This proposal will identify, clone and sequence the Gemini viruses which are collectively called African cassava mosaic disease (ACMD) and Indian cassava mosaic disease (ICMD). These virus clones will be used to screen cassava germless, used in national breeding for resistance. Methods of inoculation, such as ballistic gun, agro inoculation and pin inoculation will be compared and the most suitable screening technology transferred to breeders in Africa. The epidemiology of ACMD will be studied both in the field and through laboratory tests on the cassava genotypes. The cloned genomes of viruses will be used to determine gene function and the requirement for infection of cassava. The data obtain will be used to devise novel control measures which will be tested in the laboratory. All breeding material will be rated for virus resistance against all virus clones by ballistic mechanical inoculation.