Cotton

Presented byZUBY GOHAR ANSARI TAM/14/026

Introduction• Cotton- King of fibres• Cotton-white gold, one

of the most important commercial crops of the world.

• Cotton is derived from Arabic word “qutun”.

• Cotton remains the backbone of Indian rural economy especially in dry land areas.

Types of cotton: 4 cultivated species in cotton

Gossypium hirsutum(34% area) new world cotton G .barbadense(<1% area) (n=26)

G .arboreum(15% area) old world cotton G .herbaceum(6% area) (n=13) Hybrids (45%area).

Origin:• arboreum: India• herbaceum: Arabia, Persia• barbadense: South America• hirsutum: Mexico and Gautemela

Area, production and productivity of cotton

Region Area(M ha) Production(M.t) Productivity(t/ha)

World 35 23 650

India 8.87 23.2 444

States in India Maharashtra (2.89) Gujarat (8.9) Gujarat (729)

Gujarat (2.08) Maharashtra (3.6) TN (688)

AP (1.04) AP (3.2) Punjab (641)

Climate:• Warm season (tropical) crop.• Cotton can be profitably grown

in regions with rainfall of 900-1000 mm.

Temperature:• Germination: 32 to 34 0C• Crop growth: 43 to 46 0C• Night temperature: 15 to 20 0C

Altitude:• 1200 to 1500 m Light intensity:• 400 to 500 Cal Cm-2day-1

SOILS:• Cotton is grown in a wide

variety of soils• Grown as rained crop in deep

black soils and medium black soils.

• Grown under irrigation in alluvial soils and other light soils.

• Sensitive to water logging.• Moderately acid tolerant

PH=5.5 to 6.0• Saline tolerant (7.7 ds/m-

salinity threshold).• Ideal depth of soil is 0.6m

Physiology of cottonSeed germinationMobilization of assimilatesPhysiology of vegetative growthPhysiology of reproductive

growth

Botany

• Warm season• Perennial (grown as an

annual though)• Woody shrub• C3• Indeterminate• Dicot with

cotyledonary leaves• Malvaceae family

Botany – Two main groups. - Old World cotton

- diploids (2n) - G. arboreum - G. herbaceum

- New World cotton - allo tetraploids (4n) - G. hirsutum - G. barbadense

Seed germination• The seed is pointed on one end (the

micropyle) and rounded on the other (the chalaza).

• The chalaza is the primary site of water and oxygen absorption during germination.

• The tip of the primary root, or radicle, is the first part of the plant to emerge through the micropyle.

• The cotyledons that will nourish the new seedling with the hypocotyl below them ready to elongate and push the seedling through the soil.

• The gossypol glands visible throughout the inside of the seed are also visible in the tissues of the growing plant.

Germination and Seedling Development• Germination begins as the seed absorbs water and

oxygen through its chalaza after planting. • The water swells the dormant tissues, and cell growth

and division begin to take place. • The radicle emerges through the micropyle, and

grows deeper into the soil, providing a taproot that will supply water and nutrients throughout the life of the plant.

• The hypocotyl elongates from the radicle and forms an arch or crook that begins to push up through the soil, a brief period often referred to as the “crook stage”(c).

Germination and Seedling Development

Seedling emergence normally takes place 4 to 14 days after planting. At the soil surface, the hypocotyl straightens and pulls the folded cotyledons out of the soil (d), a process known as epigeal germination.

After the cotyledons are pulled through the soil surface, they unfold and expose the epicotyl and the apical meristem, or growing point, which will be the source of subsequent growth (Figure e-f).

At this point, germination and seedling emergence are complete and the plant begins its active vegetative growth.

The Cotyledons and First True Leaves The cotyledons (Figure 3) serve a dual

role in germination. Before they unfold, they supply stored

food to the germinating seedling. After the cotyledons unfold, they

produce chlorophyll, become green, and produce energy through photosynthesis.

The apical meristem emerges at the base of the cotyledons and all further vegetative and reproductive growth of the plant occurs through the meristems.

A week or so after seedling establishment, the first true leaf appears above the cotyledons .

The first leaf shifts the plant’s primary energy source from storage to photosynthesis and signals the move from emergence to vegetative growth.

