Pollination is an essential step in the reproduction of flowering plants and is also crucial in agriculture in regard to fruit development, seed output, and the creation of new varieties of plants. However, at least 18 viruses can infect the mother plant through the fertilized flower (horizontal transmission by pollen). Horizontal transmission by pollen is epidemiologically important for viruses infecting perennial crops, since pollen grains from infected trees continue to be scattered every year. The mechanism how pollination with virus-infected pollen grains causes systemic viral infection to healthy plants has been unknown since the first report of horizontal transmission by pollen in 1918.
Via Ed Rybicki