Agriculture Reference
In-Depth Information
This leads to more rapid development of new varieties. The entire span of genetic
traits is available for use, expanding the range of useful traits available for develop-
ment of new germplasm.
The two major transgenic traits that are found commercially today are
Bacillus
thuringiensis
(Bt) and Roundup-ready (RR) (Roundup is a glyphosate herbicide)
crops. Bt is a soil-dwelling bacterium that produces a
cry
protein toxin when it sporu-
lates that specifically acts in the gut of certain insects and causes the gut of the insect
to become leaky and thus kill the pest. There are several specific
cry
proteins that
have specific activities against different orders of insects, including the Lepidoptera
(moths and butterflies), Diptera (flies and mosquitoes), and Coleoptera (beetles). The
main
cry
genes in commercial production are specific to the Lepidoptera and are
used to control these insect pests in cotton (bollworm) and maize (earworm and stem
borer). The gene that codes for the
cry
protein is introduced into the crop plant using
the two techniques listed (gene gun or agrobacterium), where it gets incorporated
into the crop genome. When the transgenic plant is eaten by a member of the cater-
pillar family, the gene enters the gut of the caterpillar, where it produces the insecti-
cidal protein that causes the gut to become leaky and kill the caterpillar. This protein
is very animal specific and does not react in the same manner in humans and thus
poses no biosafety risk. Spores and crystalline insecticide proteins produced by the
Bt organism are also marketed for pest control and used in organic farming for pest
control. It is regarded as environmentally friendly with little or no effect on humans,
wildlife, or beneficial insects like bees. Interestingly, Bt sprays are approved for use
on organic farms, but transgenic crops are not. Since the gene for the
cry
protein is
found in the chromosomes of the transgenic crop, all plant tissues produce the
cry
protein throughout crop growth and thus help protect the plant from insect attack.
Molecular scientists can also engineer plants in which only specific plant tissue
phases of the plants' life have the gene active or turned on, but this is not yet found
in presently grown commercial transgenic crops.
A similar system is used in developing herbicide-resistant transgenic crops. In
the case of RR crops, the gene was isolated from an
Agrobacterium
soil bacteria
and incorporated into various crops. It imparted herbicide resistance to glyphosate, a
broad-spectrum, translocated herbicide that kills most plants it enters. Of the various
herbicides available for modern agriculture, it is considered to pose less health risk to
humans and have fewer negative environmental effects. Glyphosate is definitely less
toxic than other herbicides presently used to control weeds in agriculture.
In 2006, transgenic crops exceeded 100 million hectare (ha) globally, with soybean
(60 million), maize (25 million), cotton (10 million), and canola (5 million) the major
commercial crops using this technology (ISAAA, 2006). Herbicide tolerance has the
largest hectarage (75 m), followed by Bt (15m) and the rest with both these traits. The
major countries growing transgenic crops were the United States (55 m), Argentina
(18 m), Brazil (11.5 m), and Canada (6 m). China and India also had significant acre-
ages of these crops (3.5 m), mostly using Bt cotton. In 2006 in the United States, 89%
of soybeans, 82% of cotton, and 61% of maize were transgenic. This means that many
food items in supermarkets in the United States contain these materials.
An example of transgenic crop use in a developing country is found in India
(Herring, 2007). Cotton is a major crop in that country for use domestically and for
