Yoshida - 1981 - Fundamentals of Rice Crop Science

1 .1. OUTLINE OF THE LIFE HISTORY
The rice plant usually takes 3–6 months from germination to maturity, depending
on the variety and the environment under which it is grown. During this period,
rice completes basically two distinct sequential growth stages: vegetative and
reproductive. The reproductive stage is subdivided into preheading and postheading
periods. The latter is better known as the ripening period. Yield capacity, or the
potential size of crop yield, is primarily determined during preheading. Ultimate
yield, which is based on the amount of starch that fills spikelets, is largely
determined during postheading. Hence, agronomically, it is convenient to
regard the life history of rice in terms of three growth stages: vegetative, reproductive,
and ripening. The vegetative stage refers to a period from germination to the
initiation of panicle primordia; the reproductive stage, from panicle primordia
initiation to heading; and the ripening period, from heading to maturity (Fig. 1.1).
A 120-day variety, when planted in a tropical environment, spends about 60 days
in the vegetative stage, 30 days in the reproductive stage, and 30 days in the
ripening period.
The vegetative stage is characterized by active tillering, gradual increase in
plant height, and leaf emergence at regular intervals. All contribute to increasing
the leaf area that receives sunlight. Tillering may start when the main culm
develops the 5th or 6th leaf. Active tillering refers to a stage when tillering rate —