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Field status and dynamics of cassava mosaic disease in Zambia
Rabson Mulenga: Zambia Agriculture Research Institute; Patrick C. Chikoti: Zambia Agriculture Research Institute; James Legg: International Institute of Tropical Agriculture; Olufemi Alabi: Dept. of Plant Pathology & Microbiology, Texas A&M University
<div>The status of cassava mosaic disease in Zambia was determined during a country-wide survey conducted in 2014 in farmers’ fields in six major cassava-growing provinces (Luapula, Lusaka, Northern, Eastern, Western and Northwestern). A symptoms-based assessment of CMD was performed on 30 plants of a predominant variety counted along two diagonals to determine disease incidence and severity. Incidence was calculated as a percentage of symptomatic plants out of 30 counted plants while severity was rated using the standard 1 to 5 scale. Assessment of infection type (cutting- or whitefly-borne) was made and values for whitefly-borne infections were transformed into multiple infection units. The results indicated that mean CMD incidence was lowest in Northern (44%) and highest in Lusaka province (81%); averaged 57% across all six provinces. Mean CMD severity varied significantly (χ<sup>2</sup>= 249.8, df = 10, P < 0.001) among provinces ranging from 2.8 in Eastern to 3.0 in Northwestern province. Mean CMD incidence was higher for cassava landraces (~25 to 86%) than improved varieties (~32 to 60 %). Disease severity also varied between landraces (2.2 to 3.0) and improved varieties (2.7 to 2.8). Cutting-borne infections accounted for ~92% of CMD-affected plants relative to 8% for whitefly-borne infections. DNA fingerprinting of field survey samples revealed the occurrence of <i>African cassava mosaic virus</i>, <i>East African cassava mosaic virus</i> and <i>East African cassava mosaic Malawi virus</i> as single or mixed infections of different proportions. The results underscore the importance of clean plant materials for sustainable management of CMD in Zambia.</div>

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