Plant viruses are extremely minute infectious particles consisting a protein coat and a core of nucleic acid. They have no means of self-dispersal, but rely on various vectors (including humans) 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.
Viruses are frequently transmitted through propagated material but, depending on the virus, can also be transmitted via insect or mite vectors, pollen, mechanical transfer via contaminated hands and tools, or nematode vectors in the soil. Some viruses can be transmitted via seed, but generally these are a minority and therefore seed propagation is often a useful way to ensure virus free plant material.
CMV is vectored by several aphid species which feed on a broad range of plants and this contributes to spread of CMV 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.