Nicotiana tabacum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Nicotiana tabacum L.

Protologue: Sp. pl.: 180 (1753).

Family: Solanaceae

Chromosome number: 2n= 48 (amphidiploid)

• Nicotiana virginica C. Agardh (1819),
• N. mexicana Schlecht. (1847),
• N. pilosa Moc. & Sessé ex Dun (1852).

• Tobacco (En).
• Tabac, tabac commun (Fr)
• Indonesia: tembakau, tabako, bako
• Malaysia: tembakau
• Papua New Guinea: brus
• Philippines: tabaco (general), tabaku (Sulu)
• Cambodia: thnam' chuëk
• Laos: ya:, ya: dét
• Thailand: yasup (general), chawua (Khmer-Surin)
• Vietnam: thuốc lá.

N. tabacum was domesticated in Central and South America more than 2000 years ago and does not appear to exist anymore in a truly wild state. This amphidiploid species probably evolved from interspecific hybridization between diploid parents (N. sylvestris Speg. & Comes and N. otophora Griseb. or N. tomentosiformis Goodsp.) occurring naturally in north-western Argentina. When the first Spanish explorers arrived in the Caribbean and Americas towards the end of the 15th Century they found that tobacco smoking was widespread among the local people. They quickly adopted the habit, initially for medicinal purposes but soon mainly for pleasure, and introduced tobacco cultivation throughout the world. The first tobacco was planted in Europe around 1560 and in North America (Virginia) in 1612. From the Philippines it was brought to Malaysia, Indonesia, China, Japan and India in the early part of the 17th Century. In Europe, pipe smoking became very popular and tobacco for this purpose was imported from the Americas: Virginia produced in the south-eastern states of North America and Spanish from Caribbean islands and South America. However, by the end of the 18th Century this profitable trade had declined due to increased domestic tobacco production in Europe. Most of the tobacco grown in Asia was used locally for chewing and for smoking in cheroots or traditional cigarettes. Very little was traded internationally until the development of the cigar tobacco plantation industry in Java and north-eastern Sumatra after 1860.

Cigarette smoking was first introduced into Europe after 1855 by soldiers returning from the Crimean war. The subsequent popularization of cigarettes on a global scale, particularly after World War I, was an important impulse for the tremendous expansion of world tobacco production: 2.4 million t in 1925 (Asia 55%, Americas 33%, Europe 10%), 3.8 million t in 1957 (Asia 43%, Americas 37%, Europe 17%) and 5.5 million t in 1980 (Asia 47%, Americas 30%, Europe 23%).

Cured tobacco leaves are smoked, chewed or sniffed (as snuff) for their taste and flavour, but particularly also for the stimulating and mildly narcotic effects of the alkaloid nicotine. The final use of tobacco leaves is determined by several factors, including cultivar, climate, soil and methods of curing (drying) after harvesting. More than 90% of all tobacco is manufactured into cigarettes: mainly flue-cured, broad-leaf Virginia (mild), but also light air-cured Burley (thin-leafed) or Maryland types, which are stronger flavoured and often used for blending. Aromatic or oriental tobacco is produced from sun-cured small-leafed Smyrna, Samsun and Virginia types. The manufacturing of cigars requires three different types of dark air-cured tobacco leaves: filler (Brazil-Bahia, Havana, Kentucky, Criollo), binder (Havana, broad-leaf Connecticut and Java) and wrapper (Sumatra-Deli, Java shade grown, Havana, Cuba types). Pipe and snuff tobaccos may be prepared from blends between several types, including fire-cured Kentucky and Virginia, or air-cured Burley and Maryland. American cigarettes are made from a blend between Virginia, Burley, oriental and Maryland tobaccos, whereas English cigarettes contain Virginia tobacco only. The cigarette manufacturing process also includes steeping the leaves in special flavoured liquids (the recipes are company secrets), to improve the tobacco's flavour and curing properties. Indonesia produces the typical clove cigarette "kretek", which is made from a blend of tobacco and shredded cloves (dried flower buds of Syzygium aromaticum (L.) Merrill & Perry) and first appeared in Java around 1890. Annual production of these clove cigarettes increased from 11 billion in 1934 to 170 billion in 1996. In Indonesia pounded fresh tobacco leaves are included in local medicinal solutions to treat wounds and ulcers. Nicotine extracted from leaves of N. tabacum, but especially those of N. rustica L., which have a higher nicotine content, was formerly used as an insecticide.

