The Importance of Agrobiodiversity
The genes, species, ecosystems and human knowledge which are being lost represent a
living library of options available for adapting to local and global change. Biodiversity
is part of our daily lives and livelihoods and constitutes the resources upon which
families, communities, nations and future generations depend.
As reflected in this statement from the 1995 Global Biodiversity Assessment of the
United Nations Environment Programme (UNEP),
there is a growing awareness of the profound importance of the earth's biological
diversity, or biodiversity, and also of human responsibility for curbing its destruction.
Over the past decade, a series of important steps have been taken to protect
agrobiodiversity in particular, which mainly includes the plant genetic resources on which
agriculture depends. These and further efforts are vital for enabling countries and
communities to meet their food needs, for improving rural livelihoods, and ultimately for
protecting the well-being of all people now and in the future.
One major step was the creation of the Global Plan of Action for the Conservation and
Sustainable Utilization of Plant Genetic Resources for Food and Agriculture. This resulted
from a conference organized by the Food and Agriculture Organization (FAO) of the United Nations in 1996 at
Leipzig, Germany. Two years later, during a regional FAO-organized conference at CIAT
headquarters in Cali, Colombia, Latin American countries expressed a strong commitment to
research needed for effective implementation of the Global Plan.
These actions grew out of a much earlier step, the establishment in 1983 by the FAO of
an intergovernmental forum called the Commission on Plant Genetic Resources (now the Commission on Genetic
Resources for Food and Agriculture). The Commission has developed a global system for
the conservation and sustainable use of food and agriculture plant genetic resources.
Agrobiodiversity Conservation at CIAT
As an active part of that system, CIAT conserves, studies, and uses the genetic
resources of selected plant species in the American tropics. The region harbors a wide
array of food crop, forage, and other species that are valuable for human and animal
nutrition and provide key environmental services, not only in the Americas but in other
parts of the world as well.
These plant genetic resources can be conserved through two basic approaches. First,
with in situ methods, plants are continuously produced in their natural habitat or at
locations whose climate and ecology are similar to that habitat. The second approach is ex
situ conservation, which refers to storing seeds or other reproductive materials in
climate-controlled germplasm facilities.
The main advantage of in situ methods is that they allow the natural evolution of
plants to continue, so potentially valuable new genetic variation can be collected from
time to time for ex situ conservation. A major disadvantage is that the rural communities
responsible for in situ conservation may have to make difficult tradeoffs between this
activity and agricultural production. A further problem is that scientists cannot always
characterize plants properly in their original habitats or farm settings, and this can
limit the availability of valuable information.
With ex situ conservation, in contrast, scientists can assess the genetic makeup and
adaptation of plant species under controlled conditions in laboratories and experimental
fields. This makes it possible for researchers as well as farmers and others to easily
access germplasm with known characteristics, which remain relatively constant over time. A
further advantage of ex situ conservation is that it helps restore germplasm that has been
lost in the wild. Each approach, then, has strengths and weaknesses, and the two are
highly complementary.
CIAT promotes closer integration of in situ and ex situ conservation by various means.
First, the Center continually seeks to improve the efficiency of germplasm conservation at
its own facilities in Colombia. Second, our scientists strengthen the capacity of partner
organizations to conserve neotropical plant species through both ex situ and in situ
methods. And third, we bring together specialists in classical germplasm evaluation and
molecular genetics to characterize and evaluate ex situ collections. These activities help
build the knowledge base and human resources needed to link ex situ collections with in
situ conservation initiatives.
In connection with this work, CIAT operates a large, state-of-the-art plant gene
bank—the Genetic Resources Unit (GRU)—at
its headquarters in Palmira, near Cali. Three additional sites in Colombia (Santander de
Quilichao and Popayán in Cauca Department and Tenerife, Valle) provide seed
multiplication services to systematically replenish the germplasm collections. The main
job of the GRU's 40 staff is to safeguard this material, which consists mainly of common
beans, cassava, and tropical forages.
In addition, our staff test and improve conservation techniques, characterize and
evaluate germplasm, make the resulting information widely available to research partners,
and build local capacity for germplasm conservation by providing advice, expertise, and
training as a support to national research programs in the region. The project also
promotes public awareness of the need for preserving plant genetic resources.
