Orange fleshed sweet potato and lessons for a Code Red crop crisis

by Robert Mwanga | International Potato Center
Thursday, 16 March 2017 16:20 GMT

In this 2015 file photo, Justina Kabuli and her 12-year-old son Andrew remove weeds from their field of sweet potato crops in Chiyobola village, close to the town of Chikuni in the south of Zambia. REUTERS/Darrin Zammit Lupi

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* Any views expressed in this article are those of the author and not of Thomson Reuters Foundation.

Accelerated crop breeding is needed to tackle spreading plant disease and drought that threatens many African food staples

Being a crop breeder in the modern world sometimes feels like being a fire fighter equipped with a very slow truck. The threats to food production, particularly in places like sub-Saharan Africa, spread rapidly as climate change takes hold.  But as the flames of plant disease and drought threaten to engulf many different food staples, it can take crop breeders seven or eight years to reach the scene with a new disease-resistant or drought-tolerant variety that can extinguish the blaze.

That was the challenge we faced in 2008 when a group of scientists from the International Potato Center and the International Food Policy Research Institute came together to develop drought and disease-resistant varieties of orange-fleshed sweet potatoes for sub-Saharan Africa. We knew these sweet potatoes could provide a powerful one-two punch: fighting hunger while addressing the vitamin A deficiency that regularly puts more than 100 million Africans at risk of blindness. But given all the obstacles in our way, we were concerned that it could take close to a decade to get the work done.

In eastern and western Africa, the problem was an assortment of plant viruses that were devastating sweet potato harvests. In southern Africa, the issue was chronic and intensifying drought.  There was also a complicated array of consumer preferences to deal with. For example, people in east and central Africa prefer a drier, starchy sweet potato. In Ghana, people tend to eat a "less sweet" sweet potato.

But ultimately we came up with a plan, described in a new study published earlier this month that delivered a wide assortment of improved varieties in just four years. That’s record time in the world of sweet potato breeding and in crop science in general.

Essentially we embraced a divide and conquer strategy. We dispatched teams of scientists to different parts of Africa where they worked with national agriculture research organisations to focus exclusively on the key problem in that particular region. 

The southern Africa team worked in Mozambique to breed for drought tolerance. The east and central Africa team set up field trials in Uganda to focus on plant viruses that are common in that area, but not as prevalent in the other regions. In Ghana, we concentrated on breeding some of the sweetness out of the sweet potato so it would find a home on a west African dinner plate that typically includes more savoury fare.

The impact of the effort, which garnered the 2016 World Food Prize, is a powerful argument to adopt accelerated crop breeding strategies. The 15 drought-tolerant varieties released in 2011 to farmers in Mozambique played a key role in helping families deal with the severe drought that caused a food crisis in the region. Farmers who planted these new sweet potatoes generated a healthy harvest, within a very short period (3 to 4 months). Maize planted in the neighbouring fields was wiped out. 

In Uganda, where plant disease had pushed average yields down to 4.4 tons per hectare, a fraction of the global average, new disease-resistant sweet potatoes are producing more than 10 tons per hectare. And they have the added benefit of requiring fewer inputs and less labour.

Meanwhile, we now have a very powerful weapon for fighting vitamin A deficiency. The orange-fleshed sweet potato gets its colour from naturally occurring beta-carotene, a nutrient the body converts into Vitamin A. Regularly eating even small portions can eliminate the vitamin A deficiency that affects 68 percent of children in Mozambique and 38 percent in Uganda.

That gets to another challenge overcome by this project. Orange-fleshed sweet potatoes were not that common in Africa. Farmers mainly had been planting yellow and white fleshed varieties, relatively weak sources of Vitamin A. Getting people to accept these more nutritious varieties required adding a marketing component to our work. My colleague, Maria Andrade, would drive around Mozambique in a bright orange Toyota Land Cruiser festooned with pictures of sweet potatoes. There were radio spots, theatrical presentations and even songs written to promote the virtues of the orange-fleshed varieties.

The menu of food products available in Africa that use the orange-fleshed varieties was also expanded. A sweet potato puree is being used to make nutritious "golden biscuits" while sweet potato flour can now be an ingredient in the chapati breads popular in east Africa. 

This combination of the accelerated breeding and creative marketing could provide a template going forward for dealing with the growing number of food challenges facing sub-Saharan Africa. For example, in some regions, climate change is expected to require a switch not just to new and improved varieties but to an altogether different mix of crop types.

Crop scientists are ready to embrace their role as the first responders of food security. But, just like any first response, speed will be critical. So we need investments to fund the infrastructure, technology and partnerships that can quicken the pace of plant breeding. That way, we can be fighting a food crisis at the first sign of smoke, and deliver solutions long before we are facing an inferno.

Robert Mwanga is a plant breeder at the International Potato Center and the 2016 winner of the World Food Prize.

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