Yoshida - 1981 - Fundamentals of Rice Crop Science

GROWTH AND DEVELOPMENT OF THE RICE PLANT 31
1.28. Synchronous growth of a tiller, a leaf, and roots of a rice plant (adapted from Fujii 1974).
After germination, one radicle emerges and elongates to a maximum length of
about 15 cm; it functions until the seventh-leaf stage. Mesocotyl roots emerge from
the axis between the node of the coleoptile and the base of the radicle. Mesocotyl
roots develop only under such conditions as deep seeding or when the seed is
treated with chemicals.
The rice root system is basically composed of nodal roots. Each node usually
develops about 5–25 roots. When the development of root, leaf, and tiller is
examined, it is more convenient to regard an internode rather than a node as a unit
(Fig. 1.30). A leaf and thin roots emerge from the upper region of the internode
whereas a tiller and thick roots develop from the internode’s lower region. Roots
developing directly from the culm’s nodal regions are called primary roots. The
diameter of the primary roots ranges from 0.5 mm to greater than 1 mm. As
growth advances, the primary roots develop branched secondary roots, which in turn
develop tertiary roots, and so on. Under lowland conditions, rice is known to
develop sixth-order branched roots. The root diameter becomes successively