Since long, breeders have modified the genetic make up of plants and animals through conventional breeding methods. Breeders have developed new crop varieties using the existing genetic variability or by creating new variability, which is the prerequisite for any breeding programme. Conventional breeding methods have the disadvantage of a thousands of genes getting transferred in each cross, which may or may not be of use along with the desired ones in the target species. Another major limitation in conventional breeding includes the barriers for gene transfer through incompatibility and species differences.
The genetic engineering (GE) technology has made possible the insertion of desired foreign gene(s) to overcome problems of sexual incompatibility and species barriers between organisms. This technology helps the breeders and molecular biologists to introduce only the gene of interest with more selective modification and represents a significant advance. It is nothing but the mere extension of conventional breeding methods. The primary aim of the modern biotechnology is to make a living cell to perform a specific useful task in a predictable and controllable way. The outcome of GE technology is a transgenic / genetically modified (GM) product. The transgenics have many advantages, of which some include the potential to resist biotic and abiotic stresses, adds nutritional quality to the product, etc., resulting in productivity increase. Biotechnology has been identified as a promising research area with widespread applications in diverse fields of agriculture (1,2). The hue and cry regarding the impact of GM crops on biodiversity has created hypes regarding economic, social and ethical concerns. However, several workers contradicted the fears expressed regarding the risks and hazards of GM crops but still concerns on the safety of GM foods creating controversies.
The impact of GM crops in developing countries has not been studied extensively and concerns regarding the possible effect of transgenics on biodiversity are probably raised because of lack of understandings of modern commercialized agriculture. GM crops may affect the diversity but it is the trait or acquired property that interacts with the environment and not the transgenic plant per se. In transgenics the new gene is introduced irrespective of the boundaries, whereas, in conventional breeding it adds variants of a given gene (new alleles). In both cases equal chances are there that the introduced gene may probably result in any side effects because it finds itself in different genetic context or background and expresses differentially (position effects) in the present genome.
Gene flow- the flip side Fears are expressed sometimes that the transgenic plant itself may become a weed and the introduced gene may be sexually transmitted into wild relatives and traditional varieties. The concerns that GM crops themselves becoming weeds and leading wild weed populations to become 'superweeds' is contradicted by Crawley and coworkers (3) who concluded from their experiments that GM crops are less persistent than their conventional counterparts and are less invasive. In the past, several exotic species like Triticale (a cross between durum wheat and rye), Trithordeum (a cross between wheat and oat), released for cultivation and where these risks also prevailed, did not result in such controversies. The main component of gene flow is the out crossing rate. But the reports says that even in highly self pollinated crop intraspecies, out crossing takes place to limited extent 4 and Langevin (5) reported 1-52 % hybrid seed set in weedy red rice growing sympartically with the cultivated rice in Louisiana. Therefore, the chance of gene flow can not be ruled out for conventional breeding methods also. The risks poised regarding the fear of gene flow are of equal concern in both conventional breeding and GM crops.
The escape of transgene providing pest resistance to wild relatives may not have serious environmental problem as genes for resistance are often found in wild relatives. Weediness could be a matter of concern when the herbicide resistance genes flow and get introgressed into wild relatives of the crop. As the gene flow from herbicide resistant GM crops have serious implications on wild populations there is need to search ways 6 to reduce its escape from GM to wild weedy species. Interspecies gene flow (3) is extremely low and depends on the presence of a large population of related species in the center of diversity. The gene flow from a GM crop would depend on the mode of reproduction, rate of out crossing, sexual compatibility, proximity with wild relatives and relative fitness of crop-weed hybrid.
If, the horizontal gene transfer is so simple and if new genes could swap with so much ease between species we would all have been lost in one big evolutionary melange a long time ago. But because of the possibility of gene flow, GM crops should be planted according to the local flora, with specific restrictions. Assessment of realistic risks for gene transfer through pollen is available for many regions (7) and agriculturally sound procedures need to be developed for different regions. The debate could end with a case to case study of GM crops and it would not be wise to denigrate the technology itself. According to Watson - "Never postpone experiments that have clearly defined future benefits for fear of dangers that can't be quantified".
