Pollen tubes introduce Raspberry bushy dwarf virus into embryo sacs during fertilization processes.

We developed a fertilization method in which pollen tubes entered into embryo sacs without any need to contact surrounding female sporophytic cells by using Torenia fournieri (Torenia) plants under the condition of hindering movement of the virus from a stigma, which is the first infection site leading to systemic infection. When RBDV-infected Torenia pollen grains were used for the developed fertilization method, the virus was transmitted to the seeds by pollen tubes germinating from them. On the other hand, no seeds were infected with the virus when Torenia plants were pollinated with healthy Torenia pollen grains in combination with RBDV-infected raspberry pollen grains, which caused the virus infection in the stigma by penetration of their pollen tubes arrested in its style. Our results indicate that vertical transmission of RBDV by pollen occurs in the transport of the virus into embryo sacs by pollen tubes reaching the embryo sacs.