Cotton Fiber Development & Maturation

Cotton Plant Development

A summary of the growth & development of a cotton plant—from seed germination to maturation.

Cotton plant development occurs in a very specific sequence of events. The stages of reproductive growth and cotton plant development must be optimized to ensure ideal fiber production. Developing a better understanding of the biological mechanisms of cotton plant growth and development is essential for the continued profitability of the cotton industry.

Each growth stage is critical for abundant fiber development. Individual seeds contain the embryonic plant for the next generation and after the seed goes through the fertilization process, cotton plant growth, fiber development, and maturation begin.

The five cotton plant growth stages include germination and emergence, seedling establishment, leaf area canopy development, flowering and boll development, and maturation.

The first three steps in fiber development—initiation, elongation, and secondary wall synthesis—take place while the fiber is living, and they’re controlled by the biological processes that regulate cell growth and development.

Cotton Plant & Fiber Development Stages

• Germination & emergence
• Seedling establishment
• Leaf area canopy development
• Flowering and boll development
• Maturation

Cotton Fiber Development & Processing E-book

Download the full e-book to get a detailed explanation of each stage or get an overview of the plant and fiber development stages below.

Cotton Fiber Development and Processing E-book

Seasonal Patterns of Plant Development

Although cotton is naturally a perennial plant, modern agricultural processes require that the crop be managed as an annual—re-planted and harvested each year to produce the largest and highest-quality yields possible. This combination of a perennial growth pattern and agricultural management as an annual results in tremendous variability in boll maturity at the time of harvest. Cotton plant development proceeds through five main growth stages: germination and emergence, seedling establishment, leaf area canopy development, flowering, and boll development, and maturation.

The cotton seed contains a seed coat surrounding an embryo with two well-developed cotyledons. The embryo axis contains radicle, hypocotyl, two cotyledons, and poorly developed epicotyl.

Germination begins within the first few hours after moisture enters the seed. The result is increased oxygen uptake and the utilization of stored energy reserves to build new cells and tissues during embryonic growth. The seed/embryo swells as water is absorbed, and causes the seed coat to split. Under the most favorable conditions for germination, the radicle emerges through the pointed micropylar end of the seed in two to three days and the radicle becomes the primary root that grows downward into the soil.

After emergence and initial exposure to light, the cotyledons develop chlorophyll and develop the capability to synthesize food via photosynthesis.

The tissues between the radicle and cotyledons (i.e. the hypocotyl) grow rapidly and arch near the cotyledons. As the hypocotyl continues to elongate, the cotyledons and embryonic shoot are pulled up through the soil surface to complete “emergence.” During this process, the seed coat is typically shed and left behind in the soil.

When the cotyledons are free of the soil, they unfold and expand. After emergence and initial exposure to light, the cotyledons develop chlorophyll and develop the capability to synthesize food via photosynthesis.

Root Development

Much of the early development of the cotton plant is focused on growing a substantial root system to absorb nutrients and water from the surrounding environment and transport those materials to the above-ground portions of the plant.

The primary root, or taproot, penetrates the soil rapidly and may reach a depth of up to 10 inches or more by the time the cotyledons unfold. And depending on conditions, cotton plant root development may proceed at a rate of .5-2 inches per day. Because the above-ground portion grows less rapidly, the roots can often reach three times deeper into the ground than the plant itself.

Numerous lateral roots spread outward from the taproot, forming a mat of roots extending several feet down and out into the ground. The largest portion of the root system is located within three feet of the soil surface and root length density can vary considerably depending on soil and plant conditions. The total root length continues to increase as the plant develops and doesn’t decline until the maximum plant height is reached and fruit begins to form.

Shoot Development

The cotton plant has a main stem that consists of a series of nodes (points of leaf and bud development) and internodes (length of stem between nodes). The main stem is erect and supports a spiral arrangement of leaves and branches that develop from a node in a location immediately above where the leaf joins to the main stem. The two types of branches that are produced include vegetative and fruiting.

• Vegetative branches are structurally similar to the main stem and normally arise from the main stem near the ground. The number of vegetative branches produced depends primarily on the environment and plant spacing.
• Fruiting branches develop from buds on the main stem or from vegetative branches and are defined by the presence of floral buds, flowers, and fruit. Once fruiting begins, fruiting branches tend to be produced at each successive main-stem node.

Leaf Growth

Leaf growth is relatively slow at first compared to root growth and the average life span of a leaf is about 70 days. The three main types of leaves produced are cotyledons, prophylls, and true leaves. The first true leaves formed on the cotton seedling are usually heart-shaped, whereas subsequent leaves are lobed.

