The coat protein (CP) gene of the potato virus Y (PVY) strain N605 has been cloned into a plant binary expression vector and introduced into the potato variety Bintje. The transformed lines, Bt6, that contained two copies of the CP gene showed complete resistance to the homologous strain PVY-N605 and a good resistance to the related strain PVY-O803 in the greenhouse. The good resistance of Bt6 to primary and secondary infections by PVY was confirmed in two successive field tests where the virus was transmitted by its natural aphid vector.

Potato plants transgenic for the coat protein (CP) gene of Potato virus Y strain N (PVY(N)) were examined for the accumulation of the transgenic PVY(N) CP. The protein remained undetectable in healthy plants of lines Bt6 and Bt10 that are completely or partially resistant to this virus, but accumulated when the plants were infected by a related strain, PVY(O). One possible explanation was that the transgenic CP is stabilized by integration into the capsid of the infecting virus. To investigate this, virus particles originating from these plants were examined by immuno-electron microscopy. Heterologous encapsidation was observed between the infecting PVY(O) virus and the transgenic PVY(N) CP. These results have implications for the understanding of the mechanism of CP-mediated protection and assessing its impact on agricultural ecosystems.