One of the most contentious areas of agriculture - Washington ...

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1 Δεκ 2012 (πριν από 4 χρόνια και 10 μήνες)

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Biodiversity,
Biotechnology

and the
Environment



Barbara A. Schaal

Department of Biology

Washington University

St. Louis, MO 63130

schaal@biology2.wust.edu


Abstract:

The widespread use of genetically modified crop
s has precipitated acrimonious
debate on the health effects, environmental safety, and ethics of genetically modified
agricultural species. The debate is contentious, often with unsubstantiated claims of both
potentially harmful and beneficial effects. H
ere we examine the possible effects of GM
agriculture on issues of the environment and biodiversity. Possible negative aspects of
GM agriculture include unanticipated
effects on non
-
target organisms, gene flow between
GM crop or animal and closel
y related wild species, and hybridization resulting in new
weedy taxa. Positive effects include reduction in agrochemical use, reduction in harvest
pressure on native species, and new methods for

bioremediation, among others.

The
demand for GM crops in
developing countries is expected to be high, due to their
potential for greatly enhancing yields. But, the widespread application of GM agriculture
to the tropics presents new challenges. In the tropics, systems of agriculture are both
variable and diffe
rent than in developed countries. Tropical regions contain high levels
of native biodiversity, and many wild relatives of agricultural species are often growing
within the vicinity of their derived domesti
cated plants and animals. A
ssessment of
the
envir
onmental consequences of

GM agriculture is essential. In some cases environmental
benefits may accrue, in other cases GM agriculture may negatively effect both the
environment and biodiversity. Only by carefully applying science
-
based knowledge can
the
effects of GM agriculture
, both positive and ne
g
ative,

be accurately determined.


2

Introduction:


The use of genetically modified organisms, both plants and animals, in agriculture
has resulted in

an acrimonious debate. The wide spread planting

of
genetically

modified
(
GM
)

crops has generated contention around such issues

as health, the environment,
economics, international relations
,
the
business practices of large corporations

and ethics,
among others
.

One of the most active areas of debate is the potential effect of GM
agriculture on the environment

(NRC
Bo
ard on Agriculture
Report, 2002
)
. The debate is
highly polarized with one extreme claiming that GM

agriculture will greatly harm both
global agriculture and the environment
.


S
trong advocates
, on the other hand,

maintain
that there are few, if any, new risks and that genetically modified crops may, in fact, be
the savior of both global agriculture and the environment.

As with many highly polarized
debates, there is a vast middle ground that
, in the

case

of GM agriculture
,

acknowledges
the great potential of biotechnology but also raises science based concerns.

An
unfortunate aspect of the controversy is the tendency to see the issue in either black
or
white; biotechnology is either good or bad. In fact, biotechnology involves many species,
both plants and animals, with a wide range of genetic modifications that are placed in a
diversity of agricultura
l and natural systems located across

a wide range of
geographical
sites. Whether or not an application of biotechnology has potential harmful, beneficial or
neutral effects on the environment is both species and context specific.


Biotechnology vs. traditional breeding:


Before we go on to examine the effe
cts of biotechnology on biodiversity, our
topic here, we need to define what is a genetically modified organism. And, we need to
determine how genetically engineered varieties
differ
from conventionally bred plants
and animals. Currently most of t
he concern about biotechnology and the environment
centers on genetically modified agricultural plants (GM crops), although genetically
modified animals including mammals, fish and crustaceans are all being developed for
agricultural use. Genetically modi
fied agricultural species, for our discussion here, are
those plants and animals that have specific genes introduced into them by modern

3

methods of biotechnology, that is,
the organisms are
genetic
ally

transformed
. The term
genetically modified organism

(GMO)
,
often
used to describe a
variant produced by
biotechnology, is somewhat misleading. All of our domestic species
, plants and animals,
have undergone
significant genetic

modification

from their original wild ancestors, first
during the course of domestication by early agriculturalists and then by

modern breeding

(Wang, et al., 1999)
. Biotechnology is a way of genetically modifying organisms that is
based on methods of DNA manipulation, the ability to insert genes from one species into
the genome of another.


