Viruses Infecting Cassava in Kenya

A survey of cassava viruses was conducted in major cassava-growing regions of Kenya. A total of 185 leaf samples and 62 stem cuttings from plants with viral disease symptoms were collected and analyzed by biological, electron microscopy, enzyme-linked immunosorbent assay, and polymerase chain reaction. All samples from western Kenya had cassava begomoviruses (African cassava mosaic virus [ACMV], East African cassava mosaic virus [EACMV], and Uganda variant [EACMV-UG]) in either single or in mixed infection. However, all samples from the Coast region were infected with only EACMV, a begomovirus. In addition, 15 samples had mixed infections of EACMV and three other hitherto unidentified filamentous viruses. The viruses observed were 200, 500, 650, and 750 nm long, respectively. In addition to rod-shaped and some flexuous viruses, as seen in a crude sap preparation, pinwheels also were observed, indicating a possible association of some of the viruses with the Potyviridae family. The symptoms induced by these viruses in Nicotiana benthamiana were very severe and often caused about 50% death of the test plants. Back inoculation onto cassava resulted in 100% infections. This finding provides evidence that, other than begomoviruses that cause serious diseases of cassava in Africa, filamentous viruses also are present and, despite their limited distribution, they could reach local significance and, most probably, be as serious as begomoviruses. The implications of these findings are discussed and recommendations for future work suggested.