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Virus Strain Differences in Eradication of Potato Viruses X and S. Frances C. Mellor, Plant Pathologist, Canada Agriculture Research Station, 6660 N.W. Marine Drive, Vancouver 8, British Columbia; Richard Stace-Smith, Plant Pathologist, Canada Agriculture Research Station, 6660 N.W. Marine Drive, Vancouver 8, British Columbia. Phytopathology 60:1587-1590. Accepted for publication 2 June 1970. DOI: 10.1094/Phyto-60-1587.

Virus-free plants of 18 cultivars of potato (Solanum tuberosum) were developed by eradicating potato virus X (PVX) and potato virus S (PVS) from infected plants. The viruses were eradicated by heat treatment followed by nutrient culture of axillary buds 0.3-0.8 mm long. Potato virus X was usually eradicated more readily than PVS, but ease of eradication of both viruses varied with the source plant. Unusually heat-tolerant strains of PVX occurred in two cultivars; heat-tolerant strains of PVS in seven. For eradication of some of the most heat-tolerant strains of PVS, the size of the bud excised was of critical importance but, within the limited size range used, bud size usually had little influence on virus eradication. A treatment period of 6-8 weeks was optimal. Longer treatment periods actually increased the proportion of infected plantlets in some instances.