Containing Transgenic Plants and Their Genes
Gene flow among plants has been one of the most debated topics pertaining to transgenic plants. The acquiring of a gene from one plant by another has deterred many environmentalists away from supporting transgenic plants. The most publicized concern is the spread of a beneficial gene to plants in the wild. This idea has created what we now call “Superweeds.”
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| (Permission pending Mahyco Seed, 2000) | (Permission pending from Wilson, Jeff) |
Transgenic to transgenic Plant Gene flow
Herbicide-resistance can be transferred by herbicide-resistant plants to other herbicide-resistant plants. This event is called “gene stacking.” Gene stacking is the accumulation of beneficial, foreign genes in one organism. Gene stacking occurs when plants of the same species that live near each other are engineered with different genes. Triple herbicide resistance in canola plants has been attributed to gene stacking. Three groups of canola were planted in one area. Each group was resistant to one herbicide. Individuals from the three groups accumulated genes from all the groups, and became triple herbicide-resistant. Gene stacking in canola has become very common in Canada (Beckie, H.J., and et al., 2004). The problem with gene stacking is that if one of these triple herbicide-resistant plants dispersed into another field, it could be come a triple herbicide-resistant weed. If the canola from Canada invaded fields used for soybeans, the canola would essentially be a triple herbicide-resistant superweed (Beckie, H.J., and et al., 2004; Pew Initiative, 2003).
Transgenic to non-transgenic plants gene flow
Outcrossing
Outcrossing occurs when the pollen of a transgenic plant fertilizes a non-transgenic plant. Outcrossing was thought to be a minor threat early on, because of the conditions needed for outcrossing to occur. For outcrossing to occur the plants had to be in the same habitat, have the same chromosome number, and have the same phenology. These claims were partly true. The plants involved in outcrossing do have to be closely related, however, it was for outcrossing to occur than previously thought. Maize and teosinte can transfer genes to each other in the wild. Also, cotton plant species in Florida have transferred genes among their populations. To prevent outcrossing transgenic plants should be grown in areas where there are no relatives of the transgenic plants. This isolation of transgenic plants would be very difficult, since plants can transmit pollen over long distances (Shelton , A. M., and et al., 2002).
Biotechnology companies produce herbicide-resistant crops and Bt crops that farmers can plant. Herbicide-resistant crops can tolerate having herbicide sprayed on them. Herbicide-resistant crops contain genes that encode their resistance to certain herbicides. These genes can be transferred to other plants, given that the recipient plant can incorporate the gene into its genome. Superweeds are weeds that have acquired herbicide-resistance by acquiring genes from transgenic crops. Several species of weeds have become resistant to Round-Up herbicide. Normal ryegrass, waterhemp, and goosegrass have all developed resistance to Round-Up while in their native habitats. . Superweeds can out-compete normal weeds, because of the high selection pressure that herbicides exert on weed populations (Martinez-Ghersa, and et al., 2003). Bt crop gene transfer presents the same problems as herbicide-resistant crops (Pew Initiative, 2003). The genes for Bt toxins could be passed to weeds, which would allow weeds to kill insects that usually eat them. Weeds that have these beneficial genes have a comparative advantage over normal weeds. Weeds that have Bt toxins or herbicide-resistance can out-compete weeds that do not. These weeds can persist in habitats where normal weeds would die from herbicides or insect predation (Pew Initiative, 2003). Superweeds can use Bt toxins to kill its natural predators, so that only normal weeds get eaten. Superweeds have the potential to spread through the environment, because they have acquired ways to overcome traditional methods of limiting them. For this reason, superweeds are also called invasive (Pew Initiative, 2003).
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This website was created by
Kevin Saunders, Helen Nguyen, and Chris Wrobleski
as part of an undergraduate assignment at Davidson College.
Send questions or comments to chwrobleski@davidson.edu.
© Copyright 2004 Department of Biology, Davidson College, Davidson, NC 28035.