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Jun 052015
 
Photo: Bill & Melinda Gates Foundation

Farmer Maria Mtele holds recently harvested orange-fleshed sweetpotatoes in a field in Mwasonge, Tanzania.

Sweetpotato has a long history as a lifesaver. The Japanese used it when typhoons demolished their rice fields. It kept millions from starvation in famine-plagued China in the early 1960s and came to the rescue in Uganda in the 1990s, when a virus ravaged the cassava crop.

In sub-Saharan Africa, sweetpotato is proving crucial in the fight against blindness, disease and premature death among children under five. And, as agriculture becomes more market-oriented across the continent, sweetpotato has some significant advantages: it requires fewer inputs and less labour than other crops such as maize, tolerates marginal growing areas and can mature within four months.

On these fertile grounds, researchers across the globe are not underestimating the importance of sweetpotato as a staple crop.

“Yields achieved by resource-poor farmers in sub-Saharan Africa are typically low,” says Roland Schafleitner of the International Potato Center (CIP), based in Peru.

“Improved and well-adapted sweetpotato varieties with increased tolerance to drought, pests and diseases will have a positive impact on food and income security in sub-Saharan Africa and can significantly contribute to increasing productivity,” he says.

Roland was Principal Investigator of two research projects funded by the CGIAR Generation Challenge Programme (GCP), which developed genetic and genomic resources for breeding improved sweetpotato.

At the outset of the work, Roland says: “Breeding efforts were limited by the crop’s genetic complexity and the lack of information available about its genetic resources.

“It was clear that if we could develop genetic tools and make concerted efforts towards understanding the gene pool of sweetpotato, the breeding potential of the crop would improve.”

Photo: Bill & Melinda Gates Foundation

Farmer Mwanaidi Rhamdani at work in an orange-fleshed sweetpotato field in Mwasonge, Tanzania.

Sub-Saharan Africans getting their vitamin A from sweetpotato

Photo: CIP

Sweetpotato diversity.

Malnutrition does not always mean a simple lack of calories; research suggests that nutrient shortfalls are an even bigger killer. Vitamin A deficiency is a leading cause of blindness, infectious disease and premature death among children under five and pregnant women in sub-Saharan Africa and Asia.

Sweetpotato comes in a wide range of colours. Varieties with dark orange flesh are naturally very rich in the pigment beta-carotene, which the body converts into vitamin A. However, the sweetpotatoes traditionally grown in Africa are pale-fleshed and low in beta-carotene. African consumers were not used to eating colourful sweetpotato – and these orange-fleshed varieties were in any case not well adapted African growing conditions.

Recent years have therefore seen a collaborative effort by researchers across the world to breed orange-fleshed sweetpotato varieties fortified with high levels of beta-carotene, and even enriched with other nutrients, that have also been crossed with local varieties and so are adapted to local conditions and tastes. A crucial part of these efforts has also been to create public awareness and encourage people to grow, eat and buy these new varieties.

Photo: HarvestPlus

Two cheeky young chappies from Mozambique enjoy the sweet taste of orange-fleshed sweetpotato rich in beta-carotene, or pro-vitamin A.

All of this adds to the growing momentum behind sweetpotato. The growing awareness of sweetpotato’s potential nutritional benefits for the poor and food insecure, as well as its value for subsistence farmers as a reliable crop that withstands drought and requires minimal inputs, mean that it is growing in significance.

Photo: HarvestPlus

Orange-fleshed sweetpotato can be used to make a variety of tasty products from doughnuts to chapati.

More than 95% of the world’s sweetpotato crop is grown in developing countries, where it is the fifth most important staple food crop. It is particularly important in many African countries: Madagascar in Southern Africa; Nigeria in West Africa; and those surrounding the Great Lakes in East and Central Africa – Uganda, Malawi, Angola and Mozambique.

According to 2013 figures from the Food and Agriculture Organization of the United Nations, 3.6 million hectares of sweetpotato were harvested in Africa. While the average global yield of sweetpotato per hectare was 14.8 tonnes, across all East African countries in 2013 it was only half this, at 7.1 tonnes per hectare. In West African nations the average yield was even worse, at 3.7 tonnes per hectare.

