Cotton is a most important fiber and commercial crop of the world which is cultivated in tropical and semi tropical regions of the world. The cotton is also known as 'white gold'. India stands first in area, third in production and seventeenth in productivity. In India, Punjab, Haryana, Rajasthan, Madhya Pradesh, Gujarat, Maharashtra, Andhra Pradesh, Karnataka and Tamil Nadu are major cotton growing states. These states contribute about 95 per cent to the national cotton production. Cotton production has become reduced due to biotic and abiotic stresses. Among biotic stresses, insect pest incidence becomes a major constraint in cotton production. To meet the changing needs of present day requirements and for developing improved varieties in cotton, genetic engineering is an effective technique through which transgenic plants are developed by tissue culture. The genetic engineering helps in manipulation of foreign genes and tissue culture is essential for genetic transformation. The foreign gene cannot be inserted into the whole plant. It can only be inserted into single cells. The genetic transformation can be achieved through cell culture or protoplast culture.

Bt cotton and its action against boll worm
The genetically engineered organisms are called transgenics or genetically modified organisms. Bt cotton refers to the Bacillus thuringiensis. The Bt is short form of ubiquitous soil bacterium Bacillus thuringiensis. This bacterium is gram positive and spore forming that forms parasporal crystals during stationary phase of its growth cycle. The synthesized crystalline (Cry) protein called 'endotoxins' are highly toxic to certain insects and kill by acting on the epithelium tissue of midgut of caterpillars. These proteins are characterized by their insecticidal activity and are therefore grouped into five classes.

Crystalline protein - Effective against
Cry I - Lepidoptera insects
Cry II - Lepidoptera and Diptera insects
Cry III - Coleopteran insects
Cry IV - Diptera insects
Cry D - Lepidoptera insects

The first transgenic plant was developed in 1983 in tobacco in USA. The first transgenic cotton plant was developed in 1987 in USA by Monsanto, Delta and pine companies. Later on, the research work on development of transgenic bollgard cotton has two types viz. Bollgard I and Bollgard II. The Bollgard I contains Cry 1 Ac Bt gene in its genome. The Bollgard II is the next generation transgenic Bt cotton. It has combination of two genes, viz. Cry 1 Ac and Cry 1 Ab into cotton genome. Bollgard II has 4-5 times more effective than Bollgard I. the Bollgard cotton confers resistance to bollworms. Roundup ready cotton was another transgenic cotton which is resistant to herbicides and is commonly used for control of weeds in cotton crop. This is grown in USA and some other countries.

Why Bt cotton is needed?
In cotton, insect pests causes significant yield losses. Among the insect pests, bollworms occupy a major portion in reduction of yield. There are three types of bollworms, viz. American bollworm (Helicoverpa armigera), pink bollworm (Pectinophora gossypiella) and spotted bollworm (Earias vitella) affect the cotton crop and causes sever yield losses. Use of insecticides is not economically and environmentally feasible and some times development of resistance in insects against insecticides. Hence, there is a need to develop resistant cotton cultivar against bollworms to control yield losses due to bollworms. Due to the absence of resistance source to the bollworms in the germplasm of cotton, the Bt cotton is the only ray of hope to control bollworms. Genetic Engineering Approval Committee (GEAC) under ministry of environmental management, Govt. of India has approved three Bt cotton varieties viz. MECH 12, MECH 162, MECH 184 (producing Cry 1 Ac gene insecticidal protein) for commercial cultivation after 6 years of trials. As per the GEAC recommendations for the cultivation of Bt cotton should be in 80:20 ratio i.e., 80 per cent for Bt cotton and 20 per cent for non Bt cotton. It is expected that the use of Bt cotton will reduce the adverse effects of insecticides on;
• Natural enemies and parasites on bollworms,
• Beneficial insects,
• Human health and environmental conditions,
• Organisms such as earthworm, blue green algae, nitrogen fixing bacteria etc.

Advantages of Bt cotton
Bt cotton has several advantages over non Bt cotton. The important advantages of Bt cotton are briefly pointed out as bellow:
1. Increases yield of cotton due to effective control of three types of bollworms, viz. American, Spotted and Pink bollworms.
2. Insects belonged to Lepidoptera (Bollworms) are sensitive to crystalline endotoxic protein produced by Bt gene which intern protects cotton from bollworms.
3. Reduction in pesticide use in the cultivation of Bt cotton in which bollworms are major pests.
4. Reduction in the cost of cultivation and lower farming risks.
5. Reduction in environmental pollution by the use of insecticides rarely.
6. Bt cotton exhibit genetic resistance or inbuilt resistance which is a permanent type of resistance and not affected by environmental factors. Thus protects crop from the attack of bollworms.
7. Bt cotton is ecofriendly and does not have adverse effect on parasites, predators, beneficial insecticides and organisms present in soil.
8. It promotes multiplication of parasites and predators which help in controlling the bollworms by feeding on larvae and eggs of bollworm.
9. No health hazards due to rare use of insecticides (particularly who is engaged in spraying of insecticides).
10. Bt cotton are early in maturing as compared to non Bt cotton.

Disadvantages of Bt cotton
Bt cotton has several advantages but it has some limitations also, which were given as below;
1. High cost of Bt cotton seeds as compared to non Bt cotton seeds makes not afforded by small and marginal farmers of India.
2. Effectiveness upto 120 days, after that the toxin producing efficiency of the Bt gene drastically reduces.
3. Adverse effect on insecticide manufacturing companies due to reduced use of pesticides significantly by Bt cotton.
4. Adverse effect on the employment of those persons engaged in pesticide industries.
5. Ineffective against sucking pests like jassids, aphids, whitefly etc.
6. Promotes malpractices such as mixing of low-cost non Bt cotton seeds with high cost Bt cotton seeds for sale. This severely affects on cotton production and economic condition of the farmers using such fake seeds.

The resistance breeding is the cheapest, safest and most efficient method of protecting crop plants from biotic and abiotic stresses. The transgenic Bt cotton with inbuilt genetic resistance to bollworms will help in protection of natural enemies of insect pests by reducing the use of pesticides. Moreover, it will reduce environmental pollution and health hazards caused by pesticidal use. Further, there is a need to develop multiresistant varieties with improved quality and quantity of cotton crop which will available to the farmers at cheaper cost.

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