H
ow does traditional plant and animal breeding compare to

the production of new
varieties by biotechnology? Modification of wild species to make them more useful or
compatible to humans is an ancient process. Humans from the earliest times have
interacted with native biodiversity and have used this biodiversit
y for
their own benefit.
Early

farmers in the Middle East,
Asia
, South America

and Africa began to grow plants
near their villages
that they had collected for food or fiber
,

first in the wild. They chose
plants with traits that were most useful, the individual with bigger s
eeds or which had
longer and tougher fibers, and they used the seeds of these plants to begin the next
generation of plants. Over many generations
morphological and genetic
differences
accumulated between the domesticated crop and its
wild relative. In some species

such
as

corn

the process so changed the crop that the wild parent species of the crop is no
longer obvious by morphology al
one. In the development of other

crops, such as wheat
or kales, dif
ferent species have been crossed
, to incorporate genes from one species into
t
he genome of another

(
e
.
g.
Simp
son and Ogorzaly, 2003)
. The concept of using genes
from different species as a basis for improvement is a well
-
established principle of plant
and animal bree
ding. E
arly farmers
developed
plant varieties
for

their local regio
n
and
when the new varieties were useful, they traded seeds and animals over vast geographical
scales.
Often these new
,

introduced varieties crossed on their own with
local landraces
and native species.
The introduction of

a species or variety

into new

geographical
regions in many cases had

a profound effect on biodiversity, by

altering agricultural
practices, by introducing species which displace
d

native species, or by altering

4

community dynamics.

Agriculture has a long history of
impacting
both native
biodiversity
and the envir
onment.


What are some of the characteristics of traditional crop breeding today? First, a
source of new genes or traits is obtained. The s
ource

in traditional breeding is from
either ot
her varieties of the same crop,

or from wild relatives or closely related species.
Traditional crop

breeding is an inexac
t science

and many genes beyond those for th
e
selected trait are introduced.

S
ometime
s whole sections of chromosomes

are trans
f
erred
,
which may introduce

genes that produce an undesirable trait, such as
early dropping of
seeds or that

reduce
crop yield

(Simmonds and Sma
rtt, 1999)
. After the initial cross, the
progeny and their progeny are crossed repeatedly over several g
enerations in order to
eliminate
these
undesirable genes and to

co
ncentrate desirable traits. This

process may
be very slow, particularly in the case of perennial crops such as bananas or cassava where
the generation length, the

time to first flowering, may be

s
everal years. Even in annu
al
crops the process is slow. Of course, t
his is not

to imply that traditional breeding is
unsuccessful. All of our crops are based on traditional plant breeding, including those
used in the US as well as those of the green re
volution, which has increased the yield of
important crops such as rice in Asia. Regardless of future technological advances,
traditional plant breeding will be an important source of new varieties, or will provide the
background stock for new crops produ
ced by genetic engineering. In fact traditionally
bred varieties of crops are extrem
ely i
mportant in this age of GM varieties.

The
choice of
which background or

variety to use for genetic transformation is critical. Some of the
earliest efforts at producing

GM

crops were far from successful because a relatively poor
variety was chosen as the stock for transformation
--
this hap
pened in tomatoes making
the
GM

lineage commercially unviable.


