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 [NAIROBI] Researchers have generated cassava genome sequence that will enable better understanding of the genetic basis of traits such as disease resistance, food quality and time to maturity.
According to the researchers, cassava boosts food security and nutrition for more than half a billion people worldwide.

“The study has generated quality cassava genome sequence. It includes 97 per cent of the estimated genes.”

Morag Ferguson, International Institute of Tropical Agriculture (IITA), Kenya


The study which started in 2012 and its findings was published in the journal Nature Biotechnology last month (18 April) was aimed at increasing the genomic resources for cassava, says Morag Ferguson, a co-author of the study and a molecular geneticist at the International Institute of Tropical Agriculture (IITA), Kenya.
“The study has generated quality cassava genome sequence. It includes 97 per cent of the estimated genes,” Ferguson tells SciDev.Net. “The large amount of DNA [genetic material] sequence information provides insights into the origin of cassava and resources for the improvement of cassava”.
Ferguson adds that the genome relates to African cassava varieties, particularly those with resistance to cassava brown streak disease (CBSD), a devastating viral disease affecting cassava in southern, eastern and central Africa.
The researchers identified the order of the genetic letters of 53 cultivated and wild cassava plant materials (Manihot esculenta) from Africa, Asia, South America and Oceania — a process called genome sequencing. They also sequenced five cassava-related plants such as M. glaziovii and identified the genetic components of 268 African cassava varieties.

Sequence information, according to Ferguson, revealed that some CBSD-resistant cassava varieties in Tanzania including Namikonga and Muzege, contain sections of genomes of M. glaziovii.
Ferguson adds: “Cassava is the main food security crop of the continent [Africa], providing a [high] yield in poor soils with minimal water, when other crops such as maize will fail.”

The study was conducted by researchers from countries such as Fiji, Kenya, Micronesia, Nigeria, Tanzania and United States.
Paul Kimani, a plant breeder from Kenya’s University of Nairobi says the main contribution of the findings is new information on cassava genome and a clear demonstration of the genetic relationships among the various species, including cultivated cassava, its wild relatives and others in the secondary or even tertiary gene pool.
“What it does not do is link the genes with any economically important traits such as disease resistance, nutritional quality or agronomic traits,” he says. Kimani explains that because cassava breeders often rely on a narrow genetic base of the crop, an epidemic can easily cause severe damage, leading to rapid spread of diseases such as cassava mosaic disease (CMD) and CBSD in Africa.
“The key issue is whether the wild cassava has genes for economically important traits such as resistance to CMD and CBSD, productivity and processing, which can be transferred to commercial varieties,” Kimani tells SciDev.Net.
This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.


Jessen V. Bredeson and others Sequencing wild and cultivated cassava and related species reveals extensive interspecific hybridization and genetic diversity (Nature Biotechnolgy, 18 April 2016)