(Manihot esculenta Crantz) has played an important
role on the Africa's agricultural stage. The CGIAR
system has considered it the most important root crop in sub-Saharan
Africa, and average consumption exceeds 300 kg per person
per year in some areas. Its hardy nature also means that it
is moving into more marginal areas. Nonetheless it is faced
with production constraints of pest, diseases, and poor soil
fertility everywhere it is grown on the continent. Some of
the most severe disease problems, for example the cassava
mosaic disease, are found in Africa. The CIAT project "Genetic
Enhancement of Cassava", as part of its global responsibility
for improving cassava, recognizes the importance of cassava
in Africa and aids increased productivity through the provision
of improved germplasm and training in conventional and new
methods of cassava breeding.
works closely with its sister institute, the International
Institute of Tropical Agriculture (IITA)
to ensure African farmers benefit from 30 years of cassava
breeding and the wide range of germplasm on which it was based.
In the late
eighties to early nineties, CIAT and IITA, with funding from
the International Fund for Agricultural Development (IFAD),
introduced hundreds of thousands of sexual seeds of improved,
drought-tolerant cassava germplasm, which originally came
from Northeast Brazil, but was improved at CIAT for productivity
and root quality. This IFAD project extended cassava cultivation
from its traditional areas in the humid and dry savanna ecologies
of West Africa to the region's semi-arid areas.
CMD Resistance, Resistance to Other Stresses and High Productivity
presence of cassava mosaic disease (CMD), the most important
production constraint in Africa, and its absence in Latin
America have severely limited the usefulness of CIAT cassava
germplasm in Africa. Drought-tolerant germplasm has had to
undergo further breeding at IITA before it could be useful
to farmers. This situation has now changed with CIAT having
recently identified molecular markers that are closely associated
with very high levels of resistance to CMD. CIAT can now develop,
through these markers, CMD-resistant varieties for Africa.
A project for Africa has been proposed to combine high productivity
and excellent resistance to three major biotic stresses (CMD,
cassava green mite, and cassava
bacterial blight) with well-adapted varieties local to eastern
and central Africa. This improved germplasm is expected to
increase food security for small farmers, reduce cassava prices,
increase farmers, profit margins, and make the crop more competitive
with other crops in the region and on the global market.
the Genetic Diversity of African Cassava
also assesses the genetic diversity of cassava landraces in
Africa, using molecular markers. This project is funded by
the International Programme in the Chemical Sciences (IPICS,
of Uppsala University,
Sweden). Simple sequence repeat (SSR) markers are employed
to obtain a quantitative estimate of diversity in local cassava
varieties from Tanzania and Nigeria (see some results at http://www.ciat.cgiar.org/molcas).
Further studies are being carried out in Uganda and Ghana.
The genetic diversity of African landraces will also be compared
with that of Latin American landraces to identify heterotic
pools. Activities include examining the high
genetic differentiation found in the SSR study between Guatemalan
and Nigerian landraces for heterotic groups.
elite parental lines were shipped as in vitro plantlets
from CIAT to IITA for a joint line-by-tester experiment.
than 2000 sexual seeds from six wild Manihot relatives with
high protein and dry matter content, and from advanced breeding
lines with high dry matter yield were shipped from CIAT
vitro plantlets of parental lines with CMD resistance
were transferred from IITA to CIAT and the Central Tuber
Crops Research Institute (CTCRI), India.
Marker-assisted Selection for CMD Resistance
markers developed at CIAT were tested for their fidelity
in marker-assisted selection for CMD resistance on more
than 2500 progenies that had already been established at
IITA and field evaluated for CMD resistance.
conducted marker-assisted breeding of lines to combine CMD
resistance, high carotene content, and good dry matter yield.
These lines will then be recombined (again using markers)
with high protein lines currently being developed. The goal
is to develop varieties with high contents of carotene,
protein, and dry matter, and carrying high CMD resistance.
will cross 20 elite lines from each of CIAT and IITA to two
common testers. The resulting sexual seeds will be shared
between the two centers.
Carotene Content in Cassava
this year, crosses will be made to combine high carotene content
and CMD resistance, and high protein content and CMD resistance.
The crosses will then be recombined to give lines high in
all three traits.
Developing double haploids in cassava via wide crosses between
cassava and castor IITA has made the crosses, and CIAT is
now analyzing the DNA of the hybrids to
ascertain parental contributions.
project proposal "Improving Cassava Germplasm in Uganda,
Kenya, Tanzania, Rwanda and the DR Congo for Yield, Root
Quality and Resistance to CBB, CGM, and CMD" has been
developed by CIAT, IITA, and NARS for submission to the
Rockefeller Foundation. The principal objective is the introduction
of elite parents with high dry matter yield, drought tolerance,
good culinary quality, yellow roots, and excellent resistance
to the cassava bacterial blight (CBB), cassava green mites
(CGM), and the cassava mosaic disease (CMD) to NARS in the
target countries for improving local germplasm. The project
also seeks to quicken the process using molecular marker-assisted
year, CIAT received about 10 requests from African NARS
and NGOs interested in receiving improved germplasm.
A possible initiative is being explored between CIAT and
the International Livestock Research Institute (ILRI) to
use cassava foliage as feed component for small and large
ruminants in Africa.
PhD Students from IITA
NARS scientists from Ghana and Nigeria were trained at CIAT
in the use of marker tools for assessing genetic diversity.
Ugandan PhD student are working on QTL mapping of cyanogenic
potential and dry matter content, respectively.
Nigerian PhD student has successfully completed his studies
on QTL mapping of early bulking at CIAT.
development work with IITA will continue.
collaboration with IITA, CIAT will include African NARS
as recipients of CIAT's advanced breeding materials with
combined CMD resistance.
will increase the number of participants in individual training
and begin group training in the use of marker tools.