Crops, Traits, and AcreageThe
most important transgenic crop in terms of acreage planted
is soybean, followed by corn, cotton, and canola.
The number of acres for each crop are given in the graph
below (Source: James,
2002, 2001a, 2001b, 1997). This graph is also available
hectares instead of acres.
Adoption of transgenic crops in the United States has
been far greater than in many other countries. The following
graph shows the acreage of transgenic crops in the United
States from 1996 to 2003.
In 1999, the area planted
to transgenic varieties was approximately half of the
U.S. soybean crop and about 25% of the U.S. corn crop.
The estimated worldwide area planted to transgenic varieties
in 2000 increased 11% over the 1999 area (James, 2000b). Most of
the transgenic crop varieties currently grown by farmers
are either herbicide tolerant or insect pest-resistant.
In addition to the crops listed below, minor acreages
were planted to transgenic potato, squash, and papaya.
|Transgenic crop production
area by country (source: James, 2000b)
||Area planted in 2000
(millions of acres)
||soybean, corn, cotton, canola
||soybean, corn, cotton
||soybean, corn, canola
For information on transgenic crop acreage as a percentage of the total U.S. acreage in 2000, see the news update entitled Acreage for transgenic cotton and soybeans up, corn down.
|Worldwide production area of transgenic crops and traits (source: Science 286:1663, 1999).
||Area planted in 1999 (millions of acres)
|Bt insect resistance
|Bt + herbicide tolerance
Weed control is one of the farmer's biggest challenges in crop production, because poorly controlled weeds drastically reduce crop yield and quality. Many herbicides on the market control only certain types of weeds, and are approved for use only on certain crops at specific growth stages. Residues of some herbicides remain in the soil for a year or more, so that farmers must pay close attention to the herbicide history of a field when planning what to plant there.
Herbicide tolerant crops resolve many of those problems because they include transgenes providing tolerance to the herbicides Roundup® (chemical name: glyphosate) or Liberty® (glufosinate). These herbicides are broad-spectrum, meaning that they kill nearly all kinds of plants except those that have the tolerance gene. Thus, a farmer can apply a single herbicide to his fields of herbicide tolerant crops, and he can use Roundup and Liberty effectively at most crop growth stages as needed. Another important benefit is that this class of herbicides breaks down quickly in the soil, eliminating residue carry-over problems and reducing environmental impact. Herbicide tolerant varieties are popular with farmers because they enable less complicated, more flexible weed control. These varieties are commonly marketed as Roundup Ready® or Liberty Link® varieties.
Weed-infested soybean plot (left) and Roundup Ready® soybeans after Roundup treatment. Source: Monsanto
For more information on herbicide tolerant transgenic crops see the article "Herbicide Tolerant Soybeans: Why Growers Are Adopting Roundup Ready Varieties", J. Carpenter & L. Gianessi, AgBioForum online journal, Vol. 2 No. 2, http://www.agbioforum.org/
Bt Insect-Resistant Crops
European corn borer (left) and
cotton bollworm (right) are two pests controlled
by Bt corn and cotton, respectively.
"Bt" is short for Bacillus thuringiensis, a soil bacterium whose spores contain a crystalline (Cry) protein. In the insect gut, the protein breaks down to release a toxin, known as a delta-endotoxin. This toxin binds to and creates pores in the intestinal lining, resulting in ion imbalance, paralysis of the digestive system, and after a few days, insect death. Different versions of the Cry genes, also known as "Bt genes", have been identified. They are effective against different orders of insects, or affect the insect gut in slightly different ways. A few examples are shown in the table below.
|Cry gene designation
||Toxic to these insect orders
|CryIA(a), CryIA(b), CryIA(c)
|Cry1B, Cry1C, Cry1D
The use of Bt to control insect pests is not new. Insecticides containing Bt and its toxins (e.g., Dipel, Thuricide, Vectobac) have been sold for many years. Bt-based insecticides are considered safe for mammals and birds, and safer for non-target insects than conventional products. What is new in Bt crops is that a modified version of the bacterial Cry gene has been incorporated into the plant's own DNA, so that the plant's cellular machinery produces the toxin. When the insect chomps on a leaf or bores into a stem of a Bt-containing plant, it ingests the toxin and will die within a few days.
Bt insect-resistant crops currently on the market include
Corn: primarily for control of European corn borer,
but also corn earworm and Southwestern corn borer.
A list of approved Bt hybrids is available through
the National Corn Growers Association web site (http://www.ncga.com/biotechnology/know_where/know_grow_approved.htm).
Click on the "event" name to see the list
Cotton: for control of tobacco budworm and cotton bollworm
Potato: for control of Colorado potato beetle. Bt
potato has been discontinued as a commercial product.
See our Discontinued
Products page for more information.
Corn hybrid with a Bt gene (left) and a hybrid susceptible to European corn borer (right). Source: Monsanto
Results of insect infestation on Bt (right) and non-Bt (left) cotton bolls. Source: USDA
Corn hybrids resistant to corn rootworm
Corn rootworm (Diabrotica spp.) is a serious
pest of corn in many U.S. growing areas. It damages
roots of young corn seedlings, resulting in reduced
growth and poor standability of the plant. This
insect is responsible for the application of the
largest amount of insecticide to U.S. corn fields.
What's more, to control this pest the insecticide
must be applied directly to the soil, where it
may leave residues or leach into the ground water.
By replacing these chemical insecticides, corn
rootworm resistant hybrids may provide major benefits
to environmental quality.
