Overview
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The ARC is celebrating 70 years of contribution to sweet potato research and development in South Africa in 2022. In South Africa sweet potatoes being the second largest root crop produced (82 000 t in 2018/19) following on carrots, has a well-developed commercial market but also plays an important role in food security and alleviating malnutrition. The major production areas are Limpopo, Mpumalanga, Brits area in North West, and parts of KwaZulu-Natal and Western Cape but it is grown by small-holder and resource-poor farmers in virtually all provinces of South Africa.
Sweet potato is an excellent source of carbohydrates and has a low glycaemic index (GI). Orange-fleshed types are rich in beta-carotene, a pro-vitamin A carotenoid that is converted to vitamin A by the human body. Orange-fleshed sweet potato is promoted for alleviation of vitamin A deficiency and reduce non-communicable diseases (Laurie et al., 2018). This is very relevant since the South African Child Gauge 2020 report states that: "Malnutrition hurts millions of South Africa's children now, just as it did 20 years ago". Severe acute malnutrition (SAM) remains a serious fundamental cause of child deaths in South Africa, accounting for 1/4 child in-hospital deaths. Sweet potato has been reported as good potential source of phenolic compounds and antioxidants. Polyphenols play a role in preventing many chronic diseases including cancer, cardiovascular diseases, and diabetes.
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The multidisciplinary research approach at the ARC covers the full value chain i.e. development of improved cultivars, optimization of cultivation practices, crop protection and diagnostic services, stream-lined seed systems, processing and enterprise development.
Reference:
Laurie, S.M., Faber, M., and Claasen, N. 2018. Incorporating orange-fleshed sweet potato into the food system as a strategy for improved nutrition: the context of South Africa. Food Research International 104: 77-85.
doi.org/10.1016/j.foodres.2017.09.016 (Jan).
Agronomy
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Sweet potato agronomic research at the ARC-VIMP focus on the optimization of cultivation practices. Recent agronomic research investigated the horizontal placement of cuttings at planting (Hlerema, 2021). This is a popular practice used by commercial growers for Blesbok, resulting in very high root yield. In vine storage experiments, three bag treatments namely polyethylene bag without holes, polyethylene bag with 12 holes and dry hessian with vines from sweet potato cultivar "Bophelo" were stored for 3, 6, 9, 12 and 15 days at ambient temperature during summer (Hlerema
et al., 2018). The results showed that hessian bags offer the best option to prolong storage (12 days) as compared to polyethylene bags (6 days), however hessian bags are more expensive. Polyethylene bags with holes can be used if the farmer is not willing to pay the additional cost to prolong storage.
A single crop coefficient (Kc) was successfully developed and validated to adjust Kc values of sweet potato to specific climates, for improved water management of irrigated sweet potato cropping systems under semi-arid conditions (Mulovhedzi 2017, Mulovhedzi et al., 2020). This was obtained from an open-path eddy-covariance system containing energy balance sensors which was installed in a 1.3 ha field to estimate evapotranspiration. Averaged values of Kc were 0.46, 0.92 and 0.57 during the initial, middle and late growth stages, respectively. Final storage root yields were 32 t ha-1 (2014/2015) and 29 t ha-1 (2015/2016), with water use efficiency (WUE) of 89 and 85 kg ha-1 mm-1, respectively.
The dual purpose use of ARC orange-fleshed sweet potato cultivar Bophelo was investigated and found despite the negative effect on root yield, harvesting vines for nutritious vegetative part extends food availability over a longer period, thereby improving the nutritional food security of households (Nyati
et al., 2019). The total nutritional yield (leaves plus storage roots) at low irrigation regime (supplemental irrigation) and no fertilization was 0.40 kg/ha iron, 0.09 kg/ha for zinc and 11 kg/ha for β-carotene compared to 0.60 kg/ha iron, 0.15 kg/ha for zinc and 18 kg/ha for β-carotene for the well-watered, optimally fertilized regime.
The forecasted reduction in rainfall in several parts of South Africa due to climate change, necessitates research on drought stress adaptation. In-field rain water harvesting is for instance a production system which was tested for growing orange-fleshed sweet potato at household level (Laurie et al., 2017). The ARC-VIMP will embark on a new research program "Roots-to-resilience" as one of 20 consortium members as part of the European Union Horizon2022-2027 funding instrument. We hope to test e.g. root phenotyping using tubes on sweet potatoes at different water regimes.
Contact:
Dr Hintsa Araya
References:
Hlerema IN. 2021 Studies on vine storage methods, planting technologies, paclobutrazol treatment, planting density and weevil management on sweetpotato (Ipomoea batatas L. LAM) cultivars promoted in South Africa. PhD Thesis. Alice: Dept of Horticulture, University of Fort Hare.
