RAS question
Bt cotton, India's only approved GM crop, incorporates genes from which bacterium to confer insect resistance?
Correct answer: (B) Bacillus thuringiensis.
Bt cotton gets its insect resistance from Cry genes taken from the soil bacterium Bacillus thuringiensis.
Explanation
Bt cotton is named for Bacillus thuringiensis, a naturally occurring soil bacterium that produces proteins active against certain insects. Bt cotton contains Cry genes, including Cry1Ac and Cry2Ab, from this bacterium. These genes encode Cry, or crystal, proteins that are toxic to bollworm larvae such as Helicoverpa armigera. That is why Bacillus thuringiensis, not a general plant-transformation bacterium or a nitrogen-fixing microbe, is the source linked to insect resistance. In India, Bt cotton was approved in 2002 and remains the only commercially grown genetically modified crop.
Why the other options are wrong
- (A) Agrobacterium tumefaciens can be used as a vector to introduce genes into plants, but it is not the source of the insecticidal Cry genes in Bt cotton.
- (C) Rhizobium leguminosarum is associated with nitrogen fixation in legume root nodules, so it does not explain Bt cotton's bollworm resistance.
- (D) Pseudomonas fluorescens is described as a bio-control agent against fungal pathogens, not as the source of the Cry genes used in Bt cotton.
Concept
This tests applied biotechnology: how a transgenic crop gains a specific trait from an inserted gene. It recurs in RAS because GM crops, biosafety and agriculture-linked science are standard Science and Technology themes.