TRANSGENIC BT TECHNOLOGY
C Kameswara Rao
Foundation for Biotechnology Awareness and Education
In the year 2008, 25 countries have commercialized genetically engineered (GE) crops. Global cultivation of GE crops increased from 1.7 mill ha in 1996 to 125 mill ha in 2008, accounting for a cumulative acreage of two billion acres (800 mill ha) (James, 2008). Issues related to the impressive growth of GE crops and the diverse benefits of 13 years of commercialization of GE crops are discussed in detail by James (2008).
Transgenic technology, involving a wide range of pesticidal genes from the universally occurring soil bacterium Bacillus thuringinesis (Bt), dominates the scenario of GE crops. A gene from any source (such as Bt) is the transgene, which when successfully incorporated into the genome of another organism, the recipient becomes the transgenic organism. An isogenic is the organism into which the transgene was introduced.
While the terms Bt cotton, Bt corn, Bt potato, etc., are familiar, the level of understanding of what the technology actually means, what it can and what it cannot do, is very poor. Bt technology is also the most focused target of vehement anti-tech activism.
The objective of this review is to provide basic information on a variety of issues such as the biology of Bacillus thuringiensis, its proteins, use of Bt as a biopesticide, transgenic Bt crops, biosecurity regulation of transgenic crops and the benefits and limitations of the technology, which are very important components of public awareness essentially needed for informed decision making, answering the scientifically unsound criticism of the technology.
2. BACILLUS THURINGIENSIS, Bt PROTEINS AND TOXINS
2.1 Bacillus thuringiensis
Bt is a rod shaped, non-pathogenic, Gram-positive, soil bacterium, discovered in 1901. Bt is among the most thoroughly studied bacterial species of agricultural importance, its diverse aspects having been researched for over a century. The book ‘Bacillus thuringiensis: Biology, Ecology and Safety’ (Glare and O’Callaghan, 2000) refers to over 8,000 research publications by over 10,000 biologists, in over 60 years, and deals with most of the issues raised against the use of Bt. Ignorance of this and other subsequent publications on Bt or a deliberate indifference to them, led to a much exploited misunderstanding of Bt technology.
2.2 Concept of Bt
The term Bt now refers to not a single simple species entity, but to a large group of subspecies and varieties, based on over 60,000 isolates, collected from all over the world (Glare and O’Callaghan, 2000). There are more than 80 serologically characterized (using specific antibodies) types of Bt.
The controversy about distinguishing Bacillus thuringiensis from the related but pathogenic Bacillus cereus and Bacillus anthracis was adequately addressed (Maagd et al., 2005). When types of Bt can be identified serologically, a microbiologist can certainly distinguish the three species.
2.3 Bt in nature
Bt was isolated from several thousand soil samples from 80 different countries. It commonly occurs also on the aerial parts of plants such as leaves and on even thoroughly washed fruits and vegetables we consume. It may be present in water, possibly as a wash off from the soil and plant surfaces. Bt may be transported in the atmosphere, as inferred from its presence deep in the polar ice cap.
Bt grows and competes, but poorly in soil. Bt or its proteins may persist for about 100 days in soils, for 24 hr in running water and for 12 days in stagnant water bodies (Glare and O’Callaghan, 2000). Bt seems to require an association with plants and insects to perpetuate for longer periods in nature.
2.4 Bt as a biopesticide
Bt produces a wide range of insecticidal proteins that have been in use in pest control since 1938. There are about a 100 biopesticides exclusively based on Bt and over 90 per cent of commercial biopesticides, used even in organic farming, contain Bt.
2.5 Bt proteins and their encoding genes
Bt produces a large number of proteins that are toxic to specific insect groups under specific conditions. Bt also produces a) several enzymes, b) some compounds that lyse erythrocytes, and c) some that are enterotoxic to vertebrates. Bt toxins are produced either within the bacterial cell (endotoxins), or on the cell surface (exotoxins).
