February 10, 2006
Zephaniah
Dhlamini, SciDevNet
Summary
Discussions
about the role of agricultural science in boosting food
production tend to be dominated by controversy over the
characteristics of genetically modified (GM) crops and the
implications of their use. But this has tended to overshadow
consideration of the many other contributions that cutting-edge
research can make to increasing crop productivity. This briefing
summarises the main ways in which these non-GM techniques are
helping plant breeders to develop and propagate new crop
varieties.
Zephaniah
Dhlamini is a former consultant to the plant breeding and
genetics section of the International Atomic Energy Agency.
Introduction
In the intense
debates around the applications of modern biological research to
agriculture and food production, genetic modification (GM
techniques) — and the novel crops that result from their
application — tend to attract the lion’s share of public
attention.
This is
despite the fact that such research offers a range of other
tools and techniques that do not involve genetic modification,
and yet can still make major contributions to agriculture.
One result of
the disproportionate focus on GM crops is that policymakers in
the developing world often lack adequate information on the
nature and potential use of non-GM biotechnologies.
This briefing
seeks to help fill this information gap by summarising the
characteristics of the most common non-GM biotechnologies that
are being developed and applied to crop improvement in the
developing world.
Drawing on the
Food and Agriculture Organization’s (FAO) database on
Biotechnologies in Developing Countries (BioDeC), it focuses on
four types of non-GM biotechnology: tissue culture, molecular
markers, diagnostic techniques and microbial products. [1]
Tissue culture technologies
One technology
that deserves greater attention from both the public and
policymakers is the use of tissue culture, the most widely used
application of which involves creating copies of plants through
a process known as micropropagation.
In essence,
micropropagation involves taking tissue (known as an ‘explant’)
from a plant and growing it on sterile media containing
substances essential for growth. Once it is growing well,
samples of this culture can be taken and used to grow entire
plants under laboratory conditions.
The technique
is currently used mainly with perennial crops that can reproduce
vegetatively, producing new stems directly from the existing
ones rather than needing to be pollinated and produce seeds.
It can be used
to create millions of new ‘clones’ from a single plant, each
genetically-identical to the parent plant.
The method can
be used to produce large quantities of high-quality plant lines,
to eliminate pathogens from infected planting materials, or to
produce 'true-to-type' material from desirable plant lines.
Micropropagation has been developed over many decades, and can
now be considered a ‘mature’ plant biotechnology. It is already
widely used in developing countries, especially Asia – in
particular as a result of the immense market in China for plants
generated in this way.
It is
relatively cheap, and has been shown in general to increase
productivity (especially of root and tuber crops, such as sweet
potatoes and potatoes).
Its most
common application in developing countries involves producing
virus-free plantlets by heat-treating the explant to kill any
viruses present and then culturing cells from its 'meristem',
the plant's actively growing tissue.
Because
micropropagation cannot, however, guarantee that plants will be
virus-free access to a virus diagnostic facility is essential.
Micropropagation in developing countries: some examples
In China's
Shandong Province, a micropropagation project that created and
distributed virus-free sweet potatoes led to an increase in
yields of up to 30 per cent. By 1998, productivity increases
were valued at US$145 million annually, raising the agricultural
income of the province's seven million sweet potato growers by
three to four per cent in one season. Government subsidies
helped to encourage adoption of the technology and keep the cost
of the planting material low. [2]
In Kenya, the
commercial micropropagation of disease-free bananas is currently
being carried out. The initiative has been shown to offer
significantly higher financial returns than traditional growing
practices. [3]
In Vietnam,
introducing improved, high-yielding potato cultivars able to
resist the late-blight disease has seen yields double, from 10
to 20 tonnes per hectare. The farmers are themselves multiplying
their plantlets through micropropagation, making the seed more
affordable. [4]
Anther culture
and embryo rescue
Another widely
used tissue culture technique, 'anther culture', uses the
immature pollen-producing organs of a plant to generate fertile
'haploid' plants, which have half the full set of genetic
material.
These plants
can later be crossed to produce pure homozygous 'diploid'
plants, with identical copies of each gene, thus eliminating
undesirable variation in key traits.
