Achieving food security in Africa largely depends on growing
high-yielding crops, such as rice, that are also well adapted to the
continent’s harsh environment. GRiSP, through the Institut de Recherche pour leDéveloppement (IRD), International Center for Tropical Agriculture (CIAT), andAfrica Rice Center (AfricaRice), is building genetic bridges between African
and Asian rice to accelerate the development of new robust and high-yielding
rice varieties suitable for Africa.
Cross-breeding between different species of rice can produce new plants
that stand up better to drought, salty soil, diseases, and insect pests. Since
the 1990s, AfricaRice has been crossing African rice (Oryza glaberrima), which is particularly resistant to drought and
diseases, with O. sativa, the
high-yielding Asian rice species most widely grown in the world, to create the
New Rice for Africa (NERICA) varieties.
NERICA rice has been hailed as a major advancement for Africa and could
help Africa achieve much higher rice productivity. Currently, 78 NERICA
varieties are available to rice farmers in sub-Saharan Africa, and, by 2011,
adoption had reached more than 700,000 hectares.
The right gene mix
The initial problem in developing NERICA was that the two different
rice species produced sterile offspring that could not be used to grow crops.
Scientists at AfricaRice overcame this by repeatedly backcrossing into Asian
rice to restore fertility. Although the early NERICA crosses exhibited low susceptibility
to disease and insect attacks, the backcrossing process reduced the proportion
of the African rice genome in the final NERICA varieties, consequently reducing
the desired tolerance of pests.
“What if we were to increase the proportion of O. glaberrima genes—would we get better varieties?” Dr. Mandé
Semon, an upland rice breeder at AfricaRice, wondered. He proposed reversing
the gene route and bringing the desirable genes from Asian rice into African
rice instead. However, sterility was still going to be a problem.
The bridge from sterility to
fertility
To solve this problem, the iBridges (interspecific Bridges) project was
launched in 2005 as a close cooperation among IRD, CIAT, AfricaRice, the
Philippine Rice Research Institute, and African national agronomic research
bodies such as the Institute of Rural Economy in Mali and the Institute of
Environment and Agricultural Research in Burkina Faso. Originally supported by
the CGIAR Generation Challenge Program, the second phase of iBridges is now
being advanced under GRiSP.
Cutting-edge research under Mathias Lorieux, IRD director of research
and plant geneticist at CIAT, led to the fine mapping of the S1 gene,
previously identified as a key factor in interspecific sterility. Using the
rice genome maps developed by the Oryza
Map Alignment Project, the researchers identified the portion of the chromosome
responsible for sterility.
“This resulted in the design of a genetic model that explains the
sterility of interbred descendants, and opens the way to further research into
the genetic control of sterility,” said Dr. Lorieux, who is also the iBridges
co-project leader along with Dr. Alain Ghesquière of IRD. “Being able to
identify the few and rare fertile individuals from interspecific crosses early
in the breeding process eliminates many stages previously required for
interspecific breeding and accelerates the development of new and improved
African-Asian varieties that fully embrace the rich diversity of African rice
alongside that of Asian rice.“
Open pool
Thanks to the partnerships that are being fostered by GRiSP, plant
breeders now have access to the complete genetic diversity available in African
rice. Under GRiSP, the iBridges project aims to develop new and fertile rice
varieties derived from crosses between elite O. sativa and O. glaberrima
rice varieties.
“We hope that the iBridges will make a significant breakthrough in
improving African rice varieties,” said Dr. Lorieux. “It is the African rice
farmers who will directly benefit from this technology, and this will certainly
contribute to Africa’s food security.”
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