Genetic engineering presents an alternative to traditional plant bree
ding. Using
the techniques of molecular biology
,

a single gene that codes for a desired trait, such as
insect resistance, increased protein c
onte
nt, or tolerance to drought

is isolated and then
combined with a promoter sequence that will allow the gene to

be expressed. This
combination of genes is then introduced directly into the plant genome. The concept is

5

actually quite simple, although the techniques are technologically complex

(
see

C
hrispeels and Sadava, 2003)
. The introduction into the plant genome of foreign DNA
can be done by p
hysical means, particl
e bombardment, or it can be accomplished

biologically by
the Ti plasmid of the bacterium,
Agrogbacterium tumefaciens
, which
causes crown gall disease in plants. Once the target cells incorporate DNA, these
genetically
transformed
cells are grown by tissue culture into whole
adult plants that now
contain the foreign gene. These plants can pro
duce seeds by standard cross

pollination of
one plant by another
. Thus the plants can reproduce

and seed stocks built up. These
seeds will produce
the next generation of
plants that also will have the

new, inserted
gene.


How do plants produced by genetic engineering differ from those produced by
traditional breeding? First the process is highly specific: only
DNA
for the selected
genes
are

introduced into the plant.

A

few, s
pecific genes are added to the targe
t species,
as
contrasted
to many genes introduced by traditional breeding. Second, genes can be
introduced from a wide variety of organisms. Traditional breeding is lim
ited to closely
related species

within the same plant genus for the most part. Genetic
engineering can
use genes from across kingdoms. Plants can be engineered to contain genes from
bacteria, fungi, and animals which in turn can dramatically increase the range of traits
that a plant can express,
such as
anti freeze compounds from flounder
that
ad
apt plant
varieties

to colder environments. Likewise domestic animas can be genetically
transformed;

salmon engine
ered with growth hormone

grow 2
-
3 times faster than normal
salmon.
(GM salmo
n are particularly controversial because they are highly mobile and
thus
have
a
possibility

of escaping

into native mari
ne
environments
.
)

Plants are currently
being engineered to serve as factories to produce useful compounds that are not found
in
plants
in nature
, such as the production of pharmaceuticals, plastics, and human vaccines.
A final difference between traditional breeding and genetic transformation to produce
new varieties is the time

scale
. Breeding studies take many

years whereas transformation
can be accompl
ished relatively quickly. Genetic transformation is also more efficient. In
a perennial crop such as cassava or bananas, not only does it take a long time to
com
plete
breeding studies due to generation time, it also requires vast amounts of space and l
abor

6

to grow
the
large numbers of individuals to screen for selected traits. Genetic
transformation occurs in the laboratory and after it is successful then plants are
transferred to the greenhouse and ultimately field grown.


Genetically modified plants and
animals:


Currently the most widely used varieties of GM crops carry introduced genes
either for insect resistance or for herbicide resistance. Insect resistance comes from a
natural insecticide gene found in the soil bacterium,
Bacillus thruringiensis

(Ananda
Kumar, et al., 1996)
.
B. thuringiensis

produces a family of crystalline proteins, (cry
proteins) which inhibit insect growth. The cry proteins are considered an
environmentally friendly insecticide; in fact, the bacterium is used as a natural insecticide
in organic farming. C
rops such as soybeans, corn, and cotton have been genetically
engi
neered to produce one of these c
ry proteins and are resistant to several major insect
crop pests. The other major group of GM crops is engineered to be resistant to herbicides

(Dekker and Duke, 1995)
. Fields of h
erbicide
-
resistant crops can be sprayed with
herbicides such as glyphosate (Roundup); weeds are killed by the herbicide while the
crop is unaffected. Crop yields are greatly enhanced by this efficient herbicide treatment.
US farmers have embraced GM crop
s and the percentage of overall crop acres devoted to
GM crops has risen dramatically since 1995, when GM crops became widely available.
Moreover, there is much demand among US farmers for additional GM crops such as
wheat, sorghum, and rice.


