Article - Plant Breeding
Crop Improvement: A Dying Breed
(Nature - February 6, 2003)
By JONATHAN KNIGHT
Nature 421, 568 - 570 (2003); doi:10.1038/421568a Crop improvement:
A dying breed
Public-sector research into classical crop breeding is withering, supplanted
by 'sexier' high-tech methods. But without breeders' expertise, molecular-genetic
approaches might never bear fruit. Jonathan Knight reports. Normally,
at this time of year, agricultural scientists from around the world
would be converging on the headquarters of the International Maize and
Wheat Improvement Center, known as CIMMYT, in Texcoco, near Mexico City.
They would then travel together to a desert field station near Ciudad
Obregón in northwestern Mexico to study the current crop of experimental
wheat cultivars, planted at the beginning of winter.
But not this year. For the first time in half a century, the research
centre that helped to sow the seeds of the 'green revolution' of the
1960s and '70s has been forced to skip a cycle of wheat breeding trials,
because of a lack of money. More than half of CIMMYT's fields in Obregón
lie fallow, and the trainee plant breeders are staying at home.
CIMMYT is not alone. All over the world, conventional plant breeding
has fallen on hard times, and is seen as the unfashionable older cousin
of genetic engineering. "Plant breeding is getting dumped along
the wayside for not being sexy enough," claims Greg Traxler, an
agricultural economist at Auburn University in Alabama. Government funding
of plant-breeding research has all but dried up in the United States
and Europe, and the World Bank and donor nations have recently slashed
their support for the Consultative Group on International Agricultural
Research (CGIAR), the international research consortium of which CIMMYT
is a part.
Meanwhile, a steady push by companies to claim exclusive commercial
rights to new plant varieties has progressively tied the hands of publicly
funded efforts at crop improvement. If this trend isn't halted, some
experts claim, tomorrow's supercrops may end up like many of today's
medicines: priced out of the reach of much of the developing world's
growing population. "We are headed down the same path that public-sector
vaccine and drug research went down a couple of decades ago," says
Gary Toenniessen, director of food security at the Rockefeller Foundation
in New York.
Sowing success
Classical breeders improve crops simply by crossing plants with desired
traits, and selecting the best offspring over multiple generations.
Sometimes they use chemical mutagens to disrupt crop genomes, in the
hope that some of the resulting mutants will have useful new traits.
Crosses may be as simple as letting two plants grow together, or they
may require pollination by hand. And for crops such as wheat, one parent
must first be emasculated to prevent self-pollination. In some ways,
breeding is like accelerated, targeted evolution, and as long as test
crops and seed banks are maintained, the possibilities can never be
fully exhausted.
These methods, applied intensively at CIMMYT and the International
Rice Research Institute (IRRI) near Manila in the Philippines, provided
the impetus for the green revolution. Breeders produced dwarf varieties
of wheat, maize and rice that were less likely to fall over in wind
and rain, and which could carry larger seeds. Thanks to these varieties,
farmers could use more fertilizer without risking losing their crops,
and grain harvests in some areas have doubled or even trebled over the
past three decades.
Central to CIMMYT's success in wheat was the practice of 'shuttle breeding',
in which two seasons of plant selection could be completed in one year.
Grain would be rushed from the fields in Ciudad Obregón after
the harvest in April for summer planting in Toluca, near Mexico City.
This year's cancellation of the Obregón end of the shuttle was
part of a 10% reduction in CIMMYT's programmes in the face of budget
cuts, says the centre's director general, Masa Iwanaga. This was a result
of the reduction in support for the CGIAR, which supports CIMMYT, IRRI
and 14 other agricultural research centres around the world.
Whereas the CGIAR's funding crisis has come to a head in the past couple
of years, exacerbated by the global economic downturn, the world's academic
plant-breeding labs have suffered steady attrition over a far longer
period. Molecular genetics and transgenic technologies hold great promise
for crop improvement, and have consumed a growing portion of the limited
funding pie. University administrators have reinforced this trend, tending
to replace retiring plant breeders with molecular geneticists who are
more likely to produce high-profile journal articles.
Changes in the intellectual-property environment have also taken their
toll. From the late 1960s onwards, developed nations introduced a legal
framework of plant breeders' rights, giving new varieties and cultivars
patent-like protection. The goal was to stimulate innovation in corporate
labs, but the reforms also meant that public-sector breeders were no
longer free to tinker with plants grown from commercial seed. "Plant-variety
protection was the death knell for public breeding programmes,"
says Michael Gale, head of comparative genetics at the John Innes Centre
in Norwich, Britain's leading public plant-science research institute.
