Applications of Biotechnology in Agriculture - Bt Cotton

Bt cotton is a transgenic cotton variety that contains one or more genes from Bacillus thuringiensis and therefore produces an insecticidal protein toxic to certain insect pests.

The soil bacterium Bacillus thuringiensis (Bt) produces an insecticidal protein called 'Bt toxin'.

Cotton crops are commonly attacked by bollworms, which reduce yield and increase dependence on chemical insecticides. Bt cotton was developed to provide built-in biological resistance against these pests and to reduce repeated pesticide spraying.

Cotton boll: (a) destroyed by bollworms; (b) a fully mature cotton boll

1. A gene coding for Bt toxin is isolated from Bacillus thuringiensis.
2. This gene is introduced into the cotton plant through genetic engineering.
3. The transgenic cotton plant produces the Bt protein.
4. The insect pest feeds on the plant parts.
5. Inside the alkaline gut of the insect, the inactive protoxin becomes active.
6. The active toxin binds to epithelial cells of the insect midgut.
7. Pores are formed in the gut wall, leading to cell swelling and lysis.
8. The insect dies due to gut damage.

Different cry genes control different insect pests.

Remember: Different Bt toxin genes target different insects.

• Reduces damage caused by major insect pests such as bollworms.
• Lowers the need for repeated chemical insecticide sprays.
• Can help improve crop productivity when pest damage is controlled effectively.
• Shows greater specificity, meaning the toxin acts against selected insect groups rather than all organisms.
• May reduce environmental pollution associated with overuse of pesticides.

• Insect populations may gradually develop resistance to Bt toxins over time.
• Bt cotton does not solve every agricultural problem; it mainly targets specific pests.
• Overdependence on a single control method may reduce long-term effectiveness.
• Public discussions around genetically modified crops often include ecological, economic, and regulatory concerns.

• Bt cotton is a transgenic cotton crop containing gene(s) from the soil bacterium Bacillus thuringiensis, enabling it to produce an insecticidal protein.
• This protein, known as Bt toxin, is initially produced in an inactive form called a protoxin.
• The protoxin becomes activated only in the alkaline gut environment of susceptible insects such as bollworms.
• The active toxin binds to midgut epithelial cells, causing pore formation, cell swelling, and eventual cell lysis leading to insect death.
• Different cry genes (cryIAc, cryIIAb, and cryIAb) target different pests, with cryIAc and cryIIAb controlling cotton bollworm and cryIAb controlling corn borer.
• Bt cotton reduces dependence on chemical insecticides and offers targeted pest resistance, though insects may eventually develop resistance to the toxin over time.