Tobacco is grown in some 110 countries on a total of 4.5 million ha. Averaged over 1994-1997 world production was about 6.6 million t per year of cured (dried) tobacco leaves, with Asia accounting for 58%, the Americas 21%, Europe 8%, Africa 7%, and West Asia and the Mediterranean area 5%. China alone produces 40% of the world's tobacco (exporting only 2%), the United States 9%, India 8%, Brazil 6%, Turkey 4% and Zimbabwe 3%.

With 155 000 t per year (215 000 ha) Indonesia is the 7th largest tobacco-producing country. Most of the Indonesian tobacco is consumed domestically (cigarette industry) and the 15 000 t exported consists mainly of high-quality cigar (wrapper, binder and filler) tobaccos. Other tobacco-producing countries in South-East Asia include: Thailand 60 000 t (47 000 ha), the Philippines 50 000 t (37 000 ha), Burma (Myanmar) 38 000 t (37 000 ha), Vietnam 29 000 t (36 000 ha), Malaysia 12 000 t (11 000 ha), Cambodia 5000 t (9000 ha) and Laos 3000 t (4000 ha). Thailand exports 50% and the Philippines about 20% of its annual crop, but both countries also import tobacco. About 30% of the world crop is sold on the international market, representing an estimated value of US$ 3-5 billion per year (1994-1996). Prices for cured tobacco leaves may vary from US$ 0.40 to US$ 5.50 per kg, depending on country, type and quality of the product and the current market situation of supply and demand. For instance, flue-cured tobacco may cost US$ 0.90-1.50 per kg in China and Indonesia, but US$ 3.50-4.50 in the United States and Spain, or even US$ 19.00 in Japan. In some years Indonesian dark air-cured (wrapper and binder) cigar tobacco has fetched more than US$ 12.00 per kg. The major tobacco-exporting countries (accounting for 56% of world exports) are in descending order of importance: Brazil, Zimbabwe, the United States, Turkey, India, Italy and Greece. The largest importers (accounting for 35% of world imports) are the United States, Germany, the United Kingdom, the Netherlands and Japan. Average annual consumption of tobacco varies from 0.1-3.5 kg cured tobacco per capita: e.g. 0.1 in Malawi and Nigeria; 0.5 in India, Mexico and Italy; 0.8 in Egypt, Thailand, Burma (Myanmar) and Cambodia; 1.1 in Indonesia, the Philippines, Vietnam and Brazil; 1.8 in Japan, China, Turkey, the United Kingdom and Poland; 2.5 in the United States, Hong Kong and Belgium; and 3.0 or more in Singapore, Greece, Bulgaria and the Netherlands.

Fresh tobacco leaves contain 85-90% water. This falls to 12-15% during the curing process. On a dry-weight basis flue-cured (cigarette) tobaccos contain sugars 18-20%, starch 5-8% and proteins 2%; air-cured (cigar) tobaccos contain only a few percent sugars, but proteins 3-15%. The major alkaloid in tobacco is nicotine. The nicotine content in air-cured cigar tobacco is 1.0-1.5%, in flue-cured tobacco 1.5-2.5% and in Burley tobacco up to 4%. Nicotine content determines the tobacco's strength, but flavour and quality of taste are more related to protein content. Essential oils and resins in the glandular hairs contribute to the tobacco aroma. Cured tobacco leaves have a high ash content: 12-25%. The quantity and composition of the mineral content affect quality and combustibility, e.g. chloride content in excess of 1% having a negative effect. Tobacco leaves also contain quantities of organic (citric, maleic and oxalic) acids, which react with calcium, potassium and other cations during the curing process to form salts. Air-cured tobaccos become reddish-brown because the polyphenols (tannins) present in the leaves oxidize. In flue-cured tobacco oxidation is largely prevented due to the rapid drying process, so the leaves retain a yellow colour. Nicotine mimics the action of acetylcholine at specific receptors in the central and peripheral nervous system. It stimulates the release of adrenalin, slows the heart rate and raises blood pressure. Nicotine is one of the most addictive drugs. Smoking cigarettes leads to the inhalation of tars, which are known carcinogens. There are well established correlations between smoking and lung and throat cancers, heart disease and respiratory ailments.

Seeds contain 32-42% semi-drying oil (60-75% linoleic acid) and 20% protein. The 1000-seed weight is 0.085 g.