More than 170 toxin-encoding genes have been isolated form Bt collections (Glare and Callaghan, 2000). Among the endotoxins, the insecticidal crystalline proteins, called the δ-endotoxins, are significant in Bt technology. The crystalline proteins are described para-sporal, as they are co-produced and co-exist along with spores (the means of bacterial propagation), in the bacterial cells. When the bacterial cell lyses to release the spores, the crystalline proteins are also routinely released into the soil.
The names of the genes that encode the crystalline proteins are prefixed with ‘Cry’, as for example Cry1Ab, Cry1Ac, Cry9c, etc., and the proteins that are encoded by these genes are ‘Cry’ proteins. The non-crystalline endotoxins are prefixed with ‘Cyt’.
Bt proteins are per se not toxic. To function as toxins Bt proteins require a specific set of biochemical and biological parameters which are available for different Bt proteins only in specific insect groups, which makes Bt toxins insect group specific. For example, Cry1Ac and Cry2Ab control the cotton bollworm, Cry1Ab controls corn borer, Cry3Ab controls Colarado beetle of potato and Cry3Bb controls corn rootworm. The Bt genes that are incorporated into different crops are specific to Lepidopteran (having wings covered by scales) pests on them.
2.7 Pre-requisites for insecticidal activity of Bt proteins
The following conditions are essential for an effective insecticidal activity of the Bt proteins:
a) The pest must take a few bites and ingest the plant tissue; Bt transgenics are not effective against sucking pests that do not ingest plant tissue (such as the Homopteran insects that have no scales on the wings).
b) An alkaline environment (pH 9.5 and above) in the gut of the insect pest is essential for the Cry proteins to dissolve in the gut fluids and to be converted into an active molecule to function as an insecticidal compound. This does not happen in mammalian stomachs which are highly acidic.
c) The pest specific toxic activity of different Bt toxins depends upon the presence of appropriate receptors, in the lining of the mid-gut (brush border) of the pest, which are absent form some pests, as evidenced by different Bt proteins being non-toxic to certain insect species. The toxin binds to the receptors (which are also absent from mammalian guts) and causes disturbance in the integrity of the gut wall, leading to leakage of the contents, followed by starvation and death of the pest.
Fundamentally, the alkaline gut environment and the presence of an appropriate toxin binding receptor are crucial for insecticidal activity of Bt proteins. Basing on such requirements, the genes that encode pest specific toxins are chosen for developing different transgenic crops.
3. BT CROP HYBRIDS/VARIETIES
3.1 Agro-climatic zones and crop varieties
The physical and chemical characteristics of a) the soil,
b) the quantity, periodicity and
distribution of rainfall and/or irrigation facilities, and
c) the range of temperature, are
factors important for a healthy crop life. These factors,
which vary from country to
country and even within a country from region to region,
are very critical to successful
agriculture. Taking all such relevant factors together,
several agro-climatic zones, each
characterized by a set of parameters concerning the soil,
rainfall (or irrigation facilities), and temperature, are identified in
countries with diverse physiographic features. The Planning Commission of India
has recognized 15 agro-climatic zones in
3.2 Transgenic Bt varieties
Specific Bt protein-encoding genes were isolated from Bacillus thuringiensis and incorporated into the genetic complements of several crop plants such as cotton, corn, rice, tomato, potato, soybean, brinjal and others, to develop transgenic Bt varieties tolerant of specific pests, using elegant but complex procedures of genetic engineering. This results in a crop variety with a single systemic insecticide that kills specific caterpillars feeding on the respective crop. For each crop the most damaging pest has been targeted, as for example, the cotton bollworms, corn root worm, Colarado beetle of potato, stem borers of rice and corn and the stem and fruit borers of brinjal. The objective is that, while the Bt proteins take care of the major pests, the rest can be controlled by conventional pest management practices. The transgenics containing the appropriate insect group specific genes are developed mostly as hybrids rather than as varieties. In the case of hybrids, the farmer has to buy the seed each season to derive full benefits of technology, but for the reason of farmers’ recurring expenses on seed the activists object to hybrid seeds, though they are far superior to varieties in several respects.
A gene construct (or a cassette) consisting of the chosen Bt gene is made, along with
other molecular components needed for its expression in the
transgenic crop variety.