The plant genetic resources conserved at CIAT are a component of the world
"designate collection" of the FAO. Under a 1994 agreement with FAO, CIAT makes
this germplasm available free of charge, upon request, to farmers, farmer associations,
plant breeders, agronomists, extension agencies, universities, and biodiversity institutes
with a clearly articulated need. For example, materials from the gene bank may be used for
bona fide crop improvement research, field trials, seed multiplication, and training in
genetic conservation. FAO designate materials are considered the collective heritage of
humankind and, thus, are not patentable.
To further safeguard the plant genetic resources under its care, CIAT follows the
principles and procedures listed below:
- Long-term conservation represents a commitment to both the FAO and the countries of
origin of the germplasm as a way to maintain their agricultural heritage for present and
future use.
- A set of known germplasm with specific traits is set aside for distribution on request.
- Specific amounts of germplasm are maintained for periodic monitoring of viability.
- In keeping with current practice among gene banks, one or two security backups are made
and sent to another safe location.
- Germplasm copies are made for the country of origin. It often happens that a country is
willing to maintain a replica of its agrobiodiversity once it has established its own
conservation facilities. A separate provision is made for that purpose, effectively making
the GRU a gene bank for the particular country.
Every year CIAT distributes genetic material of 5,000 to 6,000 germplasm accessions in
response to requests from around the world. For example, researchers in Central America
recently requested 4,000 bean accessions to be screened for disease resistance.
The Germplasm Collections at CIAT
The germplasm collections stored in the GRU at CIAT encompass a total of some 60,000
samples, or accessions, of about 720 plant species, including the common bean, cassava,
various wild relatives of these two crops, and a large number of tropical forage grasses
and legumes. Conserving, studying, and using this material is a major part of CIAT’s
responsibility for research on these commodities within the Consultative Group on
International Agriculture (CGIAR). In
the paragraphs that follow, we briefly describe the germplasm collections and their
importance.
Common Bean
In many parts of Latin America and Africa, beans are considered the "meat of the
poor." Their protein content is roughly double that of most cereals, and they are
rich in essential micronutrients, like iron and folic acid (one of the B vitamins). Beans
are also an important cash earner for poor farmers. About 40 percent of Africa’s bean
harvest, for example, goes to market, generating farm-gate revenues of about one-quarter
of a billion US dollars per year. Latin America is the world’s leading bean-growing
region, accounting for nearly half of global production.
The CIAT bean collection contains over 40,000 accessions, of which 26,500 are
cultivated Phaseolus vulgaris, or common bean. About 1,300 accessions are wild
species of P. vulgaris. The rest are distant relatives. A subset of the overall
holdings serves as a core collection for CIAT’s and other organizations’ bean
breeding work. This subset, which is representative of the diverse environments in which
beans have evolved and are grown, consists of about 1,400 accessions of domesticated
common beans and 100 accessions of wild beans. Researchers at CIAT and national partners
in Latin America and sub-Saharan Africa have evaluated this core collection for a range of
traits, such as insect and disease resistance and tolerance to low phosphorus. Useful
materials have been identified and incorporated into breeding programs at CIAT and
elsewhere.
A good example of the value of preserving bean genetic diversity is the unique popping,
or ņuņa, bean. Native to Bolivia and Peru, it may be the most ancient of all beans,
though it is practically unknown elsewhere in the world. Unlike other common beans,
popping beans can be toasted—just like popcorn—and have a peanut-like taste.
The bean collection at CIAT includes samples of about 300 ņuņa landraces. In 1996 the
first improved popping bean variety—named Q'osco Poroto—was released by the
Peruvian Ministry of Agriculture. Promoters of the new bean near Cusco are working to
create new markets for it, particularly as a nutritious snack food for tourists and school
children. Increased market demand would boost the incomes of the small farmers who grow
ņuņas in poor highland areas. The ņuņas also have a decided ecological advantage.
