To provide more efficient conditions for a method, said method comprising using, as a medium,a plant, which belongs to a specific family such as Solanaceae and is graft-compatible with different families, and allowing a character regulator to function in a plant belonging to a different family. A plant virus for producing a character regulator is selected as a substance to be delivered and then the selected plant virus is delivered, through a plant which belongs to a specific family such as Solanaceae and is graft-compatible with different families, to a plant belonging to a different family.