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BRIEFING NOTES
November 2010
Developing Drought Tolerant Crops for African Agriculture
Nicola Atkinson, Centre for Plant Science, University of Leeds
Drought is the primary cause of yield loss in
agriculture throughout the world, and is
currently the most common reason for global
food shortages. Three-quarters of the most
severe droughts in the last ten years have
been in Africa, the continent which already
has the lowest level of crop production. With
climate change predicted to exacerbate the
problem of water security in Africa, it is
imperative to find solutions to minimise the
damage due to drought. This briefing
examines currently available and potential
future options for improving the drought
tolerance of crops in Africa, as well as
outlining techniques for water conservation in
agriculture.
Background
Agriculture uses over 86% of all fresh water supplies in
developing countries, and over 70% of fresh water
worldwide. As the world population grows from the
current 6.7 billion to 9 billion in the year 2050, water
supplies will become stretched to their limit. It is
estimated that demand for water will increase by 40%
over the next twenty years as competition for water
intensifies between people and agriculture 1. Currently
one third of the world’s arable land is affected by
drought 2, a figure which is set to increase particularly
due to climate change.
Drought in Africa
Drought is now the single greatest problem in African
agriculture, and the main barrier to increased crop
productivity and development of food security 3. In the
1996 World Food Summit, the need to combat drought
was identified as a major target in reducing the number
of undernourished people by 2015. However during
that time the total number of undernourished in Central,
East and Southern Africa has actually increased. One
third of Africans live in drought-prone regions, and thus
acute drought events frequently affect millions 4. In May
and early June 2010 a severe drought affected 10
million people across Niger, Chad, Mali and Cameroon.
The loss of livestock and crops caused increased food
prices and led to food insecurity and an estimated 7.1
million people hungry in Niger alone. The UN World
Food Programme classified the situation as a critical
humanitarian crisis 5. The severity with which drought
affects Africa is largely due to its agricultural system. In
sub-Saharan Africa, agriculture is on average 95%
rain-fed meaning that the effects of drought are likely to
be more damaging than in developed nations where
irrigation is more prevalent 6. Therefore in such
predominantly agricultural countries a large proportion
of the population depends directly on rainfall for its
survival. Land degradation and declining land
productivity due to desertification have also
confounded the problem, and are expected to cause a
loss of two-thirds of arable land in Africa by 2025 7.
Climate Change
Global warming is expected to intensify the effects of
drought in Africa, as weather becomes generally
warmer and drier 3. The Intergovernmental Panel on
Climate Change (IPCC) projects an increased drying
for southern Africa during dry months, putting 350-600
million people at risk of increased water stress by 2050.
Parts of the Sahara will experience the greatest
agricultural losses due to climate change, with impacts
of between 2 and 7 % of GDP. Central and Western
Africa are also vulnerable with likely losses between 2
and 4 % GDP. The IPCC also estimates a reduction in
growing period for many areas, a decrease in suitable
rain-fed land extent, particularly land suitable for maize
growth 8.
Briefing Note. November 2010. Developing Drought Tolerant Crops for African Agriculture. Nicola Atkinson
Economic impact
The social and economic costs of drought in Africa are
immense. As a result of the drought in 1990/1991,
agricultural production in Zimbabwe dropped by 45%,
leading to a decline in manufacturing output of 9% and
drop of GDP by 11%. In Kenya, the 1999-2001 drought
cost an estimated 2.5 billion dollars, a significant
proportion of the country’s economy. Significant cost is
also incurred by the global economy in the form of food
aid. The World Food Program spent 1.5 billion dollars
between 2003 and 2005 to alleviate food shortages in
sub-Saharan Africa as a result of drought.
Desertification of agricultural land also causes mass
migration into urban areas, exerting further stress on
resources and infrastructure and contributing to urban
poverty. In Kenya desertification has led to increased
migration into Nairobi, a city which has swelled by over
800% in the last 40 years 7. Thus the eradication of
poverty and establishment of food security in Africa is
inextricably linked to the mitigation of the effects of
drought and desertification, and the establishment of
affordable technology to help achieve this.
Solutions for combating
drought
Mitigation of the effects of drought in Africa may be
achievable by the employment of various different
technologies, individually or in combination. This paper
examines the current and future options available to
increase water conservation in agriculture, including
novel water-use strategies. The focus of the report is
on the development of drought-tolerant crop varieties.
Water conservation strategies
Several novel methods are available or currently being
developed that allow the minimisation of drought
impact through water conservation techniques.
