Question

What are Bt crops? Explain in brief about how they are produced with a suitable example.

Answer 1

These are genetically modified crops that are produced by the methods of genetic engineering. These are obtained by the means of the alteration in genes of the bacteria known as Bacillus thuringiensis. Examples include Bt cotton, Bt brinjal, Bt soybean.

Complete answer:
Bt crops are the transgenic crops producing the same toxin that the bacteria Bacillus thuringiensis have i.e. Bt toxin and thereby protecting the crops from pests. It is the genetically modified crops that are widely used in agriculture. The toxin gene has been cloned from the bacterium Bacillus thuringiensis and been expressed in plants to provide resistance to insects without the need for insecticides and thus used as a bio-pesticide. Examples include Bt cotton, Bt corn, rice, tomato, potato and soyabean etc.
Bacillus thuringiensis produces some proteins that kill certain insects such as lepidopterans (tobacco budworm, armyworm) , coleopterans (beetles) and dipterans (flies, mosquitoes). Bacillus thuringiensis forms protein crystals during a particular phase of their growth which is having insecticidal protein. This crystal protein is incorporated into the crops by the help of vectors like Agrobacterium tumefaciens or by the help of physical methods.

Additional information: The choice of genes depends upon the crop that we want to modify and the targeted pest because most of the Bt toxins are insect group specific. The toxin coded by a gene named as cry gene that is various in numbers and each one is specific for a particular plant. Examples include cryIAc and cryIIAb produces the proteins that control the cotton bollworm whereas cryIAb controls corn borer.

Note: Bt toxin is does not kill the Bacillus thuringiensis because the toxin’s protein exist as inactive proteins but once it is ingested by the insects, the inactive toxin gets converted into active form due to the alkaline pH of the gut which solubilise the crystals. The activated toxins get bound to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis of the insect and eventually cause death of the insect.