Upload Now
In this article we will discuss about the transgenic crops for plant breeding.
Conventional plant breeding has been extremely successful and increased financial support for plant breeding will be necessary if plant breeding is to both maintain and improve crop yields.
However, there are some limitations inherent in conventional plant breeding such as lack of practical access to useful germplasm due to sexual incompatibility barriers or undesirable linkage block and concomitant time lags in incorporating useful genes into existing varieties.
Indeed, many transgenic approaches to crop improvement arise from a lack of suitable conventional approaches to dealing with a particular agronomic problem or need. For many pests and pathogens which seriously limit agricultural productivity, transgenic approaches may provide new options where current options are lacking in their efficacy or existence.
Transgenic approaches can therefore be of use for a broad range of crops and areas where there are limited options available through conventional breeding e.g. nuclear male sterility, improved heterosis breeding, reducing toxic compounds, herbicide tolerance, generating novel resistance genes.
Transgenic approaches have considerably broadened the range of gene-pools which are now accessible for crop improvement purposes. For instance, the application of useful gene transfer from microorganisms through genetic engineering techniques range from the introduction of vaccine antigen genes to aluminium tolerance genes to food plants.
Isolated plant genes can now be usefully transferred between sexually incompatible crop plant species. In the context of on-going debates regarding transgenic crops, public funding agencies should not forget that modern biotechnologies such as plant tissue culture, molecular genetic mapping and marker assisted selection could still have a major impact on any conventional crop improvement approaches which decide to limit themselves to the genetic variation accessible within the primary to secondary gene pools.
Biosafety Assessment:
Biosafety assessment requires that risks, benefits and needs be given a balanced assessment in relation to transgenic organisms. Many opponents of plant biotechnology cite biosafety as the key risk based issue for the more stringent regulation of transgenic plants.
At one end of the extreme, environmental groups are now calling for a moratorium in some European countries on the planting of ‘genetically modified foods’. The other end of the extreme would be no regulations regarding transgenic organisms.
Much controversy and public scaremongering has been generated by anti-biotechnology groups over the ‘safety’ of transgenic plants in relation to their perceived negative impacts on human health or the environment.
A new development has been that many of the anti-biotechnology groups have conceded that there are benefits to be had from the application of genetic engineering for addressing human medical problems. However, it is the application of genetic engineering to agriculture that is now the key focus of attention of the anti-biotechnology interest groups.
Indeed, civil society perceptions of agricultural biotechnologies in many countries are now distorted because of highly polarised lobbyist campaigns between the biotechnology -industry on the one hand and anti-biotechnology groups on the other.
The independent presence of public sector agricultural biotechnologists and scientists has often been lacking from this on-going polarised debate. Similarly, many membership based organisations which are more broadly representative of civil society such as trade unions, producers organisations and farmers organisations have also not been involved in these debates.
Switzerland is unique in having conducted a referendum to democratically assess public opinion regarding a number of genetic engineering issues. On June 7 1998 40% of the Swiss population voted in a referendum which called for a moratorium on the cultivation of genetically modified crops, bans on research on transgenic animals and on patenting of genetically modified organisms.
The socio-economic cost of non-access to some transgenic crops which may be of utility to farmers is rarely factored into risk-assessment procedures. Assessment of the immediate needs of different groups of farmers and consumers could feasibly become an integral component of biosafety risk-assessment procedures, where costs and benefits could be seen in more social, rather than solely environmental terms exported from countries where food surpluses are a normality.
The issue of who decides what level of risk farmers/consumers should be exposed to be also an important consideration for any countries development of biosafety regulations. This is an area where promoting the greater participation of organisations who actually represent the needs of different groups of farmers and/or consumers could be most appropriate.
Many of the most vocal environmentalist or consumer organizations may not actually be very representative of farmers or consumer’s needs. Membership based NGOs may provide a better reflection of farmers and consumer views than single interest lobbyist NGOs.
