Differential Spread of Potato virus Y (PVY) Strains O, N:O and NTN in the Field: Implications for the Rise of Recombinant PVY Strains in New Brunswick, Canada

Potato virus Y (PVY) is a major cause of yield and quality loss in potato crops worldwide. Recently, populations of PVY strains have shifted dramatically toward recombinant strains such as PVY NTN and PVY N:O . A 2010 to 2016 survey of PVY strains in commercial fields of New Brunswick (NB), Canada, and five field trials tracking PVY spread in NB and Manitoba, were conducted to study the current status of PVY strains and their relative rates of spread. In NB, PVY O dropped from 82% of infections in 2010 to 14% in 2016, replaced mostly by PVY NTN (64%) and PVY N:O (22%).In field trials with Russet Burbank and Gold rush varieties, PVY NTN spread most effectively compared to PVY N:O and PVY O . Strain-specific PVY spread varied with the potato variety, possibly due to selective PVY O resistance in Goldrush, mostly expressed at the plant-to-plant transmission level with little difference in transduction to tubers in infected plants. Relevance of in-field differences in spread of strains to changes in regional PVY populations, and potential mechanisms responsible, are discussed.