The develop
ment of the next generation of GM crops is actively proceeding and
we can expect a diversity of
new
approved crop varieties. These crops will expand the
range of GM agriculture for the kind of species that is genetically modified, for the
geographical regions

where GM crops are grown and for the type of trait engineered into
the crop. Currently being developed are new crops that have disease resistance to
pathogens, that have increased protein content, that have more healthful lipids, and that
are engineered
to produce pharmaceutical compounds, among
others. Development of
GM varieties

is not limited to
row crops such
corn, soy, and cotton. Work is being

7

conducted on producing new varieties of trees for wood and pulp, ornamental plants for
gardening and landscaping, and new fo
rage grasses. A large effort is underway to
engineer
new crops for the developing world. These varieties are being
produced
to
provide food security and alleviate nutritional inadequacies
that are
found so often in the
developing world. At the same time, animal
biotechnology is rapidly proceeding. For
example
,

many Asian countries have large aquaculture industries and efforts are
underway to produce genetically transformed fish and crustaceans that are resistant to
disease, that grow rapidly and that are adapted
to
the conditions of
aquaculture. These
applications of biotechnology present particular challenges since these animals are highly
mobile. While it outside of our discussion here, there are also well
-
established efforts to
genetically transform insects such as mosquitoes,

to alleviate them as vectors of disease.


The Biotec
hnology in the Tropics: Issues


The development of genetically modified plant and animal varieties for the
developing world presents challenges for assessing their environmental impact.

Why do we need t
o specifically assess the environmental impact of GM agriculture in
tropical regions? Why are the lessons
already
learned from
GM agriculture in the
developed

world inadequate? There are several reasons: both the type of agriculture and
the environmental conte
xt of agriculture is different in
tropical
developing countries than
in the temperate developed world. First is the type of agricultural system. In developed
countries modern agriculture is characterized by fields of a crop grown in monoculture
with large inputs
of fossil fuel in the form of agrochemicals, fertilizers, pesticides and
herbicides. Developing and tropical countries have a greater range of agricultural
practices. Indigenous people can use traditional intercropping or swidden agriculture that
utilize
s many plant species and varieties

with little to no agrochemical use
. Many crops
are grown in small gardens, orchard or fields
and come in close contact
with local
native
biodiversity. And,
increasingly
,

modern agricultural methods are being employed for the
major crops such as corn
and soy.




8

For our discussion of biodiversity and the environment
,
the
most significant
difference between agricultural systems of the developed and developing world is the
ambient levels of biodiversity, both in natural habitats and as part of an agricultural
ecosystem. The tropics have t
he grea
test natural biodiversity on

earth, with a stunning
number of plants, animals, fungi, bacteria, etc. Moreover, the biological relationships
among species are complex. Species
often
have
highly specialized ecological

niches and
are
often

closely t
ied to other species in the community by feeding relationships, by
competition, parasitism or mutualisms. These intricate connections between species
potentially make tropical species and communities vulnerable when biological
perturbations occur. The con
cern is that tropical communities

may be
highly
sensitive to
perturbations and because of the elaborate interrelationship, subject to ripple effects (the
relationship between community complexity and stability is a long standing debate in
ecology

(
eg, Tillman and Downing, 1994
). The combination

of high species diversity
and potential sensitivity to disturbance
requires

careful

evaluation of
the potential
environmental effects of GM agriculture in tropical regions.


Another important aspect of biodiversity in tropical regions needs to be
considered. In
the US, most of our major crops have been imported from other regions of
the globe and are not grown here in contact with their wild ancestors. Thus corn, wheat,
rice and soy are all crops of either the old world (wheat, rice, soy) or Mesoamerica
(corn).

