|
The
Plant Journal |
|
Volume
33 Issue 1 |
|
|
|
|
|
GM SPECIAL ISSUE |
|
The release of genetically modified crops into the environment |
“For
GM crops, the best and most appropriately defined reference point is the impact
of plants developed by traditional breeding. The latter is an integral and
accepted part of agriculture. In many instances, the putative impacts
identified for GM crops are very similar to the impacts of new cultivars
derived from traditional breeding.”
Also
see http://www.sdcma.org/GMFoodsBrochure.pdf
“…and
keep being asked, despite the fact that all supposedly relevant research has
been performed. The answers given are apparently not satisfactory. This may
indicate that many of the concerns raised about GM crops reflect more the concerns
about the changing nature of agriculture at large (Beringer, 2000), which draws on values and
philosophical positions that are not readily changed upon the presentation of
technical information. We acknowledge the prime importance of socio-economic
and other issues for a proper technology assessment (Bruce and Bruce, 1998; EFB, 1999; NCB, 1999) and realise that prudent
and transparent linking of science and politics may be the biggest challenge
for the overall evaluation of GM crops (Levidow and Carr 2000). …….The
baseline taken in this review is the impact of non-GM crops and the effects of
agriculture in general.”
Risk assessment
tries to find answers on the following three questions for each individual
case:
|
|
Question 1:
what can go wrong? (=the possibility of harm), |
|
|
Question 2:
how likely is that to happen? (=the probability of that harm occurring), and |
|
|
Question 3:
what are the consequences if it happens? (=the consequence of that harm). |
“…This
choice is often based more on the perceived outcome of a risk analysis than on
the probabilistic calculation of a risk. Unfortunately, risk calculation and
risk perception are not very (cor)related.
What experts measure is generally not what most people
perceive as risk. It is now generally accepted, for example, that the
perception of risk of a given issue differs greatly between experts on that
issue and non-experts”
“..The
issues of risk of GM crops deal with the ecology and toxicology of GM crops
upon release and use. It is a continued discussion whether more broad 'risks'
should be part of the basic biosafety assessment (Commandeur et al., 1996; Sagar et al., 2000). Countries and
stakeholders still disagree considerably about the extent to which issues such
as sustainability, globalisation, ethics and
socio-economics should be part of a GM crop risk assessment”
“Two
general concepts have been proposed to guide the ecological risk assessment in
regulatory and associated procedures: the concept of familiarity and, more
recently, the precautionary principle…This interpretation implicitly reflects a
demand for a risk-free world. In such an interpretation, the principle seems
not a very suitable or decisive principle to base decisions and regulation on.
The main argument against this interpretation is that 'doing nothing' is a
decision too, with its own premises and consequences…. In case of GM crops it
may be worthwhile to have the precautionary principle work both ways and
require its application to the overall situation of potential costs and
potential benefits (De Kathen, 1998;
Goklany, 2000). “
|
|
Question 4:
what are the consequences if we do NOT allow this GM crop? |
Botanical files
consist of data on a particular plant and provide an index of the likelihood
for:
|
|
Factor 1:
dispersal of pollen, Dp, |
|
|
Factor 2:
dispersal of reproductive plant parts, such as seeds or fruit, collectively
called diaspores, Dd, and |
|
|
Factor 3:
the distribution frequency of wild relatives, Df. |
If
any one of the Dp, Dd or Df values is '0', no ecological effects are to be expected
from the cultivated plants…Botanical files indicate the likelihood of gene flow
from a particular GM crop plant to its wild flora, but ignore the potential
impact of the transgene on crop and recipient wild
relative. Therefore, botanical files have to be combined with knowledge about
the transgenes
|
|
Factor 4:
description of gene, Dg, |
|
|
|
Factor 5:
description of nutrition, Dn. |
|
A five-digit 'D'
code would than summarise all safety considerations
for the growth and consumption of a particular product from a transgenic crop
grown in a given region… way of labelling
Will
transgenic crops invade agricultural and natural ecosystems?
