An Assyrian relief carving from 870 B.C. showing artificial pollination of date palms.
What is Plant Breeding?
For several thousand years, farmers have been
altering the genetic makeup of the crops they
grow. Human selection for features such as faster
growth, larger seeds or sweeter fruits has dramatically
changed domesticated plant species compared to
their wild relatives. Remarkably, many of our
modern crops were developed by people who lacked
an understanding of the scientific basis of plant
Despite the poor understanding of the process, plant
breeding was a popular activity. Gregor Mendel himself,
the father of genetics, was a plant breeder, as were
some of the leading botanists of his time. Mendel's
1865 paper (http://www.MendelWeb.org/Mendel.html)
explaining how dominant and recessive alleles could
produce the traits we see and could be passed to offspring
was the first major insight into the science behind
the art. The paper was largely ignored until 1900, when
three scientists working on breeding problems rediscovered
it and publicized Mendel's findings.
Major advances in plant breeding followed the revelation
of Mendel's discovery. Breeders brought their new understanding
of genetics to the traditional techniques of self-pollinating
and cross-pollinating plants.
Plant breeder Sally Clayshulte collects pollen
Corn breeders, particularly, tried numerous strategies
to capitalize on the insights into heredity. Corn
plants that had traditionally been allowed to
cross-pollinate freely were artificially self-pollinated
for generations and crossed to other self-pollinated
lines in an effort to achieve a favorable combination
of alleles. The corn we eat today is the result
of decades of this strategy of self-pollination
followed by cross-pollination to produce vigorous
hybrid plants. Information on the history of corn
breeding is available in an article written by
L.W. Kannenberg for the Ontario Corn Producers
The art of recognizing valuable traits and incorporating
them into future generations is very important
in plant breeding. Breeders have traditionally
scrutinized their fields and traveled to foreign
countries searching for individual plants that
exhibit desirable traits. Such traits occasionally
arise spontaneously through a process called mutation,
but the natural rate of mutation is too slow and
unreliable to produce all the plants that breeders
would like to see.
In the late 1920s, researchers discovered that
they could greatly increase the number of these
variations or mutations by exposing plants to
X-rays. "Mutation breeding" accelerated after
World War II, when the techniques of the nuclear
age became widely available. Plants were exposed
to gamma rays, protons, neutrons, alpha particles,
and beta particles to see if these would induce
useful mutations. Chemicals, too, such as sodium
azide and ethyl methanesulphonate, were used to
Examples of plants that were produced via mutation breeding are given in the table below.
||Method Used to Induce Mutation
|St. Augustine grass
Quite a few flower cultivars have been developed via mutation breeding, among them some of the cultivars of Alstroemeria, begonia, carnation, chrysanthemum, dahlia, and snapdragon.
Mutation breeding was particularly popular in
the United States during the 1970s. Although interest
has waned somewhat in recent years, occasional
varieties continue to be produced using these
methods. For example, the new herbicide-resistant
wheat variety Above (http://wheat.colostate.edu/above.html)
was developed using exposure to sodium azide.
Mutation breeding efforts continue around the
world today. Of the 2,252 officially released
mutation breeding varieties, 1,019, or almost
half, have been released during the last 15 years.
For more information on mutation breeding, go
to the International Atomic Energy Agency's site
and click first on "introduction" and
then on "FAO/IAEA Mutant Variety Database."
A rose grown in tissue culture.
Another method for increasing the number of mutations
in plants is tissue culture. Tissue culture is
a technique for growing cells, tissues, and whole
plants on artificial nutrients under sterile conditions,
often in small glass or plastic containers.
Tissue culture was not developed with the intention
of causing mutations, but the discovery that plant
cells and tissues grown in tissue culture would
mutate rapidly increased the range of methods
available for mutation breeding.
More information on tissue culture of plants
is available at http://www.jmu.edu/biology/biofac/facfro/cloning/cloning.html.
A lesson on the basics of tissue culture http://croptechnology.unl.edu/viewLesson.cgi?
LessonID=957885612 is available at the Crop
Technology web site maintained by the University
of Nebraska at Lincoln.
It was during the 1970s also that haploid breeding
was heavily utilized. Spontaneously occurring
haploid plants, those having half the normal number
of chromosomes, were discovered in the 1920s,
but haploid breeding was not a practical technique
until methods for the controlled production of
haploid plants were developed. Once a haploid
plant has been obtained, its chromosomes are artificially
doubled to return the plant to the normal number
of chromosomes. Such a plant is valuable because
the chromosomes that were created by artificial
doubling are exact copies of the chromosomes that
were present in the haploid plant.
