Yoshida - 1981 - Fundamentals of Rice Crop Science

GROWTH AND DEVELOPMENT OF THE RICE PLANT 11
when the tip of a seedling emerges from the soil or water surface and, thus,
includes both germination and postgermination growth. Seedling emergence is an
appropriate term for the very beginning of rice growth in the field.
1.3.2. Counting the leaves
The age of a rice plant is conventionally expressed in calendar days after germination
or seeding. This is convenient for a particular variety under a particular
environment. The calendar day, however, cannot be used when comparing growth
under different temperature and water regimes because the rate of leaf development,
hence, physiological age, is very much affected by environment. Even for
the same location and variety, variable weather conditions affect the rate of
seedling growth.
Counting leaves on the main culm is the best way to provide a physiologically
meaningful age for the rice plant. At germination, the coleoptile emerges and
grows about 1 cm. after which the first leaf begins to emerge. The first leaf appears
to lack a leaf blade and grows about 2 cm long. The second leaf has a welldeveloped
leaf blade and starts to emerge before the first leaf has completed
elongation. The third leaf and succeeding leaves emerge after each preceding leaf
has fully elongated (Fig. 1.9). Because the first leaf appears to lack a leaf blade, it
is sometimes called a prophyll or incomplete leaf. Following this terminology, the
second leaf is counted as the first. Hence, special attention must be paid to the
1.9. Counting leaf number of the rice plant.