Factors affecting seed and seedling development• SOIL: Cotton emerges the quickest from warm, moist soil.• TEMPARATURE: Low temperatures (below 60 degrees F)

hinder germination by slowing metabolic processes.• LIGHT: High or low temparatures also affect the seed and

seedling germination process. Light pigment -Phytochrome seen in two forms Pr and Pfr forms.

• Other factors: Physical impedance, such as crusting, does not slow germination, but it can prevent the hypocotyl from emerging.

• This often causes thickening of the hypocotyl and a condition referred to as “big shank” or “thicklegged” cotton, resulting in reduced seedling vigor.

• Generally, the longer it takes for emergence to occur, the greater the risk of plant death and yield loss.

Mobilization of seed reserves• During early stages dicot sps obtain nutrients from

endosperm and in later stages assimilates deposited from mother plant.

• This is facilitated by vascular strand which branches from vascular tissue running through pod and passes through funiculus in to integuments.

• Passage of assimilates through the funiculus and from seed coat in to cotyledons by fission aided by transfer cells.

• There is no symplastic connection between seed coat and embryo and the assimilates pass in to apoplast.

• Then they are taken up by embryo and redistributed symplastically and utilized in reserve synthesis.

• Stages of Growth• The developmental phases for cotton can be

divided into five main growth stages: • (1) Germination and emergence• (2) Seedling establishment • (3) Leaf area and canopy development • (4) Flowering and boll development and • (5) Maturation

Growth Stage Days

Planting to Emergence 4 to 9

Emergence to First Square 27 to 38

Square to Flower 20 to 25

Planting to First Flower 60 to 70

Flower to Open Boll 45 to 65

Planting to Harvest Ready 130 to 160

Root development • As the plant grows, the radicle that originally emerged from

the seed becomes a taproot, from which lateral roots begin to form and grow which makes the basal root system.

• Other “higher order” roots then develop from this basal root system which have a functional life of about 3 weeks.

• They form when environmental conditions are good, and then dies when unfavourable conditions prevails.

• As the plant matures, the roots continue to spread and probe deeper in the soil profile for water and nutrients.

• Most of the roots found between 1 and 3 feet deep in the soil, but large quantities of roots can still be found more than 4 feet deep in the soil.

• The amount of roots generally peaks during the cotton flowering phase then declines as the plant partitions more carbohydrates to the developing bolls (Figure b).

Development of root

Root development

Vegetative Growth of cotton• Cotton has an indeterminate growth habit and can

grow very tall under favourable conditions.• Growth regulators, such as mepiquat chloride, are

generally applied to cotton to slow internode elongation, especially for well-fertilized irrigated cotton.

• Otherwise,vigorous cotton varieties with plenty of water and nutrientscan develop very tall, heavy vegetative growth.

• The first vegetative structures that appear on the main stem are main stem leaves are called nodes.

• Leaves that arise directly from the main stem are referred to as main stem leaves, are referred as subtending leaves.

• The fruit produced by a branch will primarily receive carbohydrates produced by the leaf subtending that fruit.

• Fruit produced closer to the main stem will receive more carbohydrates from the main stem leaf than fruit produced at more distal positions.

• A fruiting bud, called a square, begins to form fruiting branch. • As this square develops, the portionof the fruiting branch between the main stem and the square also elongates.

• This portion of the fruiting branch is also called the internode, similar to the portion of the main stem between main-stem nodes.

• The axillary meristem produces a second position square and subtending leaf.

• As many as four squares may be produced in this fashion on a fruiting branch.

Leaf and Canopy Development Initially the carbohydrates produced by the leaves are used to produce roots and more leaves. Once reproductive structures begin to develop, carbohydrate

supplies are slowly shifted to the developing fruit. As the fruit load on the plant increases and ages, the

carbohydrate demand increases, and development of leaves steadily declines.

Therefore, fruit development occurs with a leaf population that is steadily aging. Leaf photosynthesis does not remain constant as the leaf grows and develops. A cotton leaf reaches its maximum photosynthetic capacity at about 20 days of age, after which it declines.

Development of Fruiting and Vegetative Branches

• The branches on a cotton plant can be classified as either vegetative branches (monopodia first 4-6 nodes) or fruiting branches (sympodia 5-7+ nodes).