The technique
is popular among breeders as an alternative to the numerous
cycles of inbreeding or 'backcrossing' usually needed to obtain
pure lines.
In vitro
anther culture is now used routinely for improving vegetables,
such as asparagus, sweet pepper, eggplant, watermelon and
Brassica vegetables. It is also used, though to a lesser
extent, for cereal crops such as rice, barley and wheat.
A further
refinement of the technique is the so-called 'microspore
culture'. This involved isolating and culturing the cells from
which pollen grains develop, and can yield up to ten times as
many haploid embryos as anther rescue.
A further
tissue culture technique, known as 'embryo rescue' (or sometimes
'embryo culture') involves crossing species that are not
normally sexually compatible. In nature embryos that result from
such ‘wide crosses’ usually fail to develop. But in the
laboratory, wide crosses can be used to transfer genetic traits
from wild relatives of crops (i.e. secondary and tertiary gene
pools) into cultivated crop plants (primary gene pools).
An example is
triticale, a relatively new hybrid variety that is the result of
a cross between rye and wheat.
New Rice for
Africa: a tale of two techniques
Both embryo
rescue and anther culture have recently been used extensively in
the successful development of the so-called New Rice for Africa
(NERICA).
Breeders at
the Africa Rice Center (WARDA) in Benin, for example, have used
both techniques to cross Oryza sativa (Asian rice) with
Oryza glaberrina (African cultivated rice). Farmers have
selected new rice varieties from the resulting germplasm, with
qualities such as higher yields, shorter growing seasons,
resistance to local stresses, and higher protein content than
traditional African varieties.
The new
varieties have been released in Cote d’Ivoire, Nigeria and
Uganda, and are being evaluated in Benin, Burkina Faso,
Ethiopia, The Gambia, Malawi, Mali, Mozambique, Sierra Leone,
Tanzania and Togo.
WARDA
researchers suggest that some 200,000 hectares will soon be
under NERICA cultivation, producing about 750,000 tonnes of rice
per year, and leading to an annual saving on rice imports of
nearly US$90 million. [5]
Molecular marker techniques
A second set
of non-GM biotechnologies that are having a growing impact in
crop development are a range of techniques that use 'molecular
markers'. These are relatively short and easily-identifiable
strips of DNA whose location can indicate the presence in a
plant's genome of a gene with desired characteristics.
The physical
proximity on the genome between the marker and the gene
responsible for a particular trait means that scientists can
select for the marker, rather than the gene itself. The value of
'molecular markers' to plant breeders is therefore that they
allow plant species to be investigated at the level of their
DNA, and for the knowledge generated in this way to be used to
manage genetic variation and diversity in plants.
The first
generation of molecular markers, known as restriction fragment
length polymorphisms (RFLP), required slow and expensive ways of
reproducing lengths of DNA through a process known as DNA-DNA
hybridisation.
However the
invention of the technique known as polymerase chain reaction
(PCR), which amplifies short segments of DNA and thus makes them
easier to identify, gave rise to a second generation of faster
and less expensive molecular markers. The most common of these
are randomly amplified polymorphic DNA (RAPD), amplified
restriction fragment length polymorphisms (AFLP), and simple
sequence repeat (SSR).
Cost-effective
techniques based on molecular markers have many applications in
plant breeding, and the ability to detect the presence of a gene
(or genes) controlling a particular desired trait has given rise
to what is called 'marker-assisted selection' (MAS).
This approach
makes it possible to speed up the selection process. For
example, a desired trait may only be observable in the mature
plant, but MAS allows scientists to screen for the trait at the
much earlier plantlet stage.
Other
advantages of techniques based on molecular markers as that they
make it possible to select simultaneously for more than one
characteristic in a plant. They can also be used to identify
individual plants with a particular resistance gene without
exposing the plant to the pest or pathogen in question.
However, the
current cost of applying these techniques is high, which means
that for many breeding programmes — particularly in the
developing world — they may be unaffordable.
