Variability in P1 gene redefines phylogenetic relationships among cassava brown streak viruses
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Variability in P1 gene redefines phylogenetic relationships among cassava brown streak viruses Willard Mbewe1,2* , Fred Tairo3, Peter Sseruwagi3, Joseph Ndunguru3, Siobain Duffy1, Ssetumba Mukasa2, Ibrahim Benesi4, Samar Sheat5, Marianne Koerbler5 and Stephan Winter5
Abstract Background: Cassava brown streak disease is emerging as the most important viral disease of cassava in Africa, and is consequently a threat to food security. Two distinct species of the genus Ipomovirus (family Potyviridae) cause the disease: Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). To understand the evolutionary relationships among the viruses, 64 nucleotide sequences from the variable P1 gene from major cassava producing areas of east and central-southern Africa were determined. Methods: We sequenced an amplicon of the P1 region of 31 isolates from Malawi and Tanzania. In addition to these, 33 previously reported sequences of virus isolates from Uganda, Kenya, Tanzania, Malawi and Mozambique were added to the analysis. Results: Phylogenetic analyses revealed three major P1 clades of Cassava brown streak viruses (CBSVs): in addition to a clade of most CBSV and a clade containing all UCBSV, a novel, intermediate clade of CBSV isolates which has been tentatively called CBSV-Tanzania (CBSV-TZ). Virus isolates of the distinctive CBSV-TZ had nucleotide identities as low as 63.2 and 63.7% with other members of CBSV and UCBSV respectively. Conclusions: Grouping of P1 gene sequences indicated for distinct sub-populations of CBSV, but not UCBSV. Representatives of all three clades were found in both Tanzania and Malawi. Keywords: Cassava brown streak viruses, Evolution, Diversity
Background Cassava (Manihot esculenta Crantz, Family: Euphorbiaceae) is an important staple food crop for over 800 million people across the globe [1]. Although cassava is known to be vulnerable to at least 20 different viruses, the two most economically damaging viral diseases in Africa are cassava mosaic disease and cassava brown streak disease (CBSD). The diseases have been associated with production losses worth more than US$1 billion every year [2]. Recent developments in cassava research have shown that CBSD is emerging as the most important viral disease of cassava in * Correspondence: [email protected] 1 Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901, USA 2 School of Agriculture and Environmental Science, Department of Agricultural Production, Makerere University, P. O. Box, 7062 Kampala, Uganda Full list of author information is available at the end of the article
Africa, and is consequently a threat to food security [1]. Two distinct species of the genus Ipomovirus (family Potyviridae), Cassava brown streak virus [3] and Ugandan cassava brown streak virus (UCBSV [4, 5]) cause the disease. In this paper, both viruses are collectively called CBSVs. The characteristic symptoms of CBSVs include typical ‘feathery’ chlorosis and yellow patch s
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