• Annual herb, 1-2.5(-3) m tall, with thick, unbranched (except when topped), erect stem, with well-developed taproot.
• Leaves and stem green (except for white Burley cultivars), covered with multicellular hairs, some glandular and sticky. Leaves arranged spirally, 20-35 per plant (higher numbers in certain indeterminate cultivars; number fairly constant for each cultivar), sessile; blade ovate-lanceolate or elliptical, 5-50 cm × 5-25 cm, entire, with slightly undulating margin, decurrent, usually with an auriculate base, pinnately veined.
• Flowers borne in a terminal thyrsoid panicle, up to 150 per inflorescence; pedicel 1-2(-2.5) cm long, subtended by a bract; calyx cylindric-campanulate, 1-2.5 cm long, with 5 unequal pointed teeth; corolla salver-shaped, tube 3.5-5.5 cm long with throat inflated, hairy, usually pale pink, rarely white or carmine red, limb 10-15 mm wide, acutely 5-lobed to pentagonal; stamens 5, inserted on the corolla tube, filaments of unequal length, anthers small, dehiscing longitudinally; ovary superior, 2-locular with a fleshy axile placenta carrying numerous ovules, style long, slender, with capitate, 2-lobed stigma.
• Fruit a 2-valved, ellipsoid to ovoid or globose capsule, 1.5-2 cm long, the greater part enclosed by the calyx.
• Seeds numerous, 2000-5000 per fruit, ovoid to globose, very small, 0.4-0.6 mm long, surface finely reticulate, light to dark brown. Seedling with epigeal germination.

Tobacco seed remains viable for more than 10 years when stored dry and cool. There is no dormancy, except that freshly harvested seed should be allowed a post-ripening period of 3 weeks. It will then give 95% germination within 5 days after sowing. Seeds of most cultivars require light for germination. Seedlings are ready for transplanting to the field 35-45 days after sowing, when 15-20 cm tall, with a rosette of 4-5 leaves. The taproot is usually broken in transplanting and a mass of fibrous roots develops from several horizontal laterals. The mature root system is extensive but rather shallow and tobacco plants are susceptible to lodging under strong wind, particularly when bearing a full-size inflorescence. Flowering starts 50-60 days after transplanting. The anthers dehisce when the flower unfolds and at that time the stigma is sticky and receptive. Self-pollination takes place normally, but nectar-collecting insects may bring about 4-10% cross-pollination. The fruits are ready for harvesting 3-4 weeks later.

The first and lowest leaves are mature about 2 months after transplanting, when the colour changes from livid or bluish-green to yellowish-green, particularly along the edges. Dormant axillary buds will only develop into lateral branches, called suckers, after topping or when the plant has lodged. Tobacco has an economic life span of about 5 months.

The genus Nicotiana includes some 65 species, mostly endemic to the Americas and a few to Australia. Most are diploid (2 n = 24) except for 9 amphidiploid species, including N. tabacum and N. rustica. At least 10 Nicotiana species have been used in the past by indigenous peoples for ritualistic, medical or hedonistic purposes because of their intoxicating nicotine content. A system of gametophytic self-incompatibility is common in many diploid Nicotiana species, but N. tabacum and N. rustica are self-compatible and largely self-fertilizing. Wild Nicotiana species have dehiscent capsules causing early dissemination of the seeds, whereas the cultivated N. tabacum and N. rustica possess indehiscent capsules as a result of human selection.

Tobacco is cultivated under a wide range of climatic conditions, from Sweden (60°N) to New Zealand (40°S). It requires a frost-free period of 90-110 days after transplanting and at high latitudes seedlings are therefore raised in glasshouses. Mean temperatures for optimum growth are 21-27°C, with lower and upper limits of 13°C and 37°C. Water requirements are 300-400 mm, evenly distributed during the growing season. Cigarette (e.g. Virginia) tobaccos need a dry period at the end of the season to obtain the required thickness and yellow colour of cured leaves. To produce thin and elastic leaves, wrapper tobacco needs a high humidity (70% at noon) and a reduced sunshine intensity (70% of maximum sunshine). Clouds occurring on rainy days act as a natural filter for the sunlight. The quality of Deli cigar wrapper tobacco is said to be determined in the first place by climatic conditions and only in the second place by soil conditions. To mimic the growing conditions of North Sumatra, cigar wrapper tobacco is now cultivated under shade not only in other parts of Indonesia (Java), but also in Connecticut (the United States).