Root of the problem
The figures reinforce Gale's view: until the 1960s, breeding for crop
improvement was largely a public endeavour, but a survey of US plant
scientists in the mid-1990s found more than twice as many breeders in
the commercial sector than at universities and government agencies combined1.
And although breeders' skills are still alive in the private sector,
they are now working to subtly different ends. For seed companies and
agribiotech firms, the top priority has been developing crops that can
maximize profits from the intensive agricultural practices that are
widely used in the developed world. Sadly, there is less money to be
made in seeding a second green revolution for the world's poor.
In recent years, of course, the big news in the commercial and public
sectors has been transgenic technology, rather than conventional breeding.
Genetically modified (GM) crops that are resistant to the effects of
broad-spectrum herbicides or that carry genes for insecticidal toxins
have been widely planted across North America — but simultaneously
shunned by European consumers, who are deeply suspicious of the technology.
The welter of media coverage has obscured recent achievements in classical
breeding, and although breeders generally view transgenics as a valuable
tool, they stress that conventional breeding is far from obsolete.
In fact, for many GM crops, there is a comparable conventionally bred
variety. The seed company Pioneer Hi-Bred, based in Des Moines, Iowa,
for instance, produces a conventional, herbicide-resistant oilseed rape,
or canola, that has similar advantages for weed control as its GM counterparts.
And whereas the GM 'golden rice'2, engineered to contain a gene that
boosts the production of vitamin A by people who eat its grain, has
attracted much publicity, conventional breeding is also being deployed
to improve the nutritional value of this staple crop. IRRI has produced
a cultivar of rice called IR68144 that bears grain rich in iron3, and
so could be used to combat anaemia. Even for crops such as the banana,
which is unable to reproduce sexually without specialist human intervention,
conventional breeding may still have a role to play (see "Bananas
in the fertility clinic").
What's more, the GM crops developed so far generally involve only the
addition of a single gene. Looking to the future, it's unclear whether
complex traits, which are thought to involve multiple genes, will be
amenable to manipulation through genetic engineering. "In the long
term, you need heat tolerance, salt tolerance, greater yield and so
on," says Paul Gepts, a crop geneticist at the University of California,
Davis. "Some say you can do it with genetic engineering, but we
just don't know how those systems work and how those genes interact."
By contrast, practical experience has shown that conventional breeding
can be used to improve a suite of subtle traits simultaneously.
All of this makes Donald Duvick, who was head of research at Pioneer
Hi-Bred until his retirement in 1990, concerned about the future of
crop improvement should the agribiotech giants lose their enthusiasm
for transgenics. "I worry that the results will be so far in the
future that industry will say 'we can't wait that long'," he says.
If so, the depleted public-sector effort in plant breeding may be ill-equipped
to take up the slack.
There are already hints that some companies are pulling back from long-term
investments in high-tech crop improvement. Only last month, the Swiss-based
multinational Syngenta closed its Torrey Mesa Research Institute near
San Diego, which was a major force in crop genomics. And both Syngenta
and its US rival DuPont, which owns Pioneer Hi-Bred, have recently withdrawn
funding from the John Innes Centre. "The industry is in turmoil,"
says Gale.
Against this sombre background, can anything be done to safeguard future
progress in crop improvement by reviving the science of plant breeding
in the public sector? There is no easy answer, but some experts suggest
that the future lies in boosting the power of conventional breeding
by marrying it to genomic and other molecular-genetic techniques, while
making a concerted effort to break with the proprietary approach to
intellectual property that is currently blighting the field.
Jorge Dubcovsky's genetic techniques aim to give traditional breeding
a technological boost.
One beacon of hope comes from a consortium of researchers at 12 institutions
headed by Jorge Dubcovsky, a wheat molecular geneticist at the University
of California, Davis. Its primary tool is 'marker assisted selection'
(MAS). This technique, enthusiasts claim, could offer to plant breeding
what the jet engine has brought to air travel. Traditionally, breeders
have relied on visible traits to select improved varieties. For pest
resistance, for example, that means examining mature plants in the field
over successive generations to see which survive best in the face of
attack by pests, before carrying out new crosses. MAS, however, relies
on identifying marker DNA sequences that are inherited alongside a desired
trait during the first few generations. Thereafter, plants that carry
the trait can be picked out quickly by looking for the marker sequences,
allowing multiple rounds of breeding to be run in quick succession.
