Nicotiana tabacum, common tobacco

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Taxonomy

cellular organisms - Eukaryota - Viridiplantae - Streptophyta - Streptophytina - Embryophyta - Tracheophyta - Euphyllophyta - Spermatophyta - Magnoliophyta - eudicotyledons - core eudicotyledons - asterids - lamiids - Solanales - Solanaceae - Nicotianoideae - Nicotianeae - Nicotiana - Nicotiana tabacum

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Brief facts

• Cultivated tobacco, Nicotiana tabacum is a member of the Solanaceae family, which also includes eggplant, pepper, petunia, potato, and tomato.
• Plants are stout, thick-stemmed herbs or single-stemmed shrubs with large oily hairy leaves that expand directly from the stem (sessile, no petioles) or have broadly winged petioles. Tubular flowers are nearly regular with the petals spreading at right angles to the broadly inflated tube (salverform). Flowers are usually pinkish, but ranging from white to red; the flowering is diurnal (day opening).
• Linnaean name of the genus (Nicotiana) was coined after French diplomat Jean Nicot, who is said to have brought seeds of tobacco from Portugal to France in the 16^th century.
• Nicotiana occur largely in the Americas and Australia, with a single species in Africa (Namibia); cultivated species (N. tabacum and N. rustica) have been spread worldwide by humans.
• N. tabacum, a native of Tropical America, has been cultivated since pre-Colombian times.
• It is the most widely grown commercial non-food plant in the world. As such it holds a high importance in financial and economic policies in many countries.
• The pyridine alkaloid nicotine is one of the best-studied plant resistance traits. It is extremely toxic to most herbivores because it interacts with the acetylcholine receptors in the nervous systems. Consequently, it was one of the first insecticides used to control pests in agriculture. Some insects adapted to nicotine-producing plants and even might use nicotine for their own protection. For example, tobacco specialist Manduca sexta (tobacco hornworm) tolerates doses of nicotine that are fatal to unadapted herbivores. Although it grows slower on high-nicotine diet, some studies suggest that high nicotine content might protect it from its parasitoid, Cotesia congregata, which exhibits higher mortality in larvae parasitizing on tobacco-fed hornworms.
• N. tabacum is one of three principal hallucinogenic plants used by indigenous tribes in Amazonian Ecuador and Peru. Consumption of tobacco (tsaank) includes chewing, drinking juice, snuffing, and smoking. The smoke helps to protect from evil spirits. Males consume juice from steeped tobacco leaves at the age of six to help them to achieve arutam (spirit vision). It is the first hallucinogen taken by apprentice shamans. After becoming acclimated to tobacco, they switch to stronger hallucinogens.
• The physiological effects of tobacco are biphasic. Small doses stimulate the central nervous system, depress hunger and thirst, and relieve pain. Large doses can produce catatonia, diarrhea, nausea, respiratory failure, visions, and trance.

Genome structure

• N. tabacum is an amphiploid species (2n=48) resulting from an interspecific cross between N. sylvestris (2n=24) and N. tomentosiformis (2n=24). N. tabacum has a very large genome size compared with other cultivated solanaceous plants. At approximately 4.5 billion base pairs, it is 1.5 times the size of the human genome. As with the human genome, the vast majority of these base pairs occur as highly repetitive sequence.

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Developmental stages (life cycle)

Life Cycle Stages

N. tabacum is a perennial plant but cultivated as annual. The crop needs a minimum of 120 frost-free days and can be grown in a variety of soils.

• Seed stage MeSH
  • Dormant seed
  • Germinated seed
    MeSH Seed germinates in 7-14 days at 65 °F.
• Vegetative
  • Seedling
    MeSH Unlike most other annual agricultural crops, tobacco has a small seed (1 oz=300,000 seeds), which cannot be sown directly in the field; seedlings are raised in carefully selected and tended seedbeds where protection is given against heavy rain and excess sun; young seedlings are planted out by hand or mechanical transplanter, and spacing between seedlings and rows varies with the kind of tobacco and with the location.
  • Before topping After growing for 2-3 months after transplanting, plant develops 12-22 leaves (for example, 12-16 leaves for dark tobacco and 18-22 leaves for burley); topping involves removing a small bunch of compact leaves which formed at the top of the plant so that the plant would not develop flowers.
• Flowering Plants that were not topped enter their reproductive stage normally.
• Mature Mature plant stays six to nine feet tall and has about 20 leaves.
  • After topping
    • Ripening For tobacco ripening means that its leaves gradually become ready for picking. Plants are ready to harvest about 5-7 weeks after topping. Burley leaves become yellow; dark tobacco leaves become thick, brittle, and oily. Leaves are usually cut late afternoon and allowed to wilt 2-3 hours or overnight.

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Leaf classification

Plant Leaves

Tobacco is picked when leaves are "ripe". Leaves ripen progressively from the bottom of the plant to the top, so lugs are picked first and tips picked last. Typically tobacco is picked six times, with three leaves taken per pick and six leaves in the final pick. Gradual picking may continue for 2 months.

