Genetically Modified crops
How far will science progress?
2.38 In plants, the first genes to be manipulated were those for herbicide tolerance. There were several reasons for this, the first being that it was possible. The genes for herbicide tolerance are single genes and therefore much easier to isolate and manipulate than the multigene complexes responsible for such important traits as salt tolerance and drought resistance. Secondly, it made sense to the companies who were to finance the research and development (R&D), since herbicide tolerance is about creating a selective herbicide from a non-selective herbicide. Such herbicide-tolerant GM plants are examined for safety by regulatory authorities. Thirdly, although modern selective herbicides are very effective they are expensive and, unlike the broad-spectrum herbicide 'Roundup', can persist in the soil. A number of these GM herbicide-tolerant crops are now being grown, and soymeal from Monsanto's herbicide-tolerant 'Roundup ready' soybeans is already on the European market.
2.39 Biotechnology has the capability of producing many new plant products. A number of different types can be described:
application of a range of gene-inactivating techniques to reduce the activity of or switch off specific unwanted genes (paragraph 2.22). These might be fruit softening, toxin or allergen genes;
introduction of new plant genes or enhancement of existing gene action to improve starch or oil yield, modified oils or starches, enhance fruit flavour, colour or nutrition;
introduction of genes to confer resistance to herbicides, pests or pathogens, or to enhance resistance to environmental stresses like drought, heat or cold;
introduction of new plant genes to enhance the production of hybrid crops or to modify seed production by inducing apomixis, so that hybrid vigour can be effectively 'fixed' for harvest and resowing (paragraph 3.39).
2.40 It is very difficult to predict exactly when these new developments will become commercially available, but it is possible to arrange them in an approximate time sequence:
continued development of rapid genetic typing methods to speed conventional plant breeding systems, leading to the identification of genes responsible for desirable traits, and their transfer to other species, for example between cereals;
continued development of genetic manipulation, along the lines of herbicide tolerance, involving one or more genes, with the production of plants resistant to many herbicides, and a wide variety of pathogens, including viruses, bacteria and fungi, thus greatly reducing or eliminating the huge losses due to these agents;
continued development of novel fertility systems, leading to the production of new F1 hybrids, with increased yields;
continued development of fruits and vegetables with longer shelf-lives and better shipping characteristics;
modification of crops to produce oils with properties more suitable for industrial use, fats more suitable for the human diet and modification of starches and other carbohydrates for either dietary or industrial use;
isolation of genes that control development to manipulate flower shape and colour for the horticultural industry. Mauve carnations are already available. Other applications are possible such as blue roses, geraniums that smell of roses or lawns that (almost) never need mowing;
genetic modification of fruits and vegetables with the aim of improving flavour, texture and nutritional content and, in particular, to ensure that levels of the micronutrients that appear to be increasingly important for health are either maintained or introduced at appropriate levels;
elimination of genes for toxic or allergenic substances (peanuts can cause a fatal allergic reaction in some people); for example, by the use of antisense technology to block the activity of genes;
isolation and utilisation of more complex genetic systems such as those controlling salt tolerance and drought resistance, making possible the production of plants which can be grown in a much wider range of environments;
isolation and modification of genes that control plant development and differentiation; for example, the plant's flowering time, so that it may be possible to produce plants that come to maturity more quickly, or plants such as oilseed rape that could be grown further north in countries like Canada and Sweden, and aspen trees that are fertile within the first year. Conversely, it would be advantageous sometimes to delay flowering, in annual non-seed crops such as lettuce and potato;
as timber and pulp increasingly come from cloned plantations they could be modified for pest and disease resistance, and have their juvenile period substantially reduced to aid breeding programmes;
production of drugs and vaccines in plants;
introduction of new genetic systems into the plant to increase yields by, for example, modifying photosynthesis or enabling crops such as wheat to fix nitrogen;
application of GM technologies to bring orphan crops, particularly in tropical developing country agriculture, into commercial production.
production of plants for cleaning up polluted areas.
2.41 To take a specific example, genetic modification of potatoes could:
increase the availability of UK varieties by extending the growing seasons through the introduction of stress tolerance characteristics;
improve flavour and mash texture through modification of starch and sugar content;
reduce the water content in potatoes and alter cell-wall composition to limit the fat retained in crisps and chips;
extend shelf-life by suppressing sprouting and reducing rot;
reduce chemical residues by introducing herbicide tolerance, disease- and pest-resistance traits.
2.42 During the period from 1986 to 1997, approximately 25,000 transgenic crop field trials were conducted on more than 60 crops with 10 traits in 45 countries. No adverse effects on food safety or the environment have been noted, relative to production in non-GM current varieties. Of this total of 25,000, 15,000 field trials were conducted during the first 10-year period and 10,000 in the last two-year period. Seventy-two per cent of all transgenic field trials were conducted in the US and Canada. By the end of 1997, 48 transgenic crop products, involving 12 crops and six traits, were approved for commercialisation in at least one country by 22 owners of technology, of which 20 were private-sector operators. (23) The crops include soybean, cotton, oilseed rape, potato, maize, tomato and pumpkins, and the traits insect, virus and herbicide tolerance, delayed ripening, male sterility and changes in oil composition (Table 2.1).
Click here to view Table 2.1. This will appear in a new browser window.
2.43 There are several other crops where transformation could be agronomically valuable. Wheat has been technically difficult to transform, but GM wheat is expected to enter the market soon. Research on the genetic modification of rice, cassava, yam, pearl millet and sorghum is being undertaken in public-sector institutions.
Footnotes
23 James C (1997) Global Status of Transgenic Crops in 1997, ISAAA Briefs No. 5, ISAAA: Ithaca, New York. ISAAA is the International Service for Acquisition of Agri-biotech Applications. It monitors and evaluates the availability of biotechnology for transfer to the developing world. In addition, work is being undertaken in the developing world to assist national programmes, to identify priority needs for biotechnology applications, and to develop and implement priority proposals.
