First report of the occurrence of East African cassava mosaic virusUganda (EACMVUG) in Angola

Abstract

Cassava mosaic disease (CMD) is the major production constraint on cassava ( Manihot esculenta ) in Angola. Previous reports derived from single samples recorded the presence of African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) in Angola. Regional CMD monitoring initiatives have predicted the spread into northern Angola of EACMV-Uganda (-UG), the unusually virulent (aggressive) recombinant strain associated with the African CMD pandemic (Legg et al ., 2006). In view of this threat, an assessment survey was conducted in north and central Angola in April 2008. Eighteen cassava fields were sampled in Bengo, Cuanza Norte, Malanje and Uige Provinces. Moderate to severe CMD symptoms were observed in most fields. Sixty-three of 65 samples obtained from these fields tested positive in TAS-ELISA using monoclonal antibody SCR 20. PCR was performed using primer pairs previously described for the specific identification of ACMV, EACMV, EACMV-UG, East African cassava mosaic Cameroon virus (EACMCV) and Indian cassava mosaic virus (ICMV) (Ogbe et al ., 2003), East African cassava mosaic Malawi virus (EACMMV) (Zhou et al ., 1998), East African cassava mosaic Zanzibar virus (EACMZV) (Were et al ., 2004) and South African cassava mosaic virus (SACMV) in mixed infections. This revealed the occurrence of ACMV, EACMV and EACMV-UG, but not EACMZV, EACMMV, SACMV or ICMV. Single infections of ACMV and EACMV were detected in 32·3 and 9% of samples, respectively. Mixed infections of ACMV with EACMV, EACMV with EACMV-UG and all three viruses were detected in 35·3, 1·5 and 16·9% of samples, respectively. ACMV, detected in 84·6% of samples, was the predominant species, followed by EACMV (63%) and EACMV-UG (18·5%). Significantly, EACMV-UG occurred most frequently in the northernmost part of the surveyed area (Uige Province) immediately to the south of the Bas Congo region of the Democratic Republic of Congo, already known to be affected by the pandemic. These findings significantly broaden the known geographical extent of the CMD pandemic and draw attention to the urgent need for the large-scale deployment of resistant cassava varieties, which have been used to reduce losses in pandemic-affected regions of East Africa.