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 aphids
- TSWV is vectored by thrips, especially the western flower thrips
- TMV is very easily spread mechanically on tools and fingers
- PepMV is mechanically transmitted, although seed transmission is possible
- TMV is occasionally transmitted via seed
Several of these viruses can infect other garden plants. CMV has a very wide range of hosts, not only among cucurbits. TMV also affects tobacco and potato. TSWV affects many plants in the tomato family (Solanaceae) and also gloxinias (Sinningia), arum lilies and dahlias.
PepMV was first detected in Europe in 1999. Although it is controlled by plant health regulations gardeners do not need to report suspected outbreaks, but should not save seed from affected plants for re-use. See the Defra Plant Health Portal for more information on symptoms.
A number of other non-indigenous viruses and viroids are a threat to tomato production in the UK. Details can be found in this Defra factsheet.