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Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
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OCR for page 1
Introduction
Farmers have been cultivating plants for millenia. Over the years,
increasingly sophisticated tools have been applied to crop improvement.
Modern plant breeding techniques, for instance, have been used to
create new varieties adapted to specific environments or needs- such
as crops that are easier to harvest or that are resistant to disease. These
breeding practices have been augmented by chemical technology. Pes-
ticides are now widely used to protect crops from insect infestations.
Herbicides have largely replaced mechanical cultivation as the method
for controlling weeds. And fertilizer is routinely used to replenish the
nutrients lost from the soil. These breeding strategies, agricultural chem-
icals, and improved cropping practices have boosted agricultural pro-
ductivity in the United States to its current high.
Despite these successes, crops are still lost to pests, diseases, and
climatic extremes. Fertilizer and other chemicals are now consuming an
increasing share of the farm dollar. At the same time, there is growing
concern about the effect of these chemicals on the environment. Agri-
cultural problems are more pronounced in the Third World, where the
population is rising steadily. Without improvements in agricultural tech-
nologies, demand for food is expected to outrun supply early in the
next century.
Molecular biology and genetic engineering offer new tools to meet
these and other agricultural needs. Molecular biologists are learning how
to transfer foreign genes into plant cells. They are doing on a molecular
level what plant breeders have been doing with whole plants for cen-
turies: combining genes in new ways to create improved crops. Working
with single genes, rather than whole plants, offers several advantages.
One advantage is specificity. Classical breeding introduces genes that
complicate the process of crop improvement. In a sexual cross, the entire
1
OCR for page 2
2
GENETIC ENGINEERING OF PLANTS
genomes of two plants are combined even though the breeder may be
trying to transfer a trait controlled by a single gene. It takes repeated
back crosses to eliminate the extraneous genes and thus many years to
create an improved variety. Using molecular techniques, a gene can be
snipped from one plant and spliced into another in a single experiment.
Perhaps more important, genetic engineering opens up a new source
OCR for page 3
INTRODUCTION
3
of genetic variability that can be used in crop improvement. Breeders
can work only with plants that are cross-fertile. By contrast, genetic
engineering offers the promise of selecting valuable traits from any
organism. For instance, research is already under way on the transfer
of the genes for nitrogen fixation from bacteria to plants. Another ap-
proach might be the transfer of genes for herbicide resistance from weects
to crop plants.
If genetic engineering techniques can be mastered, they could be used
in the design of plants that are hardier, higher yielding, more nutritious,
or less expensive to produce such as plants that require fewer pesti-
cides, fungicides, or fertilizers. Other possibilities include plants that
can thrive in marginal conditions, on soils that are too salty, too acidic,
too wet, or too dry.
The genetic engineering of plants, however, is still in its infancy.
Fundamental questions remain about the feasibility of some of these
techniques. Last year, researchers demonstrated for the first time that
a foreign gene can be successfully inserted into a plant and made to
function. Yet extensive research will be necessary before these tech-
niques can be used in practical crop improvement schemes. Molecular
biologists must identify agriculturally important genes from the 5 million
or so contained in most plants. They are searching for vectors to carry
foreign genes into a plant cell. And they must develop reliable methods
for regenerating plants from single cells in culture. Such experiments
are just beginning. In acictition, little is known about how plants will
respond to the introduction of foreign genes if, for instance, yield or
vigor will suffer.
Progress in plant genetic engineering has been hampered by the lim-
ited knowledge of plant biology. The successful application of genetic
engineering to plants will require fundamental breakthroughs in the
understanding of gene expression and regulation, as well as increased
knowledge of plant physiology, biochemistry, development, and me-
tabolism. Yet relatively few scientists are trained in either plant molecular
or cellular biology, and few of these scientists have any experience in
addressing agricultural questions.
It is too early to assess with accuracy either the potential or limitations
of genetic engineering for crop improvement. At this stage, gene transfer
is not expected to have a significant effect on agricultural production
practices until the late 1990s. Other, simpler techniques, based on the
ability to culture and regenerate plant cells, are already proving a short-
cut in the selection and breeding of some crops. Yet in the near term,
the biggest contribution of gene transfer and other new technologies
will be to fundamental knowledge. The ability to identify and isolate
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4
GENETIC ENGINEERING OF PLANTS
single genes is a valuable too] in the stucly of gene structure and function.
This knowledge can then be used to devise more effective strategies for
crop improvement through classical breeding and, eventually, through
· · —
genetic engineering.
In May 1983 the Board on Agriculture of the National Research Council
held a convocation to discuss the potential contribution of genetic en-
gineering to agriculture. Speakers from numerous disciplines discussed
the research opportunities presented by the new genetic technologies,
as well as their implications for funding and training in the plant sci-
ences. The following report is based on that discussion.
I
Representative terms from entire chapter:
crop improvement