 Partial root-zone drying. A new technique is in
use whereby part of the root system is irrigated
normally whilst the other half is exposed to drying
soil. The crop receives signals from the drying
roots and activates water-conservation strategies,
whilst photosynthesis continues as normal. Field
trials from China, the USA and Australia on fruit
trees and vineyards show that water-use efficiency
is dramatically increased in the crops, which use up
to 18% less water per day. There is no associated
yield loss, suggesting that this may be a viable
candidate for minimising irrigation in sub-Saharan
Africa 9.
2
 Irrigation scheduling. Research has shown that
maintaining crops under a slight water deficit can
lead to increased carbohydrate loading of fruit and
reproductive structures, giving a higher yield whilst
reducing excess vegetative growth. Various
methods can be used to sense or monitor the
stress levels of plants, for example by monitoring
sap flow or evapotranspiration rates, and irrigate
accordingly. Success in improving water-use
efficiency has already been demonstrated in crops
such as tomato, grapes and olives 10,11. A
disadvantage lies in the cost of equipment, which
can often be high and thus unsuitable for many
types of African agriculture 12.
 Alternative crops. Many indigenous African
legume species are well adapted to environments
where drought and low nutrient levels are common.
Often these are overlooked as crops in favour of
exotic species such as peanut or soybean. The
promotion of native species of highly nutritious
nitrogen-fixing legumes could be a strategy for
ensuring food security in Africa, as well as reestablishing agriculture in arid regions 13.
 Basic water conservation strategies. The
practice of mulching using crop residues and the
reduction of soil tillage cause water use efficiency
of the plant to increase, at the same time as
reducing evaporation from the soil and controlling
weeds. These can have a substantial impact on the
total water needed for agriculture 14.
Drought resistant crops
In order to improve yields in a climate increasingly
frequented with periods of low rainfall, the development
of drought-resistant crops is a crucial target. In 2003
the
United
Nations
Industrial
Development
Organisation identified drought-tolerant crops as one of
the five most important biotechnological interventions
needed in Africa 2. However, improving yield in
drought-prone environments is particularly difficult due
to the complex nature of plants’ interaction with the
environment. The key objective is to create a crop
variety which produces a high yield under drought
stress, whilst not compromising yields during
unstressed conditions. Various results have been
achieved by both public and private organisations using
a combination of conventional breeding, molecular
breeding and transgenic technologies.
Briefing Note. November 2010. Developing Drought Tolerant Crops for African Agriculture. Nicola Atkinson
Conventional breeding
Crops can be improved with respect to a certain trait by
carrying out crosses between plants which show the
desired characteristics. Breeders first access
populations with heritable genetic variation in yield, for
example, and then identify traits which can act as
markers for drought tolerance. The following desirable
traits have been identified by scientists as ideal
breeding targets for drought-resistant crops 3,15,16.
 Extended crop duration in wheat, so that crops can
be grown at different times of year
 Delay of leaf senescence (aging) in sorghum so
that plants stay greener longer and allow further
uptake of water
 Increased kernel number per plant in maize and an
absence of barrenness.
 Reduced canopy temperature in maize.
 Early vigour in rice.
 High water-use efficiency, for example improved
biomass acquisition compared to transpiration rate.
Biotechnology and modern molecular breeding
techniques are now implemented to assist conventional
breeding. These involve finding certain regions of DNA
which are associated with a particular trait and then
using them to identify favourable offspring of a cross
(marker assisted breeding). This technology is distinct
from genetic modification because genetic information
is not manipulated or transferred between plants.
Below are examples of current projects aiming to
produce drought-tolerant crops using conventional
breeding techniques.
Maize
Maize is the third-most widely grown cereal in the
world, after rice and wheat, and feeds more than 300
million people in sub-Saharan Africa alone 3. Maize
yields in the developed world average 8.2 ton/ha, whilst
the average yield in less developed countries is 3.5
ton/ha 17. This difference in yield is largely influenced
by drought and confounded by the fact that developing
world maize production is often dependent on erratic
rainfall and reduced access to irrigation. Thus maize is
the primary target for the development of drought
tolerant crops in Africa. Two current projects for
improving drought tolerance are:
 The International Maize and Wheat Improvement
Centre (CIMMYT) has produced hybrid droughtresistant maize varieties specifically selected for
Southern Africa. The crop shows increased yields
of up to 20% under stress when tested in field sites
in Zimbabwe and Kenya 18. The variety, ZM521,
3
has been released and is already known to be
cultivated on over 1 million ha in sub-Saharan
Africa.
