A Bt crop is one that has been
genetically modified to mimic the soil bacterium, Bacillus thuringiensis, for
increased protection from insect pests such as European corn borer in corn, and
tobacco budworms, cotton bollworms and pink bollworms in cotton.
History of Bt
Japanese biologist,
ShigetaneIshiwatari was investigating the cause of the sotto disease
(sudden-collapse disease) that was killing large populations of silkworms when
he first isolated the bacterium Bacillus thuringiensis (Bt) as the cause of the
disease in 1901.
Ernst Berliner isolated a
bacteria that had killed a Mediterranean flour moth in 1911, and rediscovered
Bt. He named it Bacillus thuringiensis, after the German town Thuringia where
the moth was found. Ishiwatari had named the bacterium Bacillus sotto in 1901
but the name was later ruled invalid. In 1915, Berliner reported the existance
of a crystal within Bt, but the activity of this crystal was not discovered
until much later.
Farmers started to use Bt as a
pesticide in 1920. France soon started to make commericialized spore based
formulations called Sporine in 1938. Sporine, at the time was used primarly to
kill flour moths. In 1956, researchers, Hannay, Fitz-James and Angus found that
the main insecticidal activity against lepidoteran (moth) insects was due to
the parasporal crystal. With this discovery came increased interest in the
crystal structure, biochemistry, and general mode of action of Bt. Research on
Bt began in ernest.
In the US, Bt was used commercially
starting in 1958. By 1961, Bt was registerd as a pesticide to the EPA.
Up until 1977, only thirteen
Btstrains had been described. All thirteen subspecies were toxic only to
certain species of lepidopteran larvae. In 1977 the first subspecies toxic to
dipteran (flies) species was found, and the first discovery of strains toxic to
species of coleopteran (beetles) followed in 1983.
What Bt means?
BACILLUS THRUINGIENSIS
There are different ways of
moving genes in a plant to produce desirable traits. One of the more
traditional ways is through selective breeding. A plant with a desired trait is
chosen and bred to produce more plants with the desirable trait. More recently
with the advancement of technology is another technique. This technique is
applied in the laboratory where genes that express the desired trait is
physically moved or added to enhance the trait in the plant. Plants produced
with this technology are considered to be transgenic. Many times it is also
referred to as Genetically modified (GM).Results of insect infestation on
Bt (right) and non-Bt (left) cotton bolls. Source: USDA
DISADVANTAGES OF Bt
CROPS
1- Bacillus thuringiensis (Bt) is
a ubiquitous soil bacteria that produces a protein with insecticidal
properties. This protein has been genetically engineered into crops, such as
corn and cotton, to prevent damage by foraging insects. Concern over
genetically modified food safety has been prevalent since its incorporation in
the early 1990s. However, to date, there is no evidence to indicate that Bt
crops pose a danger to human health or to the environment.
2- The most serious disadvantage
is that long-term effects of genetically modified organisms is not known. BT
varieties of GM crops are the result of taking DNA from a bacteria and
inserting it into the seeds of corn, cotton, potatoes or other crops. This
makes it possible for the plants themselves to produce substances that repel
insects. Having that ability is good for insect control, but could have
negative long-term effects on animals and humans who eat the crops.
More immediate concerns are
possible contamination of non-GMO varieties and the crops becoming invasive in
the environment. There are reports that genetically-modified crops have
contaminated non-GMO varieties and that invasiveness has occurred.
METHODS OF MAKING Bt
CROPS-
Genetically engineered plants are
generated in a laboratory by altering their genetic makeup. This is usually
done by adding one or more genes to a plant's genome using genetic engineering
techniques.[20] Most genetically modified plants are generated by the biolistic
method (particle gun) or by Agrobacterium tumefaciens mediated transformation.
Plant scientists, backed by results of modern comprehensive profiling of crop
composition, point out that crops modified using GM techniques are less likely
to have unintended changes than are conventionally bred crops.
In research tobacco and
Arabidopsis thaliana are the most genetically modified plants, due to well
developed transformation methods, easy propagation and well studied genomes.
They serve as model organisms for other plant species.
In the biolistic method, DNA is
bound to tiny particles of gold or tungsten which are subsequently shot into
plant tissue or single plant cells under high pressure. The accelerated
particles penetrate both the cell wall and membranes. The DNA separates from
the metal and is integrated into plant genomeinside the nucleus. This method
has been applied successfully for many cultivated crops, especially monocots
like wheat or maize, for which transformation using Agrobacterium tumefaciens
has been less successful. The major disadvantage of this procedure is that
serious damage can be done to the cellular tissue.
