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OCR for page 65
6
Conclusions and Recommendations:
Plants
Numerous ways exist to modify plants genetically. We have
grouped them into three broad categories: classical, cellular, and
molecular. Classical methods include sexuad hybridization, embryo
culture (rescue), undirected mutagenesis, and anther and ovule cul-
ture. CeBular methods include cell fusion and tissue culture to
produce somaclonal variation. Molecular techniques include several
methods (such as recombinant DNA and electroporation) that result
in specific insertions of defined DNA sequences.
.
Methods used for genetically modifying plants include cIassi-
cal, cellular, and molecular techniques. The molecular tech-
niques are the most powerful and precise for incorporating
new traits.
Plants genetically modified by classical techniques have been
highly beneficial to society during this century. These benefits are
expected to continue and grow In the years ahead through the ad-
ditional applications of recently developed molecular and cellular
techniques. Farmers and consumers wiD be the major beneficiaries of
the Unproved econorn~c productivity that should keep farmers more
competitive in the world markets, while improving food, feed, and
new plant products through production practices that me compatible
with the environment.
65
OCR for page 66
66
.
Society will continue to benefit greatly from genetically mod-
ified plants.
WHAT DOES PAST EXPERIENCE TEACH US?
About Introductions
Over the past hundred years, plant breeders and other agricul-
tural scientists have accumulated vast experience and information
about the introduction of genetically modified plants into the en-
vironment. ~ fact, ahnost all of the major crops currently grown
in the United States have been introduced from foreign sources and
further bred ~ the United States for improved characteristics. New
weed species also have been introduced, although most weeds were
introduced in early colonial times, 200 to 300 years ago. Our past
experience with these introductions leads to two conclusions: (1)
Considerable success has been achieved in introducing and com-
mercializing genetically modified crops and other plants, and (2)
problems (economic or environmental), when they occur, are usually
minor or manageable.
Domesticated species, such as most field crops, pore little di-
rect threat to the environment. Problems that have resulted from
introductions have been indirect, such as increased soil erosion zl.nA
associated with managed ecosystems, such as farms. These problems
can be effectively controlled by altering such farming practices as
crop rotation, cultivation, cultivar selection, or choice of herbicides.
Extensive experience has been gained from routine field introduc-
tions of plants modified by classical genetic methods. For example,
an individual corn, soybean, wheat, or potato breeder may introduce
into the field 50,000 genotypes per year on average or 2,000,000 in
a career. Hundreds of million of field introductions of new plant
genotypes have been made by American plant breeders in this cen-
tury. There have been no unmanageable problems from these field
introductions through the use of established practices.
_ , _~ ~
.
Plants modified by classical genetic methods meet the famil-
iazity criterion on the basis of experience with hundreds of
minions of safe introductions over decades. Current oversight
practices of such field introductions are appropriate, and no
additional oversight is required.
OCR for page 67
67
About Genetic Modification
The majority of genetic modifications that are being proposed
for domesticated crops by molecular methods are similar to those
already achieved by classical means. These include resistance to her-
bicicles, pests, drought, and salt as well as compositional changes
in the seed or other plant parts. The genes being used to obtain
these traits may differ Tom those used in the past, but so far these
genes have introduced traits with which we have considerable experi-
ence. Therefore, our experience with the introduction of plants and
genetic modifications by classical means is relevant to the mtroduc-
tion of plants modified by newer methods such as recombinant DNA
techniques.
Molecular genetic methods differ from classical and cellular
methods in that molecular genetic methods involve manipulation
of not more than a few genes and their associated regulatory ele-
ments. These genes and their elements are usually weD characterized,
whereas classical and cellular methods may modify many genes but
with limited characterization. Most plants modified by the molecular
techniques proposed for field research have been modified only by the
addition of one or a few characterized genes within the genome of a
domesticated plant. In contrast, classical procedures such as sexual
hybridization and some cellular procedures such as cell fusion result
in the recombination of entire genomes of the two parental cells.
Because the specific gene products added by molecular techniques
are better characterized than those added by classical procedures,
questions about the changes effected In plants modified by molecular
techniques can be asked and answered more precisely.
Experience gained so far from field research on molecularly mod-
ified plants, as well as from extensive laboratory and greenhouse
research, supports the following conclusions:
Crops modified by molecular and cellular methods should
pose risks no different from those modified by classical genetic
methods for similar traits. As the molecular methods are
specific In terms of what genes are being added, users of these
methods will be more certain about the traits they introduce
into plants. Dissimilar traits will require careful evaluation
in small-scale field tests where plants exhibiting undesirable
phenotypes can be destroyed.
