V10 offers broader protection with two mild strains than with one single mild strain
Treating a plant with two mild strains of a virus offers broader protection against PepMV than if plants are treated with just one strain. This has been shown in an experiment with V10 in which a mild Pepino Mosaic Virus (PepMV) isolate inhibited the symptoms of aggressive virus isolates belonging to two different strains by less than 50%, whereas V10 inhibited the symptoms by 100%. In this case, yields from plants protected with V10 were 2.5 times higher than from plants protected with one mild strain.
Because the two aggressive strains (Ch2/EU) often occur together in a mixed infection, the use of mild strains that protect against both aggressive isolates is recommended. This is endorsed by EPPO, among others.
Read the article of EPPO (The European and Mediterranean Plant Protection Organization)
The earlier plants are treated with mild strains, the more fully they are protected
The earlier in its development a plant is treated, the better. However, the plant must be treated carefully so that the treatment does not impede its growth. Tomato plants can be treated from 2-3 weeks. Young plants are inoculated with V10, a product made up of two mild strains of the virus. Introducing a mild virus into a plant activates RNA silencing in the plant. RNA silencing is a process in which the plant protects itself against subsequent infections with similar viruses. A certain length of time is required before the plant can protect itself against pepino mosaic virus. After being treated with V10, there is a short period of time in which the plant needs to build up resistance. After this period, it can protect itself against aggressive isolates of the virus.
In summary, therefore, the earlier we inoculate a plant with a mild virus, the earlier the plant is protected. Moreover, young plants are also more susceptible to virus infection, so a mild virus spreads more rapidly through the whole plant at this stage.
Read the article for more information on the use of cross-protection in plants.