• Vegetative branches, like the main stem, are referred to as monopodia (meaning “single foot”) since they have only one meristem.

• Because vegetative branches have only one meristem, they grow straight and erect, much like the main stem. Vegetative branches can also produce fruiting branches.

• The branches from which fruiting buds arise are called fruiting branches, or sympodia (meaning “multiple feet”), because each fruiting branch contains multiple meristems.

• Fruiting branches have a “zig-zag” growth habit, as opposed to the straight growth habit of the vegetative branches.

• The “zig-zag” growth habit is a consequence of the stop-and-go growth of the fruiting branch.

• Vegetative branches are produced after fruiting branches, and develop at nodes directly below the node at which the first fruiting branch was developed.

• For instance, if the first fruiting branch is initiated at main-stem node 5, a vegetative branch may develop at main-stem node 4.

• The cotyledons are oriented opposite each other on the stem, but the true leaves and branches of the cotton plant occur in a 3/8th alternate phyllotaxy, meaning the distance from one leaf to the next is 3/8th of a complete turn around the stem.

• Branches on the main stem also show this 3/8th alternate arrangement, since they grow adjacent to the leaves.

• Nodes are numbered in the same order the leaves are numbered where the cotyledonary node is considered node 0.

• New fruiting branches are generally believed to develop approximately every 3 days, although recent studies show that this developmental rate varies.

• Squares are produced at new positions on a fruiting branch approximately every 6 days.

• The age of fruiting structures on a cotton plant can be mapped according to this time sequence.

Formation of the Cotton Bud From Square to Bloom During the 21-day period from square to bloom, there are several

recognized developmental stages of the cotton flower bud. A “pinhead” square is the first stage at which the square can be

identified. The next stage of square growth is “match-head” or “one-third

grown”square. Just prior to the time the flower opens, a candle shape. Period of square development prior to bloom is “squaring.” A cotton plant typically blooms or flowers for about 6 weeks.

The Cotton Flower• First visible structures of square are the leaf-like bracts, or

epicalyx. • Three bracts surround the flower bud in a pyramid-like shape. • The cotton plant produces perfect flowers, meaning the flower

contains both male and female organs.• The first square is typically visible on node 5 to 7 about 35 days

after planting.• Anthesis, or a flower bloom, occurs approximately 21 days after the first square appears.• When a pollen grain reaches the stigma, it germinates into a pollen tube. • The pollen tube grows through the style, the micropyle, and into the ovule chamber, where fertilization takes place.

Stages of Flowering• Flowering is important to cotton production because pollinated flowers form

cotton bolls. • The bloom process takes several days, and bloom age can be estimated by the

bloom characteristics. • On the day a flower opens it is white in color. • Pollination of that flower usually occurs within a few hours after the white flower opens.• On the second day the flower will have a pink-like color, and a red coloron the third day. • Approximately 5 - 7 days after a flower appears it usually dries and falls from the plant exposing the developing boll. • Occasionally a flower will stay attached to the developing boll for a longer period. • This is referred to as a bloom tag.

• A phenomenon often seen in a cotton field is square shedding .

The shedding of squares may be the result of several factors, including water stress, shading, nutrient deficiencies, high temperatures, high plant populations, high percent fruit set and insect damage.

• Inaddition, the reproductive cellsformed during square development are very sensitive to environmental conditions.• High temperatures and humidity, andnutrient deficiencies can inhibit gameteproduction and result in flower sterility and ultimately square loss.

Fruit Shedding

• Sterility may also decrease seeds per boll and locks per boll. • One cause of pollen sterilization and subsequent yield loss is

misapplication of glyphosate in Roundup Ready® cotton.• Flowers and young bolls may also be shed from the plant

due to the same factors that lead to square shedding.• Generally, though, the sensitivity of squares, flowers and

bolls to shedding can be related to their age. Young fruiting forms are more likely to be shed than are more developed squares and bolls.

• Boll Development• After pollination occurs the boll begins to develop. Under optimum

conditions it requires approximately 50 days for a boll to “open”. Boll development can be characterized by three phases:

• Enlargement, Filling, and Maturation.• The enlargement phase is seen for 3 weeks. During this time the fibers

produced on the seed are elongating and the maximum volume of the boll and seeds contained there in are attained.

