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Incidence of Potato Virus X in Foundation and Certified Seed of Seven Cultivars. S. M. Tavantzis, Assistant Professor, Department of Botany and Plant Pathology, University of Maine, Orono 04469. S. G. Southard, Research Assistant, Department of Botany and Plant Pathology, University of Maine, Orono 04469. Plant Dis. 67:959-961. Accepted for publication 16 February 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-959.

Differences in levels of infection of potato virus X (PVX) between foundation and commercial seed of seven cultivars were determined by testing 4,315 tubers with enzyme-linked immunosorbent assay. Atlantic, BelRus, Katahdin, Kennebec, Ontario, Russet Burbank, and Superior were the cultivars included in the study. Commercial seed of all cultivars except Kennebec had a significantly (P = 0.05) higher percent infection and titer than those of foundation seed. Kennebec was the only cultivar for which virus incidence or titer did not increase when grown commercially. Incidence of PVX in foundation seed of cultivar Ontario, which was freed from the virus by heat treatment and meristem-tip culture, remained as low as 1% for 7 yr after treatment. Some growers were able to maintain percent infection and titer of PVX as low as that of the foundation seed released to them even after 3 yr or more of propagation. In contrast, seed of the same cultivar suffered high levels of PVX contamination when grown by other growers operating at the same location.