Piche, L. M., Singh, R. P., Nie, X., and Gudmestad, N. C. 2004. Diversity among Potato virus Y isolates obtained from potatoes grown in the United States. Phytopathology 94:1368-1375. Potato field isolates (Solanum tuberosum) of Potato virus Y (PVY) collected from the midwestern and western United States were characterized using serological, molecular, and biological assays. PVY field isolates were grouped into the previously defined categories: PVY O , European PVY NTN , North American PVY NTN

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... , and PVY N:O recombinant and four previously undefined groups. Studies reported here agree with published reports from Europe and elsewhere in North America as PVY isolates capable of causing veinal necrosis in tobacco indicator plants appear in high frequency. In contrast to European experiences, PVY tuber necrosis isolates have a PVY O coat protein rather than that of PVY N . Several PVY N:O recombinant isolates induced potato tuber necrotic ringspot disease (PTNRD) in the highly susceptible potato cv. Yukon Gold. The PTNRD symptoms produced by these PVY N:O recombinants were atypical compared with lesions found on the same cultivar infected with either the European or North American PVY NTN isolates. These PVY N:O isolates produced a roughly circular, sunken necrotic lesion on the surface of the tuber instead of the typical external sunken ring pattern displayed by PVY NTN isolates. This study establishes the complex nature of PVY populations within the U.S. potato industry and clearly demonstrates the diverse nature of PVY in the United States.