DISTRIBUTION OF BEGOMOVIRUSES INFECTING CASSAVA IN AFRICA
H.K. Were, S. Winter, E. Maiss
Cassava mosaic disease (CMD) caused by cassava begomoviruses is the major constraint to cassava production in Africa. To gain an overview of the identities and distribution of viruses causing the disease, 230 leaf samples and 185 hardwood stem cuttings from major cassava growing countries in sub-Sahara Africa were collected and analyzed. Symptoms of diseases caused by different begomoviruses in cassava were indistinguishable, however, the most distinct and outstanding feature of Uganda variant cassava mosaic virus (UgV) infections was the huge reduction in tuber formation by the infected plants. Symptoms in Nicotiana benthamiana plants infected with an ACMV isolate from Kenya, ACMV-KE, could be distinguished from those induced by an ACMV isolate from Nigeria, ACMV-NG, as the former induced bright yellow blotches on the leaves of infected plants. N. benthamiana plants doubly infected with ACMV and UgV developed the severest symptoms. Serological and molecular analysis of the samples revealed that all three cassava begomoviruses were found in Western Kenya. All samples from the coastal province were infected with EACMV only and no other begomovirus was found in this area. Analysis of samples from other countries showed that ACMV was the only virus found in West Africa, except for EACMV in a few samples from Nigeria, Cameroon and Guinea. UgV was detected in samples from Uganda and Democratic Republic of the Congo (DRC). The movement of this virus and how it possibly displaces ACMV in cassava is discussed.