Selective Breeding, Genetic Modification and Non-Food Crops
For centuries, agriculture has modified the genetic constitution of plants by selective breeding. In selective plant breeding, the genes of individual plants are mixed by conventional breeding, and the resulting offspring screened for those that show desired characteristics. The chosen offspring plants are then subject to further rounds of breeding and selection until the desired characteristic is exhibited reliably and to the required degree.
Advances in biotechnology are making it increasingly routine to link certain characteristics of an organism with particular genes (i.e. specific segments of DNA) which it possesses. It is also possible to isolate individual genes and copy or alter them. Once copied or altered, the genes do not have to be put back into the organism from which they came, but can be put into a different species altogether. The term "genetic modification" refers to these methods of altering the genetic make-up of an organism. Genetic modification can be used to change certain characteristics of a plant variety or to transfer characteristics (via copied genes) from one species to another.
So far as crops are concerned, genetic modification techniques have been used to give existing crops traits that make them easier to grow (such as herbicide tolerance and resistance to insects). Varieties of soya, maize and rapeseed that have been modified in this way are the result of studies of plant genetics that took place a decade ago. Many examples are already grown commercially in the USA, while in the EU trials are under way.
The next generation of genetically modified crops is set to move away from varieties developed simply for ease of farming to ones in which the mixture of chemicals which the plants produce (e.g. fatty acids, carbohydrates and proteins) is altered. Changing the profile of the plants' chemical constituents is of interest to the food sector (to give benefits in nutrition or cooking properties) but may also have value for non-food crops. Some genetically modified varieties of this type are already available (e.g. soybeans with a reduced saturated fatty acid content) and many others are expected to be developed over the next five years or so.
Further developments could result in crops producing specific chemicals for industry that plants currently do not make at all, using sunlight as a source of energy. Developing suitable plants may however require modification of a greater number of genes than has been necessary to produce the current genetically modified crops (e.g. those with herbicide resistance), and thus may be more difficult to achieve. Current expectations are that developing the knowledge and technology required for some of these products will take at least five to ten years of research. This concept is sometimes referred to as the "roofless factory".
Genetic modification raises issues of wide public concern with respect to the potential impact on the environment, even when not directly linked to the human food chain. The need for carefully-controlled experiment and rigorous evaluation of environmental issues is another factor which must inhibit the development and acceptability of such products. However, advances in biotechnology, such as molecular marker assisted selection, also offer methods of accelerating the selective breeding process without using genetic modification (BBSRC Q 139). If the gene that produces the desired characteristic has been identified, the offspring can be screened for this gene without waiting for the plants to grow and be tested. This technique may be especially valuable for plants that take many years to develop fully (IACR p73).