Are GM and non-GM plant breeding methods different?
Non-GM plant breeding uses
a range of methods; each produces plants with unique properties. GM plant breeding also produces plants with
unique properties.
Non-GM plant breeding includes the following methods:
All methods have unique properties that cannot be achieved by other methods. GM breeding [5] cannot be used to make polyploids, or recombine thousands of genes (pollination), or cause random unpredictable genetic changes (mutation breeding). Similarly mutation breeding cannot be used to introduce single genes into crops from different organisms (GM breeding), or induce polyploidy, or recombine thousands of genes (pollination).
Does the ability to
insert genes into crops from different classes of organisms make the products
of GM breeding fundamentally different?
There appear to be no compelling scientific reasons why all GM crops are uniquely different from all non-GM crops. The uniqueness of a crop variety is determined by the nature of the genetic change, rather than the plant breeding method by which it is produced. It is possible to fine-tune a crop by the insertion of genes by GM from the same crop. This is likely to be a change well within the capability of gene transfer by pollination. Alternatively, GM plant breeding could be used to introduce a gene for pest resistance from a bacterium, which could not be achieved by gene transfer by pollination.
Is it innately more
hazardous to introduce a gene from a bacterium compared with a gene from a
related plant?
It is possible to insert a wide range of genes from different organisms into crops by GM breeding, therefore careful safety assessment is essential. But many sexually compatible relatives of crops contain extremely dangerous properties. Toxins are commonly present in plants as defence against pests and diseases. It is possible to introduce a deadly nightshade type toxin into the cultivated potato by conventional breeding or another toxin gene from a bacterium by GM breeding. Both would be dangerous and equally unacceptable.
Genetic modification
makes it possible to introduce similar pest resistance genes into different
crops (e.g. Bt) and therefore does it have a greater potential for breakdown?
Different crops have a different spectrum of pests and diseases and therefore will usually require different resistance genes to control them (e.g. different Bt genes or other resistance genes). This issue has important parallels with the use of a narrow genetic base in conventional breeding, as illustrated by the corn blight problem in the USA in 1970. It is not a unique feature of GM crops, but will require intelligent strategies for deployment and management.
[1] Gene transfer by pollination. This involves gene transfer into crops by pollination with plants
from the same species, different species or different genera. This method makes it possible to recombine
many thousands of genes from different plant parents. Embryo culture has made it possible to hybridise plant species
that are unlikely to form in nature.
Plants with desirable genetic combinations are selected and undesirable
ones discarded following extensive testing and evaluation.
[2] Induced mutation. In its simplest form, seeds are exposed to
radiation or chemical mutagens to cause random unpredictable genetic changes in
crops. There is no control over the
number or kind of genetic change produced.
It can cause random changes in individual genes, breaks in chromosomes,
loss of chromosome fragments or rejoining of chromosomes in different
combinations. Induced mutation is also
believed to cause the destabilization of naturally occurring mobile genes
(jumping genes or transposons) that are likely to cause genes to be controlled
in novel and unpredictable ways. The
utility of mutation breeding relies on careful evaluation and elimination of
plants with undesirable characters.
Surprisingly, a high proportion of the food we buy (especially cereals)
has had mutation breeding practised somewhere in its plant breeding history.
[3] Cell selection. Plant tissues grown in culture are
genetically unstable. This instability
is used in breeding as a source of genetic variation for the selection of crop
characters in cultured cells. The most
common use of this method is for the selection of herbicide tolerance by adding
the herbicide of interest into the culture medium. Cells are selected that have tolerance to the herbicide, and
herbicide tolerant plants are grown from these cells. This method has the potential to select for an array of genetic
changes that confer tolerance to the herbicide in culture. Inevitably, it inadvertently incorporates
other mutations with unknown function as part of the cell selection process. There is evidence of gross chromosomal changes
in cultured cells and the destabilization and movement of naturally occurring
mobile genes
[4] Induced polyploidy. This involves treating plants with a
chemical (colchicine) that doubles the number of chromosomes in the crop and,
therefore, doubles the amount of DNA in every cell in the crop plant. Induced polyploidy has been used in the
breeding of some grasses and clovers used commercially. It is also used in breeding other kinds of
crops, especially for the production of interspecific and intergeneric hybrid
crops e.g. wheat – rye hybrids (triticale).
[5] GM plant breeding. Allows the isolation of genes from different
classes of organisms e.g. from the same crop species, different plant species,
viruses, bacteria and animals, and their incorporation into crop plants. The method can be used to incorporate one or
several genes into a crop plant that has many thousands of genes (wheat has
c.70 thousand genes). As the inserted
gene has been characterised at a molecular level (its genetic information
defined), its position in the genome and its function can be assessed with a
precision impossible for most non-GM plant breeding methods.