 A drought- and weed-resistant variety of maize that
was developed by the International Institute of
Tropical Agriculture (IITA) has been released for
cultivation in West Africa. The maize shows
increased yield under drought conditions as well as
resistance to the parasitic weed Striga
hermonthica, the two greatest constraints to maize
cultivation in Africa 19.
Rice
Rice has been the fastest growing food crop in subSaharan Africa over the last ten years, where demand
for the crop is far outstripping supply. A new type of
rice has been developed by the Africa Rice Centre
(WARDA) by crossing the traditionally cultivated Asian
variety (O. sativa) with the traditional African variety (O.
glaberrima) to create offspring which exhibit the best
characteristics of both. Advantages of the new varieties
include higher yield, early maturity and resistance to
pests, as well as drought tolerance. In Benin, Cote
d’Ivoire, Guinea and Gambia the rice, known as
NERICA (New Rice for Africa) has had a high adoption
rate amongst farmers 20.
BOX 1. GM Legislation in Africa
 Genetically modified crops were first commercialised in
1996, and are now planted in 23 countries covering a
total of 114.3 million hectares worldwide 24,25.
 In 2003 the Cartagena Protocol on Biosafety (CPB)
was established as part of the Convention on Biological
Diversity (CBD), and has since controlled all
transboundary movement of Genetically Modified
Organisms (GMOs).
 The African Model Law on Safety in Biotechnology was
implemented by the African Union in 2002, as a
guideline for the setting up of National Biosafety
Frameworks (NBFs).
 By July 2009 thirty-eight African countries had ratified
the CBD and agreed to set up NBFs. Of these only
South Africa, Egypt and Burkina Faso have thus far
commercialised the cultivation of GM crops.
 Several other African countries including Kenya have
passed laws allowing field trials on GMOs, a move that
will greatly facilitate the research and development of
commercial products 26.
Briefing Note. November 2010. Developing Drought Tolerant Crops for African Agriculture. Nicola Atkinson
Transgenic technology
Public sector projects
Transgenic technology (or genetic modification) is the
transfer of a gene or genes from one species or
individual into another by genetic engineering. It is
estimated that although conventional and markerassisted breeding may be able to increase the
productivity of crops like maize up to two-fold over the
next 20 years, the addition of transgenic technology
could provide a three-fold increase 3. Although
legislation allowing the cultivation of GM crops in Africa
is not yet widespread (See Box 1), there is increasing
pressure from governments and scientists in Africa to
develop transgenic technology to meet Africa’s
agricultural needs 21. The Nuffield Council on Bioethics
stated in 2004 that “The use of GM crops, in
appropriate circumstances, can have considerable
potential for improving agriculture and the livelihood of
poor farmers in developing countries.”22 Further to this
the Royal Society proposed in 2009 that research into
solving the “Grand Challenge” of global food insecurity
should include both conventional breeding and genetic
modification 23.
Since transgenic technology was first introduced in the
mid 1990s, most GM crops grown have focused on
traits such as herbicide or insecticide resistance. These
can be achieved by the transfer of a single gene, as in
the case of Monsanto’s ‘Roundup Ready’ crops in
which the gene CP4 EPSPS provides resistance to the
herbicide glyphosate 24.
Drought tolerance poses a more complex problem for
transgenic technology as it is a quantitative trait which
is multigenic (controlled by many genes). Several
potential transgenes confer drought resistance in the
laboratory but when tested in field conditions are
ineffective. However some progress is being made in
identifying transgenes that enhance survival under
stress whilst maintaining yield under normal water
supply.
Scientists from Cornell University have produced rice
that is resistant to drought as a result of the
accumulation of the sugar trehalose (See Box 2). It is
proposed that this genetically modified version may
increase yields by up to 20%. The researchers plan to
obtain patent protection for the modification and ensure
that the technology will be publically available to
developing world farmers. It is thought that the
transgene may also provide stress tolerance in the
cereals maize and wheat 22,28.
Commercial projects
The agricultural biotech company Monsanto is a leader
in the field of drought tolerance research, particularly in
maize, and sales of a commercially available variety of
drought-tolerant maize are expected to begin in 2012.
The variety offers 8-22% yield improvement under a
drought stress that typically reduces yields by 50%,
depending on the exact environment. The transgene
used is not publically known, but is likely to be one
which improves the photosynthesis of the plant under
stress conditions. Agreements with the companies
BASF, Evogene and Dow have been established by
Monsanto in order to identify further candidates for
drought tolerance 3,27.
