Viruses are among the smallest pathogens infecting other living organisms. Plants are also susceptible to a large number of viruses that can cause serious diseases.

Viruses consist solely of a piece of genetic material (RNA or DNA) and a protein coat, or capsid. They therefore cannot survive independently and need other organisms to multiply and spread. Plant viruses replicate in plant cells and use insects (especially aphids and whitefly), mites, nematodes, soil fungi and even humans and our tools to move from one host to another. There are specific interactions between viruses and their vectors. Cucumber mosaic virus (CMV) is transmitted by aphids, for example, and tomato spotted wilt virus (TSWV) by thrips.

Therefore, controlling viral diseases not only entails starting with clean and certified plant material but also involves monitoring and controlling the transmitters (vectors) of plant viruses. Vigilance is essential, because new viral diseases can appear in plants when changes in populations of viruses and their vectors give rise to new situations.