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Whether cultivated or wild, all the cottons of the world belong to the genus Gossypium, and four domesticated species of cotton are currently under cultivation. Two are “Old World” species: Gossypium arboreum is cultivated in India, and remains a fairly important crop there; G. herbaceum is grown only as a local crop in the drier areas of Africa and Asia. Both these species are diploid (2n = 26). The domesticated “New World” cottons, G. hirsutum and G. barbadense, are allotetraploid, characterized by 26 pairs of chromosomes (2n = 52) (Lee 1984). Cultivation of G. hirsutum, often referred to as Upland cotton, makes up about 90% of the current world production of 80 million bales, and about 99% of the US cotton crop. G. barbadense (commonly referred to as Egyptian or Pima cotton) accounts for most of the remaining production, and is used in the manufacture of luxury fabrics and sewing thread. The economic impact of commercial cotton production is significant; the value of the US crop is roughly $4 billion (US$) annually (USDA Agricultural Statistics 1991). |