The construct basically consists of sequences of
nucleotides (the building blocks of DNA,
the genetic material), a) to initiate the expression of the
selected gene, b) to promote such
expression, c) the actual sequence for the gene and d) a
nucleotide sequence to signal the
completion of the process of expression. Using one of
several methods, this construct is
incorporated into the genome of a (chosen primary) variety
of the crop, which then comes
to be called an event. A large number of plants are
developed from the event, through
micropropagation (tissue culture) for agronomic and
biosecurity evaluation. Since the
primary variety may not be suitable for cultivation in all
countries or even in different
regions in the same country, the event has to be
transferred into the genomes of other
varieties suitable for cultivation in different parts of
the world. For example, the event
MON 531, containing the Cry1Ac gene, was used to develop
the Bt cotton variety of
Coker 312, which is not suitable for cultivation in
The costs of developing so many different hybrids with the same transgenic event and the costs of the associated regulatory processing of all these hybrids escalate steeply by the time the transgenic products reach the consumer.
3.3 Gene stacking
Most transgenics contain only one transgene, such as for
pest tolerance or herbicide
tolerance. In order to compound the benefits, more than one
gene is used in the
development of a transgenic, by gene stacking or
pyramiding. Transgenic cotton
containing two pesticidal genes Cry1Ac and Cry2Ab
(MON15985, Bollgard II) is in
commercial cultivation in many countries, including
Gene stacking can also occur in nature. If two transgenic varieties of the same crop are tolerant of a different herbicide each, natural intercrossing of these two varieties may result in a hybrid tolerant of both the herbicides. Similarly, the progeny of a cross between a pest tolerant and a herbicide tolerant variety would be tolerant of both the pest and the herbicide.
3.4 Acquired resistance and refugium
A prolonged exposure to a toxin at sub-lethal doses may result in the development of gene-based resistance in organisms, called acquired resistance. Famous examples of such acquired resistance are mosquitoes resistant to DDT, crop pests resistant to chemical pesticides and human pathogenic bacteria resistant to antibiotics. There is a possibility of crop pests acquiring genetic resistance to Bt proteins in Bt crops, due to natural variation in susceptibility to a particular toxin in the caterpillar populations. Nevertheless, over a decade of cultivation of various Bt transgenics in different countries has not thrown up any instances of acquired resistance of the concerned pests to Bt toxins.
Acquired resistance is a very slow process but may build up to significant levels over several generations. In order to de-accelerate the development of acquired resistance, the regulatory frame work in all countries has stipulated that about five rows of the non- Bt iosgenic plants should be planted along with the Bt crop and this is called the refugium (border or barrier). A certain number of the caterpillars feeding on Bt plants may escape death and if there was mating among these worms, the resulting progeny are likely to be tolerant of Bt toxins to various degrees. The caterpillars feeding on the non-Bt refugium are not exposed to the Bt toxin and so would be susceptible to it. In the presence of a refugium, a certain proportion of the progeny would be from the mating of Bt-exposed and Bt-unexposed worms, and this progeny would be far less tolerant of the Bt toxin than the progeny from Bt-exposed worms. The refugium would thus retard the pace of acquired resistance.
It is that much more difficult for acquired resistance to
build up from a transgenic with
two stacked Bt genes such as Bollgard II, than from
a transgenic with a single Bt gene.
Cotton farmers in
4. EXPRESSION OF TRANSGENES
4.1 Natural variation in gene expression
The tendency to vary is the only consistent feature of Nature. All species of organisms, whether wild or cultivated, show naturally inherent variation in physical, chemical and physiological features, which is also the basis for distinguishing different speciesand/or varieties. Each species or variety shows some variation in several features both between and within its populations. Nevertheless, species and varieties have a set of discernible and invariable features characterizing their identity. All transgenic Bt cotton varieties contain some quantity of Bt protein, though the actual quantities of the protein may vary from one variety to the other, as well as within each variety. In addition, there is
a) variation related to time (temporal), based in the age of the individual/population reflected in the growth phase such as vegetative, flowering, fruiting and other stages, and
b) spatial variation within an individual specimen reflected in different parts of the plant such as the root, stem, leaf, floral parts, fruits and seeds.
