Antagonism and Synergism Characterize the Interactions between Four North American Potato Virus Y Strains

Potato virus Y (PVY) is one of the most important constraints to potato production worldwide. There is an increasing occurrence of recombinant PVY strains PVY NTN  and PVY N-Wi  and a decline in the incidence of PVY O , the predominant nonrecombinant strain. We hypothesized that this dynamic may be due to the ability of these recombinant strains to antagonize and/or outcompete PVY O . Thus, in this study, we sought to investigate interactions between these four PVY strains in  N. tabacum  as well as in potato tubers and foliage. Overall, our study showed that the nature of the interactions between these PVY strains is tissue and species dependent. Specifically, PVY NTN , the main causal agent of potato tuber necrotic ringspot disease (PTNRD), was shown to be highly adaptable to both hosts and to outcompete PVY O , especially in leaves of  N. tabacum  and potato. Furthermore, PVY N-Wi  was found to repress PVY O  in potato tubers but act synergistically in potato leaves. The foliage necrosis caused by PVY O  in cultivar ‘Ranger Russet’ was observed to be more severe in plants coinfected by PVY N-Wi  and PVY N:O , respectively, resulting in plant death. Strikingly, this PVY O -induced necrosis was observed to be suppressed by PVY NTN  in doubly infect potato plants and there were very low levels of the latter in potato foliage. Thus, aphid transmission of virus in plants infected by PVY NTN  and PVY O  will likely be inefficient, compared with tuber transmission. These interactions may, at least partially, explain the decreasing incidence of PVY O  in United States potato production regions. We also found that replication and cell-to-cell movement of these PVY strains in tubers at 4 ° C was similar to levels at ambient temperature. This is also epidemiologically important given that seed potatoes are routinely stored at low temperatures for use in the next crop. Thus, during storage, these viruses continue to replicate in seed tubers.