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January 11, 2008
Source:
SciDev.Net
by T.V. Padma
Climate change threatens food
crops across the world. Now scientists are re-focusing their
efforts on crop resilience, rather than yields.
Among the most worrying aspects of climate change is its effects
on the world's food supply. The worst-case scenario is stark:
Africa's Sahel region will produce fewer cereals, rice
cultivation in Asia will be under threat, there will be fewer
vegetables — with potatoes and beans potentially wiped out — and
livestock and fisheries will be severely stressed.
Climate change is making crop scientists review their research
agenda. Until now, their main focus was on improving yields. But
with successive International Panel
on Climate Change (IPCC) reports warning that increased
droughts and floods will shift crop systems, 'climate-proofing'
of crops has become crucial. The
Consultative Group on International Agricultural Research
(CGIAR) institutes are now investigating how to make crops' more
resilient to environment stresses.
Working blind
But efforts are hampered because few climate models predict
changes for individual regions, making it difficult to predict
how climate change will affect growth and yields of specific
crops in each region.
"A partnership between climatologists and crop scientists will
be valuable in developing regional analogues," says Martin
Parry, IPCC co-chair and a scientist at the UK-based
Hadley Centre for Climate Prediction and Research.
And the need is urgent. At a meeting of CGIAR institutes in
Hyderabad, India, in November 2007, Parry said that the
estimated window for implementing mitigation and adaptation
programmes has shrunk from 30–40 years to 15.
He advised CGIAR scientists to put climate change at the heart
of research programmes.
Others agree. As Kwesi Atta-Krah, deputy director-general of the
Italy-based research organisation Bioversity International says,
"Plant breeders now need to focus on the future as well as the
present, and use the vast genetic resources in gene banks and in
the wild that hold potential for adaptation of major crops to a
changing climate."
Rice crops most vulnerable
Rice crops are most vulnerable to global warming. Studies
worldwide show that rising carbon dioxide levels may initially
increase growth, but the benefit is temporary. Rising
temperatures make rice spikelets — the slender branches
containing rice flowers — sterile, and grain yields will fall.
Asia and sub-Saharan Africa will be amongst the most severely
affected by climate change. About 90 per cent of the world's
rice is grown and consumed in Asia (where 70 per cent of the
world's poor live), and sub-Saharan Africa is the world's
fastest growing rice consumer. The most vulnerable agricultural
systems are the rain-fed uplands and lowlands that form almost
80 per cent of total rice land in Africa.
Reiner Wassman, coordinator of the Rice and Climate Change
Consortium at the International
Rice Research Institute (IRRI) in the Philippines, says IRRI
strategies should include breeding rice that can survive climate
change. He wants to see plants that can tolerate higher
temperatures and/or flooding, that flower in the mornings before
temperatures rise, and that transpire (lose water through
evaporation from leaves) more efficiently to cool the air around
them.
His hopes are buoyed by IRRI's latest research into the rice
line 'sub1', which survived submersion for 17 days (see
Scientists create flood-resistant rice). The line could provide
genes for flood tolerance.
In Africa, the Africa Rice Centre
(WARDA) is focusing on its NERICA (New Rice for Africa)
varieties. These combine traits of Africa's Oryza glaberrima —
such as drought and local disease tolerance — with the high
yields of Asia's Oryza sativa.
Looming disaster for wheat?
Drought is also a big concern for the
International Maize and Wheat
Improvement Centre (CIMMYT) in El Batan, Mexico. The IPCC's
predictions of increasing droughts spell disaster for half of
the developing world's wheat growing areas.
The problem is particularly acute in central and west Africa,
where the poor depend on wheat but get an annual rainfall of
less than 350 mm, says CIMMYT scientist Rodomiro Ortiz.
CIMMYT has launched a hunt for drought tolerance in wild wheats
and 'landraces' — traditional crops that have adapted to local
conditions over centuries. The centre is also teaming up with
the Japan International Research Centre for Agricultural
Sciences to map drought-tolerant genes in wheat and maize.
CIMMYT is using its findings in both traditional breeding and
genetic engineering programmes. For example, researchers are
working on genetically engineered wheat containing the DREB gene
of Arabidopsis thaliana — a relative of mustard plants — that
may confer tolerance to drought, saline soils and low
temperatures. CIMMYT is testing yields of genetically engineered
plants with the DREB gene under varying water stress.