By centuries of experience, biologists in general and agricultural scientists in particular, fully understand that the expression of the same gene or set of genes (reflected by the synthesis of a protein/enzyme) is influenced by several factors, some inherent in the organism and some in the environment. Some of this variation is genotypic based in the
differences in the genetic constitution (genotype) between the varieties. The other kind is phenotypic variation, the result of an interaction between the genotype and the environment, so much so the same genotype behaves differently in different areas and seasons. Cultivation and management practices also influence gene expression and so the crop’s performance. Consequently, no crop variety, either conventional or GE, can be expected to perform uniformly throughout the entire area, or history, of its cultivation. The full expression of the transgenes in a transgenic crop variety is an ideal situation, but transgenic varieties may behave differently depending upon the genotype of the recipient variety and on where and how it is being cultivated, as has happened also in conventional agriculture all through. Most of the factors that affect gene expression are beyond the control of the plant breeders and biotechnologists, once a variety is chosen for transgenic development.
4.2 Variation in the expression of Bt genes
Even when Bt crop varieties are cultivated in the
recommended agro-climatic sub-zones,
there would be significant differences in the expression of
Cry1Ac gene in them.
The general health of the crop is an important factor in
realizing the full genetic potential
of a crop variety. The expression levels of a gene may
decrease as the age of the crop
advances. There may be differences in expression levels
between young and older parts
such as the leaves or between comparable parts in
vegetative and reproductive phases.
Such variation in the expression of Bt event in
cotton was observed in
Soil characteristics, rain fall, the severity of pests and diseases, adequate, appropriate and timely farming inputs such as irrigation, weeding, fertilizer, supportive pesticide application, all have a direct or indirect influence on the performance of the crop and may affect the expression of the transgenes and so the benefits derived from transgenic technology. All these factors, inherent in the varieties and/or the environment vary from one crop season to another, making the difference between supraoptimal, optimal or suboptimal performance of a crop or even its failure.
Transgenic Bt technology produces crop varieties that are only tolerant of the targeted pests and not fully resistant to them (GEAC, 52nd Meeting, 2005). The farmer has to be advised on the varieties suitable for cultivation on his land, and the appropriate cultivation practices and precautions needed in every crop season, in order to derive the maximum possible benefit during each season. The objective of transgenic technology is to derive cost effective benefits of the technology over a considerable period of time and not in a particular season or in a particular region in a season. No crop variety has ever performed uniformly season after season in all regions of its cultivation.
Ignoring the factors that control crop performance is poor crop husbandry. Technology should not be blamed for ills befalling for reasons of poor management that lie beyond the realm of a particular technology.
4.3 Quantification of gene expression
Expression of transgenes varies with the nucleotide sequence of the gene, its promotor, and the point of insertion of the gene in the DNA of the transgenic variety, the internal cell environment, as well as several external factors in the environment. It is necessary to know how a Bt gene is expressing in a transgenic variety, in order to evaluate its effectiveness against the targeted pest. Comparing the density, morbidity and mortality of pest populations, on the Bt and its isogenic non-Bt variety, is one way of doing this. But a more direct way is to accurately quantify gene expression in terms of the protein/enzyme it helps to synthesize. There must be a certain minimum quantity of the Bt protein in the plant parts, particularly during the more vulnerable phases of the crop, to control the pest. The quantity of Bt protein present in different parts of the plant during the crucial phases of pest damage such as the boll formation in cotton, would give an idea of the effectiveness of the technology in a particular Bt variety.
