Dynamics of PVY strains in field grown potato: Impact of strain competition and ability to overcome host resistance mechanisms.

Potato virus Y (PVY) is the most important viral pathogen affecting potato crops worldwide. PVY can be transmitted non-persistently by aphids that do not colonize the host plant, resulting in a rapid acquisition and transmission of the virus between plants. PVY exists as a complex of strains that can be distinguished according to their pathogenicity, serology and genomic analysis. While virus incidence remains low in Scottish seed potato crops, PVY has become the increasingly prevalent virus. The monitoring of PVYN and PVYO serotypes has revealed a recent shift towards PVYN which now accounts for more than 90% of all PVY cases. A survey of the molecular diversity of PVYN isolates indicated that 80%-90% belong to the recombinant European (EU)-NTN group, with North-American (NA)-NTN and non-recombinant EU-N variants accounting for the remainder. The shift from non-recombinant to recombinant PVY isolates is a common trend observed worldwide. Surveys of a range of PVY isolates representing the main strain and phylogenetic groups suggest that PVY has the ability to overcome hypersensitive response-mediated resistance with significant differences between isolates of the same strain group. Contrastingly, genes mediating extreme resistance (Ryadg , Rysto ) provide efficient resistance to PVY transmission to progeny tubers. Transmission experiments in field conditions of PVY isolates representing the three main molecular groups (PVYO , PVYEU-NTN , PVYNA-NTN ) indicate that PVYEU-NTN has the highest transmission rate. Our results suggest that PVYEU-NTN isolate has a competitive advantage over PVYO and PVYNA-NTN isolates which is likely to be an important factor in shaping the evolution of viruses and the population dynamics of PVY.