GMO Myths and Truths

een found to be unreliable and incomplete:
● A study on GM brassicas, potato and blackberry
found that the use of three antibiotics
failed to completely remove A. tumefaciens.
Instead, the A. tumefaciens contamination
levels increased from 12 to 16 weeks after
the GM transformation process and the A.
tumefaciens was still detected 6 months after
transformation. 180
● A study on GM conifers found that residual A.
tumefaciens remained in the trees 12 months
after the genetic transformation but were not
detected after this time in the same plants. 181
However, these experiments only examined the
first GM plant clones. In the GM development
process, such GM clones go through a long process
of back-crossing and propagation with the bestperforming
non-GM or GM plant relatives in order
to try to produce a GM plant that performs well
in the field and expresses the desired traits. The
important question is whether A. tumefaciens
carrying GM genes survives this back-crossing and
propagation process and remains in the final GM
plant that is commercialised.
To the best of our knowledge there have been
no studies to assess whether any A. tumefaciens
remains in the final commercialised GM plant.
The study on GM conifers examined the initial
GM clones that were grown on, not plants that
had been cross-bred and propagated over several
generations, as GM crops are before they are
commercialised, so it does not provide an answer
to this question.
However, this question should be answered
before a GM variety is commercialised, in order
to avoid unwanted consequences that could be
caused by residual A. tumefaciens in the final GM
plant. Examples of consequences that should be
excluded are the transfer of insecticidal properties
to bacteria, or of herbicide tolerance to other
crops or wild plants. The study discussed above
(5.12.3) shows that the introduction of GM genes
into crop plants could have consequences to
organisms outside the plant kingdom, through
the mechanism of infection by fungi carrying A.
tumefaciens, which in turn carry GM genes. 177
The consequences of such HGT for human
and animal health and the environment are not
predictable, but are potentially serious. The health
and environmental risk assessment for any GM
variety must demonstrate that the GM plants have
been completely cleared of GM A. tumefaciens
before they are approved for commercialisation.
5.12.4. Gene transfer by viruses
Viruses are efficient at transferring genes from
one organism to another and in effect are able to
carry out HGT. Scientists have made use of this
capacity to create viral gene transfer vectors that
are frequently used in research to introduce GM
genes into other organisms. Such vectors based on
plant viruses have also been developed to generate
GM crops, though no crops produced with this
approach have been commercialised to date. 182 183
The viral vectors that are used to generate GM
crops are designed to prevent the uncontrolled
transfer of genetic material. However, because the
long time period during which virally engineered
crops would be propagated in the environment,
and the large number of humans and livestock
that would be exposed to this GM genetic material,
there is a real, though small, risk that unintended
modifications could occur that could lead to virusmediated
HGT – with unpredictable effects.
Another potential risk of virus-mediated
HGT comes from GM crops engineered to
contain a virus gene, in particular those carrying
information for a viral “coat” protein. This is done
in an attempt to confer resistance of the crop from
actual infection and damage by the family of ‘wild’
virus from which the viral GM gene was derived.
However, it has been suggested that if a GM crop
containing a viral gene of this type was infected
by the viruses, it may result in exchange of genetic
material between the GM viral gene in the plant
and the infecting virus, through a process known
as recombination. This can potentially result in a
new more potent (“virulent”) strain of virus. 184,185
The reasons for these concerns are as follows.
The GM viral gene will be present in every single
cell of the crop. As a result, the large-scale
cultivation of such a viral GM gene-containing
crop will result in an extremely high concentration
of particular viral genes in fields. It has been
suggested that this provides an unprecedented
opportunity for genetic material recombination
GMO Myths and Truths 93