4
Public-private partnerships
A recent partnership has been put into place between
the International Maize and Wheat Improvement
Centre (CIMMYT) and Monsanto. The aim is to make
drought tolerant maize which is available royalty free to
small-scale farmers in sub-Saharan Africa. The project,
called Water Efficient Maize for Africa (WEMA), is
funded by the Bill and Melinda Gates Foundation. It
combines conventionally bred maize lines from
BOX 2. Mechanism of transgenic drought
resistance. Case study: trehalose
biosynthesis in rice.
Trehalose is a natural sugar that is produced by
desiccation-tolerant plants known as ‘resurrection plants’.
These plants can survive long periods of drought, as the
high levels of this sugar stabilise biological molecules and
protect the plant tissues during dehydration, allowing it to
photosynthesise under stress conditions.
Trehalose is synthesised naturally in a two-step reaction
catalysed by two enzymes TPS and TPP. The two genes
encoding these enzymes are found in the bacteria E. coli.
The genes can be isolated from the bacterial DNA and
transferred into rice using specialised infective bacteria
called Agrobacteria tumefaciens. These bacteria can
carry DNA into plant cells without damaging the plant,
and in this way the E. coli genes can be inserted into the
rice DNA. The genes are attached to a certain signal
section of DNA which is activated in response to stress.
In this way the two enzymes for trehalose synthesis are
only produced when the plant encounters drought stress,
and therefore no resources are wasted under normal
conditions. Transgenic rice plants containing the E. coli
genes have high levels of trehalose which leads to
drought and salt tolerance, as well as increased
photosynthetic capacity 28.
Briefing Note. November 2010. Developing Drought Tolerant Crops for African Agriculture. Nicola Atkinson
CIMMYT with marker assisted breeding and a leading
drought-tolerance transgene from Monsanto. The
resulting transgenic variety is due to be released in
2017 in sub-Saharan Africa, and will be implemented
by the non-profit organisation African Agricultural
Technology Foundation (AATF) through national seed
companies. Target countries are Kenya, Uganda,
Tanzania, Mozambique and South Africa 3,29.
Adoption of new crop varieties
Various challenges surround the adoption of new
products, both conventional and GM, by farmers in
Africa. When implementing new technologies for the
mitigation of drought stress, socio-economic and
infrastructure issues should also be considered and
addressed concurrently. The key points are
summarised below:
 Small scale farmers in Africa often have little
excess capital to accommodate the risks
associated with
adopting a new technology, particularly when the
new crops look the same as their normal
counterparts
under
non-drought conditions.
Therefore the success of new seed varieties will
depend on low cost and widespread availability, as
well as the infrastructure necessary for accurate
product information 30.
 Farmers in drought-prone environments tend to
minimise costs by keeping seed from a previous
harvest, known as open-pollinating varieties (OPV).
This seed can be planted year after year. However
hybrid seed varieties produced by seed companies
are likely to be more drought-tolerant than OPVs,
as the quality and seed treatments are better.
Hybrids also provide higher yields under nondrought conditions. A system for the generation
and distribution of affordable hybrid varieties is
therefore important for delivering food security 3,31.
 The lack of a coherent regulatory framework in
many African countries means that research into
GM technology is limited in comparison to more
developed countries (See Box 1). Present
regulations are modelled on systems in which risks
from GM foods were over-estimated, and are thus
costly and difficult to implement 3.
 Concerns have been raised over the safety of GM
technology, leading to a moratorium on GM
products in several Western European countries.
Pressure groups fear in addition that the
introduction of GM technology to Africa will lead to
a dependency on large seed companies that will
eventually lead small-scale farmers into further
debt. Furthermore the intellectual property rights of
5
seed companies over the technology may cause
prices to remain inhibitory 31.
Overview
Drought is the most significant barrier to improving crop
yields in Africa and therefore impedes development of
food security and poverty alleviation. The effects of
drought in Africa are likely to increase due to climate
change and population growth. Research needs to be
carried out into a variety of technologies to reduce the
effects of drought, including novel water-use strategies
and the development of drought-tolerant crops through
conventional and transgenic methods. Some
successes have already been demonstrated in
improving crop yields under drought stress conditions,
and African governments should seek to invest in both
private and public sector projects in order to develop
these. Despite current legislative barriers, GM
technology may prove a useful avenue in future African
drought research. Infrastructure, cultural agricultural
practices and socio-economic factors should also be
considered when introducing novel technologies to
farmers in Africa.
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