1993 Volume 62 Issue 3 Pages 359-362
Growth direction of primary roots is a quite important factor determining distribution of a rice root system. Our group has developed and improved a method for estimating the growth direction of each primary root. We do not have, however, any method to evaluate the spatial distribution of primary roots of a root system and to compare different root systems. In this paper, the root system model was proposed on the assumption that primary roots of the model elongate uniformly in any direction. A consideration of the model showed that (1) the frequency distribution of primary roots with reference to their growth angle θ (to the horizon) was cosθ, (2) the average growth angle of all primary roots was around 32.7°, and (3) the number of primary roots with growth angle of 0-30°was the same as those with 30-90°. The root systems of rice cultivars Musashikogane and IR50 were examined using the model. Both of the root systems were a little sparse in horizontal-oblique direction and a little dense in oblique-vertical direction. A more detailed analysis showed the varietal difference : root system of Musashikogane was deeper than that of IR50. These data indicated the effectiveness of the model as a standard to evaluate root systems.
