"Across East Africa’s semiarid, densely populated plains, thousands of villages depend on the sweetpotato for food security."

On-farm trials are important for testing techniques and refining research objectives.

"Without the sweetpotato," says Robert Odeu, "there would be a terrible hunger." Robert is from Dokolo village in Soroti Province in northeast Uganda. A decade of civil war has killed off the villagers’ cattle, the parasitic striga weed has attacked the corn and sorghum, and a virulent mosaic virus has devastated the cassava crop. Dokolo village is not alone. Across East Africa’s semiarid, densely populated plains, thousands of villages depend on sweetpotato for food security.

Sweetpotato is dependable. Once the plant forms edible roots, a hungry family can start eating; an established patch keeps producing, despite drought, for months. Sweetpotato is flexible. Farmers can stagger production across the region’s two rainy seasons, from April into June/July and from August into November/December. They can leave the crop in the ground, harvesting piecemeal as needed, or they can harvest everything at once. While the supply lasts, families boil or steam the roots, eating them with pungent, groundnut sauces.

Food security, however, is as much about processing as it is about production. When the dry season sets in, weevils start to proliferate. To keep the sweetpotato crop from being destroyed, villagers harvest whatever is left in their fields. This surplus can tide them over during the long December-to-April dry season—if it can be kept from spoiling.

On behalf of his village, Robert Odeu works on a joint postharvest project sponsored by CIP and Uganda’s National Agricultural Research Organization (NARO). Its objective is to use traditional storage technologies in new ways. To help villagers keep fresh sweetpotato longer, NARO’s Kwanda Research Institute has introduced storage pits constructed from local materials. A typical circular pit is about a meter deep and a meter and a half wide. Once the pit is cleaned out, farmers compact the walls and cover the bottom and sides with dried grass. Roots are then packed into the pit, in a pattern that permits sufficient air circulation. A straw roof is set over the top, braced from below by a bamboo frame. Thus protected, fresh roots can be kept two to three months.

Drying is the traditional way to preserve sweetpotato. For a coarse inginyo, women crush and sun dry chunks of fresh root. For amukeke chips, the men slice up the roots into round, flat pieces, which the women then spread out to dry; both keep for between four and five months. Dried sweetpotato is boiled in sauces along with beans and vegetables. For the starchy staple, atapa, women grind up dried chunks or chips into a coarse flour, which is rehydrated in water, boiled, mashed, and then eaten directly as a thick porridge. Milled sorghum or millet can be mixed in, along with tamarind fruit, lemon, or mango.

"Villagers prefer the sliced amukeke chips," says CIP food scientist Vital Hagenimana, "because the quality for processing is higher and they store better; unfortunately, processing chips is much more tedious." To speed up chip production, NARO has designed a durable iron-slicer with an adjustable, hand-cranked blade. A small work group can slice about 180 kilos of sweetpotato roots an hour, or about a metric ton a day. Three Soroti villages are experimenting with this system.

The commercial demand for a high-quality amukeke chip is expanding. Millers grind the chips into flour, which is sold in the towns, mostly for making atapa. The flour can also be used in baking. Deep-fried dough for mandazi, and for many types of cookies, can be made almost exclusively with sweetpotato flour. For cakes and bread, up to 50 percent of the flour can be obtained from dried sweetpotato, although it has to be very white, and very clean. Fresh mashed sweetpotato can also be mixed directly into the dough. In taste tests, consumers said such additions improved the color, texture, taste, and freshness of deep-fried buns, chapatis, and mandazis. The finished product is also less greasy.

In cooperation with NARO’s postharvest program, CIP sponsored a three-day processing workshop at Soroti’s District Farm Institute in Serere. More than 50 village women attended, plus members of community organizations and even some local bakers. They spent a day testing recipes and experimenting with different amounts of sweetpotato flour. They tried out the slicing machine, debated the best oven construction, and examined the storage pits. Prospects for baked goods are very promising as there is an established demand, processing technology is available, and the high price of imported wheat makes substituting sweetpotato flour a virtual necessity.

Sweetpotato—fresh or dried—is a staple for almost every village in Soroti. It also makes a good feed for hogs. According to Dai Peters, CIP rural development specialist, "keeping hogs helps villagers convert their surplus sweetpotato into a source of capital; hogs become small saving accounts with short-term maturity." To ensure digestibility, fresh roots should be boiled, and vines, which provide a good source of protein, need to be chopped up. Using roots as feed does not diminish food security. As Dai explained, "villagers start raising hogs in July, when the first sweetpotato harvest begins. Roots are abundant into December, and the hogs are sold off at Christmas time, just as the dry season gets underway."