In many cases there are no close relatives to the imported crop and the crop is
grown in genetic isolation fr
o
m the native biodiversity. The environmental concerns
regarding gene flow between crop and wild relative and its effect on biodiversity are not

a major concern
. As genetically modified plants and animals are developed for tropical
species and their use inc
orporated into the agriculture o
f developing nations, the effects
of gene migration between GM species and wild relatives will have increasing
importan
ce. We might expect that for many species the contact between crop or GM
animal and wild ancestor will be more frequent

in regions of high biodiversity
. Close
contact, which raises the possibility of gene flow, is more likely in some tropical regions
for several reasons. First, many g
enera are species rich in the tropics which offers many
more native candidates for gene flow (cross pollination) between wild and domesticated

9

species. Second, many tropical crops are not as highly domesticated as are the major
crops of the world. These
local varieties may be genetically much more like the
ir

wild
ancestors or relatives that live near by and hence more likely to produce fertile offspring
when crossed. Finally, many regions in the developing world still use locally adapted
landraces of a cro
p; these landraces are

of great importance

since they
contain
valuable

agricultural biodiversity, and are a genetic resource for future crop improvement. It is
important to consider the effects of GM
crops
on this aspect of
agricultural
biodiversity
as well as the potential effects

on native biodiversity.


Up to now we have drawn a distinction between the agriculture and biodiversity
of developed and less developed countries. This distinction is far from complete. In the
US several crops are grown in close association with their
wild ancestors (
e.g.
sunflowers) or weedy relatives
have been introduced
(rice, sorghum, pannicum). And,
large monoculture fields of GM crops are
increasingly
common

in developing countries.
While the environmental issues that center on biotechnology are the same globally, their
relative

importance varies with crop, geographical region, and community context.


Finally, before we consider the specific effects of biotechnology on biodiversity,
two important and related points need to be made. First, many of the issues that are
currently a
concern for GM agriculture
have been long standing
concerns for traditional
agriculture as well. Harm to non
-
target organisms

from pesticides and herbicides
, gene
flow, and the production of weeds has all plagued agriculture. The fact that these are
concerns for conventional agriculture implies neit
her that these
issues
can be ignored for
biotechnology derived crops (supposedly since these are not new concerns), nor does it
mean that GM agriculture should be avoided because it, along with conventional
agriculture, affects the environment. Second,
the
debate regarding biotechnology
is often
confined to
whether there is harm from GM agriculture. It needs to be emphasized that
GM agriculture has not only potential liability for native biodiversity, but also potential
benefits for biodiversity as well. The potentia
l effects of biotechnology can only be
determined correctly if they are assessed in the context of
and
compared

to
current
agricultural practices. Given that we are not going to stop the practice of agriculture, we

10

need to determine the relative risk of GM plants and ani
mals to the risk

associated with
current varieties.


Effects of Biotechnology on Biodiversity: Potential Concerns:


What are the concerns about the effect of GM agriculture on biodiversity and the
environment? First we consider the effect that biote
chnology derived species might have
on non
-
target organisms. This issue was dramatically brought forward in
a
1999

study of
Monarch butterflies and Bt corn (Losey, et al., 1999). Monarch caterpillars were fed Bt
corn pollen in a laboratory experiment.

The caterpillars responded negatively to the Bt
pollen (Bt is particularly effective against lepidopteron
s
) and the larvae either exhibited
stunted growth or were killed. After this initial report, which caused uproar, the question
was asked if this mort
ality actually
occurs
in the field. Scientific risk assessment showed
that, in fact, few larvae are likely to be affected by Bt pollen
in the field
due to a number
of factors (Sears, et al., 2001). The Bt corn used for the initial experiment had the Bt
toxin
expressed
in high levels
in the
pollen whereas new va
rieties of Bt c
orn have little
c
ry protein in pollen. Other studies show that the timing of pollen release, the dispersal
curve of pollen over distance and the proximity of milkweed (the larval food source) to
corn fields all were suc
h that Bt corn would have a minimal effect the mortality of
milkweed larva. While the conclusions here were that Bt pollen may not be major factor
in monarch mortality, it raises significant questions about the effect of Bt toxins on other
insect species,

particularly lepidopterons, and also about the effect of Bt in the soil and on
soil arthropods, bacteria, worms, etc. Such risk assessment studies have been done for
only a few organisms.


