Because tomatoes are one of the world's most popular
vegetables, they have benefited from a long history
of genetic improvement that continues in the transgenic
age. Lycopene, a naturally occurring constituent
of tomato, is a nutritional factor related to
Vitamin A. Tomato varieties with transgenically
enhanced lycopene content are under investigation.
Another trait of interest is delayed ripening.
Tomatoes that ripen slower can remain on the vine
longer and develop improved flavor, compared to
commercial varieties that are picked at the green
stage. The Flavr-Savr® tomato, one of the earliest
approved transgenic crop varieties, was a delayed
ripening variety. Because the trait was incorporated
into a variety that performed poorly otherwise,
it was not a commercial success. For more information
on transgenic tomato research, see http://www.ars.usda.gov/is/
Salty soils are an increasing problem in many
parts of the world. Many crop plants, including
tomatoes, are killed by high salt levels in soil
and irrigation water. The development of a salt-tolerant
tomato offers the possibility that tomatoes could
be grown on land that was previously unavailable
for agriculture. Scientists (Zhang
and Blumwald, 2001) at the University of California
and the University of Toronto have developed a
tomato plant that is able to tolerate high levels
of salt and that holds the salt in its leaves,
so the fruit will not taste salty. It will take
an estimated three years before salt-tolerant
tomatoes are available commercially. A story on
the potential benefit of this new trait in tomatoes
is available at http://www.guardianunlimited.co.uk/international/story/
Improved nutritional content and delayed ripening are transgenic traits of
interest in tomatoes. Source: USDA
Two tomato plants
artificially inoculated with bacterial speck disease. Plant on
left has been genetically engineered with a gene for resistance
to the disease, and plant on right is a susceptible,
non-engineered variety. Source: Dr. Steve Tanksley, Cornell
Developing kernels of rice. Source: USDA
Millions of people in the world suffer from Vitamin A deficiency, which
leads to vision impairment and increased susceptibility to diarrhea,
respiratory diseases, and measles. Rice is a staple food in many
countries, particularly in Asia, but does not contain Vitamin A or its
immediate precursors. By inserting two genes from daffodil and one gene
from a bacterial species into rice plants, Swiss researchers have produced
rice capable of synthesizing beta-carotene, the precursor of Vitamin A
(Ye et al.,
This rice variety is now being crossed into adapted varieties, with field
tests possible in a year or two.
Canola is a major oilseed crop. Transgenic research has focused on
improving the nutritional quality of canola oil by enhancing the Vitamin E
content or by modifying the balance of fatty acids.
Nutritionally improved oils are the goal of transgenic research in canola.
Improved Turfgrass for Lawns and Recreational Areas
There are a number of environmental concerns associated with the current
use of turfgrass. These include
- the amount of chemicals applied (fertilizers, herbicides,
fungicides, and even green dyes);
- the large quantity of water required to keep lawns healthy,
especially in the West;
- the energy required to mow lawns.
New transgenic turfgrass varieties will address some of these concerns by
incorporating genes for herbicide tolerance, disease and insect
resistance, reduced growth rates (meaning less mowing), and tolerance to
drought, heat, and cold. The first such product on the market will most
likely be Roundup Ready® varieties of Kentucky bluegrass, creeping
bentgrass, and buffalograss. Weed control in lawns of these varieties can
be accomplished with the herbicide Roundup, which is more environmentally
friendly than currently used herbicides like 2,4-D.
Food crops engineered to produce edible vaccines against infectious
diseases would make vaccination more readily available to children around
the world. Because of their palatability and adaptation to tropical and
subtropical environments, bananas have received considerable research
attention as a vehicle for vaccine delivery. Transgenic bananas containing
inactivated viruses that cause cholera, hepatitis B, and diarrhea have
been produced and are currently undergoing evaluation.
A disease-resistance trait, an anti-pest trait, and a herbicide-resistance trait are all being pursued, but no commercial varieties are now on the market. White mold (Sclerotinia) is a serious problem for sunflower producers in some areas. Resistance to this disease would expand the area in which sunflowers can be grown and might improve yields in areas of current cultivation. A commercially available cultivar is not expected before 2005. Resistance to the Argentina looper, an insect that eats sunflower leaves, is also being investigated. Some research has been done on developing sunflowers that can tolerate being sprayed with the weed killer Roundup. This trait would allow a farmer to spray his field for weeds while not killing the crop. For more information on transgenic sunflower research, see
Field of sunflowers. Source: USDA.
Forest trees such as poplar, aspen, and spruce
have been transformed with various genes to provide
resistance to insects, tolerance to herbicides,
and higher levels of the commercial product. For
example, reducing the lignin content of a tree
can make it easier to recover wood pulp. For a
range of views on the potential risks and benefits
of transgenic trees, see presentations from a
symposium at http://pewagbiotech.org/events/1204/index.php3#agenda.
Some transgenic tree species now being tested
Transgenic trees probably will not be commercially available until at least 2006. Source: Kaiser, J. 2001.
Page last updated : March 11, 2004
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