Florence Munguti at the KEPHIS facility in Muguga where they do virus cleaning for sweet potatoes and other plants. Photo Credit: Murimi Gitari

Inside the plant clinic supplying Africa with clean potato vines and seeds

Murimi Gitari
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[rt_dropcap_style dropcap_letter=”A” dropcap_content=”S the pressure of climate change piles and nutrition needs increase in the subSaharan Africa, improved crop varieties like vitamin A-rich orange-fleshed sweet potato have been identified as part of the solution.”]

But timely access to clean and quality sweet potato vines or seeds by farmers has remained elusive.

Many farmers often recycle sweet potato vines from one season to the next, causing a build-up of diseases and viruses, which in turn reduces the root yields. Florence Munguti, the Deputy Director of Kenya Plant Health Inspectorate Service (KEPHIS) Plant Quarantine & Biosecurity Station in Muguga, notes that the growth in sweet potato production and processing has also increased the need for clean, or disease-free planting material in sub-Saharan Africa. KEPHIS, in collaboration with International Potato center (CIP), has been multiplying clean planting material for the highly nutritious orange-fleshed sweet potato at its plant clinic at Muguga for distribution to farmers.

“Orange-fleshed sweet potato offers this part of the world a timely and resounding answer to malnutrition and that explains why we have embarked on provision of clean materials for planting. Using quality seed ensures higher yields of root for consumption and marketing,” says Munguti. Sweet potatoes are attacked by over 20 viruses.

The main viruses worldwide are sweet potato feathery mottle virus (SPFMV) and sweet potato chlorotic stunt virus (SPCSV).

Effects on yields by SPFMV or SPCSV alone are minor, but complex infection by the two or other viruses yield losses of 50 percent. The orthodox way of controlling viruses in vegetative propagated crops is by supplying farmers with virus-tested planting material.

The KEPHIS plant clinic has the capacity to diagnose and eliminate the viruses using different tissue culture technologies. This process is followed by a re-testing to confirm that the planting material is clean from the viruses. The plantlets are then acclimatised (by slowly adjusting temperature, light and humidity) to be able to grow in ambient temperatures in a soil, sand and manure mixture in screen houses.

The screen houses are used for protection from insects such as whiteflies and aphids, which spread viruses. After two to three months growing in the screen house, sweet potato cuttings (approximately 3 node cuttings) are harvested for sale to multipliers. The multipliers then bulk up large quantities of planting material in open fields for sale to farmers for root production. In high virus pressure areas, some multipliers use net tunnels to keep their seed stock free from the virus-vectors before undergoing rapid multiplication in insect-free screen house facilities at KEPHIS Muguga.

“The station has capacity to undertake virus indexing and clean up on germplasm. It facilitates movement of clean germplasm in East and Central Africa with the cleaning process utilising Thermotherapy (Heat treatments) and meristem tip-culture. “KEPHIS has invested in improving the infrastructure of the station with greenhouse containment facilities and screen houses for supporting germplasm multiplication,” said Munguti, who is currently undertaking her PhD studies in Plant Pathology at the University of Nairobi.

Salome Kivuva, a laboratory technician, said the purpose of tissue culture is to ensure they get clean planting materials and supply them to the farmers.

“We pick the materials from the greenhouse and then sterilise them and plant in a nutrient media that consist of macro and micro elements which have the same element as those in the soil. The materials are then taken to lamina flow whereby we infuse into the nutrient media,” she says.

KEPHIS and CIP receive sweet potato collections from sub-Saharan Africa at the plant clinic and also from institutions affiliated with CIP for virus cleaning. “Before distribution of any variety, it should be virus-free to avoid spread of diseases into farms. After the cleaning of the materials and testing, we repatriate them to country of origin,” said Rosemary Njenga, who is in charge of germplasm acquisition, virus cleaning, testing and distribution at CIP.

With the help of KEPHIS and KALRO, they sometimes take the orangefleshed sweet potato for national trials and if they pass the national trials than what they have, they adopt the material for farmers in Kenya and bulk them in case there are countries that want to import them. Other countries prefer taking invitro plants that are kept in test tubes. Mozambique tops on the list of countries who bring their materials for virus cleaning. Others are Rwanda, Malawi, Uganda, Tanzania and Zambia.

The plant clinic offers other services such as diagnosis of pests or diseases found on plant materials intercepted at the point of entry, samples brought by farmers, identification of the pathogens and pests causing plant damage, advisory on disease and pest management strategies and training students and farmers on areas related to crop protection The plant pathology clinic diagnoses disease and nematode problems in plant and soil specimens, carries out identification of the pathogen, and then advises farmers on disease management (prevention/control) options.

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