Furthermore,
there are relatively few useful molecular markers for traits
that are important to plant breeders, such as those leading to
increase yield. As a result, only a handful of crop varieties in
farmers’ fields have so far been developed through MAS.
However the
relative cost-effectiveness of conventional breeding methods
compared to using MAS depends on the circumstances. Where the
characteristics of new, experimental crops can be examined in
the field, conventional breeding methods can be very
cost-effective.
But where this
is not possible, or is particularly costly or difficult, the use
of molecular markers can be significantly cheaper. [6] This is
the case, for example, with breeding projects that involve
multiple genes, recessive genes, the late expression of the
trait of interest, or seasonal and geographical constraints.
Molecular
markers can also be used to characterise germplasm in situations
in which a detailed database of the genetic material of
different varieties of a particular plant species has been built
up. Indeed DNA-based genetic markers are often more useful for
studies of genetic diversity than morphological and protein
markers because their expression is not affected by
environmental factors.
As the BioDeC
database reveals, molecular markers are already being widely
used for characterising and managing germplasm in many
developing countries.
DNA and immuno-diagnostic
techniques
In addition to
seeking ways of breeding better, stronger or higher-yielding
crops, much agriculture research and development focuses on ways
of fighting plant diseases. This is a key area of research as
many crop diseases are difficult to diagnose, especially at the
earliest stages of infection. Successful diagnosis can also be
made harder by the fact that a number of different viral
diseases exhibit similar symptoms.
In such
circumstances, diagnostic efforts can be assisted by molecular
assays -- such as enzyme-linked immunosorbent assay (ELISA) –
that can precisely identify viruses, bacteria and other
disease-causing agents.
ELISA has
become an established tool in disease management in many farming
systems. Indeed it is now the most widely used commercial
diagnostic technique in all regions of the developing world.
In addition,
diagnostic assays have been developed that identify a wide range
of other organisms, chemicals – including undesirable
by-products such as aflatoxin – and impurities that affect food
quality. [7]
A relatively
new but increasingly powerful technique for identifying
pathogens and other organisms in agriculture is known as DNA
diagnostics. This works by identifying a suspected pathogen from
details of its DNA.
Most DNA
diagnostics are now based on the PCR. Until recently, this was
problematic because the effectiveness of PCR was based on the
heat-resisting properties of the enzyme Taq polymerase,
which is heavily protected by patents.
More recently,
however, Taq polymerase has come to be treated as a
‘generic’ biochemical reagent, substantially reducing the cost
of PCR applications in research and commerce.
Microbial products for
agriculture
Pest control
and soil enrichment are as important to agriculture as accurate
disease diagnosis. Products based on microorganisms play an
increasing role in both processes, and include biocontrol agents
(or 'biopesticides'), 'biofertilizers' and products that aid
fermentation and food processing.
In Africa and
much of Asia, research in biocontrol and biofertilisation is
still at the early stages. But countries such as China, India
and the Philippines, as well as several in Latin America, are
already routinely using advanced techniques. Some of their
results are already being tested.
Bio-pesticides
Although
conventional chemical pesticides are still widely used across
the developing world, some countries are shifting to the use of
newer types of pesticide that are more selective and less toxic
to humans and the environment, as well as remaining effective at
lower rates of application.
A small but
growing proportion of these are biopesticides, based on
naturally occurring organisms or substances. These include
microbial pesticides such as Bacillus thuringiensis (Bt),
Trichoderma, Verticillium, Bauveria and
Bacillus subtilis; plant extracts; and nematode worms or
viruses such as the nucleopolyhedrosis virus (NPV) that are
'entomopathogenic' i.e. they attack insects.
Other
biocontrol agents include pheromones, growth regulators and
hormones. Many of these agents are increasingly used in
integrated pest management (IPM), which uses a variety of
methods — from monitoring pests to planting pest-resistant crops
— to minimise the use of pesticides .
Bio-fertilisers
Recent
progress on biofertilisers has been equally impressive. For
example, there has been much research on biological nitrogen
fixation (BNF), the process by which microorganisms in the soil
'fix' atmospheric nitrogen, mostly within subsoil plant nodules,
and make it available for assimilation by plants.