In Central Java the main area of cigarette tobacco is on the Dieng plateau at about 1000 m elevation, where generally better quality is produced. Soils most suited to tobacco cultivation are light to medium loams with good water-retaining capacity and slightly acid reaction (pH 5.0-6.0). Soils must be well drained, since tobacco is very sensitive to waterlogging. Cigar-type tobaccos require more fertile soils than Virginia tobacco. Since combustibility is an essential quality component of cigar and cigarette tobacco, the chloride content in the soil should be low, preferably no higher than 40 ppm irrigation water should have a chloride content not exceeding 25 ppm.

Tobacco is propagated by seed. Seedlings are raised on shaded beds. Generally 10 g of healthy seed are needed to produce enough seedlings to plant one hectare, but only one third of this amount is needed if the seed is pelleted. The medium for raising seedlings is a mixture of soil and compost, and should be steam-sterilized at 100°C for one hour to prevent infection by soilborne pathogens. NPK fertilizer is applied before sowing. The total area of seedbeds is usually 80-100 m²for each hectare of crop. Maintenance includes daily watering, manual weeding and control of diseases and pests. Thinning is carried out to remove weak and spindly seedlings. After thinning the number of seedlings should not exceed 400 per m². Plants are hardened off 7-10 days before transplanting by gradually removing overhead shade and reducing watering. Tobacco is planted in the field at 45-55 cm within the row and 75-110 cm between rows. Seedlings grown in small polybags or trays establish more readily than bare-rooted seedlings grown on traditional beds. The average plant density is 18 000-25 000 per ha for most tobacco types, except oriental tobacco (>60 000 plants/ha).

Most tobacco is rain-fed. Sprinkler and furrow irrigation may be applied, to supplement inadequate rainfall. In low-lying and flat fields ditches are needed to improve drainage after heavy rainfall. The soil is tilled periodically to remove weeds, to increase soil aeration, to promote root growth and to ridge the soil around the plants. Topping by removing the developing inflorescence is general practice in most tobacco types (except wrapper and oriental tobaccos) to improve leaf yield and quality, but any suckers that develop subsequently should be removed. Proper fertilizer application is important to obtain high yields of high-quality tobacco. The type and rate of fertilizer application depend on the tobacco variety and soil conditions. Flue-cured tobacco, for example, needs lower rates of nitrogen and higher rates of phosphorus than cigar tobacco. Fertilizer rates are of the order of 20-60 kg N, 20-50 kg P₂O₅, and 30-70 kg K₂O, the latter to be applied as K₂SO₄. Crop rotation is essential to prevent the build-up of soilborne diseases (e.g. bacterial wilt) and pests (e.g. nematodes).

In South-East Asia tobacco is subject to various major diseases and pests. They attack all plant parts at all growing stages. The most serious disease is caused by the soilborne bacterium Pseudomonas solanacearum, resulting in decay of the roots, followed by wilting. In the wrapper tobacco area near Medan, North Sumatra, only crop rotation can reduce the incidence of and damage by P. solanacearum. The duration of the non-tobacco cropping period and the type of crops included in the rotation are of great importance. In Java the wilting disease is less destructive because an annual crop rotation with irrigated rice reduces the pathogen level.

Black shank (Phytophthora nicotianae var. nicotianae) is an important and destructive root and stem disease in the South-East Asian tobacco areas. In Java losses are considerable and in the 1990s losses were also reported from North Sumatra. Plant sanitation and the use of resistant cultivars in combination with crop rotation and nematode control reduce the build-up of this soilborne disease. Soil application of metalaxyl reduced disease incidence in Java. Fusarium wilt (Fusarium oxysporum f.sp. nicotianae) is another root and stem disease occurring in the South-East Asian tobacco production areas, especially in rotations with sweet potato (Ipomoea batatas (L.) Lamk).

Frog-eye (Cercospora nicotianae), which produces white-brown spots on the leaves, can be a serious problem in wrapper tobacco during wet weather. The susceptibility to frog-eye increases with maturation of the leaves. Infection occurring a few days before harvest may result in green spots on the leaves after curing. Early leaf picking can prevent leaf damage when there are signs of an impending outbreak of frog-eye. A systemic fungicide (Benomyl) is sometimes used.

In seedbeds the major problem is damping-off of seedlings caused by Pythium spp. and Rhizoctonia solani. Soil sterilization and adequate aeration can considerably reduce damping-off. Another preventive measure is thinning seedlings to reduce air humidity around the plants. Once the soilborne fungus has arrived, via infested soil, agricultural equipment, surface or irrigation water or infected transplants, losses can be substantial. Seedlings in affected seedbeds should be destroyed and the seedbed soil should be steam-sterilized before it is used again.