Another issues is the cross pollination between crop and closely
related species

(Ellstrand, et al., 1999)
. Gene flow is the migration of genes from one population or
taxon into another. Gene flow has a homogenizing effect, making populations that
exchange genes
genetically
similar. Why is such gene flow or cross
-
pollination a
concern? First it can alte
r the gene pool of native species. When the native species are
wild relatives or ancestors of domesticated species, homogenization of populations can

11

result in the loss of critical genetic biodiversity. One of the hallmarks of domestication is
a genetic b
ottleneck that results in a decline in genetic variability within the domesticated
plant or animal species. In some cases up to 80% of the genetic variation that was
originally in the wild species is lost during domestication (Olsen and Schaal, 2001).
Th
us, populations of wild ancestors are extremely important for future crop
improvement, since they can
potentially
contain many useful genes. As an example, the
green revolution in Asia was fostered by new high yield varieties of rice. Genes were
incorporated from ri
ce’s wild ancestor,
Oryza rufipogon
, and included such traits as
disease resistance, small stature, a
nd response to fertilizers. Another

concern with gene
flow from GM crops into the wild ancestor is that GM traits may cause selective changes
that sweep throu
gh wild populations and result in a decline in variation. Any loss of
variation would include some useful traits. Such loss of variation could also compromise
the ability of wild populations to adapt to environmental change, either biological or
physical
.


Our own work on rice in Thailand indicates significant gene migration between
crop and wild ancestor. The gene flow curve for rice is leptokurtic; while most genes
migrate at small or moderate distances, there is a long tail of low levels of gene dispe
rsal
across large distances. In the case of rice, we can detect hybridization

between crop and
wild ancestor

by detecting plants that are morphologically intermediate between
cultivated and wild species. Our rice work illustrates another concern, the production of
weedy hybrids. The
worry is that when a GM crops hybridizes with a wild ancestor, the
hybrid offspring will lead to the formation of a vigorous weed (called super weeds by
some). This is again a situation found in conventional agriculture, where there are many
crop
-
weed sys
tems. Such hybridization is of particular concern in Thailand, where the
wild ancestor of rice grows in close contact with cultivated rice. In Thailand, gene flow
results from changing agricultural practices and
results in plant
hybrids
that

are very
aggressive in growt
h, interfere with rice cultivatio
n, and cause a decline in yield
. The
concern for biodiversity is that these weeds will then spread outside of the fields and
negatively impact native species. Work of Allison Snow and colleagues on hybrids of Bt
sunflowe
rs and native sunflowers has indicated that hybrids may have an enhanced

12

fitness relative to the wild sunflowers (Snow, et al., 2002). The hybrid sunflowers have
incorporated the Bt gene from the transgenic sunflowers and are resistant to attack by
some l
epidopteron
s
. Bt hybrids have greater seed production than the wild sunflowers,
thus raising
the specter of gene flow altering both the gene pool of the native sunflowers
and producing a new, weedy taxon. But,
whether or not these negative affects actually
occur still needs to be

acce
ssed.


In

global regions with high biodiversity, we expect that many related species will
be growing in close proximity to crops. The likelihood of gene migration between
closely related taxa is an issue that needs to be carefully evaluated. We expe
ct that the
results of such evaluations will vary depending on crop

species
. In some cases where the
crop is growing in
adjacent
to the wild ancestor, where the crop has not accumu
lated
major genetic differences that

isolate it
from the wild ancestor, and when there
is no
reproductive isolation or lack of pollinators, gene flow is likely. On the other hand for
some species there will be no gene migration between crop and wild relatives due to lack
of compatibility, variation in flowering time, or spatial isolation of

t
he crop from wild
relatives.
This conclusion is both encouraging and discouraging, since
either
the
detection or risks or the absence of risks

in

one species does not
bear on risk

assessment
of

gene flow

in other
agricultural

species
.

E
ach species n
eeds to be carefully accessed
separately and any generalizations need to be
drawn
with great care.


