Abstract
Twenty typical Indica and Japonica rice varieties were tested for resistance to root lodging using a push-pull gauge for two years. Pushing resistance varied from 0.56 N to 2.57 N among the 20 varieties. Kanto PL12 was selected as a lodging-resistant variety, M401 as a moderately resistant variety, and Kinuhikari as a sensitive variety. The growth angle of the crown roots of the three varieties was measured as 10 days after heading, and we found that the number of roots growing in a shallower direction (0∼18°) was highest in Kanto PL12, followed by M401 and Kinuhikari. Next, the growth angle of crown roots in the 20 varieties was measured by basket-method. We divided the growth angle of crown roots, from 0° (horizontal) to 90° (vertical) at 23 days after sowing, into five equal ranges and found that the lodging-resistant varieties had many crown roots growing at an angle between 36° and 54°. We also found that lodging resistance was highly correlated with the pulling strength of the crown roots of the seedlings. Thus, it is concidered that the lodging-resistance of varieties can be evaluated by the number of crown roots growing at an angle between 36° and 54° or pulling strength of the thick roots of the seedlings.