Field kits have been developed to quantify Bt proteins in transgenics. The Bt gene construct is introduced into the experimental bacterium Escherichia coli, so that the gene product is more easily purified from the transgenic bacterium, than from a transgenic crop variety. Antibodies are raised against this purified protein, and these antibodies are used to quantify the Bt protein in the transgenic variety, through an enzyme-linked immuno-assay method. This procedure results in a colour reaction whose intensity gives the measure of the quantity of the protein involved. Quantification of Bt proteins by this procedure is relatively simple and with little instruction and minimal facilities, a semiskilled worker can conduct the test. However, the simplicity of the test itself is its undoing. The test is expected to work with a little bit of hand-crushed tissue of the Bt transgenic plant. Unfortunately, quantification of expression of the Bt gene is sensitive to the following factors (Shantharam and Kameswara Rao, 2006):
a) Kits from different sources vary in their details, such as whether the antibodies used were monoclonal or polyclonal. Kits based on polyclonal antibodies are good enough to find out if any Bt protein is present in the tissue, but are not very
exact to quantify the protein that occurs in microgram quantities. Though monoclonal antibodies provide for a more accurate quantification, most kits are based on polyclonal antibodies, as the production of monoclonal antibodies is more technically involved and so more expensive. There have been complaints on the accuracy and consistency of several of these kits, but authentic data are unavailable. Actually it is necessary that the kits available on the market were assessed for their reliability.
b) The tissue should be properly homogenized and the protein extracted in an appropriate buffer. Crushing a bit of a tissue in water is not an exact scientific way of extracting even most of, if not all of, the protein in the tissue.
c) The excised plant part should be used immediately for assay. Protein degradation is quite rapid in excised and stored tissue.
d) There would be differences in the protein content depending upon whether the part used for assay was from a plant in the vegetative or the reproductive phase. Hence the results can be compared only between similar parts of similar age taken from plants that were in a comparable physiological state of development.
e) Mature leaves, bolls and seeds are more fibrous and harder, and contain several chemical compounds such as resins, oils, phenolics, etc., which accumulate with the age of the part and which may interfere with the extraction of the protein in the tissue.
Not observing these precautions would result in incomparable, unreliable and misleading data.
5. SUBSTANTIAL EQUIVALENCE OF TRANSGENICS AND THEIR ISOGENICS
The US Food and Drug Administration (FDA) routinely and
stringently used the
Principle of Substantial Equivalence (PSE) for decades to
assure the public of the safety
of foods and drugs. This criterion refers only to the
product and not the process of its
production. On account of the high standards of FDA’s
regulatory oversight, most other
countries generally approve drugs and pharmaceuticals on
the basis of FDA’s approval.
PSE is now being applied to products from genetically
engineered organisms (GEOs), in
order to assure the consumer that the product is
'Substantially Equivalent' (SE) to its
conventional counterpart and so is safe for human consumption.
In the context of
modern agricultural biotechnology, PSE is frequently an
issue for serious discussion
The FDA has long considered GE crops to be substantially
equivalent to conventional
varieties and required no other regulatory review. However,
using the ‘provision for
voluntary consultation’, biotech companies in the
The policy of the FDA did not result in any health concerns
but invited criticism on
account of, a) the FDA itself has a mandatory process for
approving transgenic animals,
Products from transgenics of such crops as soybean, tomato,
corn, cotton, etc., on the
The presence in the GEOs, of new genes that would code for fats, proteins or carbohydrates, that may be toxic or may cause allergies or may adversely affect the nutritional value of the product, prevents certification as SE or GRAS, without
appropriate and adequate testing.
While in the
In the application of PSE, the comparison should be between the GE variety and its isogenic, which is the basic variety into which a transgene was inserted. The certification is to the effect that the GE crop variety is substantially equivalent to its isogenic, in genotype, marked characteristics and performance, but for the transgenes and their anticipated characteristics. If the isogenic were safe, the transgenic would be equally safe, provided that the newly introduced transgenes do not exercise any adverse effects by themselves or through altering the expression of any other genes of the
isogenic, in the transgenic environment. Such an assurance requires scientific evaluation of the crop variety first, and then of its products. This involves additional efforts, time and expense, raising consumer costs.
At no time, transgenics can be substantially equivalent to their isogenics in their entire genotypes and this is not related to transgenic technology. Even to start with, members of the same population are not entirely genetically identical. In addition, mutations occur naturally and randomly, involving different genes. Lethal mutations are naturally eliminated. Mutations of the genes of the desired characteristics are eliminated in the process of selection, but those that do not affect the desired characteristics escape attention and accumulate. After a certain number of generations, a critical genetic analysis will contravene SE, although SE can be established for the genes of the desired characteristics. Such a situation would cause problems in some countries, where the regulatory authorities apply the principle of SE more in letter than in spirit, and a lot more strictly than in other countries.