Virus diseases such as tobacco mosaic virus (TMV), cucumber mosaic virus (CMV), "krupuk disease" or tobacco leaf curl virus (TLCV) and tobacco etch virus (TEV or "Rotterdam B") are of importance in almost all tobacco-growing areas of Indonesia. In the Philippines TMV is the most destructive virus disease. TMV is spread mechanically by humans, via implements and by contact from plant to plant during field operations. Cured leaves of mosaic-infected plants carry the virus for several years.

In South-East Asia insects cause considerable damage to leaves and stems and sucking insects such as aphids (Myzus persicae), whitefly (Bemisia tabaci) and thrips (Thrips tabaci) are also vectors of virus diseases. The leafworm (Spodoptera litura) and the budworm (Helicoverpa spp.) are the most predominant pests. In cigar tobacco areas in Java, integrated control of leafworm and budworm is practised by monitoring moth populations with sex pheromones, by scouting, and by removing egg colonies, hand picking of larvae, and spraying with pesticides whenever needed. The cutworm (Agrotis ipsilon) is found in areas where cabbage is grown in rotation with tobacco. The most important sucking insect is Myzus persicae, the vector of CMV and TEV. The whitefly is the vector of TLCV, and thrips is the vector of TSWV (Tomato Spotted Wilt Virus). Dry weather is favourable for the development of these insects. Therefore the occurrence of insect-transmitted virus diseases tends to increase during the dry season.

Cured leaves of tobacco can be infested by the tobacco beetle (Lasioderma serricorne). Control is carried out by monitoring insect populations in warehouses with red-light traps and in freight containers with sex pheromone (Lasio trap), and fumigating tobacco bales in the warehouse with phosphine. Root-knot nematodes (Meloidogyne spp.) are a worldwide serious pest in tobacco, only to be controlled by crop rotation or temporary inundation (e.g. after irrigated lowland rice).

Harvesting is a critical factor in producing high-quality tobacco. In tropical areas harvesting starts 50-60 days after transplanting. Normally a leaf is considered mature when its tip has just turned yellow. Wrapper type cigar tobacco is harvested earlier to produce light-coloured leaves. Cigar filler and cigarette tobaccos are, however, harvested at a later stage to obtain a better flavour.

In South-East Asia all types of tobacco are harvested by individual leaf picking (priming), starting with the lowest leaves, 2-4 at the same time, at 2-5 day intervals. Leaf position on the stem determines the quality of tobacco. From the bottom upwards the leaves are classified into sand leaves or lugs (4-6), foot leaves or cutters (6-8), middle leaves (6-8) and top leaves (4-6 leaves). In cigar tobacco sand and foot leaves are the best to be used as high quality wrappers. In cigarette tobacco middle leaves may have a better taste and aroma than bottom leaves, but for producing low nicotin cigarettes lower leaves are more suitable. Leaves to be flue or fire cured must be fully mature before harvesting, but if they are to be air or sun cured, they are harvested before full maturity.

World average yield of cured tobacco leaves is 1.5 t/ha. Average yields per ha are 2.5 t in the United States, Japan and Australia, 1.9 t in Zimbabwe, 1.7 t in China, 1.3 t in India and 0.8 t in Turkey and Malawi. National averages per ha in South-East Asia are: Indonesia 0.7 t, Vietnam 0.8 t, Malaysia and Burma (Myanmar) 1.0 t, Thailand 1.3 t and the Philippines 1.4 t. In Indonesia, low-input smallholder plots may produce only 400 kg/ha against 1.6 t/ha on large commercial estates. Seed yields are up to 25 g/plant, and potentially 450-600 kg/ha.

Tobacco leaves are usually strung back-to-back on sticks before being placed on racks in enclosed barns for curing. There are several ways:

• flue curing (cigarette tobaccos), in ventilated brick barns, heated for 5-7 days by hot air generated by burning wood or other fuels, which passes through metal flues; temperatures are gradually increased from 35°C to 80°C during the yellowing, colour-fixing and final drying stages;

• air curing (cigar, Burley and Maryland tobaccos), in thatched, bamboo or wooden barns with ventilating hatches, over a period of 3-4 weeks; early wilting and yellowing is followed by increasing ventilation to promote gradual drying at temperatures not exceeding 45°C;

• fire curing (dark cigarette, pipe and chewing tobaccos), in thatched or wooden barns with small open fires in pits in the floor to provide smoke, over a period of 2-3 weeks; temperatures gradually increasing from 35°C to 50°C.

