Cassava geminiviruses occur in all cassava growing areas of Africa and are considered to be the most damaging
vector-borne plant pathogens. At least seven species of these viruses have been identified. We investigated
genetic variation in East African cassava mosaic cassava Cameroon virus (EACMCV) from naturally infected
cassava and from experimentally infected Nicotiana benthamiana. Results showed that the populations of
EACMCV in cassava and in N. benthamiana were genetically heterogeneous. Mutation frequencies in the order
of 10−4
, comparable to that reported for plant RNA viruses, were observed in both hosts. We also produced an
EACMCV mutant that induces reversion and second site mutations, thus suggesting that a high mutation
frequency facilitates the maintenance of genome structure and function. This is direct experimental evidence
showing that cassava geminiviruses exhibit a high mutation frequency and that a single clone quickly
transforms into a collection of mutant sequences upon introduction into the host.