Alan Raybould
Institute of Terrestrial Ecology
Furzebrook Research Station
Wareham, Dorset BH20 5AS, UK
Crops that have been genetically modified to tolerate herbicides or be
resistant to insect pests or viruses are now grown commercially. Within
the next ten years crops with modifications for fungal and bacterial
disease resistances and a range of abiotic stress tolerances will also
be available. These crops are often assumed to pose a risk to
biodiversity. However, we need to be very clear about whether
genetically modified crops pose threats that are qualitatively different
from conventional crops.
Some of the threats to biodiversity posed by genetically modified crops
are simply those of modern agriculture. Habitat destruction and loss of
traditional varieties will continue regardless of whether genetically
modified crops are widely used. Indeed if, as promised, genetic
modification results in higher yields and lower inputs, particularly of
herbicides, then biodiversity loss may be slowed by the introduction of
genetically modified varieties.
The potential novel effect of genetically modified crops is the
escape of the modified genes (transgenes) into the non-agricultural
environment. This may occur by spread of feral populations of the crop,
or by hybridisation between crops and wild species. Either way, the
transgene is seen as having the potential to increase plant fitness and
so create superweeds that displace native vegetation.
It is impossible to generalise about the genetic or phenotypic
characteristics of a weed. However, experience from species
introductions and plant breeding suggests that there will be few
additional risks from a genetically modified crop in regions where the
conventional form is already grown. The largest risks will come from
modifications that allow crops to be grown in new environments. The
major exception to this familiarity principle is genetically modified
virus resistance, which could produce new virus types via recombination
between viruses and virus-derived transgenes.
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