 Cassava (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 is also a source of commercial animal feed, fiber for the paper, and textile
manufacturers, and starch for the food and pharmaceutical industries.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.
CIAT has been conducting cassava improvement research since the mid-1970s. Some
selection criteria used by breeders, such as yield potential and dry matter content, apply
across the various ecosystems in which cassava is grown. Others, like resistance to
particular diseases and pests, are specific to a given ecosystem. While the overall
cassava collection held in trust for the UN Food and Agriculture Organization (FAO) by CIAT’s Genetic Resources Unit (GRU) contains 6,000 clones, screening and selection work by
CIAT breeders centers on a smaller but representative subset or core collection.
Here are some key achievements of CIAT’s collaborative cassava breeding work:
- High-yielding cassava lines have been developed that are especially suited to industrial
uses like starch production.
- Genotypes with high levels of resistance to bacterial blight and super-elongation
disease as well as good agronomic performance have been selected in eastern Colombia.
- Sources of resistance to different races of bacterial blight have been identified.
- Genotypes with good resistance to various root rot pathogens have been identified and
crossed to combine or "pyramid" the resistance genes.
- Resistance to whiteflies has been detected in some cassava lines and is being combined
with desirable agronomic traits.
- Sources of resistance to green mites have proved stable across sites.
- Analysis of cassava roots and leaves for micronutrients has shown good potential for
increasing levels of vitamins and minerals in the roots and leaves.
- Genotypes showing longer storability of roots have been selected and are being crossed
for use in the breeding program.
For many key agronomic traits, the on-farm behavior of a cassava variety or breeding
line will vary from one agroecosystem to another. So, it is important for producers or
researchers who are requesting improved cassava materials to provide CIAT with specific
information about the intended production or testing environment. Likewise, requests
should indicate the intended use of the cassava—for example, for direct human
consumption as fresh roots, for manufacturing industrial starch, or for animal feed chips.
These factors strongly influence the selection of suitable varieties.
The main ecosystems for cassava production are listed below, with examples of
representative countries or regions of production:
Subhumid tropics, with bimodal rainfall of 800-1500 mm per year.
Examples: Colombia’s Atlantic coast, northeast Brazil, northeast Thailand, the
Dominican Republic, northern Venezuela, Mexico’s Yucatan peninsula, and the subhumid
belt of western and central sub-Saharan Africa.
Acid-soil savannas, with 1500-3000 mm of rain per year and a short dry
period. Examples: plains of Colombia, and Venezuela, Brazil’s Cerrados; Mexico’s
Tabasco region, Cuba, the West African savannas and the Philippines.
Humid tropical lowlands, with rainfall greater than 3000 mm per year
and no definitive dry period. Examples: equatorial West Africa, southern Vietnam,
Malaysia, West Java and Sumatra, and the Amazonian areas of Brazil, Colombia and Peru.
Mid-altitude tropics (800-1400 masl.). Examples: the Andean zone of
South America, the central Brazilian highlands, the mid-altitude areas of Nigeria,
Cameroon and East Africa.
High-altitude tropics (1400-2000 masl.). Examples: Burundi, Rwanda,
and the Andean zone of South America.
Subtropics (latitudes higher than the tropics). Examples: Argentina,
China, northern Vietnam, Cuba, Paraguay, South Africa, and southern Brazil.
Semiarid tropics, with unimodal rainfall less than 800 mm per year.
Examples: Northeast Brazil, northeast Colombia, semi-arid belt of West Africa, Tanzania,
Mozambique, and coastal Ecuador.  |
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