ABSTRACT
Viruses belonging to this group are called Geminiviruses because they have unique, paired or twinned particles about 18 × 30 nm. They are also unique in being the only group of plant viruses known to possess circular, single-stranded DNA genomes which in at least some cases are bipartite. A number of plant diseases suspected of being caused by viruses and transmitted by whiteflies and leafhoppers were studied for many years without the causal agents being identified. Most purified preparations of Geminiviruses contain predominantly geminate particles about 18 × 30 nm with varying numbers of polyhedral particles about 18 nm in diameter. In all the cases studied, Geminivirus particles accumulate in the nuclei of infected cells. However, there are some instances where particles have also been observed in the cytoplasm. The particles of most Geminiviruses are confined to phloem cells, but some also appear to invade other tissues.