The Effects of Biotechnology on Biodiversity: Potential Benefits:


Up to this point we have explored potential negative consequences of GM
agriculture on biodive
rsity. But, there are also some potential positive aspects as well.
These
benefits
frequently stem from a mitigation of current agricultural practices such as
pesticide
or herbicide
application. Most of the world uses agrochemicals in varying
amounts for thei
r fields and crops. Different regions of the globe use different kinds of
chemicals
and
in vastly different amounts, with tropical agriculture of developing
countries often having very high
rates of pesticide
applic
ation
. Some rice fields in SE
Asia are sprayed
with pesticide
several times
a week, jeopardizing farmers, their families,

13

and the entire ecosystem with pesticides

(Phipps and P
ark, 2002)
. Bt crops such as corn
and cotton produce their own pesticides by genetic modification and potentially require
less insecticide spray. Data from cotton fields show a c
lear reduction in pesticide use
over conventional agriculture, but possible reductions for some other crops are not
always well documented. Any reducti
on in insecticide use would be of

great benefit not
only for

human health but also to

non
-
target organi
sms

and
the na
tive biodiversity of the
region.

Reductions in agrochemical use

simply exposes

spec
ies to less pesticide, either in
the form of

direct contact or as

sequestered in the food chain.


Another major concern is the application of herbicides that are used extensively in
western agricultu
re and increasingly in developing countries. Some herbicides can be
toxic, degrade slowly, or are difficult to assay. Glyphosate (Round Up) is
environmentally benign with little if any toxicity and
degrades
quickly
. Roundup ready
crops use applications
of glyphosate as an alternative to more toxic herbicides, thus the
switch to glyphosate resistant GM crops potentially reduces any
toxic effects of
herbicides, a change in agrochemical use
which,
in turn
,

can enhance biodiversity.
Moreover, herbicide use reduces plant biodiversity and th
us indirectly affects other
species in a food chain. Less diverse plant community may lead to a less diverse
arthropod, mammal, bacterial, etc. populations. Such changes can then have a ripple
effect through the food chain.


New varieties of GM crops tha
t are currently being developed will be engineered
to respond more readily to fertilizers or are drought resistant. Such crops afford the
possibility of reducing fertilizer application and irrigation, both processes that
significantly modify native habita
ts and lessen biodiversity


Other potential benefits include providing alternative
, ca
sh generating

crops for
local farmers

in the developing world
.
In many
regions of the developing world

with
low
agricultural

production
, local farmers subsidize their diets by hunting animals. Such

bush meat


may often
be
species that are rare or even endangered
.

E
conomic stability
from new cash crops
can
reduce the

harvest pressure on native biodiversity
.
One of most

14

intriguing aspects of GM for environmental benefit is the use of geneticall
y engineered
plants that have been modified to take up and sequester toxic substances such as heavy
metals

(
Bizily
, et al., 2000)
. These specialized plants, developed for bioremediation, are
sown as a lawn on a toxic spill site, grown, and the resulting plants then harvested an
d
disposed of as toxic waste. Several years of treatment can effectively remove
contaminants and dramatically reduce the levels of toxins in the soil.



GM agriculture offers the hope of reducing agrochemical use by developing
plants that produce their ow
n insecticides, thereby reducing the need for pesticide
application, by developing plants that are resistant to herbicides which allows
modification of application schedules (see below) and by developing plants that require
less fertilizer application. Su
ch potential benefits are particularly important in tropical
regions where pest pressure on crops is exceedingly high and very large amounts of
pesticide can be used. In a recent study of potential use of GM crops in developing
countries, Qaim and Zilberm
an

(
2003
)

illustrated that the demand for GM crops could be
high in developing countries due to their expected enhancement of yield. At the same
time, data from I
ndia on cotton indicates that Bt

cotton greatly reduces the use of
pesticides to reach the sam
e yield. To prevent a loss of 20% yield, Bt cotton requires
pesticide application of .8 kg/ha while non
-
Bt cotton requires an application of 4.8 km/ha,
a six
-
fold increase

(Qaim and Zilberman, 2003)
. Not only are such reductions in
pesticide good for biodiversity, they are critic
al for the health of local farmers who often
suffer from the effects of frequent applications of toxic pesticides, pesticides whose use is
often banned in the US.



