Sweet potato is a popular food security crop in South Africa and also has considerable commercial value. Fusarium wilt (FW) caused by the fungal pathogen Fusarium oxysporum, is widespread in both commercial and smallholder sweet potato production areas in South Africa (Thompson et al. 2011) and has been reported worldwide. To date, only F. oxysporum f. sp. batatas has been identified as a pathogen associated with FW in South Africa (Thompson 2004). There is a thus a lack of information available on which other F. oxysporum formae speciales are associated with the Fusarium oxysporum species complex (FOSC) associated with FW on sweet potato in South Africa. Symptoms on sweet potato plants include wilting, leaf yellowing and browning of vascular tissues in the lower stems. Preliminary molecular identification of South African isolates of FW in sweet potato indicated there are other formae speciales besides F. oxysporum f. sp. batatas associated with the disease. As part of the project, isolates of the Fusarium oxysporum species complex were characterised using phylogenetic analysis. Fusarium isolates from diseased sweet potato plants were collected from symptomatic sweet potato plant material and/or soil samples in the Gauteng, Limpopo, North West, Mpumalanga and Western Cape Provinces of South Africa. Phylogenetic analyses of the TEF and β-tubulin gene regions showed two distinct genetic groupings, closely related to known formae speciales, including F. oxyporum f. sp. vanillae, F. oxyporum f. sp. lycoperscici, F. oxyporum f. sp. radicis-lycoperscici and F. oxyporum f. sp. batatas.
We further are involved in developing an integrated disease model for Fusarium wilt in sweet potato. Non-pathogenic F. oxysporum and Trichoderma species, known for their ability to reduce the incidence of Fusarium wilt in other crops, are screened for suppression in disease development. As the cost of chemicals are high as well as not environmental friendly, a disease management strategy involving biological control is a feasible alternative. These results will increase sustainable sweet potato production in areas in South Africa where the disease has devastated fields.
Contact: Dr Mariette Truter and Dr Rene Sutherland
Thompson, A.H. 2004. Fungal diseases. In: J.G. Niederwieser (Ed.). Guide to sweet potato production in South Africa Pretoria. ARC-Roodeplaat, Pretoria pp. 81-84.
Thompson, A.H., Narayanin, C.D., Smith, M.F. & Slabbert, M.M. 2011. A disease survey of Fusarium wilt and Alternaria blight on sweet potato in South Africa. Crop Protection 30: 1409-1413.
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