Hlerema, I.N., Taruvinga, B., Laurie, S.M., Ndou, P., Eiasu, B. and Du Plooy C.P. 2018. Cost Effectiveness and Influence of Storage Bag Type on the Quality of Sweet Potato Vines.
Journal of Agricultural Science 10(9): 47-54.
Laurie, S.M., Nhlabatsi, N.N., Ngobeni, H.M., Tjale, S.S. 2017. The effect of in-field rain water harvesting on orange-fleshed sweet potato biomass and yield.
Journal of Agricultural Science 9(10):1-9. DOI:10.5539/jas.v9n10p1
Mulovhedzi, N.E. 2017. Quantifying water use and nutritional water productivity of two sweet potato (Ipomoea batatas) cultivars grown in South Africa. MSc thesis, University of Pretoria. https://repository.up.ac.za/handle/2263/65920
Mulovhedzi, N.E., Araya, N.A., Mengistu, M.G., Fessehazion, M.K., du Plooy, C.P., Araya, H.T., van der Laan, M. 2020. Estimating evapotranspiration and determining crop coefficients of irrigated sweet potato
(Ipomoea batatas) grown in a semi-arid climate.
Agricultural Water Management 233:106099. DOI: 10.1016/j.agwat.2020.106099
Nyathi, M.K., Du Plooy, C.P., Van Halsema, G.E., Stomph, T.J., Annandale, J.G., Struik, P.C. 2019. The dual-purpose use of orange-fleshed sweetpotato (Ipomoea batatas var. 'Bophelo') for improved nutritional food security. Agricultural Water Management 217:23-37. DOI: 10.1016/j.agwat.2019.02.029
Breeding
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The ARC-VOP has an excellent history in sweet potato breeding since 1952. To date, 31 cultivars have been released from the breeding program. Most of these cultivars are cream-fleshed and three constitute three of the five major cultivars grown commercially in South Africa, namely, Blesbok, Bosbok and Ribbok.
The year 1995 brought new beginning for the ARC sweet potato program when focus on the needs of small-scale farmers and from 2003 provitamin A biofortification for nutrition security were included (Laurie et al. 2015). Between 2003 and 2013, 14 sweet potato cultivars were released of which seven are β-carotene enriched sweet potato varieties and nine improved cream-fleshed sweet potato varieties with sweet taste and some drier texture. Currently the most popular informal market cultivars (Laurie et al. 2017) are Ndou and Monate (cream, dry), and β-carotene enriched Bophelo and the latest addition Khumo (meaning richness), which was released in 2020.
Development of new varieties is achieved through hybridisation and sourcing of seeds with desired traits, followed by selection of superior lines over 4-5 growing seasons whilst the number of evaluation sites increases and number of lines decreases. Taste testing for consumer acceptability is an integral part of evaluation. Recently an artificial inoculum screening method has been developed and promising lines has been screened in the glasshouse against virulent Fusarium wilt isolates (Mphela, 2018). At the last phase, off-station trials are conducted at research stations/on-farm to evaluate their stability and adaptability in varying climatic areas before release of superior varieties. The breeding programme relies on the comprehensive genebank collection of 360 accessions maintained
in vivo in glasshouses and/or
in vitro in tissue culture.
Commercial companies may enter into a Material Transfer Agreement with ARC to evaluate new breeding lines for the commercial industry on their premises. A catalogue is available on request.
Much attention were devoted to improving the nutritional value of local sweet potato accessions, linking similar efforts in Sub-Saharan Africa (Mwanga et al., 2020). Combining ability, heterosis and heritability of were determined for root protein, β-carotene, sugars and mineral composition (Naidoo et al. 2021) and aimed at improving protein content, NIRS models were developed for rapid quantification of protein content (Magwaza et al., 2016).
Cultivar development of sweet potato has, up to now, been largely phenotype-based selection. Being a partner in the European Union Horizon2022-2027 funded project "Roots-to-resilience", the ARC-VIMP project endeavours to screen selected sweet potato lines for drought resilience and to embark on incorporating genomics tools into applied breeding efforts for this crop to ultimately generate improved cultivars, leading to increased production under unfavourable abiotic conditions.
Contact: Dr Sunette Laurie and Ms Whelma Mphela
References:
Laurie S.M., Faber M., Adebola P., Belete A., 2015. Biofortification of sweet potato for food and nutrition security in South Africa. Food Research International 76: 962-970.
Laurie, S.M., Mtileni, M.M., Mphela, W.M., and Tjale, S.S. 2017. Performance of informal market sweet potato cultivars in on-farm trials in South Africa. Open Agriculture 2(1): 431–441 https://doi.org/10.1515/opag-2017-0047
Magwaza LS, Naidoo SIM, Laurie SM, Laing MD, Shimelis H. 2016. Development of NIRS models for rapid quantification of protein content in sweetpotato [Ipomoea batatas (L.) LAM]. LWT – Food Science and Technology 72: 63-70.
