Plant viruses share many of the characteristics of those that infect animals, though they do not cross infect (plant viruses only infect plants). Viruses are extremely minute and consist of a protein coat and a core of nucleic acid. They have no means of self-dispersal, but rely on various vectors to transmit them from infected to healthy plants. Once viruses penetrate into the plant cells they take over the cells’ nucleic acid and protein synthesis systems and hijack them to produce more virus. They then require another vector to feed on the infected tissue and carry them to a new host.
CMV is vectored by several aphid species which feed on a broad range of plants and this contributes to the very wide host range of this virus.
The ‘cucumber’ in its name only reflects the fact that cucumber happened to be the plant from which it was first described. In fact its host range is extremely wide among vegetables, flowers and some weeds, though fruit crops are rarely attacked. In some weeds the virus produces no symptoms, but these weeds can still act as a source of infection.
CMV is occasionally transmitted through seed in around 20 plant species.