Common
distinctive attributes of weeds such as seed dormancy, phenotypic plasticity,
indeterminate growth, continuous flowering and seed production, and seed
dispersal (Baker, 1965; 1974), have been bred out of the most important crop plants
over thousands of generations.. These characters are
not candidates for gene transfer back into crops, whether by genetic
modification or traditional breeding, because they would severely reduce the
agronomic performance of a crop for modern farming practices. Furthermore,
these attributes do not arise from the single or few gene transfers of genetic
modification. Therefore, genetically modified crops are no more likely to
become weeds outside farming situations than crop cultivars have in the past”…[ WHAT ABOUT DROUGHT/SALT TOLLERANCE, NATURAL ENEMY
RESISTANCE]
“Similarly,
oilseed rape is recognised as being domesticated
relatively recently (McNaughton, 1995)
and is often associated with a potential to escape from cultivation and revert
to a weedy condition. This is a consequence of high seed production, the
frequent appearance of volunteers, especially along roadsides near crop
production fields, the occurrence of wild races, and induced seed dormancy
associated with seed burial. Oilseed (rape) has been the subject of the
majority of investigations on the potential invasiveness of transgenic crops.
It represents a useful 'model system'; it is a potential worse-case scenario”
“GM
seeds of oilseed rape with modified oil content (high-stearate)
can have enhanced longevity in soil (Linder, 1998), but
the high-stearate gene also conferred reduced vigour on seedlings and presumably also reduced fecundity (Linder and Schmitt, 1995). The latter may well cancel out any
advantage resulting from enhanced seed longevity.”
“The
demographic parameters of GM oilseed rape with resistance to the herbicide glufosinate and conventional oilseed rape were estimated
over a 3-year period in twelve natural habitats involving a range of climatic
conditions (Crawley et al., 1993). No evidence
was obtained to indicate that oilseed rape is invasive of undisturbed natural
habitats. Furthermore, there was no evidence that the GM lines were more
invasive of, or more persistent in, disturbed
habitats. When there were significant differences between the genetic lines,
the GM lines tended to be less invasive and less persistent than their non-GM
counterparts. This study clearly established the relative invasiveness of
non-GM and a given glufosinate-resistant GM oilseed
rape in the absence of selection pressure from glufosinate
in the environment.” THIS COULD BE THE COST OF RESISTANCE WHEN NO HERBICIDE IS
APPLIED, NO ADVANTAGE
“A
more recent comprehensive study compared the results from monitoring
conventional and GM lines of four different crops in field experiments
established in twelve habitats and over Ten years (Crawley et al., 2001). The GM lines included oilseed
rape and maize exhibiting resistance to the herbicide glufosinate,
sugar beet exhibiting resistance to the herbicide glyphosate,
and potato containing insecticidal Cry proteins or pea lectin.
In none of these cases, the GM plants were found to be more invasive or more
persistent than their conventional counterparts…… weedy characteristics are
likely to be different when the expression of the transgene
is taken into account. In this context, the transgene-centred
approach to biosafety is important (Metz and Nap, 1997), ”
Will
transgenes outcross to other species and increase weediness?
Concerns have
been expressed that GM crops will hybridise with
related species and result in the introgression of transgenes
to weedy relatives. For transgenes conferring
resistance to pests, diseases, and herbicides it is often suggested that this
may result in enhanced fitness, survival and spread of weeds (Ellstrand, 2001).
The
opportunity for natural hybridisation between two
species in nature depends on many pre- and post-zygotic factors
|
Table 1 Factors determining the likelihood of
gene introgression from crop plants to related species |
|
Pre-zygotic barriers to hybridization |
|
1.
Spatial isolation of parent populations |
|
2.
Synchrony in flowering |
|
3.
Direction of the cross (the parent from which the pollen and ovules
originate) |
|
4.
Specific parental genotypes |
|
5.
Method of pollen dissemination and presence of pollen vectors |
|
6.
Pollen competition from maternal population |
|
7.
Environmental conditions |
|
Post-zygotic
barriers to hybridisation |
|
8.
Mitotic compatibility of the two parental genomes |
|
9.
Ability of endosperm to support hybrid embryo development |
|
10.
Direction of cross (maternal effects on seed/fruit development) |
|
11.
Number and viability of hybrid seeds |
|
Establishment
of hybrid plants |
|
12.
Seed dormancy |
|
13.
Direction of cross (maternal effects influencing seedling vigour) |
|
14.
Growth vigour of hybrid plant |
|
15.
