The role of the coat protein region in symptom formation on Physalis floridana varies between PVY strains

The Potato virus Y (PVY) cDNA full-length clone created by Jakab et al. [Jakab, G., Droz, E., Brigneti, G., Baulcombe, D., Malnoë, P., 1997. Infectious in vivo and in vitro transcripts from a full-length cDNA clone of PVY-N605, a Swiss necrotic isolate of potato virus Y. J. Gen. Virol. 78, 3141–3145] was stabilized by inserting three introns into putatively toxic genes. Using this clone, hybrid viruses were constructed by in vitro recombination. The PVY-N/NTN and PVY-N/O chimeras carried the 3′ end of NIb, the whole CP and 3′UTR region of PVY NTN and PVY O, respectively, in a PVY N genetic background. The clones proved to be stable after several passages by re-sequencing the exchanged region. Both hybrid viruses showed reduced infectivity in particle bombardment experiments, but they were suitable for further mechanical plant inoculation. In five of the six host plant species, inoculated with the two chimeras and three parental strains, the chimeras produced similar symptoms to those of PVY N. By contrast, Physalis floridana reacted with different pattern of symptoms. In this species, the symptoms caused by the N/O hybrid were similar to those of the 3′NIb-CP-donating PVY O strain, and not to those of the background (PVY N). The results suggest that symptom determinants may be different even between strains of the same virus species in a particular host.