Cotton leaves generally have a thick waxy outer covering for protection and grow to about four to six inches wide. The epidermal and glandular hairs can be found on the surface of the leaf. The waxy layer contains numerous small pores (stomates) for the entry of carbon dioxide to support photosynthesis and allow water vapor to escape. Total leaf area development continues to increase, reaching approximately three to four square yards of leaf per square yard of the soil surface in a mature crop.

Main types of leaves:

1. Cotyledons
2. Prophylls
3. True leaves

The first true leaves formed on the cotton seedling are usually heart-shaped, whereas subsequent leaves are lobed.

Reproductive Development

Due to its indeterminate growth habit, the cotton plant continues both vegetative and reproductive development throughout the remainder of the season. Reproductive growth begins with the formation of the floral buds in the apical part of the plant, giving rise to the flowers and subsequent bolls. As long as the cotton plant is growing, flowers are being produced.

Cotton is genetically programmed to produce seed for sexual production and each seed contains the embryonic plant for the next generation, composed of cotyledons, a root, a stem, and leaves.

Square Development

Buds appear first as small, green, triangular structures. The term “squares” refers to this initial bud development. The first squares are usually visible about five weeks after planting and flower approximately three weeks later.

Flower Development

Pollination & Fertilization

Seed & Boll Development

As the ovule matures into the seed, the stored nutrients are transferred from the endosperm to the developing cotyledons of the embryo. After fertilization, seeds attain their full size within approximately three weeks but do not reach maturity until the boll opens. Fertilization and fiber production are linked processes—fertilization is required for optimum fiber growth and development on the plant. While unfertilized ovules do develop fibers, the extent of development is severely limited. The boll grows rapidly after fertilization with the most growth taking place between 7 and 18 days. Full size is reached in up to 25 days. Approximately 50 days of development is required for the boll to reach full maturation but this varies based on genotype and environmental conditions.

While unfertilized ovules do develop fibers, the extent of development is severely limited.

3-Step Cotton Developmental Sequence

Step 1: Fiber Initiation

Fiber development begins just as the plant prepares to flower. As the ovule grows, immature epidermal cells of the future seed coat divide to accommodate the increase in the volume of the ovule. Non-fiber epidermal cells divide and expand in a manner to increase the surface area of the seed. At this point, something happens that nobody has been able to explain—some epidermal cells dramatically change their pattern of growth to become fiber cells. Surface cells destined to become fibers stop dividing and dramatically change their growth direction, producing extremely long, single cells that extend perpendicularly above the surface of the ovule.

During this phase, the cotton fiber produces a thin, flexible cell wall. This wall is capable of growing as the cell volume increases. The primary cell wall is similar in structure to the primary cell walls of most other expanding plant cells. The wall is coated with a waxy cuticle and is composed of a gel-like matrix of polysaccharides in which relatively rigid cellulose microfibrils are embedded. The patterns of cellulose microfibrils in the wall control the direction of cell expansion and the ultimate morphology of the fiber.

As the fiber grows, new components are inserted into the cell wall and membrane and because this new material is deposited throughout the length of the fiber, this type of cell expansion is called diffuse growth.

The transition from primary to secondary wall production is marked by the deposition of a thin layer of wall material called the winding layer, which is distinguished from the primary and secondary wall layers by the microfibrils found within. When compared to other secondary wall layers, the microfibrils of the winding layer are somewhat larger in diameter and are oriented with an opposite helical gyre.

Lots of environmental factors affect this stage in the development process. For example, daily temperature cycling (going from warm days to cool nights) can generate layering in the fiber wall causing a ring-like pattern that is visible when the walls are swollen.

During secondary wall synthesis, cellulose microfibrils are laid down in a helical pattern. Reversals are regions in the fiber where the helically-oriented cellulose microfibrils reverse their gyre. Reversals are regions in the wall where the helical gyre of the secondary wall microfibrils reverses the direction of the production of reversals in the secondary cell wall and this reversal process is unique to cotton fiber.

Learn more about the fertilization, development, and fiber maturation process in our downloadable e-book, Cotton Fiber Development and Processing.

More on Cotton Fiber Science

• Sourcing Cotton: How Fiber Quality Impacts Your End Product
• Natural vs. Synthetic Fibers: Classification, Qualities, & Life Cycle
• Cotton Fiber: Harvesting & Ginning
• Cotton Fiber Qualities & Evaluation
• Cotton Classification