Crops

Gossypium hirsutum L. - Upland cotton.

Taxonomic position:

Family: Malvaceae Juss., genus: Gossypium L., species: Gossypium hirsutum L. - Cherepanov S.K., 1995

Biology and Morphology:

Chromosome number: 2n=52. Cotton is a perennial plant cultivated as a shrubby annual. Its height ranges from 40 to 45 cm to 1.5 to 2 m tall. Cotton shrubs are spreading, compact, pyramidal and columnar. The cotton plant's stalk is strong and thin, downy or without down, green or tinged with anthocyan closer to the fall. There are three main kinds of cotton stalk branching: monopodial, sympodial and zero. The monopodial branching is typical of wild and ruderal cotton varieties growing in the tropics as trees or low shrubs. Cotton plants cultivated as annuals have sympodial branching. The first fruit-bearing branch originates in the axil of the 3rd to 10th leaf along the main stalk. There may be 2 to 3 monopodia or none at all. Cotton plants with the zero branching belong to the most recently evolved group that resulted from a spontaneous mutation. They have no sympodia, and all the buds in the leaf-axils of the main stalk develop like flower buds. Non-branching cotton plant varieties mature very early. Cotton plants have large digitilobed leaves with stipules. They are alternate and petiolar. The leaf blades are light or dark green, with or without anthocyan. The leaf blade.s surface is smooth or rugose, with or without down. Cotton plants' flowers are big with a double perianth. The calyx is connate, quinquedentate, with an epicalyx consisting of three large, distinct bracts. The corolla consists of five separate petals only connate near their base. Each flower blossoms for only one day. In the morning, the petals are yellowish (creamy-white) with violet spots at the base. In the evening, they turn deep pink. The stamens are numerous. They are arranged in two whorls. Those in the inner whorl grow together into one tube around the large pistil. The stamens of the outer whorl are reduced. The stigma is located above the column of the stamens. The anthers are light yellow or creamy-colored. The grains of pollen are big, sticky, and unable to be carried away by the wind. The fruit is a boll. Its size varies from that of a walnut to that of a small apple. It is rounded, egg-shaped, oblong, with or without a rostellum, with 3 to 5 lobes, sometimes with 6 to 7 lobes. Each lobe contains 6 to 9 seeds with hairs. There may or may not be linters. The weight of mature cotton wool in one boll varies with different cultivars from 4 to 12 g. Each plant may bear from 2 to 3 to 30 to 40 bolls. The seeds are covered with fibers of varying lengths, each seed bearing up to 15 thousand fibers. Wild cotton plant varieties have hairs up to 10 mm long, while industrial cotton plant cultivars exhibit hairs with lengths ranging from 29 to 38 mm. The weight of the cotton wool is 32 to 37 % that of the fruit. Without fibers, the mature seeds without linters are dark-brown in color, almost black. The linters may be white, brownish, gray, green or emerald-colored. One thousand seeds weigh 85 to 140 g. The seeds are oblong, egg-shaped, rounded.

Ecology.

Cotton plants are heat-loving. The optimum temperature for their growth and development is 25 to 30° C. If it falls below 25° C, the development slows down, and with temperatures below 17° C, growth is inhibited. At the same time, some wild varieties (G. sturtii) may survive brief night and morning frosts of 5-10° C. With temperatures above 40° C, the pollen becomes sterile, and numerous ovaries do not get fertilized and fall off. Cotton plants thrive in areas with shorter days. The cotton plant cultivars bred far from the equator have a poorly pronounced photoperiodic reaction. The vegetation period of early maturing cultivars lasts for 125 to 130 days. Cotton plants demand relatively few nutritive materials and little moisture. They are sown late in spring and therefore may be cultivated after most of the other crops (such as winter spiciferous crops, perennial herbs, maize grown for silage and kernels, sunflowers, sugar beet and others). However, the best precursors of cotton plants are perennial herbs (lucerne) and winter wheat. New Russian cultivars, as compared to Central Asian ones, develop a small vegetative mass. In the South of Russia, cotton plants are less demanding to the nutritive material content of the soil. To form 100 kg of cotton wool, they consume 4.1 kg of N, 1.6 kg of P₂O₅, 2.5 kg of K₂O. Thus, with an average harvest of 1,500 to 2,000 kg of cotton wool per hectare, cotton plants remove less nutrient material from the soil than winter wheat, which has an average harvest of 3,000 to 4,000 kg per hectare. Excess nitrogen may lead to overdevelopment of the vegetative mass with unwieldy vegetation that complicates harvesting. It is very important to counterbalance nitrogen with phosphorous during the first stages of cotton plants' development when their vegetative growth transforms into reproductive development. More phosphorous leads to a greater number of bolls and to a slower plant growth. A certain excess of phosphorous leads to plant aging and earlier opening of their bolls. Application of potash fertilizers is not recommended on solonetzic soils. The optimum pH value is 6.0 to 7.3. In Krasnodar and Stavropol Territories, cotton plants can be cultivated on boghara without watering. In this respect, cotton plants' cultivation is cost-efficient, as they profit from summer rainfall in July and August more than other crops. 80% of all lands in the South of Russia are suitable for cultivation of cotton plants with irrigation, provided the right cultivars are chosen and efficient agricultural techniques are used.