Agrobacteria are natural plant
parasites, and their natural ability to transfer genes provides another method
for the development of genetically engineered plants. To create a suitable
environment for themselves, these Agrobacteria insert their genes into plant
hosts, resulting in a proliferation of plant cells near the soil level (crown
gall). The genetic information for tumour growth is encoded on a mobile,
circular DNA fragment (plasmid). When Agrobacterium infects a plant, it transfers
this T-DNA to a random site in the plant genome. When used in genetic
engineering the bacterial T-DNA is removed from the bacterial plasmid and
replaced with the desired foreign gene. The bacterium is avector, enabling
transportation of foreign genes into plants. This method works especially well
for dicotyledonous plants like potatoes, tomatoes, and tobacco. Agrobacteria
infection is less successful in crops like wheat and maize.
FUTURE PROSPECTS-
The global value of biotech seed
alone was US$13.2 billion in 2011, with the end product of commercial grain
from biotech maize, soybean grain and cotton valued at approximately US$160
billion or more per year.
Players in agriculture business
markets include seed companies, agrochemical companies, distributors, farmers,
grain elevators, and universities that develop new crops and whose agricultural
extensions advise farmers on best practices.
USES OF Bt CROPS-
Improved shelf life
The first genetically modified
crop approved for sale in the U.S. was the FlavrSavr tomato, which had a longer
shelf life. It is no longer on the market. As of 2012, an apple that has been
genetically modified to resist browning, known as the Nonbrowning Arctic apple
produced by Okanagan Specialty Fruits, is awaiting regulatory approval in the
US and Canada. A gene in the fruit has been modified such that the apple
produces less polyphenol oxidase, a chemical that manifests the browning.
Improved nutrition
The GM oilseed crops on the
market today offer improved oil profiles for processing or healthier edible
oils. The GM crops in development offer a wider array of environmental and
consumer benefits such as nutritional enhancement and drought and stress
tolerance. GM plants are being developed by both private companies and public
research institutions such as CIMMYT, the International Maize and Wheat
Improvement Centre. Other examples include a genetically modified cassava with
lower cyanogen glucosides and enhanced with protein and other nutrients, while
golden rice, developed by the International Rice Research Institute (IRRI), has
been discussed as a possible cure for Vitamin A deficiency. An international
group of academics has generated a vitamin-enriched corn derived from South
African white corn variety M37W with 169x increase in beta carotene, 6x the
vitamin C and 2x folate – it is not in production anywhere, but proves that
this can be done.
Stress resistance
Plants engineered to tolerate
non-biological stresses like drought] frost, high Soil salinity, and nitrogen
starvation,with increased nutritional value (e.g. Golden rice) were in
development in 2011.
Herbicide resistance
Tobacco plants have been
engineered to be resistant to the herbicide bromoxynil. And many crops have
created that are resistant to the herbicide glyphosate. As weeds have grown
resistant to glyphosate and other herbicides used in concert with resistant GM
crops, companies are developing crops engineered to become resistant to
multiple herbicides to allow farmers to use a mixed group of two, three, or
four different chemicals.
Pathogen resistance – insects
or viruses
Tobacco, and many other crops,
have been generated that express genes encoding for insecticidal proteins from
Bacillus thuringiensis (Bt). Papaya, potatoes, and squash have been engineered
to resist viral pathogens, such as cucumber mosaic virus which despite its name
infects a wide variety of plants.
Production of biofuels
Algae, both hybrid and GM, is
under development by several companies for the production of biofuels.[
Jatropha has also been modified to improve its qualities for fuel product.
Swiss-basedSyngenta has received USDA approval to market a maize seed
trademarked Enogen, which has been genetically modified to convert its own
starch to sugar to speed the process of making ethanol for biofuel. In 2013,
the Flemish Institute for Biotechnology was investigating poplar trees
genetically engineered to contain less lignin so that they would be more
suitable for conversion into biofuels.Lignin is the critical limiting factor
when using wood to make bio-ethanol because lignin limits the accessibility of
cellulose microfibrils to depolymerization by enzymes.
Production of useful
by-products
Drugs
Bananas have been developed, but
are not in production, that produce human vaccines against infectious diseases
such as Hepatitis B. Tobacco plants have been developed and studied, but are not
in production, that can produce therapeutic antibodies.
Materials
Several companies and labs are
working on engineering plants that can be used to make bioplastics. Potatoes
that produce more industrially useful starches have been developed as well.
Bioremediation
Scientists at the University of
York developed a weed (Arabidopsis thaliana) that contains genes from bacteria
that can clean up TNT and RDX-explosive contaminants from the soil: It was
hoped that this weed would eliminate this pollution. 16 million hectares in the
USA (1.5% of the total surface) are estimated to be contaminated with TNT and
RDX. However the weed Arabidopsis thaliana was not tough enough to withstand
the environment on military test grounds and research is continuing with the
University of Washington to develop a tougher native grass.
Genetically modified plants have
also been used for bioremediation of contaminated soils. Mercury, selenium and
organic pollutants such as polychlorinated biphenyls (PCBs), TNT and
RDXexplosive contaminants have been removed from soils by transgenic plants
containing genes for bacterial enzymes.
Email: 167shailesh.bot@gmail.com
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