The official European consensus is that SE should only be
used to guide and inform
safety assessments. Codex Alimentarius, the
international set of guidelines for food
standards and safety, sees it as a starting point in the
regulatory process rather than an end
point (Codex Alimentarius Commission, 2008).
However, in the
Notwithstanding the importance given to PSE, it has been criticized as vague, ill defined, flexible, malleable, open to interpretation, unscientific and arbitrary (Ho and Steinbrecher, 1998).
On account of the concerns raised, PSE should be re-examined, and for re-defining its applicability to GE crop plants and their products, laying emphasis on a reasonable application of the principle, addressing only those genes and their products that are relevant to the objectives of developing a particular transgenic variety or product. There is also a dire need for a uniform and harmonized international policy. At the moment, there is no evidence that SE is an issue that adversely affects the safety of Bt transgenics or their products.
In the context of modern agricultural biotechnology the term Biosecurity has two components: a) Biosafety, the safety of genetically engineered (GE) organisms and/or their products to humans and animals as food, feed and medicine, and b) Environmental safety, the safety of non-target organisms, soil and water. The terms biosecurity and biosafety are often used incorrectly as synonyms.
There is no risk-free technology. It was the international scientific community, not the activists, who have identified the possible biosecurity risks from the transgenic crops and devised protocols for the identification, assessment, quantification and mitigation of risk. Science has reasonable peer reviewed experimental evidence to answer biosecurity concerns.
Biosecurity issues are unfortunately often mixed up with political, economic, management, societal and ethical issues, emotionalizing and sensationalizing the concerns, to spread fear and suspicion of GE technology. Biosecurity issues raised to oppose GE crops by antitech activists are relevant to even products of classical agricultural biotechnology, but were never made an issue in that context.
Every country that commercializes GE products has a strict
regulatory regime to ensure
biosecurity of GE products and that all questions are
answered reasonably satisfactorily
before commercialization is permitted.
7. BIOSAFETY OF BT TRANSGENICS
Bt being a universally occurring soil bacterium, all species of plants and animals in agricultural and other situations, and those that use plants as food have been exposed to Bt and Bt proteins for centuries. Bt proteins are transient in the environment. The toxicity of Bt proteins is pest specific, dependent upon a set of biological pre-requisites. The use of Bt as a conventional pesticide for over 60 years has demonstrated that it is safe to the consumers and a variety of non-target organisms.
Bt is one of the few
pesticides recommended for widespread application in North
Cry proteins were shown to be harmless to vertebrates, including
mammals and humans,
even at high doses, by ingestion, inhalation or injection.
Nevertheless, antitech activists
raise issue after issue to brand GE crops as toxic in spite
of massive evidence on their
safety as food and feed. Over 350 million people in
Several claims have been made of allergenicity of
transgenic crops, including Bt cotton in
some places in
A transgenic soybean with a gene for the Brazil nut protein developed to increase the content of methionine, an essential amino acid, was one of the targets. Though no one actually developed allergy by eating the transgenic soybean, since the transgenic is likely to affect people who are allergenic to Brazil nuts, Pioneer Hi-Bred International, the developer of the product, did not proceed with it, setting an example of self-regulation. The United States Department of Agriculture (USDA) cleared Aventis Starlink Bt corn for use as both food and feed. Since the Bt Cry9 protein in this transgenic corn was projected to be allergenic, the US Environment Protection Agency (EPA) took a precautionary measure and approved this corn only for animal feed, as animals do not generally suffer from food allergies. Bt Cry9 protein was never demonstrated to be allergenic. The US Centers for Disease Control (CDC) tested 17 samples of blood from people claimed to have developed allergenic reactions to Starlink and found that none of the blood samples showed cross-reactivity to Cry9 Bt protein. The Cry9 gene is not deployed in any commercial product now. Since transgenic products approved as only feed may accidentally get into the food products, no transgenic is now approved exclusively for use as feed. This shows that the regulatory regime is in fact functioning effectively.
