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Prevalence of maize-infecting potyviruses and maize chlorotic mottle virus in the United Republic of Tanzania during 2016-2017 growing seasons

Deogracious Protas Massawe: The Ohio State University

<div>Viruses in the genus <em>Potyvirus</em> (potyviruses) cause Maize lethal necrosis (MLN) when co-infected with maize chlorotic mottle viru<em>s</em> (MCMV). MLN causes up to 100% yield loss, threatening food security in East Africa where maize is a staple crop. To assess virus prevalence, surveys were conducted in 2016 and 2017 in 11 regions located in five agro-ecological zones: Lake (Mara and Mwanza), Northern Highlands (Kilimanjaro, Arusha and Manyara), Coastal (Tanga, Pwani and Morogoro), Central (Dodoma) and Southern Highlands (Iringa and Songwe). For each of 78 fields, 10 samples were collected on a transect and analyzed by ELISA using generic potyvirus and MCMV antisera. Of 780 samples, 338 (43.3%) tested positive for potyviruses and 176 (22.6%) for MCMV. Prevalence of potyviruses was 43% (n=70), 47.1% (n= 170), 46.9% (n=390), 37.5% (n=40), and 27.3% (n=110) in Lake, Northern Highlands, Coastal, Central, and Southern Highland zones, respectively (listed north to south). In the same samples, MCMV showed a strong north to south gradient as expected for emergence from the north, with 40%, 35.9%, 20.5%, 10.0%, and 2.7% detection in the same zones. Other viruses were also identified, including a polerovirus previously described in China, detected at 37/78 location across zones by RT-PCR. Our study reveals high prevalence of potyviruses across Tanzania’s maize growing zones, whereas MCMV shows a gradient that may rapidly shift with virus emergence or be responsive to management.</div>