Yoshida - 1981 - Fundamentals of Rice Crop Science

GROWTH AND DEVELOPMENT OF THE RICE PLANT 51
1.43. Vestiges of degenerated organs on an adult panicle and their degenerating
processes (Matsushima 1970).
fundamental difference between japonica and indica rices and since temperature
regimes during panicle development are similar in both the tropics and temperate
regions, the developmental stages described in Table 1.13 also apply to tropical
rices.
When a young panicle has grown about 1 mm long. it can be seen with the naked
eye or through a magnifying glass. Agronomists often refer to this stage as panicle
initiation for nitrogen topdressing. The duration from panicle initiation to heading
is about 23–25 days in both temperate and tropical regions.
1.9.3. How to determine the developmental stages of a growing panicle
For a precise study of the stages of panicle development, samples are sectioned and
examined under a microscope. The technique requires specialized knowledge and
skill. The following methods, however, provide simple means by which the
developmental stages can be identified (Matsushima 1970).
a. Leaf number index. When the number of leaves to be developed on the main
culm is constant, the leaf number can be taken as a measure of the plant’s
physiological age. This applies to photoperiod-insensitive varieties and to crops of
the same rice variety grown under the same environmental conditions.
Since different varieties may have different total numbers of leaves on the main
culm. the leaf number per se cannot be used as a reliable measure of the physiological
age of plants of all varieties. The leaf number index corrects for such variation:
Leaf number index =
number of leaves developed by a particulare time
total number of leaves to be developed
x 100 (1.14)