Sweetpotato has increased greatly in importance in Northern Zambia, where most households have a plot.

Food security depends on improved capacity for storage, processing, and utilization. But front-end production cannot be ignored either. Villagers typically leave some roots in the ground during the dry season. Months later, when the rains start, the roots of this hardy perennial plant re-sprout. After a few weeks, the vines are strong enough for farmers to take cuttings, which they use to re-establish the crop. Last year, the rains stopped early and started late. The result was a six-month drought that killed off most of the plants and put the region’s food supply at risk. "We managed to get multiplication going again, but it took much too long," noted Philip Ndolo, who heads up the sweetpotato program at the Kenya Agricultural Research Institute (KARI). To prevent another production crisis, Ndolo and his team work with women’s groups in 15 communities near Alupe, in Kisumu district. This year, each member will plant healthy cuttings in a small 1.5 square-meter nursery bed prepared in advance. They will water the bed as needed throughout the dry season. Then, once the rainy season starts, they can take cuttings from the vines immediately, without waiting for the old roots to re-sprout.

There is another advantage. According to CIP entomologist Nicole Smit, weevils prefer the woody vines left over from the last harvest. When farmers take cuttings from these old volunteer plants, they end up transferring weevils to their new fields. "But," Smit explains, "with cuttings from a nursery, farmers begin the next season with fresh, clean planting material less likely to be infested." Weevils cannot dig very deeply into the ground, so hilling around plants and harvesting large tubers first also helps minimize damage. Special problems posed by each of the region’s two weevil species (Cylas brunneus and Cylas puncticollis) make these defensive practices essential. So far, varietal resistance has proved elusive, and biological controls such as pheromone traps have had scant impact on weevil populations.

"Farmers selected their varieties under heavy disease and pest pressure," notes CIP breeder Ted Carey. "Under low-input conditions, their cultivars do better than improved germplasm from headquarters." Considering tropical Africa’s large number of sweetpotato landraces, plus their high dry matter content and their virus resistance, the region is viewed as secondary center of sweetpotato diversity. By crossing African types with elite varieties from CIP, Carey and his national program partners expect to get early-maturing varieties with higher yields that store well. They also expect a new selection such as SPK 004 to help combat vitamin A deficiency, especially in children. Chronic throughout much of tropical Africa, lack of vitamin A can lead to permanent blindness.

In both Uganda and Kenya, white-fleshed varieties with a high dry-matter content (30–38 percent) are preferred, both for fresh consumption and for processing. In contrast, orange-fleshed varieties, which are rich in beta-carotene (vitamin A), tend to be mushy, and their dry-matter content rarely surpasses 24 percent. Given the deficiency of vitamin A in the local diet, finding an orange-fleshed type sweetpotato that is acceptable to farmers is a priority. The quickest path to selection has come from multi-locational National Performance Trials (NPT) in which Uganda and Kenya have exchanged and screened material collected from farmers. Such trials helped Carey and his national program counterparts to identify Kenyan SPK 004. This cultivar is rich in vitamin A—3.44 milligrams per 100 grams of sweetpotato—and has an acceptable dry-matter content of 31.6 percent. Thanks to the CIP-backed research network, PRAPACE, which oversees regional distribution and field trials, varieties such as SPK 004 can be distributed quickly to neighboring countries and local farmers.

Mrs. Mwanzi of Okame village near Alupe had a plot of SPK 004 as part of an on-farm trial. She and her 10-year old daughter dug up the ground, hilled the soil, and planted it. The cuttings came from the Alupe substation. "I like a lot of varieties that are ready at different times," she says. For that reason, she also staggers her planting. Mrs. Mwanzi demonstrated her technique, cutting four long stems from a plant with her machete, each about 30 centimeters long. She put two of them together, mounded up a hill of dirt with her hands, and then pushed the stems into the hill. She took a few more cuttings and pushed them in from the side. "It is best to plant a lot of stems," she said, "in case some of them die." Mrs. Mwanzi planted SPK 004 because she had heard it was good for her children's’ health. She also planted a nursery for the dry season "to get the first new roots early and to kill the hunger."

To ensure food security, CIP and its national program partners must work on many fronts—from breeding to pest management and utilization. To characterize germplasm and eliminate duplicates, they need the tools biotechnology provides. To design effective pest control strategies, they need on-farm collaboration. They cannot ignore sweetpotato’s postharvest and marketing problems, including storage and processing. To share results, they must build up strong research networks. And, in the end, they cannot forget the last requirement: that East African villagers like Mrs. Mwanzi grow it.