Corn rootworm feeding on a young
maize root. Source: USDA
Range of damage due to corn
rootworm feeding, from severe (left) to no damge
(right). Source: USDA
Although rootworm-protected hybrids apparently offer
pest management and environmental benefits, there are
serious concerns about development of resistance to
Bt in this adaptable insect. More information about
rootworm-resistant Bt hybrids is available in articles
et al. (2001), and Ostlie
State University has a discussion of rootworm-protected
corn at http://www.msue.msu.edu/ipm/CAT02_fld/FC4-11-02.htm#4.
Rootworm-resistant corn was approved in 2003.
Have Bt crops reduced the use of chemical pesticides?
The use of Bt varieties has dramatically reduced the
amount of chemical pesticides applied to cotton. According
to a story in Science (Ferber,
1999a), US farmers used 450,000 kg less pesticides
on Bt-cotton than they would have used on conventional
varieties in 1998. Yields and profits also improved
in Bt-cotton fields. The benefits from Bt-corn, however,
were not as clear-cut. Due to the difficulty of effectively
controlling corn borers with insecticides, most farmers
do not apply chemical controls to their conventional
corn fields. Thus, Bt hybrids substituted for chemical
pesticides on only about 20% of the total US Bt-corn
area. Profitability of Bt-corn is not as certain as
for cotton; it will vary over years and locations, depending
on the intensity of the corn borer population. See our
discussion of pesticide use on Bt crops on this
Will insect pests become resistant to Bt toxins?
Although Bt genes have proven to be quite effective
in the short term for protecting against crop insect
damage, as well as reducing fungal contamination of
and Heimlich, 1999, http://www.apsnet.org/online/feature/BtCorn/Top.html],
there are concerns that widespread use of Bt varieties
will accelerate development of resistance to Bt in the
target pests. This could mean the loss of Bt as an effective,
environmentally friendly insecticide. In response to
these concerns, the U.S. Environmental Protection Agency
has mandated measures to reduce the risk of resistance
development. These measures depend on a combination
of high dose of the Bt toxin and a planting of refuges.
A refuge refers to an area planted to a non-Bt variety
that is physically close to a field planted with a Bt
variety, as shown in the diagram below.
Diagram of the BT refuge strategy, in which at least 20% of a farm's corn acreage must be planted to non-BT corn. R = resistant European corn borer adult; S = susceptible adult.
Beginning in 2000, the EPA requires that farmers growing Bt corn must plant at least 20% of their total corn acreage to a non-Bt variety. The rationale is that the few Bt-resistant insects surviving in the Bt field would likely mate with susceptible individuals that have matured in the non-Bt refuge. Thus, the insect genes (alleles) for resistance to Bt would be swamped by the susceptible alleles. Whether this strategy will work or not remains to be seen. Some of the potential problems with the refuge strategy are:
The frequency of Bt-resistant alleles in insect populations may be greater than assumed in refuge models.
Resistance to Bt in European corn borer may be semi-dominant rather than recessive.
Resistant insects surviving in the Bt field may mature several days later than susceptible insects in the refuge, thus preventing their mating.
For information on compliance with the refuge requirements,
see the news updates entitled 29%
of Bt corn farmers in U.S. broke the rules last year,
of Bt corn farmers in U.S. still breaking the rules,
compliance improves, and 14%
of U.S. Bt corn farmers still breaking the rules.
and Van Rie 2002 discuss the biochemistry and genetics
of insect resistance to Bt.
A discussion of designs for refuges is available from
the University of Illinois Extension Office at http://www.ag.uiuc.edu/cespubs/pest/articles/200203e.html.
Pioneer Hybrid explains the rules for planting a refuge
Because there are a number of web sites with extensive information on Bt crops, we refer you to them for additional information on the topic.
Papaya is a tropical fruit rich in Vitamins A and C,
but susceptible to a number of serious pests and diseases.
The transgenic variety UH Rainbow, resistant to the
papaya ringspot virus, is currently in production in
Papaya is an important source of vitamins in tropical areas. Source: USDA
For more information, refer to:
Transgenic virus resistant papaya: New hope for controlling
papaya ringspot virus in Hawaii. http://www.apsnet.org/education/feature/papaya/Top.htm
Cornell University's page on virus resistant GM
crops, including payapa. http://www.comm.cornell.edu/gmo/traits/virusres.html
Global Status of Approved Genetically Modified Plants
Agriculture and Biotechnology Strategies (Canada) Inc. maintains a database of trangenic plants that have been approved for environmental release, use in livestock feed, or use in human food. Information is organized by crop and by trait. The information can be accessed at http://www.agbios.com/_Synopsis.asp.
Transgenic Foods on the Supermarket Shelves
The cooperative extension office at Cornell University has assessed the likelihood that food products contain genetically engineered ingredients. Their assessment is available at http://www.comm.cornell.edu/gmo/crops/eating.html.
Greenpeace's List of GM and Non-GM Foods
Greenpeace, which campaigns against transgenic foods, maintains a list of food brands that they claim contain or do not contain transgenic ingredients. The list is available at http://www.truefoodnow.org/shopping_list.html.
Discontinued Transgenic Products
Several transgenic products that received approval for marketing have been discontinued for a variety of reasons. Some, such as the FlavrSavr tomato and NewLeaf potato, were available for years before they were discontinued. We have assembled a list of these products with links to more information about their history and the reason for their disappearance.