Among the commonly consumed food items, several such as walnuts, pecans, Brazil nuts, cashews, peanuts, soybeans, some varieties of rice and wheat, cucumbers, mushrooms, fish, shellfish, eggs, milk, mother’s milk, etc., and certain drugs like penicillin, cause clinically well known anaphylactic reactions in certain individuals. Even 1/44,000 of a peanut kernel may cause severe anaphylaxis in some. Food and drug based allergies cause several deaths every year. Yet, there was not even a simmer of protest against marketing such products.
8. ENVIRONMENTAL SAFETY
All the evidence indicates that Bt transgenics are very safe to all components of the environment. Over a decade’s cultivation of Bt transgenics has neither confirmed the scary scenarios aired by the critics nor has thrown up any new threats to the environment.
8.1 Super weeds
A serious negative factor projected by the antitech activists from transgenics is that they would escape cultivation and become super weeds placing other vegetation at risk. Crawley et al., (2001), basing on a 10-year study of pest and herbicide tolerant transgenic crops demonstrated that the transgenics do not become more competitive to invade the environment as super weeds, but that in fact they perished earlier than their isogenic counterparts.
8.2 Impact of Bt on non-target organisms
Glare and O’Callaghan (2000) and every country’s regulatory process provide extensive data demonstrating the safety of Bt proteins to non-target organisms.
The much publicized instance of toxicity of Bt proteins to non-target organisms was based on the study by Losey et al., (1999), who reported that transgenic Bt corn pollen harm monarch larvae, a conclusion immediately questioned by the scientific community. Subsequently, Sears et al., (2001) re-examined the issue, avoiding the flaws in the experimental design in the study of Losey et al., and concluded that impact of Bt corn pollen on monarch butterfly populations was not significant. The performance of bumble bees was not affected in any manner by Cry 1Ab Bt proteins (Babendreier et al., 2008). Chen et al., (2008) showed that Cry1C proteins were safe to parasitoids that control pest populations in many crops, in contrast to the severe damage caused to the parasitoids by the traditional insecticides.
Reports of the death of peacocks and the death of farm
animals in Andhra Pradesh and
honey bee Colony Collapse Disaster in Europe and
8.3 Gene flow from transgenics
The possibility of gene flow from transgenics and the negative impact of this on other crops, biodiversity and the environment occupy the centre stage in discussions that denigrate modern agricultural biotechnology, although the experience gained from the regulatory processes of transgenic crops and their cultivation for over two decades have not indicated any serious possibilities of gene flow or its negative consequences. Gene flow depends upon the reproductive biology and breeding behaviour of the crop in question (Kameswara Rao, 2008 c,d), which the activists have not taken into consideration.
8.4 Vertical gene flow
The essential pre-requisite for vertical gene flow is sexual reproduction between the transgenics and related plants. The transferred genes express only in the next generation. The ease of vertical gene flow depends upon the genetic relationships between the varieties and whether the crop is self or open pollinated, which Bt technology cannot change. Transgenics are no more promiscuous than their isogenics. If vertical gene flow were possible between isogenics and any related varieties or species, it would be so between transgenics and related plants too. However, centuries of agricultural experience does not indicate any alarming possibilities.
A study, much quoted by the critics as a risk of vertical
gene flow, relates to Bt maize in
8.5 Lateral/horizontal gene flow
Lateral/horizontal gene flow involves exchange of genes between genetically unrelated organisms, a fact of evolution, but not of day-to-day occurrence. It does not involve sexual reproduction and the transferred genes can express in the same generation. Transgenic technology itself is an example of lateral gene transfer. All known examples of lateral gene transfer relate to endoparasites and their hosts, as for example, the commonality of about 30 per cent of genes between mammalian intestinal parasites and their hosts.
The use of antibiotic markers in transgenic technology, to confirm genetic transformation was used to promote fear of GE technology. The argument, not supported by any tangible evidence, is that if there were lateral transfer of antibiotic resistance genes to pathogenic organisms, it would result in pathogens resistant to the antibiotics used as markers and endanger our prospects in the fight against the new pathogens using the antibiotics to which they are resistant. Supported by numerous studies, Ramessar et al., (2007) concluded that there is no scientific basis to argue against the use and presence of selectable antibiotic resistant marker genes in transgenic plants. However, to assuage the fears expressed, the use of antibiotic resistance marker genes is now minimized, as alternatives are found. The antibiotic marker genes can also be removed, after confirming genetic transformation.
