TRANSGENIC CROPS

TRANSGENIC CROPS 

      The term GMOs - Genetically Modified Organism is most commonly used to refer to crop plants created for human or animal consumption using molecular biology techniques. These plants are modified in the laboratory to enhance desired traits such as increased resistance to plant diseases, germs or improved nutrition content. The conventional plant breeding methods are very time consuming and often not very accurate. Thus GM Foods offers a novel way to improve crop characteristics such as pest resistance, disease resistance and herbicide tolerance. 

Genetically Modified Organisms

      Genetically modified organisms are organisms in which the genetic material (DNA) has been altered in a way that does not occur naturally by mating or natural recombination. This technology is known as modern biotechnology or genetic engineering or recombinant DNA technology. It allows selected individual genes to be transferred from one organism into another, also between non-related species, to give new traits to the recipient. 

Transgenic Plants

      A transgenic plant is a genetically modified organism, which contains artificially inserted gene or genes from an unrelated organism. The inserted gene (known as trans-gene) may come from another unrelated plant, or from completely different species, for example Bt. Cotton, contains a gene from a bacterium.  

Insect Resistance

      The efforts to produce insect resistant transgenic plants have been quite successful; insect resistant plants contain either a gene from the bacteria Bacillus thuringiensis has been used  since the World War I particularly in Europe to control some insect pests. Bacillus thuringiensis strain is usually classified on the basis of serological tests, and so far over 30 different serotypes have been identified. However the serotype has very little relevance to the insecticidal activity of the strain.

      The strategies to be adopted to avoid or delay the development of resistance to Bt genes are:

1. A mixture of toxic (Bt gene containing) and non-toxic (without Bt genes) cultures may be used.
2. Stacking of more than one toxin in each transgenic plant within a mixture may be followed.
3. The transgenic plants may produce a low dose of Bt toxin the act in concert with natural enemies to decrease pest population.
4. Tissues, time or signal specific expression of toxin.

Disease Resistance

      A number of naturally occurring proteins in plants has antifungal and antibacterial properties. Defensis, thaumatin, PR(Pathogen Related) proteins, lipid transfer proteins, enzymes (Chitinase, Glucanase) and enzyme inhibitors (amylase inhibitor, trypsin inhibitor) are some of them. Transgenic expression of Radish defensin  RSAFP2 in tobacco plants caused a seven fold reduction in size of lesions formed by the foliar fungal pathogen Alternaria longipes. Transgenic tobacco and Arabidopsis expressing a barly LTP2 have been generated and these plants display enhanced resistance to the bacterial pathogens Pseudomonas syringae pv tobacco and Pseudomonas syringae pv. tomato. The fruits of transgenic tomato constitutively expressing a CDNA that encodes a protein with similarity to PR4 at the C terminus exhibited enhanced resistance to the infection by Trichoderma hamatum. Transgenic plants with improved disease resistance exploited over expression of chitinase enzyme.

      The environmental pollution by chemical pesticides is avoided by the introduction of transgenic plants. Health problems associated with toxic chemicals are also minimized.

      In addition, there is also the possibility of producing vaccines, drug and other useful products from transgenic plants. It is reported that these plants may be consumed simply to have the desired effect. 
 
 

Herbicide Resistance

      Production of transgenic plants resistant to pests, diseases and/or herbicides is the major area in which molecular biologist/ biotechnologists concentrated during the last one decade. An ideal herbicide would control a wide spectrum of weeds, be harmless to crop species and have desirable environmental characteristics. But it is very difficult to obtain such an ideal herbicide by conventional methods. Hence transgenic crops resistant to herbicides provide useful tools for the future.

      Use of herbicide resistant crop varieties will help to selectively control weeds leading to increased crop yields to the farmers. 

Nutritional Quality

      The only report on a nutritionally superior transgenic plant is the riu variety containing beta-carotene synthesizing gene introduced into it. This yellow rice variety was produced by the rice biotechnologist I.Potrykus with financial association from the Rockofeller foundation (USA) and is a good source of vitamin A. 

Biosafety Assessment’ Of Transgenic Crop

      The main concerns while taking transgenic plants to the field relate to the possibilities of (i) their becoming persistent weeds (ii) of gene transfer from them to other plants making the latter more persistent or invasive, and (iii) of their being determined to the environment. In general testing of transgenic plants should progress in a stepwise manner from laboratory to growth chamber, to green house to limited field testing, to large scale field testing. Many countries have developed their own procedures and policies regulating field tests of such plants. In India DBT, New Delhi is concerned with the regulation of field testing of transgenic plants.

      There are extensive rules and guidelines for evaluating environmental and health safety aspects of genetically modified organism. Any Company involved in the use of genetic engineering techniques has to obtain approval of the Review Committee on Genetic Manipulation (RCGM) set up under the 1989 Rules in the Department of Biotechnology for conducting tests under laboratory conditions and confined field conditions. Based on these results, the RCGM makes its recommendation to the GEAC. Thereafter approval of GEAC is required for conduct of large-scale field trails for a number of parameters, which includes bio-safety, efficacy of the variety, agronomic benefits and economic advantage of the GM crop. The results of the large-scale field trials are evaluated by the Monitoring-Cum-Evaluation Committee (MEC).The GM crops approved for large scale trials are also evaluated under the Indian Council of Agriculture & Research (ICAR) testing system. The GEAC takes into consideration the recommendations of the MEC and ICAR before approving the GM groups for commercial cultivation. The bio-safety assessment includes environmental safety assessment as well as food and feed safety. Only those transgenic crops which are found to be safe for human consumption as well as the environment are approved for commercial release.  

Policy for Approving Transgenic Crops

      In the case of modern agricultural biotechnology, the benefits as well as risks vary from crop to crop, region to region and technology. It is a scientifically established fact that Gene functions differently in different crop and the impacts vary from species to species and the environment in which it is hosted. Further the performance of a transgenic crop species depends on the gene-environment interaction. Therefore a policy of case by case approval in case of genetically modified (GM) foods or food crop is being followed. As of date, the Genetic Engineering Approval Committee has approved the commercial cultivation of only one transgenic crop namely Bt. Cotton. Various Stakeholder Ministries have initiated the process of evolving a GM policy pertinent to their sector. Important initiatives are: The Food Safety and Standards Act, 2006 by the Ministry of Food Processing and Industry; Import Policy for GMO/LMO Products Under Foreign Trade Policy (2005-2009) by Ministry of Commerce (DGFT); Draft notification on mandatory Labeling by Ministry of Health and Family Welfare; Draft National Biotech Strategy, 2005 by Department of Biotechnology and National Environment Policy, 2006 by Ministry of Environment and Forests.

Future Prospects

      There is an explosion of interest in transgenic research leading to an ever expanding list of plant species in which transgenic have been produced. For example, in 1989, transgenic were produced in 15 plant species, but by 1994 this list had crossed 30. Many of these transgenic have shown sufficient promise to be taken to field trails in USA. Some of these have been cleared for human use and are either already in the market or are likely to reach the market soon. It may be projected that transgenic plants will play an important role in the world agriculture and, most likely, industry during the coming years.

Conclusion

      Transgenic crop varieties have a very bright future due to reduced cultivation easily farming operations even by illiterates/ untrained personnel suitability for large farms any other unconventional use such as antibiotic vaccine, drug, and hormone production. However in depth studies on nutritional quality and human/ animal health are required before using them in large scale.