Farmers are unable to make the most of their crops because the varieties available to them, including traditional varieties (or landraces) have low resistance to viral diseases and insect pests, and poor tolerance to drought. It is therefore crucial that when developing new varieties breeders are able to efficiently incorporate pest and disease resistance and drought tolerance traits.

Sweetpotato, in spite of its name, is only distantly related to the potato. Unlike the potato – which is a tuber, or thickened stem – the sweetpotato is a root. Sweetpotato is not related to the yam either, despite the physical similarity between the two. Sweetpotato can grow at altitudes ranging from sea level to 2,500 metres. It requires fewer inputs and less labour than other crops such as maize, and, in contrast to the potato, it can tolerate heat.

New DNA markers identified for sweetpotato disease

The sweetpotato virus disease (SPVD) is the most serious disease affecting sweetpotato in sub-Saharan Africa. It often causes serious yield losses of up to 80–90 percent.

The disease is the result of joint infection by two viruses: the sweetpotato feathery mottle virus and the sweetpotato chlorotic stunt virus. Of the two, the stunt virus is the more problematic.

Wolfgang Grüneberg, also from CIP, says that, in the years 2006–2008, 52 new DNA markers were developed as part of GCP-funded research to improve marker-assisted selection for resistance to the disease.

“The results,” says Wolfgang, Principal Investigator for the research, “looked promising for developing a large number of orange-fleshed sweetpotatoes with resistance to SPVD.”

Immediately following the development of the markers, two varieties of sweetpotato were developed using a cloned gene, Resistan, known to confer resistance to the virus. The first variety was used to improve an SPVD test system so that the disease could be diagnosed earlier if a crop was affected. The second variety underwent field tests in regions in Uganda that were highly affected by the disease.

Photo: HarvestPlus

Sweetpotato vines and roots.

Mobilising the genetic diversity of sweetpotato for breeding

The goals of the GCP-supported work were to develop a diverse genetic resource base for sweetpotato and stimulate the use of new tools in ongoing breeding programmes.

To help transfer this work from high-end laboratories to resource-poor research labs in developing countries, GCP promoted collaboration across institutions and borders. Researchers from Brazil, Mozambique, Uganda and Uruguay worked together on sweetpotato genetic research projects.

As Roland explains, the basic first steps needed to begin to ‘mobilise’ the genetic diversity of sweetpotato were developing a reference set of varieties and improving genomics tools to work with polyploid crops, i.e. those possessing multiple sets of chromosomes, such as sweetpotato.

GCP-supported researchers in Peru and sub-Saharan Africa defined a reference set of 472 varieties of sweetpotato, carefully selected and honed to represent both the diversity of the crop and its most important agronomical and nutritional traits.

“Based on a reference set, genetic markers can be developed that are associated with important characteristics of the crop and can help breeders to select favourable genotypes,” says Roland.

The gene sequences developed during the Programme are now available as a Sweetpotato Gene Index.

“Based on these sequences,” says Roland, “molecular markers have been designed that can help breeders and gene-bank curators to assess the genetic diversity of their accessions and to perform genetic mapping studies.

“Today, techniques that yield a much larger number of markers for genetic studies and selection are accessible for sweetpotato,” he says.

Photo: Bill & Melinda Gates Foundation

Mwanaidi Rhamdani (left) works with Maria Mtele in an orange-fleshed sweetpotato field in rural Tanzania.

The genetic lifelines reach Africa

Sweetpotato is one of the most important staple crops in Mozambique, ranking in third position after cassava and maize. The areas harvested in Mozambique in 2013 were 1.7 million hectares of maize, 780,000 hectares of cassava and 120,000 hectares of sweetpotato.

Photo: CIP

A child eats cooked orange-fleshed sweetpotato in Uganda.

GCP funded breeders in Mozambique and Uganda to learn how to identify genetic markers that would prove useful for future sweetpotato breeding.