The absence of a functional biosafety review system may negatively affects the local development and importation of new biotechnology products, and therefore farmers’ access to potentially useful germplasm and technologies. On the other hand, a very stringent biosafety review system can also delay or prevent farmers’ access.
Indeed, the cost of a regulatory system for biosafety within any one country is an important factor which has implications for determining which farmers will ultimately have access to biotechnology products. High regulatory costs will also have an affect on what transgenic traits are ultimately to reach farmers and will further bias research towards wide rather than specific adaptation.
High regulatory costs will select for only those traits which represent the greatest commercial gain to the developer of the variety. Such regulatory costs can be high – In the USA it can cost US$1 million to get a plant biotechnology product through the regulatory system.
If such expensive regulatory systems are used in developing countries the cost will either bias all transgenic research towards meeting the needs of the wealthier sectors of society or plant biotechnology will remain primarily at the research stage.
Also, over-stringent biosafety regulations are likely to disproportionately benefit larger companies over smaller companies or public sector bodies by acting as significant ‘barriers to entry’ to certain markets. The higher the regulatory hurdles the higher the chance that competition will be stifled between companies and that any benefits of biotechnologies will not reach poorer farmers.
For example, efforts by the US Environmental Protection Agency (EPA) to regulate some transgenic crop varieties as ‘pesticidal plants’ were opposed by 11 scientific societies representing 80,000 biologists and food professionals.
Interestingly, an alliance between the Biotechnology Industry Organisation (BIO) and anti-biotechnology groups such as the Environmental Defence Fund were in favour of such types of regulation for differing reasons.
In determining whether low income farmers will have equitable access to certain types of transgenic crops, is of relevance therefore that FAO has recently indicated that any LMO that can be considered a pest of plants falls within the scope of the International Plant Protection Convention (IPPC) and will be subject to the provisions of the Convention.
Indeed, the broader issue of whether future or anticipated socio-economic impacts of biotechnologies should be considered under the draft Biosafety protocol to the CBD is also currently a matter of debate. Many conventionally bred crops are by any biological definition transgenic as they contain genes or segments of chromosomes from totally different crop species.
For instance most of the bread wheat currently under cultivation contains a large segment of a rye chromosome. Triticale is a conventionally bred transgenic crop containing full copies of both the rye and wheat genomes that was developed 60 years ago and is now grown on more than a million hectares in Canada, Mexico and eastern Europe.
Similarly most of not all crop varieties of sugarcane, tomato, potato, rice, maize, oat, sugar-beet, black currant, plum and many other highly bred crops contain genes or chromosome segments derived from different wild relative species.
Wide crossing and embryo rescue technologies have been used by breeders for longer than genetic transformation as a means of transferring useful genes across plant species barriers. In a biological sense at least the inter species genetic modification of foods is not inherently new.
In the context of biotechnology risk assessment, there is a widely held scientific consensus that risk is primarily a function of the characteristics of a product (whether it is a purified chemical or a living organism to be field tested) and is not per se a function of the method of genetic modification.
For instance, the US National Academy of Sciences concluded that assessment of the risks of introducing recombinant DNA-engineered organisms into the environment should be based on the nature of the organism and the environment into which the organism is introduced and not on the method by which it was produced.
However, the current legal definitions of GMOs upon which most biosafety legislation is being constructed are largely ‘process’ rather than ‘product’ based in order to suggest that there is some fundamental distinction between the process of gene transfer resulting from sexual recombination and gene transfer resulting from genetic engineering.
However, the same plant gene might feasibly be transferred by either conventional plant breeding or by genetic transformation and while the products of both processes for gene transfer could in theory both be genetically or phenotypically identical, one would be labelled a GMO and the other would not.
For instance, there is little difference between mutagenesis-derived sulfonylurea or imidazolinone- resistant soybean, maize and oilseed rape and others crops with the same herbicide resistance genes transgenically introduced. Both transgenes and endogenous genes are, depending on their positions in the genome, likely to have similar rates or patterns of hybridisation.