Superior breeding
MASwheat, as the consortium is known, aims to select for 23 separate
traits in wheat, conferring resistance to fungi, viruses and insect
pests. Its members also hope to breed the grain to produce bread and
pasta of superior quality. Notably, the consortium is making all of
its marker sequences and research protocols freely available. "If
you go to our website, you have all the tools to do this anywhere in
the world," Dubcovsky says.For wheat, this admirably open approach
was relatively easy to adopt, because it is one of the few crops to
remain largely in public hands. Because wheat is self-pollinating, many
farmers simply plant a portion of their harvest each year, safe in the
knowledge that it will retain its desirable characteristics. Not surprisingly,
this has restricted the interest of commercial seed producers, who don't
see a robust market for their products.Elsewhere, however, intellectual
property is creating a heavy burden, with universities and other institutions
facing barriers to the free exchange of seed, and restricted access
to cutting-edge molecular technologies. "I wish it would all go
away," says Kent McKenzie, director of the California Rice Experiment
Station, which develops new varieties of the crop in its test fields
at Biggs, north of Sacramento.Extending the MASwheat consortium's approach
to other crops may require public institutions to band together to end
the practice of granting exclusive licences to individual companies
each time they develop a powerful technology for crop improvement. To
this end, Toenniessen has been meeting with representatives of ten 'land
grant' universities — which form the backbone of agricultural research
in the United States — to hammer out a plan. "If those in
the public sector worked collectively, they could solve their problems,"
says Toenniessen. He hopes to pioneer the approach in speciality crops
such as peanuts, broccoli, lettuce and tomatoes, in which the seed and
agribiotech industry does not have strong commercial interests.
Free for all: Richard Jefferson wants to put crop improvement within
the reach of poor farmers. Richard Jefferson would go further. His Center
for the Application of Molecular Biology to International Agriculture
(CAMBIA) in Canberra, Australia, is trying to put cutting-edge technology
for crop improvement directly in the hands of developing-world scientists
and farmers, rather than leaving them to depend on the continued health
of labs in rich countries. "The money is drying up and that is
not going to change," he says. "We need to rethink the way
crop improvement is done."
In part, Jefferson says, this will involve the transfer of transgenic
technologies. But extending access to molecular-genetic enhancements
to conventional breeding methods will also be crucial. Researchers at
CAMBIA, for instance, have developed a DNA microarray that will boost
MAS. In many crops, it is difficult to search for specific genetic markers,
because very little of their DNA has actually been sequenced. But by
immobilizing fragments of DNA from a variety of cultivars on a microarray
and then seeing which of them bind to DNA sampled from individual plants,
it is possible to look for the presence of genetic markers in these
plants in the absence of any sequence information4.
This technology has already been adopted by the International Center
for Tropical Agriculture in Cali, Colombia, for cassava improvement.
"It is extremely useful," says Joe Tohme, the centre's director
of biotechnology. By making such techniques freely available, and allowing
scientists anywhere in the world to tinker with and improve them at
will, Jefferson hopes to speed progress. Essentially, he wants to create
a crop-improvement counterpart to the 'open-source' software movement
that has managed to flourish alongside the proprietary approach of giants
such as Microsoft, which keep their programs' codes under wraps.
'Open-source molecular agronomy' is certainly a sexier label than conventional
plant breeding. But will it have sufficient cachet to reverse the current
decline in public-sector crop improvement? The food supply for future
generations in the developing world could hinge on the answer.
JONATHAN KNIGHT
Jonathan Knight writes for Nature from San Francisco.
References
- Frey, K. J. National Plant Breeding Study (Iowa Agric. Home Econ.
Exp. Station, Ames, Iowa, 1996).
- Ye, X. et al. Science 287, 303-305 (2000).
- Glahn, R. P., Chen, S. Q., Welch, R. M. & Gregorio, G. B. J.
Agric. Food Chem. 50, 3586-3591 (2002)
- Jaccoud, D., Peng, K., Feinstein, D. & Kilian, A. Nucl. Acids
Res. 29, 25e (2001).
- Remy, S., Francois, I., Cammue, B., Swennen, R. & Sági,
L. Acta Horticult. 461, 361-365 (1998).
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Nature © Macmillan Publishers Ltd 2003 Registered No. 785998 England
