Tobacco is the common name of the plant Nicotiana tabacum and to a limited extent Nicotiana rustica and the cured leaf that is used, usually after aging and processing in various ways for smoking, chewing, snuffing and the extraction of nicotine, the principal alkaloid of tobacco.(4) The species N. tabacum has never been found to grow in the wild.(1) The use of the word tobacco is generally accepted as referring to the products of the tabacum species and so it will be in what follows. Tobacco holds an unparalleled position among crop plants in the world such as:
1) It is one of the very few crops entering world trade entirely on a leaf basis.
2) It is the most widely grown commercial non-food plant in the world.
3) It holds a high importance in financial and economic policies in many countries.
4) Consumption is by way of smoking, inhaling or chewing and is a habit forming narcotic, and although bans of it's use have been attempted, it's consumption marches steadily forward.
5) Originally having religious significance, subsequent claims of medicinal benefit have alternated with accusations of a positive danger to health.
Tobacco is grown with assistance of man with the leaf as the only valuable part of the plant. Tobacco growth is restricted, by environmental factors, to about the latitudes of 60 degrees north to 45 degrees south, with the majority of the tobacco entering the world trade produced in the latitudes between 45 degrees north and 30 degrees south. Limits to it's growth are figured by the number of frost free days. Almost all continents are capable of growing tobacco but the United States, China, India and Brazil are the leading countries to grow tobacco. (1)
Natural occurrence of Nicotiana is restricted to the American continent, Australia and the South Pacific. The majority are confined to South America and this, with other geographical evidence suggests a South American origin for this genus. N. tabacum has a uniquely high proportion of alkaloids occurring as nicotine and is considered to have survived as a species by man's protection. Creation of new species through hybridization is a natural botanical occurrence. It is an accepted assumption that N. tabacum arose as a natural hybrid. N. sylvestris contributes one genome, but agreement on the other contributor is not agreed upon. Artificial creation of hybrids which results in 'synthetic tobacco' bear very close genetic similarity to N. tabacum. Cultivated tobaccos have changed immensely over time and it is unlikely that the forms of other species now available bear to close a resemblance to what existed in the distant past.(1)
Tobacco is normally grown as an annual and is potentially a woody, shrub like perennial. The tobacco plant has a very shallow root system which provides poor anchorage for the more extensive above ground development. The N. tabacum types are one of the smaller species of tobacco varieties. The leaves...