root diameter at the distribution peak of the root volume was calculated. In the distribution chart of root volume, the groups of thick and fine roots were distinguishable with a boundary at about 0.4 mm. Then, the "fine root ratio", which is the ratio of the volume of fine roots to that of all roots, the "thick root index", which is the root diameter at the peak of root-volume distribution in the thick root group, and the "fine root index" which is the root diameter at the root-volume distribution peak of the fine root group, were calculated. The results clearly showed a pattern of increase with the increase in root volume of rice and clarified the atructure of the root system based on root thickness and root volume. The root system was classified into two groups, the thick root group mainly consisting of crown roots and the fine root group mainly consisting of lateral roots. Each group had a peculiar distribution peak of root volume, and the two groups were distinguished from each other more clearly after the panicle formation stage. The "mean root-diameter index", "thick root index", "fine root index" and "fine root ratio" were suggested to be good indicators of growth of the root system and of varietal difference in morphology of the root system.
