Bt cotton

bacillus thurigenesis

1. Bt. Cotton By: 4 th semester, section A Shahroze khan Roll no. A001

2. Bt. Cotton Variety of cotton. Genetically modified cotton crop that expresses an insecticidal protein gene. Gene derived from a soil bacterium called Bacillus thuringiensis , commonly referred as Bt. Generally known to be toxic to various genera of insects but safe to other living organisms. Marketed by Monsanto, USA.

3. Bacillus thuringiensis Shigetane Ishiwatari (1901), first isolated Bacillus thuringiensis as the cause of sotto disease (sudden-collapse disease) of silkworms, named Bacillus Sotto. Bt is commonly abbreviated as Bacillus thuringiensis , is a gram-positive, facultative aerobic, rod-like, motile and sporulating bacterium. Bt is a naturally-occurring soil borne bacterium that is found worldwide Ubiquitous in nature. Produces crystals of endotoxin ( Cry protien or delta toxin) - toxic to insect mainly in their larval stage, thus they act as insecticides.

4. These crystal proteins (Cry proteins) are insect stomach poisons Insects stop feeding within two hours of a first bite and, if enough toxin is eaten, die within two or three days Important biological insect control agent. Bt crystals, sometimes referred as insecticidal crystal proteins (ICP), are protein crystals formed during sporulation in some Bt strains coded by cry genes.

5. Organism activity The B.thuringiensis strains produce three types of insecticidal toxins. crystal (Cry) toxins, cytolytic (Cyt) toxins vegetatively expressed insecticidal proteins (vip). These toxins are highly specific to certain insect species. A total number of 342 Bt toxin genes are available for research to develop insect resistant GM crops.

6. Bt. Cotton In cotton, the first transgenic plant was developed in 1987 in U.S.A. by Monsanto, Delta and Pine companies (Benedict and Altman, 2001). The transgenic cotton is of two types : Bollguard Roundup Ready cotton The former confers resistance to bollworms and the latter is resistant to herbicides. The area under herbicide resistant transgenic cotton is restricted to USA.

7. Crystalline protein

8. How Bt Works? Ingestion Solubilization & proteolytic activation Binding to target site Formation of toxic lesions

9. Epithelium Dissolving of crystals and activation of toxins Pro-toxin Activated ∂- endotoxin Receptors Toxins bind to receptors Perforation of gut membrane Crystals Hilbeck and Schmidt (2006) Fig 10: Mode of Action of Bt Toxin in Insect Gut

10. TECHNOLOGY OF PRODUCTION Main steps for developing transgenic crops : Identification of effective gene(s). Gene transfer Regeneration from protoplast/callus/tissue Gene expression to the desired level Back cross to produce varieties Field test Approval for commercialization

11. Why do we need Bt-cotton? Cotton is a long duration crop and is attacked by large number of insect pests throughout its growth and development. The three bollworms, American bollworm( Helicoverpa armigera ) ,Pink bollworm ( Pectinophora gossypiella ) and the Spotted bollworms, Earias vittella and Earias insulana are major pests and cause serious threat to cotton production resulting in significant yield losses. About 9400 M tonnes of insecticides worth Rs 747 crores were used only for bollworm control in 2001.

12. Cotton bolls are highly vulnerable to hidden insects. Bollworms, especially the pink and spotted bollworms are hidden feeders and generally do not come into direct contact with insecticide sprays. The American bollworm has developed resistance to almost all the insecticides recommended for its control in all regions of the world. Resistant sources are unavailable in the germplasm. Nearly 90.0% of all insecticides in Pakistan and about 50.0% of all insecticides in India were being unsuccessfully used for cotton pest control, until the year 2001, before Bt cotton was introduced. Of these insecticides about 70.0% was for bollworm control and the rest for sap-sucking insects.

13. What are the Impacts on the Environment? The feeding of Bt cotton seed to animal has not been reported to have any adverse effect. Seed of Bt cotton and its cake do not have any adverse effect on digestion of animals. Moreover, no allergic or toxic effect of use of Bt cotton seed and meal has been reported.

14. The oil extracted from the seed of Bt cotton has not been found to have any adverse effect on human health.

15. No adverse effect of Bt. cotton has been reported on non target beneficial insects so far. No adverse effect of Bt. cotton on the environment has been reported by any of the countries where Bt. cotton is commercially cultivated.

16. Benefits of cotton Inbuilt genetic resistance to bollworms very effective in controlling the yield losses. The resistance is governed by a single dominant gene. Reduces use of pesticides thus reducing the cost of cultivation. Provides wider adaptability. Promotes ecofriendly cultivation of cotton and allows multiplication of beneficial insects. Reduces environmental pollution which results by use of insecticides.

17. The insecticides are rarely used. An average reduction of 3.6 sprays per crop season has been reported in Bt varieties as compared to non-Bt.

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