Bt cotton is a genetically modified variety of cotton that expresses a gene from the soil bacterium Bacillus thuringiensis (Bt), which produces a protein that is toxic to certain insect pests like bollworms but harmless to other organisms. It was developed to control major cotton pests that can cause significant yield losses. Bt cotton reduces the need for insecticide use and promotes more environmentally friendly cotton cultivation while protecting yields. The Bt gene works by being toxic only to insects that ingest the Bt protein, but is safe for other animals and humans.

2. Bt. Cotton
BY: 4TH SEMESTER, SECTION A
SHAHROZE KHAN
ROLL NO. A001

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. Crystalline protein

9. How Bt Works?
1. Ingestion
2. Solubilization & proteolytic activation
3. Binding to target site
4. Formation of toxic lesions

11. 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

12. TECHNOLOGY OF PRODUCTION
 Main steps for developing transgenic crops :
1. Identification of effective gene(s).
2. Gene transfer
3. Regeneration from protoplast/callus/tissue
4. Gene expression to the desired level
5. Back cross to produce varieties
6. Field test
7. Approval for commercialization

13. 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.

14.  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.

16. 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.

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

18.  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.

19. 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.

20.  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.

21. Thanks for
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