Habitat conditions (natural, ruderal, cultivated) |
|
16.
Competition from other plants |
|
17.
Influence of pests, diseases, predators |
|
Propagation
of hybrid plants |
|
18.
Ability to propagate vegetatively |
|
19.
Persistence, dissemination and invasiveness of vegetative propagules |
|
20.
Pollen and ovule fertility (meiotic stability and chromosome pairing) |
|
21.
Ability to produce sexual progeny (selfed and
backcrossed) |
|
22.
Ability to survive over subsequent generations |
|
23.
Seed number, viability and dormancy |
|
24.
Habitat conditions, plant competition, pests, diseases and predators |
“This may result if the selective herbicide continues to be used on the derived weedy populations. While this is a potential concern, it must be remembered that the development of weedy populations with herbicide resistance is not a new situation for agriculture since herbicide-resistant plants have also been developed by traditional plant breeding and arise by entirely natural means (Conner and Field, 1995).”
Several
experimental studies have been published that all failed in demonstrating HGT
from transgenic plants to bacteria (Bertolla and Simonet,
1999; Gebhard and Smalla,
1999; Nielsen et al., 1998; Schlüter et al., 1995). This by itself is
quite remarkable because in plant science negative results are not often
considered publishable or published. In more elaborate marker-rescue approaches
with large stretches of homology, the kanamycin
resistance gene from GM maize could be retrieved in an Acinetobacter
strain (de Vries and Wackernagel,
1998). Without the artificially introduced homology in the recipient
strain, no HGT was detected, indicating that the transformation frequency is
very low” [THE MUST BE SOME ADVANTAGE FOR THE BACTERIA, EXTREME IF EVENT IS
UNLIKELY]
“Overall,
the likelihood and impact of HGT with parental plant DNA compared to transgenic
plant DNA would seem to indicate that HGT deserves less attention in the
regulatory process compared to other concerns. Unless there is a priori strong
evidence for impacts from HGT of a plant gene, such as in the case of a useful
antibiotic resistance, HGT from GM plants to other organisms should be
considered a calculable risk.
Will GM crops have secondary ecological impacts?
Considerable
ongoing research attention has focused on the secondary effects of
insect-resistant, Bacillus thuringiensis toxin
(Bt)-containing GM crops. Potential impacts are two-fold:
|
1.
|
a direct
effect on non-target insects (or other organisms) due to toxicity through
exposure to GM plant material; and |
|
2.
|
an indirect
effect on non-target insects (or other organisms) via so-called multi-trophic food chains |
”
“If
it is a species that feeds on parts of the plant, such as pollen, it may also
be affected. The latter issue is highlighted by the case of Bt-maize pollen and
the Monarch butterfly (Danaus plexippus). When pollen from a commercial variety of
Bt-maize (N4640) expressing a lepidopteran-specific
Bt gene in the whole plant including pollen, was spread onto milkweed leaves (Asclepias syriaca,
the feed plant of Monarch butterfly larvae) and fed to Monarch butterfly
caterpillars in the laboratory, the caterpillars died (Losey et al., 1999). This study led to
considerable debate over the environmental impact and relevance for the
potential risks from Bt maize. Follow-up studies to
investigate the impact of widespread plantings Bt-maize on the Monarch
butterfly essentially concluded that the impact of Bt-maize pollen from current
commercial hybrids on Monarch butterfly populations is negligible (Hellmich et al., 2001; Oberhauser et al., 2001; Pleasants et al., 2001; Sears et al., 2001; Stanley-Horn et al.,
2001; Zangerl et al., 2001).
This is based on the low expression of Bt toxin genes
in pollen for most maize hybrids, lack of acute toxicity at expected field
rates, limited overlap of pollen shed and larval activity, and the limited
overlap in distribution of Bt-maize and milkweed. In view of these follow-up
studies, it must be concluded that the Losey et al., (1999)
paper describes a phenomenon that is in no way representative for the field
situation. It shows that extra careful consideration applies when translating
laboratory experimental results in the laboratory to the real-life situation in
the field.” [HOW MANY NON TARGET INSECTS DIE DURING PESTICIDE
APPLICATION OF TRADIATIONAL CROPS?”
Partailly Paraphrased by Justin Borevitz
1/17/06