However, Ortiz cautions that the plant is still experimental.
Most published studies simulated drought conditions in
greenhouses more rapidly than would occur naturally. Ortiz wants
more experiments under natural water stress conditions.
Shrinking diversity
Scientists look for useful genes in plants grown only locally,
and CIMMYT already has maize breeding programmes that work with
local communities. But researchers fear many useful wild species
could disappear.
"Climate change is leading to significant losses of genetic
resources in several regions of the world," says Atta-Krah. He
says diversity among crop species must be effectively conserved,
managed, and used to improve crops and adapt to climate change.
One striking example of shrinking diversity is Latin America's
beans. Peter Jones, a scientist at the
International Centre for
Tropical Agriculture (CIAT) in Columbia, says that of the 17
wild species of the Arachis genus — the pea family that includes
the peanut — 12 will be extinct by 2055 due to climate change.
We must systematically map important bean species and ensure
important collections have more than five live specimens, adds
Jones.
The world's livestock are also in the danger zone. A 2006
assessment of global animal genetic resources by the UN Food and
Agriculture Organization estimated that 70 per cent of the
world's unique livestock are in developing countries. Many
breeds already risk extinction. On average, one livestock breed
is lost every month, mainly due to globalisation of livestock
markets.
Climate change will strike further blows. According to the
International Livestock Research
Institute (ILRI) in Kenya, climate change will affect
livestock by changing the yield and nutritional quality of their
fodder, increasing disease and disease-spreading pests, reducing
water availability, and making it difficult to survive in
extreme environments.
"Climate change will have impacts at the ecosystem level that
are poorly understood," says ILRI's deputy director-general for
research, John McDermott. Effects will vary between the rain-fed
highlands in the Great Lakes region of eastern Africa, the
coastal regions of south, east and west Africa, and the forests
of central Africa. The exact consequences for each ecosystem
need to be analysed in detail.
Water holds the key
The common theme in all these changes is water availability.
Already, one-third of the world's people live in river basins
where they face water scarcity. But climate change will have
other effects on agricultural irrigation.
The timing and size of river flows will change, affecting river
water schemes, says Colin Chartres, director-general of the
Sri-Lanka-based
International Water Management Institute. He adds that
receding glaciers mean less water will be available in spring,
which could affect some 17 per cent of the world's population,
including those irrigating the Indus basin. Changes in
groundwater recharge could also affect irrigation in China,
India, Mexico and the United States.
Chartes says scientists need to go beyond coarse global models,
and develop specific river-basin and farm-scale models of how
climate change will affect river water availability and lake
levels. He also calls for more precise models of how climate
change may affect fish productivity in oceans, seas and inland
fisheries.
A tentative start
As the problems become apparent, CGIAR centres are working on
better understanding their implications.
The India-based International
Centre for Research in Semi-Arid Tropics (ICRISAT) research
strategy for 2007–2012 targets climate change issues in the
short- and medium-to-longer term.
ICRISAT director-general, William Dar, says ICRISAT is working
to make millets, sorghum, pigeon pea and groundnut better
adapted to major climate stresses. The organisation has already
developed varieties tolerant to heat, high soil temperatures,
low and variable rainfall, and diseases.
What is needed now, says Dar, is a better knowledge of the
physiology behind stress tolerance, wider gene pools, and more
effective screening methods for useful genes.
CIAT is developing computer software to analyse future climate
scenarios. Examples include 'MarkSim' to simulate daily weather
for up to 100 years anywhere in the tropics, and 'Homologue' to
compare climate and soil throughout the tropics.
The International Centre for
Agricultural Research in the Dry Areas (ICARDA) has studied
how areas in and around Egypt, Morocco and Sudan are coping with
water scarcity in rainfed and irrigated grasslands, as well as
traditional watershed management systems.
But the task ahead is tough. As Jones points out, historically
the average time between scientists beginning to hunt for useful
traits and a new stable variety growing in farmers' fields has
been 46 years. "So that is how far ahead we should be looking at
the start of every project," he says.
And as one participant at the Hyderabad conference commented,
"You may put all those traits for tolerance to drought, salt and
pests in a plant — and then find it has no yield!" |
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