Heavy application of pesticides to protect crops in order to increase yield have ultimately boomeranged and given birth to the major concerns like the persistence of pesticide residues in foodstuffs 8, development of resistance among pests (9) and harm to non target organisms 10. This is of special importance in developing countries, where, at least 2 billion people that are living and working in farming areas are exposed to pesticides. The continuous and injudicious use of pesticides has resulted in development of resistance in pests and currently, more than 500 species of insects (9) show resistance to one or more chemicals and a few serious pests resist nearly all poisonous pesticides.
In case of GM crops the evolution of new insect biotypes is another area of concern. However, experiences from the commercial host plant resistance breeding has shown that there is no direct relationship between the deployment of insect resistant cultivars and the evolution of new insect biotypes (11). Plant breeders incorporate new resistance genes while insects and pathogens simultaneously evolve mechanisms to overcome them for their survival. So in this case also the chance can not be avoided and this does not mean that resistant varieties will not be bred for, accepted or cultivated. Another major concern of GM crops is their effect on non-target organisms. Bt proteins affect the stomachs of vertebrates and chances of affecting beneficial insects however remains. Although such effects are less severe 11 than those of broad-spectrum insecticides are. The incidence and dynamics of natural enemies in Bt and non-Bt fields have been observed to be almost the same (12). Even the GM crops with trypsin inhibitor13 did not show toxicity to honey bees but soybean trypsin inhibitor was found to be toxic 14 to adult honeybees. Therefore, it will be doing injustice to conclusively generalize all GM crops to be harmful but the final decision has to be taken after studying the aspect case wise, not universally. Field experiments showed that the performance of transgenic 'Bt' cotton varieties was the same as other cotton varieties except for The desired high resistance to bollworm and bud worm and with an average of 70 % 15 less chemical insecticide used than conventional cotton varieties.
According to Dr. C. S. Prakash (16) gene revolution is far more environment friendly compared to its predecessors "Green revolution". Scientists have argued that if GM crops are risky, then conventionally bred cultivars are even more risky as thousands of new genes are introduced by crossing distant relatives and since conventionally bred varieties cause no harm then very few genes introduction (through GE) should not cause irreversible damage. The risks of modern GE have also been studied by technical expert at the National Academy of Sciences and World Bank and according to them the environmental effects can be predicted by reviewing past experiences with those plants and animals produced through selective breeding. None of these products of selective breeding has harmed either the environment or the biodiversity.
If common public is focused that the development of this technology will only benefit industries and not the farmers and consumers then the acceptance of the technology and product will be very low. The need lies in the effective communication of the pursued risks and benefits among the consumer and farming communities to have its rapid acceptance. There is also need to understand its impact on human health and environment so that this technology can be used without exacerbating genetic erosion. The social issues are complex in a developing world where the so-called environmentalists are highlighting GM crops to be the monopoly of multinational companies (MNC). But the fact is that in the WTO regime, the farmers have to be globally competitive and for that due importance is to be given to the reduction in production cost and quality of the product. A report from IRRI (17) stated that in the long run the cost of molecular breeding is only $ 2 per plant while that of traditional breeding is $ 30. If this is considered, breeding with biotechnological tool is still only a fraction of the cost of traditional plant breeding. There will have to be much greater transparency in the system, and data on GM products must be publicly available and debates on risks and benefits should be conducted in public.
To adopt GM crops and their products, awareness has to be created among the farming and consumer communities regarding their benefits and effects on human life by the scientific community and leaders. NRC (18) reported that crops modified by molecular and cellular methods pose risks no different from those modified by classical genetic methods for similar traits. OECD already pointed out that GE is nothing more than a simple extension of traditional breeding. GM crops and the techniques of biotechnology offer huge benefits which if realized in an open and fair way, without suspicion of bullying big business, they have the potential to sustain the security for food and nutrition for human well being in the near future. So GE cannot be considered as universally accepted technology but the assessment should be done on a case by case basis. Only time will tell whether the introduction of GM crops today is really harmful for the environment or the developing world. In the mean time serious research has to be carried out to provide support on the effect of GM crops.
Opportunities are still untapped in developing countries until a consensus comes up among all its possible benefactress to allow the technology to run its race.
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* The views expressed by the authors in the article are personal and not
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