While many studies have speculated that any reduction of agrochemical use
would enhance bio
diversity, relatively little supporting data are available. A recent study
examines the effect of the timing and use of herbicides on arthropod community diversity
in forage beet populations in Denmark (Standberg and Pedersen, 2002). In this study the
bi
odiversity of arthropods was compared in fields treated with conventional herbicide

application (non GM crop), to
a
GM
Roundup R
eady crop (GM) with applications of
herbicide according

to label recommendations and with

a late application of

Roundup
.

15

Interesting
ly, there was no significant difference between the arthropod communities for
the conventional crop and the roundup ready beets treated according to label directions.
But, the late application herbicide had nearly double the number of arthropod species.
The authors speculate that letting weeds remain longer in the field enhanced arthropod
species diversity. Such research demonstrates not only that GM agriculture

can enhance
species diversity
relative to conventional agricultural practices
,

but also the n
ecessity of
fine tuning agricultural practices for specific crops and location.



Such studies will be criticized, pointing out that if no herbicides were used

at all
,
then there would be an even greater biodiversity. This is of course correct, but the
assessmen
t of agricultural practices needs to be made realistically and in comparison with
current practices. Biodiversity would be greatest if we had no agriculture at all;
agriculture since the time of the earliest plant domestication has reduced native
biodiver
sity. But, such arguments ignor
e the global requirements of

human populations.
We need agriculture to feed populations in cities and the expanding populations of the
developing world. The best way to minimize the negative effects of agriculture, bot
h GM
and non
-
GM is to carefully apply the learned scientific principals from ecology, genetics,
molecular biology, agronomy, etc to each agricultural situation.


Conclusions:


It is clear that many of the issues that relate to the potential environmental

effects
and biodiversity for GM agriculture are location and crop specific. Fore example, there is
no risk of gene flow between GM corn and the wild ancestors of corn in the US. But in
central Mexico such gene flow may be a threat to the few remaining p
opulations of
teosinte, corn’s wild ancestor. The wealth of bio
diversity of tropical regions is a

particular

cha
llenge for GM agriculture. In the tropics many

species are cultivated in
contact with their wild ancestor and some tropical crops may have little genetic
differentiation from their wild ancestor, thereby increasing the chances of gene flow.
Moreover, environmental interactions in the tropics are complex with food chains and
connections between species often intricate. Thus one might expect perturbations o
f

16

local species to pass through other components of the ecosystem. At the same time,
pesticide use is high in tropics with a cost to humans, the environment and biodiversity.



The only way to determine the effect of biotechnology on the environment and

on
biodiversity is conduct appropriate scientific studies including the assessment of relative
risk, measures of gene flow, determine the fitness of hybrids, assessing the effects on
non
-
target species and ecological monitoring for things gone wrong

(Kjellsson and
Strandberg, 1995)
. Thi
s is not a well
-
received answer to the general question: Is
biotechnology harmful, neutral or beneficial to the environment? This question can only
be answered for a specific case and depends on the genetically modified plant or animal,
the geographical
region where the organisms are placed, and the local biological
environment. Moreover, the effects of a genetically modified organism need to be
compared to the effects of the current local agricultural practice
s

on the environment and
biodiversity

as well
. While

such work is complex and often tedious, careful scientific
assessment of the environmental risks of biotechnology will assure that biotechnology
will develop in concert with local biodiversity and it will ultimately help in
gaining
the
public

s
confid
ence in and
acceptance of these

technologies.


17

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