Mphela, W.M. 2019. Development of Fusarium wilt resistant lines in South African Sweetpotato [Ipomoea batatas (L.) Lam]. MSc (Agric) Plant Breeding, Department of Plant Sciences (Plant Breeding), University of the Free State
Mwanga, R.O.M., Swanckaert, J., da Silva Pereira, G., Andrade, M.I., Makunde, G., Gruneberg, W.J., Kreuze, J.F., David, M, De Beck, B, Carey, E., Ssali, R., Yencho, G.J., Utoblo, O., Gemenet, G.C., Otema, M., Yada, B., Chelangat, D.M., Oloka, O., Mtunda, K., Chiona, M., Koussao, S., Laurie, S.M., Campos, H., & Low, J.W. 2021. Breeding progress for vitamin A, iron and zinc biofortification, drought tolerance, and sweetpotato virus disease resistance in sweetpotato. Frontiers in Sustainable Food Systems doi: 10.3389/fsufs.2021.616674 (15 Mar 2021).
Naidoo, S.I.M., Laurie, S.M., Booyse, M., Mphela W.M., Makunde G.S., Shimelis, H., Laing, M.D. 2021. Combining ability, heterosis and heritability of sweetpotato root protein, β-carotene, sugars and mineral composition. Euphytica 217:109 https://doi.org/10.1007/s10681-021-02829-5.
Identification and genetic characterization of viruses of sweet potato
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Sweet potato is prone to virus infections, which are associated with substantial yield and quality loss. Recent research at the Agricultural Research Council (ARC) has shown that mixed infections of viruses have a detrimental effect on sweet potato production. (Read more...)
Nematodes
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The diversity in host range and the level of losses makes the root knot
nematode (Meloidogyne spp) in sweetpotato to be among the economically
important soilborne pathogens. (Read more...)
Insects
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Sweetpotato weevil, Cylas formicarius (F.) is known as the most important insect pests which, attack sweetpotato plants. (Read more...)
Sweet potato scheme and Genebank
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At Roodeplaat the ARC maintains the only disease-indexing collection (genebank) of sweet potato in South Africa. The ARC houses a comprehensive sweet potato genebank collection of 360 accessions maintained in vivo in glasshouses and/or in vitro in tissue culture. There are ongoing efforts on characterisation of these accessions e.g. based on agro-morphologically, protein content and genetic diversity (Laurie et al., 2020; Naidoo et al., 2020; Selaocoe et al., 2021).
Viruses are the most limiting factor in production of sweet potato causing considerable loss of yield and also influence the quality. Already in the 1960's, yield degeneration was experienced by commercial farmers to such extent that it was uneconomical to grow those sweet potato cultivars. Every year healthy material of popular cultivars is taken from the virus-tested stock plants in the glass house or in vitro collection for multiplication and sold to vine growers and producers in seedling trays (Laurie et al., 2016). These are planted in multiplication blocks and then cuttings from there are used to produce sweet potato. This limit the transmission of diseases to clean soils, reduces distribution of viruses causing yield loss and also ensures that the cultivars remains true to type. In this way the sweet potato industry in South Africa remains profitable. Annually approximately 20000 plantlets in seedling trays are produced.
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Vine growers list and Order form for sweet potato plantlets is available on request
Contact: Dr Sunette Laurie and Ms Zanele Noqobo.
References:
Laurie, S.M, Myeza, P. N., Mulabisana, M. J., Mabasa, K.G., Thompson, A., Greyling, R., Cloete, M. and Adebola, P.O. 2016. In-vitro propagation and disease testing as a means of producing healthy planting materials to support root and tuber crops production in South Africa. Acta Horticulturae 1113: 225-232 (Apr) ISHS 2016. DOI 0.17660/ActaHortic.2016.1113.34 XXIX IHC
Laurie, S.M., Naidoo, S.I.M., Magwaza, L., Shimelis, H., Laing, M.D. 2020. Assessment of the genetic diversity of sweetpotato germplasm collections for protein content. South African Journal of Botany 132: 132-139. https://doi.org/10.1016/j.sajb.2020.03.041
Naidoo, S.I.M., Laurie, S.M., Shimelis, H., Laing, M.D. 2020. Agro-morphological characterisation of local and international sweetpotato germplasm from the South African collection. South African Journal of Plant and Soil 37(4): 308–320. DOI: 10.1080/02571862.2020.1791983
Selaocoe, M.E., Adebola, P., Pillay M. and Laurie, S.M. 2019. Genetic diversity of South African sweetpotato germplasm using molecular markers. Journal of Crop Improvement 33(6):814-823. DOI: 10.1080/15427528.2019.1671930
Indigenous floriculture crops | Indigenous/traditional African vegetables | Potatoes | Genebanks | Biotechnology | Agro-processing | Commercial Vegetables
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