G. Tadu1, S. Winter2*, A.M.A. Gadelseed3 and G.A. Dafalla3
1 Department of Horticulture Agricultural Research and Technology Corporation (ARTC) Wad Medani, Sudan
2 DSMZ Plant Virus Division, c/o BBA, Messeweg 11-12, 38104 Braunschweig, Germany
3 Plant Pathology Center, University of Gezira, Wad Medani, Sudan
Accepted: 07 Jul 2005
Cassava mosaic disease (CMD) caused by whitefly-transmitted begomoviruses has a dramatic impact on cassava production in Africa. A severe CMD epidemic has been caused by a recombinant strain of East African cassava mosaic virus (EACMV-UG), which has been spreading steadily from north-central Uganda into East and Central Africa. This virus presents a significant threat to cassava cultivation on the continent. EACMV-UG, in mixed infection with African cassava mosaic virus (ACMV), leads to severe disease symptoms (Gibson et al., 1996), the decline of the crop and often results in complete loss of harvestable roots. Various distinct begomoviruses implicated in CMD have been reported from significant cassava growing regions in Africa (Fodong et al., 2000; Were et al., 2004; Ariyo et al., 2005) revealing a complex virus situation. Some of these begomoviruses cause severe disease symptoms in cassava. However, only in mixed infections of the recombinant strain EACMV-UG and ACMV has an epidemiological significance been demonstrated.
Accordingly, a virus survey was conducted in 2002 in the major cassava growing regions in southern Sudan. Leaf samples were taken and stem cuttings established in the field at the Agricultural Research and Technology Corporation, ARTC, Wad Medani, Sudan. Total DNA extracts from leaves were subjected to differential PCR using specific primers for all ACMV and EACMV species and strains defined to date (Ariyo et al., 2005). Of 14 samples with conspicuous CMD symptoms, 13 contained the severe form of the recombinant EACMV-UG strain. Using several infected cassava samples, this finding was confirmed by sequence analysis of PCR amplicons obtained from DNA A genome fragments (rep gene, intergenic region and coat protein gene). ACMV was found in one sample as a single virus infection and in two other samples in a mixed infection with EACMV-UG.
The detection of EACMV-UG in almost all of the samples tested provides evidence for the potential epidemiological significance of this virus in the occurrence of CMD in southern Sudan.
Ariyo OA, Koerbler M, Dixon AGO, Winter S, 2005. Molecular Variability and Distribution of Cassava Mosaic Begomoviruses in Nigeria. Journal of Phytopathology 153, 226-231.
Fondong VN, Pita JS, Rey ME, de Kochko A, Beachy RN, Fauquet CM, 2000. Evidence of synergism between African cassava mosaic virus and a new double-recombinant geminivirus infecting cassava in Cameroon. Journal of General Virology 81, 287-297.
Gibson RW, Legg JP, Otim-Nape GW, 1996. Unusually severe symptoms are a characteristic of the current epidemic of mosaic virus disease of cassava in Uganda. Annals of Applied Biology 128, 479-490.
Were HK, Winter S, Maiss E, 2004. Occurrence and distribution of cassava begomoviruses in Kenya. Annals of Applied Biology 145, 175-184.
©2005 The Authors