BBt
cotton
Cotton and other
monocultured crops require an intensive use of pesticides as various types of
pests attack these crops causing extensive damage. Over the past 40 years, many
pests have developed resistance to pesticides.
So far, the only
successful approach to engineering crops for insect tolerance has been the
addition of Bt toxin, a family of toxins originally derived from soil bacteria.
The Bt toxin contained by the Bt crops is no different from other chemical
pesticides, but causes much less damage to the environment. These toxins are
effective against a variety of economically important crop pests but pose no
hazard to non-target organisms like mammals and fish. Three Bt crops are now
commercially available: corn, cotton, and potato.
As of now, cotton is
the most popular of the Bt crops: it was planted on about 1.8 million acres
(728437 ha) in 1996 and 1997. The Bt gene was isolated and transferred from a
bacterium bacillus thurigiensis to American cotton. The American cotton was
subsequently crossed with Indian cotton to introduce the gene into native
varieties.
The Bt cotton
variety contains a foreign gene obtained from bacillus thuringiensis. This
bacterial gene, introduced genetically into the cotton seeds, protects the
plants from bollworm (A. lepidoptora), a major pest of cotton. The worm feeding
on the leaves of a BT cotton plant becomes lethargic and sleepy, thereby causing
less damage to the plant.
Field trials have
shown that farmers who grew the Bt variety obtained 25%�75% more cotton than
those who grew the normal variety. Also, Bt cotton requires only two sprays of
chemical pesticide against eight sprays for normal variety. According to the
director general of the Indian Council of Agricultural Research, India uses
about half of its pesticides on cotton to fight the bollworm menace.
Use of Bt cotton has
led to a 3%�27 increase in cotton yield in countries where it is grown.
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