Phylogeography of Rice yellow mottle virus (RYMV) was reconstructed from the coat protein gene sequences of a selection of 173 isolates from the 14 countries of mainland Africa where the disease occurred and from the full sequences of 16 representative isolates. Genetic variation was linked to geographical distribution and not to host species as isolates from wild rice always clustered with isolates from cultivated rice of the same region. Genetic variation was not associated to agro-ecology, viral interference and insect vector species. Distinct RYMV lineages occurred in East, Central and West Africa, although the Central African lineage included isolates from Benin, Togo and Niger at the west, adjacent to countries of the West African lineage. Genetic subdivision at finer geographical scales was apparent within lineages of Central and West Africa, although less pronounced than in East Africa. Physical obstacles, but also habitat fragmentation, as exemplified by the small low-lying island of Pemba offshore Tanzania mainland, explained strain localization. Three new highly divergent strains were found in eastern Tanzania. By contrast, intensive surveys in Cote d'Ivoire and Guinea at the west of Africa did not reveal any new variant. Altogether, this supported the view that the Eastern Arc Mountains biodiversity hotspot was the centre of origin of RYMV and that the virus spread subsequently from east to west across Africa. In West Africa, specific strains occurred in the Inner Niger Delta and suggested it was a secondary centre of diversification. Processes for diversification and dispersion of RYMV are proposed.

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The major insect pests on rice in Tanzania are listed and described. They are from five orders (Coleoptera, Diptera, Hemiptera, Lepidoptera and Orthoptera) and are discussed as stem borers, stem and root feeders, and leaf and panicle feeders. This review puts together the hitherto fragmented information available on the distribution, host range, biology/life-cycle and ecology, and the management measures of the insect pests of rice. Areas for future research are also mentioned.

We report the complete nucleotide sequence of DNA-A of a begomovirus naturally infecting Jatropha curcas L. in Nigeria. Symptoms observed on infected plants were severe mosaic, mottling and blistering of leaves. The virus, which we provisionally name "jatropha mosaic Nigeria virus" (JMNV), has a monopartite genome of 2,779 to 2,789 nucleotides. Pairwise comparisons of DNA-A sequences showed that JMNV had maximum nucleotide sequence identity (72%) with a strain of tomato yellow leaf curl virus. Since there are widespread infections of jatropha in Nigeria showing similar symptoms as those investigated in the present study, JMNV may represent a significant threat to a promising bioenergy crop.

Rice yellow mottle virus genus Sobemovirus (RYMV) was first reported in Kenya in 1966. The disease caused by this virus is fast becoming a major limiting factor in the rice production in Africa and neighbouring islands. It is known to occur in eastern, western and southern African countries and, since very recently, in Central Africa. It is transmitted by insect vectors such as Chaectonema spp., Sesselia pusilla Gerst. and Trichispa sericea Guerin (all Coleoptera) and also by mechanical means. About six strains of the virus now exist. Yield losses caused by the virus range from 20 to 100%. Integrated pest management has been suggested to minimise damage caused by this disease to rice. This paper reviews the characteristics of the virus, symptomatology, host range, distribution, strains, transmission, vector dynamics and virus spread, the economic importance, and management strategies. The need of future research of RYMV is also highlighted.