BACKGROUND

A transgene is a gene from one organism that is introduced into the genome of a different type of organism. A transgene escape is a potential problem associated with crop biotechnology. Weed-to-crop hybridization has already become a problem in that gene flow has led to the appearance of new or more difficult weeds. For example, hybridization between sea beet and sugar beet has created a weed that has severely damaged Europe’s sugar production. With the introduction of genetically engineered crops, such events are expected to become more numerous because engineered genes may confer advantages to wild populations (Klinger & Ellstrand 1994).

Weed-crop hybridization can occur when pollen flows between transgenic crops and wild relatives. The resulting hybrids could establish themselves or persist for a long period and in high enough densities for the transfer of transgenes into wild populations (Linder & Schmitt 1995). If transgenic crops hybridize with nearby weedy relatives, the predicted transfer of genes will be inevitable when farmers plant these crops on a commercial scale (Marvier 2001). The movement of unwanted crop genes in the environment is possible because a single crop allele has the opportunity to multiply itself repeatedly through reproduction, making containment nearly impossible (Ellstrand 2001). Weeds resistant to herbicides are a considerable problem. Clearly, farmers do not want advantages to be transferred to weeds because their persistence could lead to lower yields due to weed damage.

One such possible advantage, of which farmers are wary, is herbicide resistance. Herbicide resistance is created in a plant by manipulating its genes to detoxify an herbicide that is sprayed on it (Simmonds and Smartt 1999). This is a beneficial trait because farmers can spray their fields with herbicides, killing weeds, while not having to worry about the effect it will have on their crops. Monsanto’s herbicide, Roundup, is used by some farmers before planting because it is effective at killing almost anything green. Roundup is considered a good herbicide because its active ingredient, glyphosate, is less toxic than many other herbicides on the market. The only problem is that after crops are planted, farmers could not spray more glyphosate because, as such an effective killer, it would kill their crops in addition to weeds. Monsanto created Roundup Ready soybeans which are herbicide resistant, specifically to Roundup. The application of Roundup without killing crops can be seen as a very positive advancement in crop production for farmers.

Although herbicide resistance is a positive trait for soybeans, it can be a major problem when transferred to weeds. “Superweeds” may arise when herbicide-tolerant crops cross-pollinate with wild cousins, resulting in herbicide-resistant weeds (Orogan & Long 2000). After a certain amount of time and exposure, any species can develop a resistance to an herbicide (Marvier 2001). To prevent creation of “superweeds,” some transgenic crops are made sterile which prevents transgene escape. But this means that farmers need to purchase new seeds after each season, which can be costly. Although tests of genetically engineered plants are currently being performed, the true risks may not be realized until the damage has occurred, as this is still a relatively new technology. Therefore when the full extent of this problem becomes clear, it may be too late for us to mitigate the effects.

The figures for this Figure Set are from two Ecological Applications articles about fitness of weed-crop hybrids. These data will allow students to better understand how effects of escaped transgenes are measured in wild populations.


Literature cited:

Ellstrand, N. C. 2001. When transgenes wander, should we worry. Plant Physiology 125: 1543-1545.

Klinger, T., and N. C. Ellstrand. 1994. Engineered genes in wild populations: fitness of weed-crop hybrids of Raphanus sativus. Ecological Applications 4 (1): 117-120.

Linder, R., and J. Schmitt. 1995. Potential persistence of escaped transgenes: performance of transgenic oil-modified Brassica seeds and seedlings. Ecological Applications 5: 1056-1068.

Marvier, M. 2001. Ecology of transgenic crops. American Scientist Mar/Apr. 2001.

Orogan, J., and C. Long. 2000. The problem with genetic engineering. Organic Gardening 47.1: 42-46

Simmonds, N. W., and J. Smartt. 1999. Principles of Crop Improvement. Oxford: Blackwell Science.