“Our African partners visited us at CIP and helped us complete the work on identifying markers,” recalls Roland. “This provided the opportunity for direct ‘technology transfer’ to breeders in the target region.”

The collaboration had, for the first time, created a critical amount of genetic and genomics resources for sweetpotato. The resulting Sweetpotato Gene Index and the new markers were published in a peer-reviewed journal, BMC Genomics (2010) 11:604.

The new genetic resources are in use at CIP in Peru and in breeding programmes in Burkina Faso, Mozambique, Uganda, Uruguay and the USA for the assessment of the genetic diversity of germplasm collections.

“The markers have been used for diversity analysis, especially at the CIP gene bank, and also in Africa,” says Roland, who says the markers will help future research.

“Such analysis guides germplasm conservation decisions, and diversity studies are a great tool to develop core collections and composite genotype sets – subsets of the whole collection – which allow for more practical screening for specific traits than large collections.”

More links

Photo: P Casier/CGIAR

Kenyan farmer Emily Marigu with her sweetpotatoes.

Mar 062015
 

 

Photo: IITA

A woman holds yam tubers in her hands in a market in West Africa.

Yam production in West Africa is plagued by unsustainable and suboptimal practices. Most farmers continue to grow local varieties that produce poor yields – and also lack aesthetic qualities that appeal to consumers, such as smooth skin and elegant tuber shape.

For a better future and a sustainable food supply, farmers need access to improved yam varieties that can tolerate changes in the climate and environment, as well as resist pests and diseases. Adopting new practices will also help farmers to increase their yields.

Yams play a key role in the food security, income generation and sociocultural life of at least 60 million people in Africa, where more than 95 percent of the world’s yam supply is produced. Worldwide, the tuber vegetable is grown and consumed across the tropics and subtropics of Asia, the Caribbean, the Pacific, and West and Central Africa. Such is the reliance on yams in parts of Africa that communities hold annual festivals to revere and celebrate the crop. The Igbo people in Nigeria hold a ‘new yam harvest’ festival every year at the end of the rainy season in August or September, when the yams are ready for harvest. People in both Nigeria and Ghana hold the ‘new yam eating’ festival, also known as the ‘hoot at hunger’ festival, which symbolises the end of a harvest and the beginning of the next cropping cycle.

Despite the importance of yams in West Africa, breeding efforts for improved varieties have been limited for a number of reasons. One is that local yam cultivars have different names in different communities, making germplasm management and research difficult. Another obstacle is the constraints on yam growth – the plants have a long growth cycle and are highly susceptible to pests and diseases, poor soil, weeds and drought.

Photo: J Haskins/Global Crop Diversity Trust

Dancers celebrate at a new yam festival in Nigeria.

Unique collaborations get yam research rolling

Photo: J Haskins/Global Crop Diversity Trust

A farmer in his yam field in Nigeria.

In 2004, the CGIAR Generation Challenge Programme (GCP) recognised the need to provide resource-poor farmers in West Africa with yam varieties that combine high yields with drought tolerance, pest and disease resistance, and good tuber quality. The Programme was created to advance plant genetics for 21 crops, with a view to improving the resources and capabilities of local breeders in developing countries. Yams were one of the crops that received funding for the first half of the 10-year Programme.

Robert Asiedu, Principal Investigator for GCP’s project assessing the genetic diversity of yams in West Africa, says the Programme improved yam breeding through its unique collaborations.

“The work was brief but the partnership arrangement was useful,” says Robert, who is Director of Research for Development at the International Institute of Tropical Agriculture (IITA), based in Nigeria.

Photo: IITA

A Nigerian farmer displays her healthy yam tubers.

His GCP-funded team included researchers from Centre de coopération internationale en recherche agronomique pour le développement (Agropolis–CIRAD; Agricultural Research for Development) in France, the International Potato Center (CIP) headquartered in Peru, the International Centre for Tropical Agriculture (CIAT) based in Colombia, the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) headquartered in India, Chile’s Instituto de Investigaciones Agropecuarias (INIA; Agricultural Research Institute), and the United States Department of Agriculture, plus experts in genome profiling and genetic analysis from Diversity Arrays Technology (DArT) in Australia. DArT provided high-throughput genotyping services that helped to profile yam’s genome.