Distribution.

Over millions of years of its evolution, genus Gossypium has managed to adapt itself to a wide range of environmental conditions: from the wet tropics of Central and South America to very arid semi-desert and mountainous areas in the subtropics. Most wild cotton plant varieties grow in the subtropics, but this plant is cultivated in many countries with temperate climates: in the South of Argentina and Australia, in North Korea, in north-eastern and north-western China, in Northern Caucasia, in Bulgaria, Romania, Italy and Spain. Nowadays cotton plants are cultivated in Russia and the Ukraine along 47° N. Spinning of longer wool and flax fibers is much more common than cotton-spinning, as shorter cotton fibers require more advanced technology. Cotton was unknown in Sumeria and Ancient Egypt, where fabrics were made from flax fiber. Cotton was not used in Babylonia at the time of Herodotus. In the Nile Valley, it only became known in 500 B.C. The oldest cotton fabrics (produced in 3000 B.C.) were found by archaeologists in India. Cultivated cotton plants were introduced to China from India long ago, but their cultivation was limited, since China traditionally was the land of silk. There cotton plants were considered decorative. However, late in the first millennium A.D., cotton plants were reintroduced to China in great numbers, and the 11th century witnessed their active cultivation. During the 16th century, cotton was imported to Egypt from Cyprus and Syria. First cotton seeds were planted in the Nile valley late in the 18th century. The Aztecs of America produced cotton fabrics and dyed them with cochineal. Cotton cultivation in the USA started with breeding of upland cotton varieties. At first a great number of cotton varieties were being bred for the Cotton Belt in the USA. In 1906 there were hundreds of cotton plant cultivars, but only 25 of them resisted Verticillium wilt (Verticillium dahliae Kleb.) and fusariose (Fusarium oxysporum ssp. vasinfectum Atk.). Of the considerable number of cotton plant cultivars (35), only 5 are practically used. Worldwide, American long-staple cotton, or upland cotton (G. hirsutum), is sown on 90% of all land used to grow cotton. The next most popular cultivar is Sea-island cotton (G. barbadense), which is cultivated on 8 % of land used to grow cotton. It is cultivated mainly in Egypt, Central Asia, the Sudan, India, Brazil and Peru. It gives the longest, the most delicate and the strongest staples, which are used to produce the costliest fabrics, such as velvet, cambric, parachute fabric, aviation cord, sewing threads, etc. G. tricuspidatum (closely related to the two varieties mentioned above) is cultivated in limited amounts in South America. These three varieties have chromosome number 2n=52. Levant cotton and Asiatic tree cotton (2n=26) have long been cultivated in Africa and Asia. Their staple is shorter and coarser than that of American varieties, but these plants are suitable for cultivation in India, the Sudan and China. They used to occupy vast agricultural lands in Central Asia. Now they are cultivated on about 2% of all the land used to grow cotton worldwide. They are cultivated mostly in India. In the world market, the fiber of Levant cotton (G. herbaceum) and Asiatic tree cotton (G. arboreum) is valued for its strength, elasticity, hygroscopic property and because it is "woolly". Wounds treated with cotton wool obtained from these cotton varieties heal faster. These cotton plant varieties possess some very valuable features, including resistance to diseases, drought, and sucking insect-pests. Their bolls do not open very wide and point downwards, which prevents soaking of fiber during rains in the fall. Cotton-growing in Russia initially relied on Levant cotton and Asiatic tree cotton, later on the so-called factory mixtures. Cultivation of cotton plants started in Central Asia in the 6th millennium B.C. In the USSR, short-staple varieties of Asian cotton were replaced by medium-staple ones. In 2004, 12 cultivars of cotton plants were approved for cultivation in certain areas: AS 4, AS 5, AS 6, AS 7, Limansky, Mikhailovsky, Pioner, POSS 1, POSS 2 and others. The main breeding agencies include: Prikaspiysky Research Institute for Agriculture in Arid Zones, Prikumskaya experimental breeding station of Stavropol Research Institute for Agriculture. All-Union N.I. Vavilov Research Institute for Plant Cultivation and joint-stock company "Russian Cotton" also participate in breeding projects.

