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GM Crops: A Farmer's Dream?

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Conferring Resistance

Disease

Pest/Herbicide

Stress

Ramifications

Increased Profit Margin

Land Use

Monoculture

Poor Farmers vs.  Rich Farmers

Cultural Backlash

Conclusions

Works Cited

 

Pest/Herbicide Resistance

Most of the development of commercial GM crops has been focused on pest and herbicide resistant crops (Pretty, 2001).  Pest resistant Bt crops were one of the first to be commercialized and have, thus far, proven effective (Conway, 2000).  In 1999, a short 4 years after the first commercial GM pest/herbicide resistant crops, approximately 40% of U.S. corn, soybean, and cotton fields were planted with such GM crops (Kalaitzandonakes, 1999). 

Pest/herbicide resistance can be conferred in a number of ways:

§         Agrobacterium-mediated gene transfer where Agrobacterium vectors carrying a promoter sequence, a terminator sequence, and the desired gene are transformed into the plant cell nucleus.  This process is good for dicot species (e.g. tomato, potato, rapeseed), but not normally good for monocot species, although it does work with rice (Jung, 2000).

§         “Microprojectile bombardment” with DNA coated tungsten or gold particles may be used to transform all plant species.  The DNA is released into the cell during its travel, and can be incorporated into the cell nucleus.  This event is rare, and this technique must be performed on plant tissue that can regenerate.  This process has been used to transform millet, barley, wheat, rice, papaya and maize (Jung, 2000).

§         Electroporation or CaCl2 and PEG can be used to transform plant protoplasts, and then grown into whole plants.  This method has been used to transform maize and rice (Jung, 2000).

§         Transformation of plastid DNA is a recent development.  Desired traits are integrated using homologous recombination between the DNA construct and the plastid DNA.  This method has not been successful with crops as of yet, but would be advantageous since it would result in high expression rates.  Also, the resistance would not be passed to future generations through pollen, an important environmental concern (Jung, 2000).

To learn how pest/herbicide resistance works on the genetic level:

Pest Resistance

Herbicide Resistance


Questions or comments can be directed to  nihesson@davidson.edu

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Last modified April 2004