Since it takes far less time to toast beans than to boil them (about 10 minutes, compared
to as much as 3 hours in the highlands), popping beans save firewood. CIAT is planning to
evaluate ņuņas with bean researchers in eastern Africa, where an added-value,
ecologically friendly bean could give sizable benefits.
Cassava
Cassava, or Manihot esculenta Crantz, is grown in over 90 countries and
provides a livelihood for half a billion people in the developing world. While this hardy
root crop serves as a staple food for many poor farm families, it also provides a
high-starch raw material for producing commercial animal feed and for other industries,
including food, pharmaceuticals, paper, and textile manufacturers.
Global production of cassava is around 152 million tons per year. Half the 16 million
hectares devoted to cassava cultivation is in Africa, with 30 percent in Asia, and 20
percent in Latin Amercia.
The CIAT cassava germplasm collection consists of 6,000 clones: landraces from Latin
America and Asia, elite clones selected by CIAT and the International Institute of
Tropical Agriculture (IITA) in
Nigeria, and several wild Manihot species. These are stored in the form of slow-growth in
vitro plantlets. For each accession, five test-tube plantlets are conserved to accomplish
various purposes. These include long-term conservation, distribution to fill germplasm
orders, security backups, and the provision of duplicates for conservation in the
germplasm’s country of origin. Some cassava germplasm is also conserved as seed. As
with beans, Center scientists have formed a representative core collection of the cassava
holdings to facilitate germplasm evaluation.
Tropical Forages
Forage is any vegetative material eaten by livestock. It includes live grasses and
legumes grazed directly by pastured animals as well as cut-and-carry biomass and fodder
such as hay, leaves, shredded sugarcane, chopped maize cobs, and dried cassava chips.
About one-third of the earth’s land surface is given over to livestock production.
This enormous area consists of native and improved pastures as well as crop lands devoted
to growing harvestable forage crops. As global demand for meat, milk, and other animal
products grows dramatically in the coming decades, so too will the need for improved
forages. Small-scale livestock producers in developing countries, faced with stiff
competition from highly efficient industrial operations, both domestic and foreign, will
have to look at new technical options, such as combinations of superior grasses and
legumes, to replace native pasture forages, which tend to be low in nutritional value.
A number of forage species collected by CIAT over the years, and in some instances
improved through our breeding work, are highly productive, have superior nutritional
value, and can contribute to more environmentally sustainable land management. Some
tolerate low soil fertility and can withstand the harsh dry season typical of many areas
of Latin America. The African grass Bracchiaria decumbens and the legumes Cratylia
argentea and Arachis pintoi are among the promising forages being promoted
by CIAT and its research partners, notably in the hillside ecosystems of South and Central
America and Southeast Asia.
The Center maintains over 22,000 accessions of forage grasses and legumes in its plant
genetic resources collection. The main components are 18,400 samples of 654 legume species
and 1,900 samples of 178 grasses. This valuable resource serves not only the international
R&D community but also CIAT’s own selection and breeding efforts. Since 1970,
national research programs in 14 countries have released 45 tropical forage varieties
(mostly grasses) derived from germplasm selections provided by CIAT. The total area
planted to CIAT-related forage varieties in Latin America is estimated at about 6.8
million hectares. There is, however, enormous potential for extending the use of improved
forage germplasm since native pasture species still occupy about 90 percent of tropical
America’s grazing area.
Conservation Methods and Procedures
Given the collections' size and diversity in terms of plant development and
reproduction, a major challenge for GRU staff is to ensure that these materials are
properly preserved, using the most reliable and advanced techniques available.
Seed of common bean and forages is kept in the GRU’s cold storage units, at a
temperature of 5ēC for short term-storage and at -20ēC for long-term storage. Relative
humidity is kept at 35 percent, at which level there is about 6 to 8 percent moisture in
the seed. Under long-term storage conditions, the seed can remain viable for several
decades.
The use of high-quality seed can substantially increase the productivity of tropical
pastures. But little is known about seed-borne diseases that reduce the yields of tropical
forages. Such is the case with the grass Brachiaria, one of the most important
forages in tropical America. In 1999, 30 accessions were selected from the GRU germplasm
collections to detect seed-borne fungal diseases. To date, 12,000 Brachiaria seeds have
been evaluated, and eight known and 10 previously unknown fungi have been identified.
