Proliferation of recombinant PVY strains in two potato producing regions of Canada, and symptom expression in 30 important potato varieties with different PVY strains

: Potato virus Y (PVY) exists as several strains with distinct symptomology and tuber yield effects in different potato varieties. Recently, new recombinant strains have proliferated and dominated local populations around the world. In this study, PVYO, PVYN:O, PVYN-Wi, and PVYNTN strains were tracked across Canada from 2014 to 2017, showing rapid evolution of populations away from the traditionally dominant PVYO to recombinants PVYN-Wi (western Canada) and PVYNTN (eastern Canada). Simultaneously, 30 potato varieties were inoculated with PVYO, PVYN:O, and PVYNTN in controlled greenhouse experiments. Foliar symptoms of primary (mechanical inoculation mimicking aphid infection) and secondary (tuber seedborne) infection were cataloged, and tuber yield measured. On average, and generally similar in primary and secondary infection, symptom expression and yield reduction were most severe with PVYO, followed by PVYN:O and PVYNTN. Strong mosaic symptoms were most commonly expressed with PVYO infection, and only seen with PVYN:O or PVYNTN in 15 and 3 varieties, respectively. Across variety-strain combinations, yield reduction was correlated with symptom severity, most strongly in PVYO-infected plants (e.g., AC Chaleur, Beljade, Envol, Norland, and Pacific Russet), and four varieties exhibited tuber necrotic ringspot disease with PVYNTN (AC Chaleur, Envol, Pacific Russet, and Yukon Gold).