Plant viruses are extremely minute infectious particles consisting of 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.
Strawberry viruses are vectored to new hosts in a number of ways:
- The vectors of Strawberry mottle virus, Strawberry crinkle virus, Strawberry mild yellow edge virus and Strawberry vein banding virus are aphids
- Arabis mosaic virus, Tomato black ring virus and Raspberry ringspot virus are vectored by soil-inhabiting nematodes (eelworms) and by seed, and these can be easily transmitted between plants on tools and hands
- Strawberry necrotic shock virus is transmitted by thrips, and is also likely to be transmitted by seed, pollen and on tools and hands.
Some strawberry-infecting viruses, for example Arabis mosaic virus, Raspberry ringspot virus and Tomato black ring virus, infect a wider range of plants, including other fruit crops, which can act as sources of infection. Some of the others are restricted to strawberries (including wild strawberries) and close relatives such as raspberry.