Arrangements for conserving cassava germplasm are considerably more complex than those
for beans and forages. The standard farmer method of propagating cassava is to plant
cuttings called stakes. Although stakes have some practical advantages as a germplasm
storage and propagation medium, they are sources of plant disease and may not be
transported across international borders. It is therefore vital that the GRU at CIAT
develop and employ alternative methods that permit convenient distribution of disease
disease-free cassava germplasm to meet growing demand from major cassava-growing regions
of Africa, Asia, and Latin America.
The cassava germplasm stored at CIAT is currently being conserved in vitro. With this
method plants are kept in test tubes in an agar solution containing minerals and vitamins
that can sustain the plant for 12-18 months. As explained below, efforts are under way to
increase the efficiency of this method and to develop superior alternatives.
The GRU's procedure for handling cassava germplasm is outlined below:
Introduction
Material is introduced in the form of seed, in vitro shoot tips, or as cassava stakes.
Plant Quarantine
To ensure that exchanged germplasm is free of pests and pathogens, CIAT follows
regulatory measures and safeguards under the supervision of the Colombian Institute of
Agriculture (ICA). ICA has
established quarantine procedures to regulate the introduction of plant germplasm and the
issuing of phytosanitary certificates that accompany germplasm for export.
Pathogen Eradication
The extreme tip of the cassava shoot, or meristem, is extracted. This part of the
plant, measuring about 0.5 cm, continuously produces leaves and internodes. Meristems are
cultured for about 12 days in a propagation medium and then undergo three cycles of
thermotherapy, or heat treatment, at temperatures ranging from 35ē to 40ēC to ensure
they are virus free. A total of 4,054 cassava clones have been processed to date through
in vitro thermotherapy techniques, that is, 70 percent of the FAO designate collection. Of
these, 1,308 clones have proven to be free of major diseases. The entire collection is
expected to have undergone thermotherapy and indexing by 2001.
Indexing of Clones
The materials are next subcultured, and a sample of each cassava clone is subjected to
standard disease indexing techniques, either ELISA or PCR. Plants free of disease are
micropropagated and preserved; those that are not are subjected to further thermotherapy.
Conservation
As mentioned above, the best option available currently is in vitro storage.
Repatriation
Part of the germplasm is sent back to the country of origin, usually in a foil package,
which is immediately put in cold storage (-20ē C).
Field Genebank
The plant is grown in the field for ongoing agronomic evaluation under normal growing
conditions, and samples are taken for conservation and characterization. Plant
multiplication is also conducted in the field.
Distribution
Germplasm can be requested through National Agricultural Research Systems (NARS), the FAO, or
directly from CIAT.
This cassava germplasm management procedure provides invaluable information for
improving crop productivity. For example, the use of micrografting to detect disease in
cassava has advanced our understanding of frog skin disease, which can cause losses up to
90 percent in some cassava-growing areas.
Research on Agrobiodiversity
The germplasm collections at CIAT are the focus of intensive research aimed at
determining how this material can be better conserved and used. For example, such work has
led to a better understanding of reproduction in the important grass species Brachiaria,
and this knowledge could help farmers increase the quantity and quality of fodder for
livestock. Other lines of research are described in the sections that follow.
Slow In-vitro Growth of Cassava
With the current in vitro method, cassava plantlets have an effective life span of only
12-18 months (in contrast to the decades-long viability of frozen seeds). After that,
tissues must be removed from the aging plantlets and recultured in fresh growth medium.
To improve the efficiency of this procedure, CIAT scientists are experimenting with two
methods for reducing the growth and thus extending the life of cassava in vitro plantlets.
The two alternatives, water deficit through osmotic substances and ethylene control,
should at least double the time before each clone has to be subcultured--thus greatly
reducing the costs involved.
With the water deficit method, researchers lower the osmotic pressure of the
tissue’s cells by sugar alcohols, growing the plant in simulated desert conditions.
This essentially slows down the plant's metabolism. The trick is determining the correct
amount and combination of the compounds; too much will kill the plant.