• Also during this time, the fiber is basically a thin walled tubular structure, similar to a straw. Each fiber develops from a single epidermal cell on the seed coat. During the boll enlargement and fiber elongation phase, the development of the fiber is very sensitive to adverse environmental conditions.

• The filling phase of boll development begins during the fourth week after flowering . At this time, fiber elongation ceases and secondary wall formation of the fiber begins. This process is also known as fiber filling, or deposition.

• Cellulose is deposited inside the elongated fiber for every 24 hours and the deposition of cellulose into the fiber cell is also sensitive to environmental conditions.

• The filling phase of boll development continues into the sixth week after pollination.

• The boll maturation phase begins as the boll reaches its full size and maximum weight.

• During this phase, fiber and seed maturation take place and boll dehiscence occurs.

• The capsule walls of the boll dry, causing the cells adjacent to the dorsal suture to shrink unevenly.

• This shrinking causes the suture between the carpel walls to split, and the boll opens.

Defoliation and Harvest Timing• Defoliants, or harvest aids, are

used to defoliate cotton, enhance boll opening, and control regrowth prior to harvest.

• These chemicals also give the producer some control over harvest timing and increase harvest efficiency.

• Cotton harvest aids can be classified into two modes of action, herbicidal and hormonal.

• Herbicidal harvest aids injure the leaf, stimulating the production of ethylene.

• Hormonal harvest-aids increase the ethylene concentration in the leaves without causing any injury.

Photosynthesis- Source to Sink Relationship• Most of the cotton plant’s carbohydrate energy is

directed to root growth prior to the time reproductive growth begins.

• This is a function of carbohydrate source to sink relationships.

• Carbohydrates are transported from supply areas, called sources, to areas of growth or storage, called sinks.

• The leaves are the primary source of carbohydrate production during the early vegetative growth of cotton.

• Carbohydrates are produced through photosynthesis in the leaves and channeled through the phloem to the roots, which act as the main carbohydrate sinks during this phase.

• The source-to-sink phenomenon also applies to the transport of inorganic nutrients and water.

• The roots are the source for all inorganic nutrients and water, which are transported through the xylem to sinks throughout the plant.

• Thus, root and shoot systems are very interdependent, and damage to either system slows growth and decreases yield.

• As bolls begin to develop, they become much stronger carbohydrate sinks than roots and shoots.

• At this stage, root and shoot growth slow, and boll development dominates plant growth, and the widely established roots continue to supply large quantities of water and nutrients to the shoot.

Physiological analysis of yield• The contribution of a single

fruiting structure to the overall yield of the cotton plant depends largely upon its position on the plant.

• First position bolls are heavier and produced in higher quantities than bolls at any other position.

• First position bolls contribute from 66 to 75 percent of the total yield of the plant, and second position bolls contribute 18 to 21 percent.

• Yield distribution research is an intensive, detailed process that involves counting and weighing bolls from each fruiting position on many plants.

• First position bolls tend to fill out more and be heavier than bolls from other positions, so the majority of boll weight on plants generally comes from the first position fruit between nodes 7 and 20.

LIGHT INTERACTION WITH COTTON LEAVES

• Phytochrome plus the blue light receptors, cryptochromes and phototropins, cause alterations in plant growth and development called photomorphogenesis.

• In addition, UV light can negatively affect cotton photosynthesis and growth when present at a sufficient intensity.

• Both too little light and too much light can have negative effects on cotton growth through effects on photosynthesis.

• Too little light fails to produce photosynthate in sufficient quantity to maximize growth thus leading to fruiting form shedding.

• Too much light, especially in the presence of low temperatures, causes reduced photosynthesis through photoinhibition.

• In either case, crop productivity is reduced.• One thing is for sure, changing light environments will bring

about change either through direct effects on photosynthetic capacity or through photomorphogenesis.

Limitations in yield• Major limitations for yield are:High vegetative growth and poor reproductive

growth due to heavy application of nitrogen.Heavy attack of pests and disease during crop

growth.Unfavourable environment conditions during

flower and boll development stages.Physiological disorders.Nutrient deficiencies.

