Abstract
The number and diameter of the crown roots of American cultivar M401 growing at various angles were measured.The number of crown roots growing at an angle between 36° and 54° to horizontal was higher than that of the crown roots growing at 0–36° and 54–90°. Pruning of crown roots growing at an angle between 0° and 54° to horizontal greatly reduced the pushing resistance and that between 0° and 36° also reduced the resistance, though less than that between 0° and 54°. Pruning of crown roots growing at 54–90°, however, did not reduce the resistance significantly. The effect of pruning of the crown roots growing at 0–36° and between 0–54° were examined in the six cultivars with different root lodging resistance. The pushing resistance was markedly decreased by pruning the crown roots growing at 0–36° in low root lodging–resistant cultivars. However, in high root lodging–resistant cultivars, the pushing resistance was not influenced by pruning of the crown roots growing at 0–36°, and markedly reduced by pruning the roots growing at 0–54°. Thus, it is considered that the crown roots growing at an angle between 36° and 54° to horizontal greatly contribute to support the rice shoot in highroot lodging–resistant cultivers.
