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Rice
Growth Stages of the Rice Plant

Mississippi's commercial rice production has increased from 300 acres in 1948 to about 200,000 acres in 1987. This publication discusses major plant development and growth stages of the rice plant.

In some places under favorable soil and temperature conditions, rice plants may grow for several years, but in the United States, they are grown as annuals. A native of the tropics, rice is best adapted to an aquatic habitat with high temperatures and humidity. Two growth stages are distinguished in rice plant development -- vegetative and reproductive.

Vegetative Stage

Germination, emergence, seedling establishment, and tillering occur in the vegetative period. This period ends when the internodes begin to elongate.

The main vegetative parts of a rice plant include the fibrous roots, stems, and leaves. The leaves of the rice plant are flat. A mature leaf has a sheath at its base that surrounds the culm (stem); the blade, which rests at an angle with the sheath; the ligule; and the auricles. The joint for the blade and sheath is often called the "collar."

Like all grasses, the growing part of the plant is at the soil line. Seed that germinate on the surface of the soil (Figure A), such as in water-seeded rice, will not develop a mesocotyl. Seed that germinate below the surface of the soil (Figure B), for example drill seed rice, will have a mesocotyl. Tillering commonly starts within 3 weeks after emergence and continues for about 3 weeks.

Figure A

Figure B

Reproductive Stage

The reproductive stage is when the nodes (solid joints) and internodes (hollow areas between nodes) develop. These make up the culm (stem) in jointing stage. The number of nodes per culm ranges from 13 to 16 and is related to the length of growing season. Normally, only four internodes elongate. The upper internode is usually the longest and bears the head, called the "panicle."

Plant Description

The rice plant has four principle parts: a fibrous root system, culm (stem), leaves, and panicle (head). The roots, culm, and leaves make up the vegetative part of the plant. The floral part consists of the panicle, spikelets, and flower.

Roots

Shortly after seed germination, the fibrous root system of the rice plant begins to develop both outward and downward from the plant's base. Finely-branched adventitious roots arise from the lower nodes of the stem (culm). The size and length of the roots vary. Drained conditions are best for good root development that is proportionate to top growth. Maximum root development is reached at the peak of the tillering stage, then begins to decrease, and toward the fruiting stage, almost ceases.

Culm (Stem)

The culm is the jointed rice stem that develops from the plumule (primary bud of the seed embryo) and is composed of solid centers and hollow internodes. Culm height varies according to management practices and varieties. Current United States varieties range from 30 to 46 inches high. The length of the growing season determines how many nodes the culm will develop (usually 13-16). Usually the top internode is the longest and bears the head.

Leaves

The mature leaf has four main parts: the sheath, blade, ligule, and auricles. The leaf varies in length, form, and tightness, and covers the stem. These mature leaves are flat and vary in length and width according to variety and production practices. The collar is the junction of sheath and blade. The swollen zone at the sheath base where it joins the culm is the pulvinus.

Just before or at about the same time the reproductive stage begins, jointing may begin. At this time, the stem elongates, and nodes, internodes, and panicles develop and are differentiated.

Panicle (Head)

Panicle formation starts when all nodes have been formed and internodes begin to elongate. Usually panicles form 3 to 4 weeks before they are noticeable in the field. It takes about 25 to 33 days from internode elongation until the panicle emerges from the plant.

The panicle is fairly dense and drooping in most varieties. The following is an illustration of a typical panicle with the different parts named.

Spikelets

One flower makes up the spikelet, which consists of a rachilla (a small axis) bearing a single floret.

Flower

The flower includes all the components and parts enclosed by the lemma and palea (hulls).

Parts of a spikelet

Flowering starts the first day the panicle emerges (usually 25-33 days from internode elongation). Flowering begins at the tip of the panicle and moves progressively downward to the panicle base. Depending on weather and variety, flowering normally lasts from 6 to 10 days. Flowering usually occurs from mid-morning to shortly after noon. Rice is normally self-pollinated, with pollen being shed just before or at the time flowers open. Flowering is delayed or stopped during cloudy, rainy, or cool weather.

The period from first heading when 10 to 20 percent of the panicles have emerged from the boot until maturity is usually 30 to 40 days. Table 1 below explains the development period for varieties commonly grown in Mississippi.

Rice Kernel Development

The rice kernel reaches its maximum length in 12 days, its maximum width in 2 days, its maximum thickness in 28 days, and its dry weight in 35 days after flowering. Before and during kernel growth, several factors may influence its development. In some cases, the hulls and kernel will be distorted, whereas in others, only the kernel is affected. The affected kernels may be throughout the panicle or only on a specific portion of the panicle.

Several factors that influence kernel development are listed below:

  1. Straighthead disease
  2. Injury from cold water.
  3. Low tempertures (below 58 °F) during flowering period (causes poor fertilization and kernel development).
  4. Rainy, cloudy or windy days during flowering period (causes poor pollination and kernel development).
  5. Nutrient deficiency during kernel development stage.
  6. High temperatures (above 95 °F) accompanied by hot, dry winds during kernel development (causes sun-checked kernels).
  7. Certain diseases (Sheath blight, stem rot, blast, and others indirectly influence kernel development, whereas brown leaf spot and kernel smut, which attack florets, directly influence development.)
  8. Mechanical damage by blackbirds or chewing insects.
  9. Insects such as stink bugs and armyworms.
    10.

Table 1. Average number of days from emergence for different rice growth stages
Variety Internode Elongation 50% Heading Maturity
(Days from Emergence)
Cypress 52 84 122
Drew 55 84 124
Kaybonnet 53 82 116
Jackson 52 80 116
Jefferson 50 75 107
Lemont 55 88 121
Litton 57 84 125
Priscilla 53 81 120

By Dr. Ted Miller, Extension Agronomist (Retired) and Joe E. Street, Rice Specialist

Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status.

Publication 1624
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director

Copyright by Mississippi State University. All rights reserved.

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