Occurrence of South African cassava mosaic virus (SACMV) in Zimbabwe

Cassava is the most important crop grown in Africa. Significant losses to cassava production occur due to cassava mosaic disease (CMD), caused by various viruses of the genus Begomovirus (family Geminiviridae). During the 1990s a severe CMD pandemic spread through Uganda and into surrounding countries. The severity of the pandemic has been attributed to a synergistic interaction between African cassava mosaic virus (ACMV) and a recombinant strain of East African cassava mosaic virus (EACMV) known as the Uganda variant (EACMV-Ug; Zhou et al.,1997). Of the CMD-associated begomoviruses, EACMV and ACMV have the widest geographical distribution. South African cassava mosaic virus (SACMV) has only been reported from South Africa, Swaziland (Berry & Rey, 2001) and Madagascar.

Cuttings of cassava with CMD symptoms (Fig. 1) were collected from Muzarabani in northern Zimbabwe. A full-length clone of the DNA A component of the begomovirus associated with the disease was produced by PCR-mediated amplification with a pair of abutting primers spanning nucleotides 1652-1697 (virion-sense primer 5'-TCGGGAAGCTTTAAGGGACTGGTTCTTTTCC-3', complementary-sense primer 5'-GGAATAAGCTTGGGCTTTCAAGAATGCAACC-3'). These were designed to sequence obtained from PCR products produced with universal primers (Briddon & Markham, 1994) and contain a unique HindIII restriction endonuclease site. The full-length PCR product was cloned into pGEM-T Easy (Promega) according to the manufacturer's instructions. The sequence of this clone (GenBank accession AJ575560) is 2800 nucleotides in length and shows the arrangement of genes typical of the DNA A components of bipartite, Old World begomoviruses. The virus is closely related to viruses of the east African cluster of CMD-associated begomoviruses including EACMV from Tanzania (80% identity) and East African cassava mosaic Malawi virus (86.8%). It is most closely related to isolates of SACMV originating from Madagascar (SACMV-M12) and South Africa (95% and 93.9% identity, respectively), with which it clusters in phylogenetic analyses (Fig. 2).

We conclude that the isolate originating from Zimbabwe is a strain of SACMV which we designate SACMV-[Zimbabwe] (SACMV-[ZW]). The occurrence of this begomovirus species in Zimbabwe indicates that its geographical range extends further north, in mainland Africa, than previously realised. This suggests that there has been trade of cassava or movement of this virus between southern Africa and Madagascar.