Cotton is a fibre, oil and protein yielding crop of global significance. The genus Gossypium to which the cotton belongs, which is a member of the natural order Malvales, family Malvaceae, series Hibisceae of the dicotyledonous group of plants.
It is cultivated in tropical and subtropical regions of more than 80 countries of the world. The major cotton producing countries are USA, China, India, Pakistan, Uzbekistan, Turkey, Brazil, Greece, Argentina and Egypt. These countries contribute about 85% to the global cotton production. India stands first in area, third in production and last in productivity among these countries.
In India, there are nine major cotton growing states which are divided into three zones, viz. north zone, central zone and south zone. North zone consists of Punjab, Haryana, Rajasthan and Western Uttar Pradesh. Central zone includes Madhya Pradesh, Maharashtra and Gujarat. South zone comprises Andhra Pradesh, Karnataka and Tamil Nadu. These states cover about 95% of cotton area and also contribute about 95% to the total cotton production in India. Three cotton growing zones differ from each other in several aspects such as soil type and topography, irrigation facilities, species cultivated,
productivity level etc. Besides these states, cotton is also grown on small areas in Bihar, Orissia, Assam, Tripura and Meghalaya. These states cover about 5% area and also contribute 5% to the
national cotton production.
There are four cultivated species of cotton viz. Gossypium arboreum, G.herbaceum, G.hirsutum and G.barbadense. The first two species are diploid (2n=26) and are native to old world. They are also known as Asiatic cottons because they are grown in Asia. The last two species are tetraploid (2n=52) and are also referred to as New World Cottons.G.hirsutum is also known as American cotton or upland cotton and G.barbadense as Egyptian cotton or Sea Island cotton or Peruvian Cotton or Tanguish Cotton or quality cotton.G.hirsutum is the predominant species which alone contributes about 90% to the global
production. In USA and Uzbekistan, more than 90% area is covered by G.hirsutum.
Click here for the information about Cotton Varieties and hybrids.[Thanks to CICR]
Perhaps, India is the only country in the world where all the four cultivated species are grown on commercial scale. In India,45%, 30% and 24.7% area is covered by hybrids, upland cotton and diploid species respectively.G.barbadense is grown on a very little area (0.3%) in the state of Tamil Nadu and Andhra Pradesh.G.herbaceum is limited to the states of Gujarat and Karnataka. G.hirsutum and G.arboreumare grown in all the major cotton growing states in India.
1. Gossypium arboreum Bracts are more or less triangular and closely invest bud and flower. Bracts have 4-5 teeth at the apex. Bolls are tapering and profusely pitted with prominent oil glands. Bolls open widely on maturity. This species is also known as Indian cotton.
Bracts flare widely from the bud, flower and boll. They have 6-8 teeth. Bolls are round and rarely with prominent shoulders. Bolls are smooth or with few shallow pits and few oil glands. Bolls open slightly when ripe.
Flowers do not have red spot at the base of petal. The staminal column is short. The anthers are loosely arranged on the staminal column. Anther filaments are larger in the upper region than in the lower region. The capsule surface is usually smooth.
Bracts are very large which cover the flower bud completely. The staminal column is long on which anthers are compactly arranged. The anther filament is of same length. Bolls are large and deeply pitted with black oil glands. Red spot is present at the base of petal.Bracts are united at the base in diploid cottons and free in tetraploid cottons. Diploid cottons have high degree of resistance to biotic and abiotic stresses, whereas tetraploid cottons have high yielding capacity and good fibre quality.
Leaves are spirally arranged on the main stem and the vegetative branches. The arrangements on the sympodia is in the form of alternative rows. The phyllotaxy of the American cotton is 3/8 while that of the Asiatic varieties is 1/3. The leaves are petiolate and stipulate. The petioles are glabrous, Pubescent or fully hirsute depending on the variety. The shape of the leaf is generally cordate and lobing is palmate. The number and depth of sinus in lobes vary. In barbadense varieties, leaves are small and the lobes rounded or very deeply cut. Leaf surface may be hairy or glabrous. Nectaries are found on the undersides of the main veins. The colour of the leaf may be varied from light green to full green.Some varieties develop a red pigment masking the full green as in red arboretum types.
The flowers are extra- axillary,terminal and solitary. On account of the sympodial development of fruiting branches, the flower opening follows a spiral course in acro-petal and centrifugal succession. The innermost bud of the lowest and oldest branch is the first to open, while the outermost bud of the highest and young set branch is the last to do so.
The flower is subtended by involucres of usually three unequal leaf like bracts, which may be free as in the American cottons or united as in the Asiatic varieties. They are generally large, ridged, entire or toothed and correspond to the principal veins. Characteristic stellate hairs are found on the outer surface. Bracteoles, alternating with the bracts on the inside of the involucres or standing on either side of the small bract, may be present. Extra-floral nectarines occur sometime on the apex of the peduncle below in the auriculate base of the bracts.
The calyx is persistent and shaped as shallow cup. It consists of five undiversed sepals with the lobes variable in size, short and broad. The calyx adheres tightly to the base of the boll as it develops. In certain varieties, three extra floral nectarines irregularly triangular in shape and surrounded by stiff hairs and present in the outer calyx. The corolla is tubular, consists of five obcordate petals in a convolute manner. The petals may be white creamy white, lighty yellow, yellow or purple in colour. In varieties, a spot of purple, sometimes may vary in intensity and extent.
Shape, locule, surface, oil glands etc.., The development of the fruit begins with the fertilization and shedding of whithered floral organs enclosing it. The first half period of maturation of a boll is spent in growth and the second half in internal development without any change in the boll size. The size and shape of the boll serves as a marker character in varietal identification.