Question
How has the study of biotechnology helped in developing pest resistant cotton crop? Explain.
Or
One of the major contribution of biotechnology is to develop pest resistant varieties of cotton plants. Explain how it has been made possible.✓
Answer
The pests that destroy the cotton balls are cotton bollworms and cotton borer. Bt cotton is created by using some strains of a bacterium, Bacillus thuringiensis (Bt is short form).
- This bacterium produces protein that kills certain insects such as lepidopterans (tobacco budworm and armyworm), coleopterans (beetles) and dipterans (flies and mosquitoes).
- Bacillus thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein.
- Bt toxin protein exists as inactive protoxins in bacteria, but once an insect ingests this inactive toxin, it is converted into an active form due to the alkaline pH of the gut, which solubilises the crystals.
- The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis leading to death of insect.
- Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into several crop plants.
- Most Bt toxins are insect-group specific. The toxin is coded by a gene named cry. For example, the proteins encoded by the genes cry IAc and cry IAD control the cotton bollworms and cry IAb controls corn borer.
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