SUMMARY

In mixed infections of Grapevine virus A (GVA) and Grapevine virus B (GVB) in non-transgenic Nicotiana plants, one-sided phenotypic mixing (GVA coat protein encapsidating GVB RNA) was detected by immunocap-ture-RT-PCR, with a frequency ranging from 33 to 75%. Immuno-electron microscopy confirmed the presence of both capsid proteins in the same virus par-ticles. Heteroencapsidation took also place in R1 seedlings of transgenic Nicotiana lines expressing GVA or GVB coat proteins, when the plants were challenge-inoculated with the heterologous virus. Finally, whole virus particles were produced when an infectious but CP-defective GVB RNA transcript was inoculated bi-olistically as a DNA plasmid into Nicotiana plants trans-genically expressing GVB CP