Cloning healthy sweet potato plants by means of tissue culture is helping to alleviate food insecurity in Zimbabwe, and while new production data is hard to come by, some studies show plantings are increasing.
"You will see people selling sweet potatoes by the roadside [in Harare, the capital] - a sight we never used to see. That is all attributable to the impact of tissue culture,” said Barnabas Mawire, Zimbabwe Country Director for Environment Africa. “Surely, in a country plagued by cereal deficits that should be a welcome development, as it means through this technique many farmers are able to put food on the table for their families."
Sweet potatoes - not officially recognized as a staple food but grown by most rural households - are a good source of starch and a substitute for maize, the most popular staple foodstuff. People have been resorting to sweet potatoes because the cost of processed starch foods like bread has been escalating.
Sweet potatoes can be processed into chips or pounded into flour, while the leaves can also be eaten as a vegetable. But the plants are vulnerable to pests and diseases, especially the sweet potato virus complex (SPVD), which tissue culture can help inhibit.
Tissue culture - a biotechnology incorporating several techniques - is used to grow improved seedlings that could then produce better fruit or flowers, and be more disease-resistant. Tissue culture technology was introduced in Zimbabwe in the late 1990s but has been around for more than 30 years. The cultured plants are grown from small pieces of plant tissue in test-tubes under sterile conditions.
Leading agricultural scientist Petr Kosina, of the International Maize and Wheat Improvement Center (CIMMYT), says the technology is used in cases where plants do not produce seed, or not enough seeds, such as bananas and pineapples. "Or [where] it is difficult to control cross-pollination, meaning seeds wouldn't have the same characteristics as the parent plants (e.g. date palms), or reproduction via seeds is… more expensive."
More plentiful food
A food security survey by the Zimbabwe Vulnerability Assessment Committee (VAC) put an estimated 1.5 million people of almost 13 million in need of assistance between October and December 2013, and this figure is expected to rise to 2.2 million between January and March 2014.
A muddled land reform programme in 2000, coupled with successive poor harvests after inconsistent rains, has seen a dramatic drop in agricultural production, leaving millions susceptible to malnutrition and in dire need of food assistance.
According to an official with the NGO, CARE International Zimbabwe, which has been promoting sweet potato plants generated by tissue culture, farmers reported yields ranging from 16 to 20 tonnes per hectare. The NGO has helped 2,700 farmers in six districts of the Masvingo province in southeastern Zimbabwe.
The national average yield of the crop is 6 tonnes per hectare, rising to 25 tonnes per hectare when grown under irrigation. According to studies, this compares well with Africa's yield average of 6 tonnes per hectare.
About 50 percent of Zimbabwe's land mass consists of communal farming areas, where 70 percent of the population reside and small-scale farmers work average plot sizes of about two hectares.
Jonathan Mufandaedza, chief executive of the National Biotechnology Authority of Zimbabwe (NBAZ) said government-led tissue culture projects had been affected by the "harsh economic conditions… [and] tissue culture has advantages, [but] scientists are still to develop techniques for producing planting material for… [all our] crop[s]." NBAZ is educating the public about the technology to popularize it.
So is this the way to go?
The University of Zimbabwe's Crop Science Department and private companies like Agri-Biotech have been supplying healthy plants and expertise to farmers since 2006. But scientists say farmers require a consistent supply of fresh planting material every few years, as the virus elimination process does not last.
The technology is improving rapidly but is still more expensive than propagating by seed. NGOs sell a tissue-culture plant for 8 to 10 US cents, ordinary plants cost 5 US cents each, and a 25kg bag of seeds costs around $30.