Yoshida - 1981 - Fundamentals of Rice Crop Science

GROWTH AND DEVELOPMENT OF THE RICE PLANT 33
1.31. Cross section of a matured rice
root (adapted from Hoshikawa 1975).
One characteristic of rice roots is the presence of large air spaces in mature roots
(Fig. 1.3 1). These air spaces are connected with those in the culms and leaves,
providing an efficient air passage system from shoot to root.
Root age can be visually classified into different groups based on formation of
rootlets, as shown in Table 1.8 (Inada 1967). Young roots without rootlets are
normally milky white in color. As age advances, a larger portion of a root near the
base successively turns yellow, pale brown, brown, and dark brown in color. The
tip portion of a growing root, however, usually remains milky white.
1.7.2. Root-shoot relationships
Weight growth of the root is closely related to weight growth of the whole plant.
This relationship is called allometry or relative growth.
Root dry weight is related to total dry weight of the plant by the following
formula:
W R = H W T
h , (1.4)
Table 1.8. Visual classification of rice roots. a
Grouping Rootlet Av Age of
formation (%) length (cm) roots (days)
I
II
III
IV
Rootlet: none 5– 7 < 3
Rootlet: ca. 50% 10–20 3–7
Rootlet: ca. 80% 15–30 7–14
Rootlet: over 90% > 30 >14
a
Adapted from lnada (1967).