Genetic Diversity of Potato virus Y in Potato Production Areas in Northeast China.

In 2011-2014, ELISA or nucleic acid spot hybridization (NASH) testing for common potato viruses or Potato spindle tuber viroid (PSTVd) was performed on 500 leaf samples collected in potato fields in the northeast provinces Heilongjiang and Inner Mongolia, China. The results revealed that 38.4% (Heilongjiang) and 27.7% (Inner Mongolia) were positive for Potato virus Y (PVY). To unveil the strain composition and population structure of PVY in the region, the multiplex RT-PCR described by Chikh-Ali et al. was performed on all of the ELISA-PVY-positive samples. Of the 158 samples whose PVY strain scenarios could be determined, PVY-SYR-II and PVY were the most abundant strains, occurring in 58.9 and 47.5% samples, followed by PVY-SYR-I (31.0%), PVY (19.6%), Eu-PVY (7.6%), NA-PVY (1.3%), and PVY (0.6%). In the 84 single-strain-infected samples, PVY accounted for 41.7%, PVY-SYR-II for 40.5%, PVY-SYR-I for 14.3%, and PVY and Eu-PVY for 3.6% each. Seven isolates representing PVY-SYR-I (HLJ-6-1 and HLJ-9-4), PVY-SYR-II (INM-W-369-12 and SC-1-1-2), PVY (HLJ-30-2), and PVY (HLJ-BDH-2 and HLJ-C-429) were sequenced and analyzed molecularly. Whereas the sequence identities for isolates belonging to the same strain group were >98.5%, they fell for isolates belonging to different strain groups to 92.7-98.1% at the genome level and 96.1-98.4% at the polyprotein level. Interestingly, the exact location of the recombination events varied among isolates within a strain group. Phylogenetic analysis of all 42 full length PVY sequences from China indicated that most clustered to various recombinant groups, despite the fact that the PVY isolates were isolated from at least five host species. Pathological analysis of four isolates representing PVY, PVY, PVY-SYR-I, and PVY-SYR-II revealed that the PVY-SYR-II isolate incited the most severe symptoms on potato cultivar Kexin 13, followed by PVY-SYR-I, PVY and PVY. The PVY-SYR-I and PVY-SYR-II isolates also caused necrotic ringspots on the tubers of Kexin 13, indicating their ability to induce the potato tuber necrotic ringspot disease in potato.