OCR for page 68
68
About Weeds
The vast majority of introduced wild species are unsuccessful in
their new habitats and therefore fad] to become established. How-
ever, on occasion introduced wild, non-native species can give rise
to problems. A better understanding of the process of species estate
lishment would enhance predictability in determining the ultimate
success or failure of an Introduced wild, non-native plant. If the
newly introduced plant poses problems, standard control measures
are usually available.
A major issue is the potential ability of genetically modified
plants to hybridize with weedy relatives to yield offspring with char-
acteristics that enhance weediness. On the basis of evidence of gene
movement between classically bred plants and weedy relatives, this
process occurs infrequently, but varies widely among crops. When
gene movement from crops to weeds occurs, the weeds become more
croplike and compete for the same resources. This phenomenon is
not believed to have caused problems In natural ecosystem, but has
within managed ecosystems.
The potential for enhanced weediness ~ the major environ-
mental concern surrounding the introduction of genetically
modified plants. The incidence of enhanced weediness has
been extremely low ~ the past and has been controllable.
CONTROL AND CONTlNEMl:NT OF GI:NETICAIlY
MODIFIED PLANT VARIETIES
An array of options exists for confining a plant to its test site.
These options include male sterility, removal of reproductive organs,
herbicides, insecticides, disinfectants, tilIage, water manipulation
(flooding and irrigation), isolation from similar plants, photoperiod
manipulation, dates of planting and restriction in the number of
locations, and physical barriers such as cages.
Titian field tests of cIassicaBy bred plants are normally carried
out with different plants having many different gene combinations.
Great care is taken to track modified properties in the plant and
to retain properties of interest by avoiding contamination with sim-
ilar plants grown in the same or nearby fields. The small scale of
plots, such ~ 20 feet long by 3 rows wide, limits the disse}nination
of a particular plant. Further, repeated and periodic observations
help ensure that undesirable genotypes are not propagated further.
OCR for page 69
69
Acreage of selected plants ~ increased over several years, and each
year observations are made of both desirable and undesirable traits.
Millions of individual plants are tested annually In the United States,
and no environmental damage has been documented from their re-
lease. Standard confinement practices have been effective in keeping
in bounds both poorly domesticated and highly domesticated plants.
Proven and routinely applied confinement methods include
biological, chemical, physical, geographical, environmental,
and temporal control, as well as limitation of the size of the
field plot.
The committee could document no case of escape of a plant
introduction from a confined experimental field plot (1 acre
or less) that has produced problems In natural ecosystems.
Confinement of plants in small field tests is almost always suc-
cessful. Particular traits may be transmitted by pollen to other
related plants in the vicinity, but most available evidence shows this
to be rare. Unless that trait confers a strong selective advantage to
the progeny of the recipient, no adverse effects will occur. ~ nec-
essary, such plants can be destroyed. Molecular genetic techniques
neither enhance nor decrease the probability of occurrence of such
genetic transfer relative to classical methods of genetic manipulation.
Established confinement options are as applicable to field
introductions of plants modified by molecular and cellular
methods as they are for plants modified by classical genetic
methods.
.
[ARG~SCA[E INTRODUCTIONS AND
COMMI:RCIAIIZATION
This report addresses small-scale experimental introduction, not
large-scale introductions ~d commercialization. As experience with
small-scale field research increases, the information gamed will per-
rn~t large-scale introductions to be approached with greater confi-
dence. A plant that exhibits desirable traits in small-scale tests will
be graduaDy increased In number and either returned to a breeding
program or released as a cultivar. Oversight mechanisms should re-
ma~n flexible to accommodate the transition that wiD occur as testing
of crops modified by molecular methods proceeds from isolated field
plots to large-scale, multisite testing. This field research Is critical to
the development of new crop varieties and hybrids.
OCR for page 70
70
An important consideration in the commercialization of plants
produced by any of the available techniques is how to deploy resis-
tance genes so that they remain effective in controlling pests. For
example, if the Bacillus thuringiens's endotoxin gene is widely used
without regard to the development of resistance, tolerance to this
useful bioinsecticide might develop. The same is true for disease-
resistance genes.
Another concern associated with large-scale use is the potential
genetic "cont~nination~ of populations of wild relatives of cultivated
plants by genes from unrelated organisms that have been introduced
into the cultivar. However, for this concern to be valid, gene ~ntro-
gression would have to occur and the resulting progeny would have
to have a selection advantage in their wild environment.
.
Experience gained through smaB-scale field research is crucial
to the large-scale use of genetically modified plants.
