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Discrimination Between Common and Necrotic Strains of Potato Virus Y by Denaturing Isoelectric Focusing. N. Watts, Postdoctoral fellow, Agriculture and Agri-Food Canada, Research Branch, Research Centre, P.O. Box 20280, Fredericton, New Brunswick E3B 4Z7; R. P. Singh, principal research scientist, Agriculture and Agri-Food Canada, Research Branch, Research Centre, P.O. Box 20280, Fredericton, New Brunswick E3B 4Z7. Phytopathology 84:991-994. Accepted for publication 29 June 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-991.

Purified virions from seven isolates of the common strain (PVY^O) and six isolates of the tobacco veinal necrotic strain (PVY^N) of potato virus Y were examined by denaturing carrier-ampholyte isoelectric focusing (CA-IEF). All gave a similar pattern of one major and either two or three minor bands. The pattern of all PVY^N isolates was identical and the coat protein was acidic (pI = 6.1 in all cases), whereas the PVY^O isolates could be divided into three distinct groups, all of which were more alkaline (pI = 6.8, 7.2, and 7.4). Isoelectric focusing followed by electroblotting and immunodetection showed the bands to be of viral origin. SDS-PAGE gave a single major band of 29.5 kDa in all cases. Isolation of virions from either potato or tobacco gave the same results. The isoelectric points of the coat proteins of 28 PVY isolates, calculated from published sequences, were significantly higher for isolates of PVY^O than for those of PVY^N. These findings suggest that CA-IEF may be used to discriminate between the common and necrotic strains of potato virus Y and that the PVY^N strain may be more homogeneous than the PVY^O strain.