PHYSIOLOGICAL DISORDERS• Physiological disorders appear in cotton as a

reflex of plant response to environmental stresses, nutritional imbalances and chemical factors.

• Their effect on productivity depends upon the crop growth stage, intensity of incidence and loss of reproductive parts during ontogeny.

LEAF REDDENING• Leaf reddening in cotton is also known as red leaf

disease (lal patti). • This disorder is an outcome of interaction of

location, variety, environmental condition and nitrogen supply.

• Apperance of red leaf symptom is primarily, due to accumulation of anthocyanin pigment.• Leaf reddening may occur at any growth stage of the crop.

Symptoms• Leaf reddening is initially seen in the mature leaves

and gradually spreads throughout the canopy. • Initially leaf margin turns yellow and later red

pigmentation is formed on the whole leaf area . In due course of time the leaf becomes dry and subsequently prone to shedding.

Intensity of leaf reddening as compared to normal leaf

• Causes of leaf reddening:• Impaired uptake of neutrients under water deficit and

waterlogging conditions• Diversion of N to the developing bolls• Synchronized boll development and high boll demand• Desiccation caused by high wind velocity• Anthocyanin (red) pigmentation due to -• Abrupt changes or drop in night temperature (below

15° C)• Nitrogen deficiency• Magnesium deficiency• Chlorophyll degradation

• Management• Adjustment of sowing time to skip over the adverse

environmental condition during boll development stage.• One or two sprays of urea (1 %) at appropriate times.• Application of magnesium sulphate (0.5%)• Adequate drainage to avoid waterlogging of the fields• Sprayingrecommended insecticides• Boll load management• Supply of adequate nutrients during flowering and boll

development particularly in hybrids• Timely inter-culture and weeding operations and other

agronomic practices and suitable cultivars.• Adoption of crop rotation and growing of intercrop to

maintain the soil health and nutritional status

PARAWILT/NEW WILT• In early 1980s a wilt like malady referred to as new wilt or

parawilt caused considerable concern amongst cotton growers across the country.

• It is also called as Adilabad wilt or sudden wilt. Unlike pathogenic wilt, which occurs in groups of plants in fields, this malady was noticed to be sporadic (random) in distribution.

Symptoms• The wilt may develop either slow or quick. The incidence is

particularly high in plants with large canopy and heavy boll load (Fig. a and b).

• In the affected plants, leaves show wilt like drooping, become chlorotic and turn bronze or red followed by drying.

• Premature abscission of leaves and fruiting parts may occur. • Leaves lose turgidity due to enhanced transpiration.• Squares and young bolls are shed and immature bolls are

forcefully opened. Wilted plants show development of anthocyanin pigment.

• Most of the wilted plants gradually recover and produce new flushes, however their contribution to yield is negligible.

Parawilt affected plants with a) large canopy and b) heavy boll load

Causes Cultivation of susceptible

varieties/hybrids

Higher demand for nutrients and moisture

Prolonged dry spell followed by soil saturation due to heavy irrigation.

Heavy clayey and deep soils

Incidence is more in ill drained soils as compared to well drained soils

Management

• Planting of wilt tolerant genotypes.

• G.herbaceum genotypes. Hybrids like JKHY 1, DCH 32, NHH 44 a

• Varieties such as LRA 5166, LRK 516 (Anjali), SRT1, MCU 5 VT, AKH 4, G 27

• Provision of adequate drainage to avoid waterlogging

• Irrigation if available may be provided during grand growth phase to avoid prolonged

• Exposure of plants to dry condition

• Excessive use of farm yard manure and fertilizers

LEAF DRYING / BURN• Leaf drying is of common occurrence in Asiatic

cotton. • It is generally seen during boll development

with the prevalence of prolonged high day and night temperatures coupled with bright sunshine hours.

• Moisture limitations at flowering and boll development augment the incidence.

Symptoms• Initially the young

leaves at the top of the canopy show necrosis near leaf margins and become dry.

• Under prolonged conditions, the necrosis gradually moves inward and dried leaves shed.

Causes

• Specific reasons for the leaf drying has not been assigned.

• However, it is possible that the higher transpiration loss of water due to the characteristic deep root system of Asiatic cotton.

• It is more common in problematic soils.