The ethylene control method makes use of the fact that the substance ethylene (the same
natural chemical that causes tomatoes and bananas to ripen) is produced within tissue
culture test tubes as a product of respiration. Its action can be altered by
ethylene-inhibiting chemicals that prolong the viability of the cultures. After 9 months
one of the test media has reduced the length of plantlets by a third, compared to the
control. Various concentrations of another ethylene-inhibiting chemical also reduced
growth and kept the plants viable with multiple sprouts. These preliminary results have
opened the way for a new experiment with selected treatments and larger number of cassava
varieties.
Cryopreservaton
Another promising option for safe, long-term storage of cassava germplasm, called
cryopreservation, involves making and freezing "artificial seeds." Cassava shoot
tips (meristems) are given a protective coating of sodium alginate and then made to
coagulate into tiny beads by immersion in a calcium chloride solution. After having their
water content reduced in a two-step process, the beads are stored in liquid nitrogen. In
this extreme environment of -196°C, all biological activity is effectively halted. The
technique allows the cassava to be conserved for 30 years or more with no maintenance
other than periodic monitoring. Furthermore, it is less labor-intensive than in vitro
culturing, requires less storage space, and allows for easy duplication and transport of
the collection to other sites. The main disadvantage is that generating whole cassava
plants from frozen beads is much more difficult than from test-tube plantlets, and the
success rate is still rather low.
This technique is being tested under a pilot project at CIAT involving 60 clones. If
successful, the project will be expanded to include the entire cassava core collection of
600 clones. Forty full plants have been regenerated from frozen shoot tips. The plants are
thawed, rehydrated, reestablished in vitro, and are eventually planted in glass houses.
Special cryoprotectants are applied to ensure that cells survive and recover for safe
duplication.
Generic Conservation Techniques
Some of the new conservation techniques being developed at CIAT can be adapted and
applied to other crops, including tropical fruits and forest species. Experience in
Colombia has shown that with slow-growth techniques the period between periodic
subculturing of vegetatively propagated tropical fruit species can be extended from just
3-4 months to 12 months or more.
National institutes in other countries as well, particularly Ecuador, Peru, and
Venezuela, have requested assistance from CIAT in adapting such techniques for
conservation of species such as passion fruit and highland papaya. The GRU has also been
asked by private industries to share information on cryopreservation protocols for use in
preserving germplasm of food crops as well as forestry and agroforestry species.
Germplasm Characterization and Evaluation
In order for the germplasm collections at CIAT to be a truly useful genetic resource,
researchers and other users need reliable data about key traits of particular materials.
To provide such information, CIAT scientists routinely characterize and evaluate germplasm
from the GRU in the field. In the case of beans and cassava, they focus particularly on
the core collections to simplify somewhat the huge task of generating useful information
about many thousands of accessions.
The tropical forage collection is particularly diverse, with more than 700 species,
ranging from small herbs to multipurpose trees. Evaluating this collection presents a
special challenge but also provides a unique opportunity for researchers and students. In
1999, 867 new forage accessions were characterized.
Partnerships
Partnerships are an essential part of CIAT's strategy to better integrate ex situ and
in situ conservation of plant genetic resources. Listed below are some of the Center's key
partners in this work:
- International Plant Genetic Resources Institute (Bioversity ), Italy. The Institute operates a global program of research and
support for the conservation of plant genetic resources, and its office for the Americas
is located at CIAT headquarters.
- Crop networks. The Bean Advanced Research Network (BARN), Cassava Biotechnology Network
(CBN), and International Network for Evaluating Tropical Pastures (RIEPT) have promoted
biotechnology applications and other steps that facilitate the use of genetic resources
for crop improvement.
- Gene banks and biodiversity institutes in the developing world. Facilities in Brazil,
Costa Rica, Colombia, Mexico, Peru, and other countries are our natural allies in
germplasm conservation. The project also has close ties with organizations responsible for
research on biological diversity.
- Universities, research institutes, and gene banks in the industrialized countries. The
project counts on support from many such organizations in a number of areas requiring
specialized expertise.
|
Consult the 