Economic value.

Cotton is an essential fiber plant. It is cultivated for its fiber used by the textile industry to produce a great variety of apparel and fabrics. Cotton seeds containing 20 to 28 % oil are used to produce oil and are a valuable source of protein. Waste from ginning and oil production is used to produce glycerin, drying oil, cellulose, linoleum and other products. Cultured cotton varieties' fiber is mostly white. However, some varieties have colored fiber, which may be brown, green or creamy-colored. Technological properties of cotton fiber depend on the following values: fiber length, thinness, strength, breaking length, elasticity, crimpiness, and maturity. Fiber length varies from 20 to 60 mm. Fiber thinness is indirectly determined by its linear density (metric number), that is by the length of the fibrils in 1 gram of fiber measured in meters. The higher this value is, the thinner the fiber. Fiber strength, or its breaking strength, is an important measure of its quality. It depends on the strength expended to break one stretched fibril. Breaking strength of different cotton cultivars and varieties varies from 4 to 7 g. Immature fibers, especially from bolls opened after night frosts, have a low breaking strength. The combination of cotton fibers. technological properties determines its industrial type. There are 7 industrial types of cotton fiber, each one having certain values of its length, thinness and breaking strength. The fiber of the 1st, 2nd and 3rd types is obtained from fine-fiber cotton varieties; the fiber of the remaining types is obtained from medium-fiber ones. The costliest and strongest fabrics are produced from the fiber of the first three types, but industry does not need them very much. The highest demand (about 70 % of all fiber) exists for the fiber of the 5th type. This is the staple fiber type used to produce mass consumption fabrics. An important characteristic of different cotton varieties is their fiber yield. It is measured as the ratio of the weight of pure fiber and the weight of raw cotton wool and is expressed as a percentage. By convention, cotton fiber yield is subdivided into low (lower than 30%), medium (from 30 to 35%) and high (over 35%). Cotton fiber yield depends on the weight of 1000 seeds and its index. Fiber index is the weight of the fiber (in grams) obtained from 100 seeds. When cotton seeds are being prepared for sowing, their long fibers are first separated by ginning (which is a primary mechanical treatment of raw cotton), after which their shorter linters are removed. Chemical removal of linters results in a desirable looseness of the seeds and eliminates the need for further treatment. Cotton seeds are sown in closed drills or wide rows (with inter-row spaces of 60, 90, or 105 cm). The farther North cotton plants are cultivated, the more plants are grown per unit of area. Cotton seeds are planted at depths of 4 to 6 cm, but preferably at depths of 4 to 5 cm. By the time of harvest, the optimum number of plants of new Russian cultivars sown per hectare (with inter-row spaces of 60 to 70 cm) is 80 to 100 thousand plants for fertile soils of Krasnodar Territory and up to 120 thousand plants for leaner soils. 12 to 14 kg of seeds are planted per hectare using exact seed-sowing machines. All the cotton planted in the .90s in the South of Russia was harvested manually. Machine harvesting is only possible when the field is flat and the plants have had their leaves removed. Cotton plants are usually defoliated. Magnesium chlorate is usually used as the defoliant. At higher concentrations, it is used as the desiccant. Cotton plants usually yield 1,500 to 2,000 kg per hectare.

References.

Cherepanov S.K. 1995. Vascular Plants of Russia and Neighboring Countries. St. Petersburg.
Kasyanenko A.G., Kasyanenko V.A., Semikin A.P., Shevtsova V.M. 1999. Cotton-Growing in Russia. Krasnodar.
State Register of Breeding Achievements Approved for Practical Application in the Russian Federation in 2004. Moscow: 2004.
Suvorov V.V. 1961. Botany. Leningrad. p. 320-324.
Zhukovsky P.M. 1971. Cultivated Plants and Their Congeners, Leningrad. pp. 385-414.

© Gashkova I.V.

© Photo Gashkova I.V.