Abstract
Potato virus Y (PVY) exists as a complex of virus strains, with many recombinants exchangingthe segments of their genomes. This high genetic diversity of the virus ensured its success in
overcoming multiple resistance genes present in commercial potato cultivars. In this work, I
investigated the geographic prevalence of PVY strains in potato crops in three countries across the
globe, in Mexico, South Korea, and Australia. The strain typing of PVY-positive samples collected on
FTA cards, was conducted by molecular typing with RT-PCR, and by whole genome sequencing. In
all three cases the PVY strain population was dominated by the tuber necrotic strain PVYNTN. I also
investigated availability of new sources of resistance in commercial potato cultivars, screening 236
progeny of a cross between ‘Yukon Gem’ and ‘Russet Norkotah’ with six strains of PVY. Two new
types of resistance were identified segregating as recessive genes: 1) resistance blocking replication
and/or cell-to-cell movement in inoculated potato leaves; and 2) resistance blocking systemic spread
of the virus. Segregation in progenies was close to 1:5 which suggested presence of four recessive
alleles in ‘Yukon Gem’ and two recessive alleles in ‘Russet Norkotah’. These new resistance alleles
were found strain-specific. Most of the lines exhibiting recessive resistance, conferred resistance to
non-recombinant and only some recombinant strains. Two strains, PVYNTN and PVYN-Wi, were able to
infect most of the resistant progeny lines. These results may explain the prevalence of these two
recombinants in potato production areas in the world.