Double Infection of Isolated Tobacco Mesophyll Protoplasts by Unrelated Plant Viruses

Isolated tobacco mesophyll protoplasts were inoculated in vitro with tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV) either as a mixture or one after another. Fluorescent antibody staining demonstrated that about 80% of protoplasts produced both viruses following mixed inoculation, and 70% after sequential inoculation. Neither synergism nor antagonism was apparent between TMV and CMV in the establishment of infection. Double infection of protoplasts occurred also with potato virus X (PVX) and TMV, or with PVX and CMV. Inoculation with a mixture of TMV, CMV and PVX caused infection of some protoplasts by all three viruses.