Improving the African Yam Bean – neglected crop

Dr Daniel Adewale at the African Plant Breeding Academy. Photo by Cathy Watson

Dr Daniel Adewale at the African Plant Breeding Academy. Photo by Cathy Watson

Dr Daniel Adewale, 47, is the world’s African yam bean expert. As he eats his lunch at the World Agroforestry Centre (ICRAF), which is hosting the African Plant Breeding Academy, he remembers his mother. “The ones my mother cooked used to take four hours. Burning kerosene for that long is too much for a farmer.”

The hard seed coat is one characteristic that he wants to breed out. The other is the anti-nutritional factors (ANF) in the grains. The ANF, such as flavonoids and phytates, reduce the beans’ digestibility, swelling bellies and causing flatulence, especially when they are not well cooked. “To break the hardness of the coat and reduce the ANFs will make African yam beans more acceptable,” he explains.

African yam bean (Sphenostylis stenocarpa) is a legume that is indigenous to Africa and widely eaten. It is an “orphan crop”, highly nutritious and culturally resonant, but undervalued by policy makers. Little data information exists on how many people consume it. Like many neglected plant species, the African yam bean has also been little researched, except, of course, by Dr. Adewale.

His passion is partly personal. He ate them as a child and youth. “I got interested because I know from experience that it keeps you feeling filled. When you eat it in the morning, you take longer before you get hungry. Say you take breakfast at 7 am, usually you would be hungry at 1-2 pm. But, with yam beans, you get hungry at 3-4 pm. This makes it a choice food for farm laborers.”

His desire to improve the African yam bean is also driven by its nutritional value. Rich in calcium and phosphorus, its crude protein content is about 29% — higher than that of cowpeas (25%) or the common bean (16-21%). The African yam bean is a vital food in West Africa, where protein energy malnutrition affects millions and approximately one third of children under five years of age are stunted.…/ouagafinal.pdf

African yam beans have the advantage of being one of only two legume species in the world — the other grows in Mexico — known to produce both beans (pulse or grain) and an edible tuber. “Culturally in West Africa, we are interested in the bean, but in Central Africa, tribes such as the Bandudu in the Democratic Republic of Congo like the tuber,” he explains.

The tuber is white fleshed, spindly and long like sweet potatoes but contains more protein than sweet potatoes, cassava or yams. The tuber and the leaves of the African yam bean can be fed to livestock. The African yam bean is also nitrogen fixer, increasing soil fertility.

At the academy, run by the University of California Davis, Adewale and 22 other senior plant breeders are studying how entire genomes can hasten plant improvement. He is one of 110 scientists and 140 technicians that UC Davis will train to work on 110 orphan crops over the next decade under the African Orphan Crops Consortium, a collaboration of, among others, the private sector (Mars, Google and biotech companies), the political (the African Union, NEPAD) and research bodies such as ICRAF, the Beijing Genomics Institute and the International Livestock Research Institute.

For his PhD, Adewale investigated 80 accessions of African yam beans at the International Institute for Tropical Agriculture in Ibadan. “I discovered wide morphological and genetic diversity. The crop behaves differently in different environments and the flowers exhibit up to 90% selfing.” An accession is “a distinct sample of germplasm kept in a gene bank for conservation and evaluation” and a “collection of plant material from a particular location”.

Orphan crops are central to quality of life and food security. African yam beans are an enduring part of the food system of the Igbo and Yoruba and were a key source of dietary protein for malnourished refugees during the Nigerian civil war (1967–70). Special meals of yam beans feature in the marriage ceremonies of Ekitis people in Nigeria and the puberty celebration of Avatime girls in Ghana.

Adewale intends to search Ghana, Togo, Benin and Nigeria for the naturally-occurring diversity of African yam beans. He hopes to find land races with thin-skinned beans and less ANF. “I will visit fields, markets and homes,” says the Nigerian scientist.

He needs at least 500 grams of seed per accession from 20 different African yam bean-growing areas in each country. It is a gargantuan task. For every accession, he must also photograph the growing plant, interrogate local knowledge and assemble “passport data” such as the GPS points, local topography, soil drainage and ecosystem.

The yam bean. Photo:

The yam bean. Photo:

But it is worth it. Previously, Adewale would have had to grow the seeds, wait for them to mature and produce beans, and then breed them conventionally, a process that could take as long as 10 years to produce a superior variety. But with what Adewale is studying at ICRAF, African yam beans with thinner seed coat and less ANF are now a prospect in 4 years.

“The African Orphan Crop Lab at ICRAF will extract the DNA for sequencing. Beijing will sequence it and ICRAF will re-sequence it. Once we know the entire genome, we can compare it with the genome of other plants. I want to discover which genes control seed coat hardness and ANFs. Later we can look at resistance to disease and climate change. In planting breeding, we take it one or two traits at a time.”

Neglected food plants are a priority for ICRAF. Some of them are trees, such as Baobab and Vitellaria paradoxa, the tree that produces shea butter. But ICRAF also cares about annual crops such as yam beans. “They are the agriculture in agroforestry,” says geneticist Dr Ramni Jamnadass, who heads the ICRAF lab, which has four Ion Proton machines donated by Life Technologies. “These are the crops that go with the trees.

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ICRAF and partners launch first African Plant Breeding Academy'

Cathy Watson

Cathy Watson is chief of programme development at the World Agroforestry Centre in Nairobi. Before joining ICRAF in November 2012, she founded and ran two NGOs in Uganda -- Straight Talk Foundation and Mvule Trust. She was made a senior Ashoka fellow for social entrepreneurship in 2006. She has also been a foreign correspondent, working for The Guardian and the BBC, among others. A graduate in biology and Latin American Studies from Princeton, she has over 30 years of work experience in Africa with a focus on trees, youth, HIV, families, and communication for social change. She holds a graduate certificate in agroforestry from the University of Missouri.

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