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Survey for cassava brown streak disease revealed for the first time the presence of a molecular variant of Uganda cassava brown streak virus in Zambia

Rabson Mulenga: Zambia Agriculture Research Institute

<div>A diagnostic survey was conducted in July 2017 in Luapula and Northern provinces of Zambia to investigate the presence or absence of cassava brown streak disease (CBSD) and its associated viruses. A total of 29 cassava fields were visited during the survey and 92 symptomatic and 24 non-symptomatic cassava leaf samples were collected from 116 plants. Mean CBSD incidence varied across fields but averaged 32.3% while mean disease severity was 2.3 on a 1-5 rating scale. RT-PCR screening of all 116 samples with one generic and two species-specific primer pairs yielded DNA bands of the expected size with the generic and <em>Uganda cassava brown streak virus </em>(UCBSV)-specific primers in all symptomatic plants. All 24 non-symptomatic samples were negative for the virus and all samples tested negative with primers targeting <em>Cassava brown streak virus </em>(CBSV). The complete genome of a representative isolate of UCBSV (WP282) was determined to be 9,050 nucleotide (nt) in length, minus the polyA tail. A comparative analysis of this isolate with global virus isolates revealed its nature as a molecular variant of UCBSV sharing 94/96% maximum complete polyprotein nt/amino acid identities with isolates from Malawi (MF379362) and Tanzania (FJ039520). This is the first report of CBSD and UCBSV in Zambia thus expanding the geographical distribution of the disease and its associated virus and further reinforcing the need to strengthen 31 national and regional phytosanitary programs in Africa</div>

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