Cotton is the world's most important natural source of fiber, accounting for almost 40% of total worldwide production. The rich history of cotton and cotton production is closely linked to expanding human civilization (Kohel & Lewis, 1984; Frisbie et al., 1989). Cotton belongs to the genus Gossypium and four species are cultivated worldwide. Levant cotton (G. herbaceum) and tree cotton (G. arboreum) are primarily grown in Asia, while the long staple sea island (American Pima, Creole, Egyptian) cotton (G. barbadense) is cultivated in Egypt, India, the West Indies and parts of the western USA and South America. Upland cotton (G. hirsutum) is the most common species cultivated throughout the world. Cotton is a perennial plant, but is grown as an annual through manipulation of irrigation, defoliants and cultivation. The harvestable portions of the plant are found in the cotton fruit. The primary product, fiber, arise from the growth of single cells on the seed surface, while the seeds are further used as animal feed or in the production of oil found in many food products.

Cotton is grown in more than 75 countries with a total production in 2006 of 116.7 million bales (∼25 400 million kg: National Cotton Council, 2007a). The current top five producing countries, in order, are China, India, the USA, Pakistan and Brazil. In the USA, cotton is grown in 17 states grouped into four major production regions (Fig. 25.1) with a total production of 21.7 million bales in 2006.