The most
studied and important nitrogen-fixing bacteria are Rhizobia.
But a number of endophytic (growing within a plant) bacteria are
now also known to do the job. Using such bacteria to fix
atmospheric nitrogen is an environmentally-friendly alternative
to applying chemically generated fertilizers.
Other
microorganisms, such as Mycorrhiza, can establish a
symbiotic relationship with both cultivated plants and forest
trees, facilitating the uptake of phosphorus and water uptake.
Inoculating plants with these fungi is an efficient substitute
(or complement) to phosphorus-based chemical fertilization.
Research on
biofertilizers -- mainly Rhizobium – is currently being
carried out in many developing countries. For example, the
UNESCO Microbiological Resources Centre (MIRCEN) project at the
University of Nairobi in Kenya has developed a Rhizobium
inoculant, known as BIOFIX, that is currently the main
inoculant available on the local market.
100 grams of
BIOFIX will treat a hectare of crops, costs about
US$1.25, and has a comparable effect to 90 kilograms of chemical
nitrogen costing about 10 times as much. [8]
Conclusion
Policy makers
and research managers need to focus more attention on the full
range of promising tools and techniques offered by modern
biological research — not only those that involve genetic
modification.
As this brief
review shows, there are already many promising non-GM
biotechnologies in the public domain that could make significant
contributions to crop improvement and agricultural management.
Each has both advantages and disadvantages, each of which needs
to be carefully assessed.
For most
developing countries, however, the main challenge is not to
develop new agricultural technologies (such as plant breeding
techniques or disease diagnostics) but to design and implement
the capacity building programmes and regulatory systems needed
to facilitate the sustainable transfer of these technologies to
the relevant farming systems.
Furthermore if
the full potential of these non-GM biotechnologies is to be
realised, they must not be adopted as stand-alone interventions.
Rather they should be treated as tools that need to be fully
integrated with other proven agricultural research and farming
practices.
References
[1] Food and
Agriculture Organization of the United Nations database on
Biotechnologies in Developing Countries (BioDeC).
www.fao.org/biotech/inventory_admin/dep/default.asp
[2] Fuglie
K.O, Zhang L., Salazar L.F., et al. Economic Impact of
Virus-Free Sweet Potato Planting Material in Shandong Province.
International Potato Center.
www.eseap.cipotato.org/MF-ESEAP/Fl-Library/Eco-Imp-SP.pdf
(1999)
[3] Mbogoh S.,
Wambugu F.,. Wakhusama, S. Socio-economic impact of
biotechnology applications: some lessons from the pilot
tissue-culture (TC) banana production project in Kenya,
1997-2002. A contributed paper submission for the XXV IAAE
Conference, Durban, South Africa.
www.iaae-agecon.org/conf/durban_papers/papers/037.pdf
(2003)
[4] Van Uyen
N., Truong V. H., Pham X. T., et al. Economic impact of
the rapid multiplication of high-yielding, late-blight-resistant
varieties in Dalat, Vietnam. In:Walker T., Crissman, C., eds.
Case studies of the economic impact of CIP-related technology.
pp 127-138. International Potato Center, Lima, Peri.
www.cipotato.org/Market/ImpactCS/seedviet.htm
(1996)
[5] Africa
Rice Center (WARDA).
www.warda.cgiar.org
[6] Dreher K.
Khairallah M., Ribant J., et al. Money matters (I): costs
of field and laboratory procedures associated with conventional
and marker-assisted maize breeding at CIMMYT. Molecular
Breeding, 11, 221-234 (2003)
[7] Dhlamini
Z., Spillance C., Moss J.P., et al. Status of Research
and Application of Crop Biotechnologies in Developing Countries
– A Preliminary Assessment. Food and Agriculture Organization
of the United Nations, Rome.
ftp://ftp.fao.org/docrep/fao/008/y5800e/y5800e00.pdf
(2005)
[8]
Zechendorf, B. Sustainable development: how can biotechnology
contribute? Trends in Biotechnology 17,219-225 (1999) |