Haploids have been used in creating cultivars
of barley, maize, tobacco, asparagus, strawberries,
and tall fescue grass. Often these plants are
more useful in basic research than in commercial
applications, but the haploid-derived barley cultivar
Tangangara was released for commercial production
in Australia in 1996. A list of haploid-derived
barley lines that are being tested for commercial
value is available at http://www.regional.org.au/au/abts/2001/t4/broughton.htm.
A diagram of the haploid breeding process is
provided at http://barleyworld.org/NABGMP/QTLFIG.HTM.
A description of how this technique is being used
to create new barley cultivars in Australia, and
how it differs from genetically engineering the
barley, is available at http://www.wintv.com.au/science/barley.shtml.
While most breeders cross-pollinate plants of
a single species, some breeding methods rely on
crosses that can be made between two species within
the same genus. A cross between Musa acuminata
and Musa balbisiana, both members of the
genus Musa, produced the bananas with which
we are familiar. Less commonly, the cross is between
members of two different genera. A cross between
wheat, Triticum aestivum, and rye, Secale
cereale, produced the grain called triticale,
which contains a copy of all the chromosomes from
A variation on the wide crossing procedure is to select
plants that have single chromosomes or chromosome arms
substituted from one species into another. Many modern
wheat cultivars, for example, contain a chromosome arm
from rye, which adds resistance to several diseases.
A list of wheat cultivars that contain a chromosome
arm from rye is available at http://wheat.pw.usda.gov/ggpages/1rscom.html
Transgenic technology provides the means to make
even more distant "crosses" than were previously
possible. Organisms that have until now been completely
outside the realm of possibility as gene donors
can be used to donate desirable traits to crop
plants. These organisms do not provide their complete
set of genes, but rather donate only one or a
few genes to the recipient plant. For example,
a single insect-resistance gene from the bacterium
Bacillus thuringiensis can be transferred
to a corn plant to make Bt corn. A description
of Bt corn is available on our Current Transgenic
Transgenic plants were first created in the early
1980s by four groups working independently at
Washington University in St. Louis, Missouri,
the Rijksuniversiteit in Ghent, Belgium, Monsanto
Company in St. Louis, Missouri, and the University
of Wisconsin. On the same day in January 1983,
the first three groups announced at a conference
in Miami, Florida, that they had inserted bacterial
genes into plants. The fourth group announced
at a conference in Los Angeles, California, in
April 1983 that they had inserted a plant gene
from one species into another species.
The Washington University group, headed by Mary-Dell
Chilton, had produced cells of Nicotiana plumbaginifolia,
a close relative of ordinary tobacco, that were
resistant to the antibiotic kanamycin (Framond
et al., 1983). Jeff Schell and Marc Van Montagu,
working in Belgium, had produced tobacco plants
that were resistant to kanamycin and to methotrexate,
a drug used to treat cancer and rheumatoid arthritis
et al., 1983). Robert Fraley, Stephen Rogers,
and Robert Horsch at Monsanto had produced petunia
plants that were resistant to kanamycin (Fraley
et al, 1983a). The Wisconsin group, headed
by John Kemp and Timothy Hall, had inserted a
bean gene into a sunflower plant.
These discoveries were soon published in scientific
journals. The Schell group's work appeared in
Nature in May (Herrera-Estrella
et al., 1983) and the Chilton group's work
followed in July (Bevan
et al., 1983). The Monsanto group's work appeared
in August in Proceedings of the National Academy
of Sciences (Fraley
et al, 1983b). The Hall group's work appeared
in November in the journal Science (Murai
et al., 1983).
These early transgenic plants were laboratory
specimens, but subsequent research has developed
transgenic plants with commercially useful traits
such as resistance to herbicides, insects, and
The rest of this web site discusses the methods
for creating transgenic plants, the plants that
have been created, their evaluation and regulation,
and the many issues that have arisen as a result
of this new phase in the history in plant breeding.
For one view comparing crop domestication, traditional
plant breeding, and genetic engineering, see the
review by Gepts,
Page last updated : January 29,
© Copyright Department of Soil and
Crop Sciences at Colorado State University, 1999-2004.
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