New Hosts of Cassava Mosaic Geminiviruses in Tanzania

Cassava mosaic disease (CMD), the most important disease of cassava in Africa, is caused by nine Cassava mosaic geminiviruses (CMGs), eight of which occur in Africa. CMGs are efficiently transmitted by the whitefly vector, Bemisia tabaci (Gennadius). However, little is known about the wild hosts of the CMGs in East Africa. This is an important shortcoming, since wild hosts may potentially play a significant role in the epidemiology of CMD. During May 2010, in a survey that covered about 50.000 km2 of north-western Tanzania, samples were collected from non-cassava crop plants or wild plants showing symptoms of mosaic. Following DNA isolation, we ran PCR reactions in an attempt to amplify near full-length DNA-A fragments of CMGs using standard universal primers (UniF/UniR). Amplicons of the expected length were produced for samples from the following host plants: Combretum confertum (Benth.) Laws., Arachis hypogaea L., Hibiscus cannabinus L., Leucaena leucocephala (Lam.) De Wit and Conyza sumatrensis (Retz.) E. Walker. The presence and abundance of adults and nymphs of the whitefly vector B. tabaci was also recorded for these plants. PCR using specific primers for African cassava mosaic virus (ACMV) and East African cassava mosaic virus (EACMV) allowed the identification of specific virus species infecting each of the host plants identified. Significantly, L. leucocephala and C. sumatrensis were each shown to be infected with both ACMV and EACMV. This study confirms the potentially important role that wild plants may play in the epidemiology of CMD in East Africa.