• Under extreme conditions, the squares and developing bolls also become vulnerable and start drying up.

Management

• Selection of heat tolerant genotypes.

• Protective irrigation may be given if irrigation facility is available at boll development stage.

• Application of soil mulch to reduce the evaporative loss of water from the soil surface.

BUD AND BOLL DRYING• This disorder is very much restricted to a few

varieties, with short fruiting branches and cluster boll habit.

• However, the disorder may occur in other varieties under extreme environmental aberrations.

Symptoms• The developing buds and bolls start drying up slowly. The

dried buds and bolls become black in color and immature bolls may crack.

• Dried fruiting bodies get retained on the plant.• Lint and seed qualities are affected.

a) Bud and boll drying in hirsutum and b) bud drying in arboreum

Causes

• Non-availability of requisite photo- assimilates to the developing bolls led to boll drying.

• Starch accumulates due to the impaired amylase (starch hydrolysing enzyme) activity in the leaves of these plants.

• Common in soils with salinity/alkalinity and also in light sandy soils with low nitrogen status.

• High temperature and dry weather during flowering enhanced this effect.

Management

• Selection of suitable genotypes: Variation is seen between the species and varieties for boll drying.

• G.hirsutum genotypes are more prone to boll drying.

• Adjustment of sowing dates.

• Timely correction of nutrient deficiency (particularly N).

• Frequent irrigation in saline soils.

BAD BOLL OPENING• Bad boll opening is also called as Tirak. • The problem is basically concerned with premature

and improper cracking of bolls, instead of normal fluffy opening .

Symptoms• Initially the leaves turn yellow and subsequently become red. The capsule

wall of the• bolls become tight and do not open completely. The affected bolls may turn

black in color with• time. The fibre as well as seed quality are affected.

Improper boll opening-a) bad boll and b) normal boll

Causes

• Soil with subsoil salinity

• Light sandy soil

• Nitrogen deficiency

• Prevalence of low humidity, warm and dry weather during fruiting period

• Low moisture and nutrient availability during boll formation

Management

• Adjusting sowing dates so that the boll formation stage is not affected by any environmental stress or nutritional deficiency.

• Appropriate nitrogen management at critical growth stages

• Frequent irrigations to reduce effect of subsoil salinity/ alkalinity.

• Timely application of nitrogen in light sandy soil.

• Use of growth retardant to check excessive vegetative growth.

CRAZY TOP• Crazy top depicts the uneven growth and

development, particularly in the meristematic region.

• The occurrence is mostly restricted to calcareous soils and often noticed in areas of irregular irrigation practices.

Symptoms• Abnormal branching and fruiting in the upper

canopy leading to crazy appearance of the plant. • Typical symptoms include distortion of plant parts,

leaves become small, rounded, cupped and thickened and shedding of fruiting forms.

Causes• Common in calcareous soils• Irregular irrigation practices or uneven trends

in the available waterManagement• Timely irrigation if facilities are available• Application of sufficient organic matter• Adequate nutrient supply

CRINKLE LEAF• This disorder is not of common occurrence.

Sometimes, when the available nutrient contents in the soil are too high or under specific conditions some of the nutrients are taken up in large quantity, these nutrients in turn may cause toxicity to the plants.

• Manganese is one such element which is taken up in large quantity under waterlogged condition or inacidic soils leading to developmentof chlorosis and crinkled leaf symptoms.

Symptoms• Mottling, chlorosis and distortion of leaves. Initially

the symptoms are seen in the young leavesCauses• Acidic soils• Calcium deficiency• Manganese toxicityManagement• Application of gypsum to neutralize manganese

toxicity and to overcome calcium deficiency• Adequate drainage to avoid waterlogging.

Bt cotton

• Bt cotton is a genetically engineered form of natural cotton which is produced by inserting a synthetic version of a gene from the naturally occurring soil bacterium Bacillus thuringiensis, into cotton.

• The primary reason this is done is to induce the plant to produce its own Bt toxin to destroy the bollworm, a major cotton pest.

• The gene causes the production of Bt toxin in all parts of the cotton plant throughout its entire life span.

• As of now some 62 Bt cotton hybrids have been developed by private seed companies, which are under commercial cultivation.

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