Genome typing of southern African subgroup 1 geminiviruses.

The relatedness of subgroup 1 geminiviruses from a variety of naturally infected southern African graminaceous hosts was compared by DNA cross-hybridization, restriction endonuclease mapping and partial sequencing. Cross-hybridization divided the viruses into three groups: those closely related to maize streak virus (MSVs), and separate groups comprising a Panicum sp. virus (PanSV) and two sugarcane viruses (SSVs). Restriction mapping and comparisons, and phylogeny reconstructions from map data, showed that mapped and sequenced maize viruses were all highly similar; that two viruses of grasses and wheat bore limited resemblance to each other and to MSV, and that a mapped local and a sequenced Kenyan PanSV were similar, but that these and the two SSVs were dissimilar to each other and to all other subgroup 1 geminiviruses. The conclusions were: that maize viruses and the two viruses of wheat and grasses are probably strains of MSV; that two SSVs are only distantly related and distinct from MSVs; that the PanSVs are closely related to one another, but also distinct from other viruses; that all of the viruses in this study are part of a 'MSV-related sub-subgroup' of geminiviruses. Partial sequencing of cloned genomes reinforced conclusions drawn from other data, and indicated a definite relationship between the mapped and sequenced Panicum viruses. The implications of the results for taxonomic and epidemiological purposes are discussed.