Indeed, if precision gene swapping or knockout mutation approaches through homologous genetic recombination are perfected for plants in the same manner that they have been for mammals it is likely that such approaches will be applied to crop improvement.
In instances where exactly the same genotype could be produced by either conventional mutagenesis or by genetic engineering, the ‘process’ based definition of a GMO will be increasingly difficult to sustain by any biological definition at least.
Many of the biological phenomena which are often cited as unique biosafety issues for transgenic crops actually also occur in conventional plant breeding or other biological processes involving non-transgenic GMOs and in wild species.
These include gene-silencing, permutations, segregation distortion, evolution of neo-virulent pest/pathogen, evolution of fungicide or herbicide tolerance, gene-flow to wild relatives, allergenicity, etc. It is sometimes contended that transgenes may display novel ’emergent properties’ when transferred to a novel genetic context.
However, conventional plant breeding and indeed agriculture itself also display emergent properties many of which have been beneficial to humanity. Standard plant breeding and selection procedures are equally applicable to the selection of the best transgenic lines from the range of lines generated through genetic transformation.
The yield benefits derived from dwarfing genes which were a major factor in the Green Revolution are an example of beneficial emergent properties from conventional breeding that were selected for by plant breeders.
At a global level the agricultural area which is currently planted with transgenic crops as developed by genetic engineering techniques is small relative to the areas under conventional crop varieties and landraces. However it is increasing as some farmers adopt transgenic varieties. The total acreage of cultivated land in the world stands at over 1.4 billion hectares which is predominantly under conventional crop varieties.
However for a few crops in a few countries (USA, China, Canada, Argentina) there are significant areas planted to transgenic varieties. In those countries where transgenic crops have been given regulatory approval, the proportion of crop area devoted to transgenic crops is increasing.
In 1997 the global area under transgenic crops was 12.8 million hectares – a 4.5 fold increase from the 2.8 million hectares planted in 1996. In 1998 it is estimated that 30 million ha of transgenic crops were planted globally.
The large increases in areas planted are currently limited to a few commercially important crops. For instance, transgenic soybean, maize, cotton and canola represented 85% of the global transgenic area in 1997, of which 75% was grown in North America.
The ‘black box’ approaches to conventional breeding based upon the generation of genetic variation followed by selection for useful phenotypes is in some ways more imprecise than single gene transfer through genetic engineering approaches.
In crosses between weedy wild relatives and their crops, tens of thousands of genes are typically recombined in the progeny plants the exact phenotypic results of which are extremely difficult to predict.
Radiation induced mutation breeding has been applied in plant breeding for decades with at least 20,000 know field tests of gamma radiation treated germplasm conducted in open field trials without any weedy or toxic mutants generated.
The FAO/IAEA Division has been instrumental in technology transfer of radiation breeding approaches to developing countries. In spite of any uncertainties inherent in conventional or mutation breeding, such plant breeding has served society well without warranting the level of restrictions that are currently being perceived as necessary for all transgenic crops.
The technologies to routinely make transgenic plants have only been in existence for over a decade or so – which is of the same order of magnitude as the time required to conventionally breed a new plant variety. Much progress has been made regarding the technologies for generating transgenic crops through genetic transformation and these technologies are constantly being improved.
Although some crop varieties and species may be more difficult to transform than others, few crop species are now considered to be ultimately un-transformable and a significant number of cereal varieties can now be routinely transformed.
In recognition of biosafety related concern over the use of antibiotic selection markers in the process for generating transgenic plants, improved transformation systems have been developed which allow the generation of marker free transgenic plants.
Transgenic Foods and Health Issues:
There has been much misinformation circulated in the popular media regarding perceived dangers to human health from use of transgenic crops or other GMOs. The recent public hysteria generated in the UK regarding transgenic foods stemmed from a non-scientifically reviewed research report on feeding trials of rats with transgenic potatoes containing a lectin with known insecticidal properties.