Sun curing for 2-4 days in full sunlight on wooden or bamboo screens is common for oriental (Turkish) and the traditional "rajangan" (cut) tobaccos in Indonesia.

After curing, cigar tobacco should be fermented to improve its combustibility, aroma, colour and texture. By making a large heap of tobacco, the temperature inside the heap rises to 50°C and this facilitates optimum enzymatic changes. The heap is rebuilt 4-5 times after the critical temperature has been reached. The average fermentation period is 100 days. The next process is grading based on colour, thickness (body) and length of the cured leaves, and degree of leaf damage. The tobacco is then pressed into bales of 60-100 kg. In cigarette tobacco the process is finished after curing, however, during storage it undergoes aging. Virginia tobacco needs to be redried to reduce its moisture content to 12%.

The relative ease of introgression by interspecific hybridization allows the large genetic diversity, present in wild diploid Nicotiana species of Central and South America to be exploited to improve cultivated N. tabacum. For instance, N. glutinosa L. has been used extensively as a source of resistance to TMV, whereas N. longiflora Cav. and N. plumbaginifolia Viv. have been used for resistance to Phytophthora nicotianae. The United States Department of Agriculture (USDA) has assembled extensive collections of tobacco germplasm from several parts of the world which has been given TI (Tobacco Introduction) accession numbers. One of these is TI 245 which has a simultaneous resistance to TMV, CMV, tobacco ringspot virus, tobacco streak virus, tomato ringspot virus, turnip mosaic virus, and potato mottle virus. Intensive screening of world collections of Nicotiana for resistances to pathogens and insects is still in progress.

Since tobacco is a self-pollinating crop, most cultivars are pure lines developed by pedigree and backcross selection methods. On the one hand, tobacco is ideal for breeding, because of its easy self- and cross-pollination, the high rate of success of interspecific crosses, the abundance and longevity of its seeds, the large range of variability present for most plant characters and the extensive information accumulated from biometrical genetic studies. On the other hand, the specific demands on product quality by the well-established tobacco market and industry pose a considerable obstacle to the introduction of novel tobacco cultivars. Most of the tobacco is therefore produced by true-breeding selections of long standing. However, the hybrid vigour of crosses between cultivars of diverse origin and the advantages of hybrids that combine multiple disease resistances with yield and quality in one genotype has stimulated hybrid breeding in tobacco.

F₁hybrids are now used to produce cigar tobacco in North Sumatra and Central Java. They combine high yield with good quality and resistance to black shank. Since soilborne and virus diseases are difficult to control by cropping methods, breeding for resistance is essential. Resistance to TMV, for example, is controlled by a dominant gene (N), derived from N. glutinosa, and based on hypersensitivity to virus infection (necrotic lesions on the infected leaves). Resistant cultivars with this type of resistance have been used commercially in the production of cigar tobacco on East Java. Resistance to black shank from N. longiflora is also controlled by a major gene.

In N. tabacum polygenic resistance to black shank is found in cultivar "Florida 301" and cigar tobacco cultivar "Timor" from Central Java. Resistance to bacterial wilt is found in some flue-cured tobacco cultivars, i.e. "Dixie Bright 101" (popular in Indonesia since the 1950s), "Oxford 26", "NC 95", "NC 2326", "Coker 187", "Coker 254", "Coker 298" and "Coker 316". With the exception of "Oxford 26" all these cultivars are resistant to black shank.

The prospects for tobacco cultivation in South-East Asia are good. Although smoking is now universally discouraged and considered to be a health hazard, it seems likely that the consumption of cigarettes will continue to increase. With the population growth in Asia and the urbanization near major production areas (e.g. North Sumatra, Central and East Java in Indonesia and Chiang Mai in Thailand), virus diseases will become more menacing because of the spread of infection from neighbouring backyard gardens. Moreover, the soilborne diseases like black shank and bacterial wilt deserve more attention, as proper crop rotation and soil management will deteriorate due to shortage of land. Tobacco has been a model plant in the development of biotechnology and is well placed to take advantage of molecular methods for genetic improvement, such as resistance to serious pests (e.g. Bt genes against tobacco budworm) and elimination of potentially hazardous constituents in tobacco smoke. Genetically modified tobacco also has great potential for yielding essential pharmaceutical and other compounds. As wood for flue-cured tobacco will become increasingly scarce, research on a more efficient use of renewable energy should be given higher priority.

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I. Hartana & H. Vermeulen