A FRAMEWORK FOR ASSESSING RISE
Most of the extensive past experience on field research of plants
that have been genetically modified by classical techniques is rele-
vant to field research of plants modified by molecular and cellular
techniques. Procedures of confinement, monitoring, and mitigation
work equally well, regardless of how the plant was produced.
The types of modifications that have been seen or anticipated
with molecular techniques are similar to those that have been pro-
duced with classical techniques. No new or inherently different haz-
ards are associated with the molecular techniques. Therefore, any
oversight of field tests should be based on the plant's phenotype and
genotype and not on how it was produced. The power of the molec-
ular methods, however, does present the possibility that plants with
unfa~riiliar but desired phenotypes may be produced. In some cases,
new genes sources may be used, but familiar phenotypes will result.
Plants with unfamiliar phenotypes should be subject to oversight
until their behavior Is predictable and shown to be nondetrimental
to the environment.
In this section, the committee proposes a decLsion-making framer
work (Fig. ~1) that allows experimental field testing based on (1)
famuliarity with the plant and genetic modification (Fig. 6-2), (2)
the ability to confine the plant (Fig. ~3), and (3) the perceived
environmental unp act if the plant should escape confinement (Fig.
~4~.
OCR for page 71
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OCR for page 74
74
Situations that are familiar and considered safe on the basis of
past experience or experimentation should be cIassifiec] as manage-
able by accepted standards (MAS). MAS plants would include, for
example, classically produced plants and other plants with familiar
phenotypes. These plants should be field-tested In a manner that
is most appropriate based on past experience in traditional plant
breeding.
All plants can be confined, some more readily than others. The
use of sterile plants is probably the best example of easy confinabil-
ity, providing that attention is paid to the dissern~nation of vege-
tative propagules. The other extreme would be to confine an open-
pollinated plant in the presence of cross-hybridizing wild relatives. In
this situation, confinement may be as strict as physical containment
in a quarantine greenhouse. It Is clear that the appropriate level of
confinement depends on the plant and the geographic area for the
field test. If confinement is difficult or uncertain, attention needs to
be given to the potential environmental ~rnpact of the introduction.
If there is potential for considerable negative environmental impact,
confinement procedures should be rigorous, ~ with screened cages.
If potential impact is low, less stringent procedures should be called
for.
As data based on field tests accumulate, it may be desirable to
lessen the confinement requirements so that a plant can be used in a
cro~improvement program. Field-test results need to be assessed for
potential negative environmental impact as a result of altered char-
acter~stic~ of weediness, toxicity, or pest resistance. Data obtained
through field testing provide the best way to assess the presence of
undesirable characteristics accurately.
The committee has also included a set of example questions
(Figs. ~1 through ~4) that might need to be asked at each phase in
the decision-making process. This is not a comprehensive list. The
importance attached to each of these questions should be determined
on a case-by-case basis.
GEOGRAPHIC FAME OF REFE1tENCE
Even though the issues discussed in this report are of interest
worldwide, it is important to keep in mind that it is written to
address the concerns of the United States. The occurrence of weedy
or wild relatives for major crops depends on geographic area. In
addition, some uses of genetically modified plants will be better
OCR for page 75
Representative terms from entire chapter:
molecular techniques
75
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76
suited for certain geographic areas than others. Therefore, each
country and geographic area will need to determine the extent to
which the introduction of a genetically modified plant wall have an
impact on its environment.
OVERSIGHT CONSIDERATIONS
It Is reasonable to ask what type of oversight is needed to pro-
tect the public welfare and environment, yet does not unnecessarily
restrict biotechnological research and commercial development. In-
stitutional or local review has a long history of success. For example,
in some cases crop certification of plants for expanded field tests and
commercialization uses established institutional review or no review.
Similarly decentralized local oversight is also used for approval of
animal, human, and other exper~rnental procedures including exper-
iments utilizing recombinant DNA techniques. Therefore, local over-
sight is seen as a suitable option for assessing the risk associated with
most research. It is desirable to delegate low-risk introductions-
probably 95 percent or more of all ongoing research to local over-
sight, so that federal oversight can be used for those few cases where
perceived risk exists because confinement Is questionable.
We also note that organizations such as government and uni-
versity research groups are underrepresented in field introductions
of plants modified by molecular techniques. This absence probably
arises from the complexity and cost of seeking regulatory approval.
This research community has played a vital role not only in develop
ing contemporary procedures and techniques, but also In most plant
improvement. If the fuB benefit of molecular modifications Is to be
realized, the academic and governmental research communities must
have access to and be encouraged to apply the technologies of cellular
and molecular genetic modification to plants and to evaluate them
through field testing.