In this case, while the researchers report was subjected to ‘political’ peer review it has not yet been subjected to peer review in scientific journals and hence all of the conflicting conclusions to date regarding the raw data are considered premature.
Many naturally occurring plant proteins and compounds can be anti- nutrients, toxic or allergenic. Indeed a significant number of crop species are toxic if not cooked or prepared properly to reduce or inactivate such compounds.
In most instances, standard procedures for assessing toxicity and allergenicity can equally be applied to conventional and transgenic varieties to identify those transgenic which are substantially equivalent to conventional varieties.
Such standard testing procedures were sufficient to identify that a methionine-rich 2S albumin from the Brazil nut was allergenic to some people and hence was not as good a candidate as a non-allergenic methionine rich sunflower seed albumin gene for gene transfer to improve the nutritional content of legumes.
Selectable marker genes are used in constructing transgenic plants containing an associated transgene of interest, but are usually not required once the transgenic plants are produced. Existing biosafety regulations have been stringent enough to disallow corn-borer tolerant maize in Europe because of the extremely low risk of antibiotic tolerance spreading in bacteria in the rumen of cattle.
Even though most selection markers in constructing transgenic are likely to pose little danger either to humans of the environment because of perceived consumer hysteria it is likely that future generations of final product transgenic plants will not contain selectable marker genes. This is because a number of quite efficient systems have now been developed for the development of ‘marker free’ transgenic.
More acceptable marker systems which are not based on antibiotic or herbicide resistance genes are also being developed. Hence it is possible that biosafety considerations regarding such genes may gradually become less of an issue as improved ‘marker free’ transformation systems become available.
Consumers have a definite right to information and hence choice regarding which foods they purchase or eat. However, consumer information is based on the premise that the information provided to the consumer is of utility to the consumer in making an informed choice.
For instance, knowledge of the biological or species composition of foods will be of use to those who suffer from allergies to particular foods or compounds. The USA requires labelling of transgenic foods that are substantially different from their unmodified counterparts, including foods that could contain a potentially allergenic compound such as a peanut protein or glutenins.
Indeed, it is questionable whether the label ‘genetically modified’ conveys any information of utility to the typical consumer in terms of making an informed choice based on what is currently known about transgenic food. Nonetheless, such labelling is increasingly perceived as necessary by both the biotechnology industry and some governments.
An increasing number of the OECD countries are implementing provisions that require the labelling of genetically modified foods. For instance, the European Union has recently approved two directives which state that labelling must be applied to novel foods and their ingredients produced through the process of genetic engineering.
Because of the commercial potential in diagnostic services for segregating transgenic and non-transgenic foodstuffs, major research efforts are now underway to develop such diagnostic methods. Indeed, the labelling of transgenic foods and products is likely to be welcomed by some companies as a means of unequivocally capturing added value.
Corporate strategy will require that any of the bio technologically generated value-added traits for food and feed, and even for industrial markets, will be stacked with a variety of input traits in a variety of combinations that will need to be segregated and identity preserved to capture the enhanced value of the end products.
This will lead to contract production and marketing systems for the resultant grains, oilseeds and their derivative products. There are now differences between international trading blocs over requirements to label products developed using genetic engineering processes.
While the USA does not require labelling of GMOs, the European Union and Japan, amongst others, have opted for labelling of food products or components produced by genetic engineering. It is likely that such requirements for GMO labelling will become a multilateral or bilateral trade negotiation issue over whether such labelling constitutes a trade barrier.
Indeed, because of consumer concern over transgenic foods in Europe there may be substitution effects generated in both directions regarding non-transgenic and transgenic foods.
For instance, countries which do not have access to technologies to produce transgenic crops and whose exports are perceived to be threatened with substitution may find that the export of labelled non-GMO derived products may be a short term strategy to maintain markets while they devise a means of diversifying their exports in the face of competition from GMO derived products.