The growth duration of the rice plant is 3-6 months, depending on
the variety and the environment under which it is grown.
During this time, rice completes two distinct growth phases:
Vegetative
Reproductive.
The vegetative phase is subdivided into
Germination
Early seedling growth and
Tillering
The reproductive phase is subdivided into
Stem elongation
Panicle initiation
Panicle development
Flowering
Milk grain
Dough grain and
Mature grain stage.
A 120-day variety, when planted in a tropical environment, spends
about 60 days in the vegetative phase, 30 days in the reproductive phase,
and 30 days in the ripening phase.
The vegetative phase is characterized by active tillering, gradual
increase in plant height, and leaf emergence at regular intervals.
Tillers that do not bear panicles are called ineffective tillers.
The number of ineffective tillers is a closely examined trait in plant
breeding since it is undesirable in irrigated varieties, but is sometimes
an advantage in rainfed lowland varieties where productive tillers or
panicles may be lost due to unfavorable conditions.
The stages under Vegetative phase includes:
Seedling stage
From sowing to transplanting stage, root formation and leaf formation
takes place.
Active vegetative stage
Growth to maximum tiller number. During this phase tiller number,
height and straw weight increases.
The duration of this phase is primarily a function of the amount
of nitrogen available to maintain the nitrogen content in the plant
above the critical load.
Tillering is closely related to nitrogen content in the plant, especially
soluble nitrogen in the culture.
The critical nitrogen content of the culm is said to be about 7 %.
Vegetative lag phase:
From maximum tiller number stage to panicle irritation
stage. The tiller number decreases, increase in height and straw weight
continues but less rapidly than before.
Varietal characteristics and climatic conditions, especially
day length and temperature, determine the duration from sowing to panicle
initation.
If total growth duration is short the reproduction phase
and the active vegetative phase overload.
The reproductive growth phase is characterized by culm elongation
(which increases plant height), decline in tiller number, emergence
of the the last leaf, booting, heading, and flowering of the spikelets.
Panicle initiation is the stage about 25 days before heading when
the panicle has grown to about 1 mm long and can be recognized visually
or under magnification following stem dissection.
Spikelet anthesis (or flowering) begins with panicle exertion (heading),
or on the following day. Consequently, heading is considered a synonym
for anthesis in rice.
It takes 10-14 days for a rice crop to complete heading because there
is variation in panicle exertion among tillers of the same plant and
among plants in the same field.
Agronomically, heading is usually defined as the time when 50% of
the panicles have emerged.
Anthesis normally occurs between 1000 and 1300 h in tropical environments
and fertilization is completed within 6 h.
Only very few spikelets have anthesis in the afternoon, usually when
the temperature is low.
Within the same panicle it takes 7-10 days for all the spikelets to
complete anthesis; the spikelets themselves complete anthesis with 5
days.
Ripening follows fertilization, and may be subdivided into milky,
dough, yellow-ripe, and maturity stages.
These terms are primarily based on the texture and color of the growing
grains.
The length of ripening varies among varieties from about 15 to 40
days.
The grain yield of rice is determined by the following four components
Growth