8.6 Impact on biodiversity
A comprehensive report on the impact of agricultural
biotechnology on biodiversity
A peer reviewed report (Sanvido et al., 2007) concluded that no aspect of credible science based on ten years of field research and commercial cultivation has indicated that GE crops have harmed biodiversity or the environment.
The Consensus Document from the Organization for Economic Cooperation and Development (OECD, 2007) on the safety of Bt proteins in transgenic plants did not identify any hazards caused by them.
9. BENEFITS FROM BT TRANSGENICS
Technologies come with some concomitant and some consequential benefits, both of which should be taken together in assessing the total benefits that accrue. Benefits of a technology should hence be weighed against minimal and acceptable risks and a favourable cost-benefit ratio.
9.1 Optimal cultivation practices are mandatory
In order to realize the benefits from the full potential of
any crop variety, it should be
grown under optimal conditions. Although cotton is hardier
than many other crops, it
performs satisfactorily only under irrigation and on a
right soil type. In
9.2 Concomitant benefits of Bt technology
The most direct and the most important benefit of Bt technology
is the control of the most
damaging pest of particular crop, such as the American
bollworm of cotton, stem borers
of rice and corn, rootworm of corn,
Bt technology imparts
only tolerance of the targeted pest of a particular crop and not total
resistance to it (GEAC, 52nd Meeting, 2005). In view
of the variation in the expression of
Bt genes, due to
various internal and external factors, two or three pesticide applications
are needed, against even the targeted pest, such as the
bollworms of cotton, instead of the
usual 10 to 20. Even so, in a country like
9.3 Consequential benefits of Bt technology
Bt technology’s consequential benefits are:
a) drastic reduction of pest pressure; suppression of
cotton bollworm on multiple
non-Bt non-cotton crops in areas with Bt cotton
was reported from
b) healthy crop, more biomass and more yield from saving losses;
c) reduced risk to farm labour involved in pesticide application; in the developing countries several thousand farm workers suffer any many of them die, due to unintended pesticide poisoning;
d) far lower concentrations of pesticide residues on the produce and in the environment;
e) reduced exposure of non-target organisms in the environment to pesticides, and so a better conservation of biodiversity; and
f) the Bt farmer experiences a far lower tension and is certainly better off with Bt technology than the earlier scenario of ‘spray and pray’.
9.4 What is not to be expected of Bt technology
Bt technology has no role to play in the following areas:
a) Yield: Bt technology has no gene based influence
on crop yield; nevertheless,
there is a substantial increase in crop product recovery
due to prevention of loss of
the crop produce caused by the pests; Bt farmers in
b) Seed germination: failure of seed to germinate is often mischievously attributed to Bt technology; causes for the failure of seed germination lie in the varieties or cultivation practices or environmental factors; the percentage of germination of the seed of a Bt variety would be about the same as that of its isogenic;
c) Non-target pests: Bt technology is specific pest targeted and has little or no effect on other pests;
d) Diseases: Bt technology does not cause or control
any viral, bacterial or fungal
diseases; such diseases as the viral leaf curl of cotton
prevalent in northern
It is a compulsive habit of the antitech activists to
repeatedly attribute farmer suicides in
10. ANTITECH ACTIVISM
The antitech activists endlessly criticize the whole technology and the biosecurity regulatory regime. They use junk science to pursue their vested interest and cause fear psychosis on the public mind against the technology. They have used diverse media, filed petitions in the Supreme Court demanding moratorium on the technology and even vandalized GE crops in field testing. Most of those who raise biosecurity issues to voice their opposition to GE crops have no locus standi in terms of knowledge and expertise to trash the combined global scientific wisdom. Unfortunately, the scientists, the agribiotech industry and the Governmental agencies have failed to stand up against the onslaught and in support of what they obviously believe as sound and safe technology.
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