• 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 and
• 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 it 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 initiation 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 initiation.
• 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 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 as 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:

1. 1. Number of panicles/m2
2. 2. Number of grains / panicle
3. 3. Percentage of ripened grains.
4. 4. 1000 gm weight.