• Tip Short, narrow leaves from the top of the plant; these leaves often have a higher nicotine content than other leaf positions.
• Leaf "Leaves" occur near the top of the plant and are long and wide with a large stems; leaves are thickest of all other leaves and have moderate nicotine content.
• Subleaf Subleaves grow below "leaves" and above cutters and lugs; they are longer and narrower than both lugs and cutters, but similar in thickness.
• Cutter Thin leaves with a narrow stem that grow above lugs; they are normally wider than they are long.
• lug Short wide leaves growing on the lowest level of the plant; they are typically thin and papery with low nicotine content.

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Tobacco diseases

Disease	Organism	Effects
Anthracnose, mildew	Colletotrichum spp., fungi, ascomycetes	Manifested in light green, water-soaked spots.
Black root rot	Thielaviopsis basicola, fungi, ascomycetes	Young roots are black, with discrete lesions or lesions along the entire length of the root; seedlings exhibit stunting and a pale green to yellow discoloration of leaves and shoots.
Black shank	Phytophthora parasitica, water molds, oomycetes	Small, irregular water-soaked spots on leaves, wilting; rots progress from leaves to the stem, and sections or branches of the plant are killed; roots are also affected.
Blue mold	Peronospora tabacina, water molds, oomycetes	Circular yellow spots up to one inch in diameter develop on the leaves. Blue-gray fungal growth is produced on the underside of these spots. Spots become light brown when the leaf tissue dies. The disease first develops on lower leaves, but it rapidly spreads to upper leaves during wet, cool weather.
Brown spot	Alternaria longipes, fungi, ascomycetes	Brown, mostly circular brown leaves' lesions 1 mm -3 cm in diameter sharply delimited by yellow halo 1 mm -3 cm.
Cyst nematode	Heterodera tabacum, nematodes	Reduced growth of individual plants, chlorosis, wilting and sometimes, death.
Frogeye leaf spot	Cercospora nicotianae, fungi, ascomycetes	May develop on the leaves of tobacco in the plant bed, field, or barn. The spots on the leaves are typically circular, with a reddish-brown margin and tan or grey colored papery centers in which black masses (fruiting bodies) of the fungus may be found. Frogeye usually occurs on the lower leaves but moves up the plant as the season progresses.
Fusarium wilt	Fusarium oxysporum, fungi, ascomycetes	Vascular wilt, chlorosis, root rot, and damping-off.
Granville wilt	Ralstonia solanacearum, bacteria	Initially appears as wilting of one or two young leaves during the hot hours of the day with recovery during the cooler evening. Leaves remains green in optimal conditions or turn light green and then progressively yellower. Necrotic areas can appear between the veins and at the leaf margins.
Powdery mildew	Golovinomyces cichoracearum (Erysiphe cichoracearum), fungi, ascomycetes	The primary symptoms are white, powder-like spots on the leaves and stems.
Root knot nematodes	Meloidogyne spp., nematodes	Roots' galling. Moderate to severe leaf chlorosis and plant stunting. Some wilting may occur.
Rattle virus or Mauche disease	Soil-borne virus	Systemic necrotic line patterns, and death or stunting of shoots.
Tobacco etch virus	Potyviridae virus	The first symptom of TEV infection is a pronounced vein clearing on expanding leaves. This is followed by necrosis of a thin line of tissue along the veins, resulting in an etched pattern. Subsequently, young leaves develop a mosaic which fades to mottling as the leaf ages.
Tobacco mosaic virus	ssRNA positive-strand virus	Stunting. The virus causes mottled (mosaic) areas on the leaves with yellow and dark green blistered areas, curling of the leaves and/or general distortion of the plant.
Tobacco streak virus	ssRNA positive-strand virus	Causes necrotic symptoms on stems and leaves.
Wildfire	Pseudomonas syringae, bacteria	Brown leaf lesions with flaccid tissue.

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Photo gallery

Tobacco transplantation

Tobacco seedlings

Tobacco cultivation

Tobacco leaves drying

Tobacco processing

Cigar making

Freshly rolled cigars

Tobacco final products

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References

• Bennett, B.C. Hallucinogenic plants of the Shuar and related indigenous groups in Amazonian Ecuador and Peru. Brittonia 1992, 44:483-493.
• L. G. BURK AND H. E. HEGGESTAD. The Genus Nicotiana: A Source of Resistance to Diseases of Cultivated Tobacco. Economic Botany, Vol. 20, No. 1 (Jan. - Mar., 1966), pp. 76-88
• Murad L et al. The origin of tobacco's T genome is traced to a particular lineage within Nicotiana tomentosiformis (Solanaceae). Am. J. Botany, June 1, 2002.
• Knapp S et al. Nomenclatural changes and a new sectional classification in Nicotiana. (Solanaceae). Taxon, Vol. 53, No. 1 (Feb., 2004), pp. 73-82.
• Steppuhn A et al. Nicotine's defensive function in nature. PLoS Biol. 2004 Aug;2(8):E217.
• W. A. Bailey. Basic Principles of Dark Tobacco Production in Kentucky and Tennessee.

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