Andrzej Kilian, DArT’s founder and director, says: “My company had a range of interactions with GCP, and I hope we had some positive impact on the outcomes.”

The researchers used molecular breeding tools – simple sequence repeat markers, or SSRs – to assess the genetic diversity of more than 500 yam accessions from Benin, DR Congo, Côte d’Ivoire, Equatorial Guinea, Gabon, Ghana, Nigeria, Sierra Leone and Togo. The assessment was a huge step forward in expanding the scientific knowledge of yam genetics, and ultimately in identifying suitable material for use in breeding programmes.

Photo: J Haskins/Global Crop Diversity Trust

Walking in yam fields.

IITA research scientist Maria Kolesnikova-Allen, also funded by GCP, says the yam work had two main objectives.

Photo: IITA

Yam vines twist up bamboo staking in a yam field.

“The primary focus of the first projects on yams involving molecular markers was to assess genetic diversity among yams originating from different West African countries and to find relationships between species. This information is important for future breeding and conservation efforts,” she says.

“Also, we were interested in confirming the use of molecular markers for analysis of yams and their potential use in breeding programmes.

“By confirming their usefulness in yam studies, we have offered a robust tool set for further studies on this crop.”

Photo: IITA

A trader displays clean and dried yam tubers at Bodija market, Ibadan, Nigeria.

As a result of the research, she says, “more knowledge and understanding has been achieved in terms of the genetic structure of yam populations in West and Central Africa, providing breeders with important knowledge for accessions selection to be included in breeding programmes.”

The genetic information that has been generated for yams will directly benefit countries in West Africa, according to Maria, “especially with IITA being positioned in the middle of the region and providing expert advice and dissemination of this information to local breeders and farmers.”

As part of her GCP-supported work, Maria supervised West African PhD students Jude Obidiegwu from Nigeria and Emmanuel Otoo from Ghana. Jude, a researcher at the National Root Crops Research Institute (NRCRI) in Nigeria, was responsible for GCP’s work on the genetic diversity of yams. His PhD assessed the genetic diversity of the West African yam collection.

African researchers carry GCP torch forward for yams

Jude is an example of how GCP focussed on fostering a base of experts on the ground in the countries where yams play an important role in people’s lives.

He was a participant in GCP’s Plant Genetic Diversity and Molecular Marker Assisted Breeding workshop held in Pretoria in June 2005. There he learned genomic DNA extraction methods, genetic and quantitative trait locus (QTL) mapping, development of core collections, and scientific proposal writing.

Photo: IITA

Woman counting money from the sales of yams at a yam market in Accra, Ghana.

“Our students at PhD level from Nigeria and Ghana were the main drivers of the projects at laboratory and field experiments level,” says Maria.

“Being involved in the projects allowed them to gain international exposure in their respective research fields and later advance their scientific career, becoming fully fledged yam scientists in their own right.

“If there be any hope of applying advanced genetics and genomics tools to the improvement of yam, it is researchers like Jude who will be the foot soldiers of that work in Africa.”

Photo: J Haskins/Global Crop Diversity Trust

A drummer adds his music to a new yam festival in Nigeria.

Maria feels there are strong foundations for further development of yam’s genetic resources after GCP’s sunset at the end of 2014.

“I would like to hope the future is bright,” she says. “As programmes for reducing hunger and poverty are multiplying and gaining momentum worldwide, I am sure the research on staple crops will be given much-needed financial support.

“I strongly believe in a partnership approach,” she maintains, drawing an analogy between GCP’s focus on crop genetics and the Human Genome Project that involved more than 300 partners collaborating between 1990 and 2003 to identify, map and sequence the human genome.

Robert agrees, forecasting that: “New projects will raise the capacity for yam breeding in West Africa by developing high-yielding and robust varieties of yams preferred by farmers and suited to market demands.”

Photo: IITA

A woman offers yam flour (known as elubo isu) for sale in Bodija market, Ibadan, Nigeria.