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Construction and Use of a Cloned cDNA Probe for the Detection of Plum Pox Virus in Plants. Christina Varveri, Station de Pathologie Végétale, Institut National de la Recherche Agronomique, Centre de Bordeaux, B.P. 131, 33140 Pont de la Maye, France; M. Ravelonandro, and J. Dunez. Station de Pathologie Végétale, Institut National de la Recherche Agronomique, Centre de Bordeaux, B.P. 131, 33140 Pont de la Maye, France. Phytopathology 77:1221-1224. Accepted for publication 18 December 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1221.

Complementary DNAs to plum pox virus (PPV) were cloned into Escherichia coli plasmid pUC9. Clones containing about 1 kb of the 3' region of PPV RNA were obtained. Subcloning of a 720-bp fragment lacking the 3' poly-A region into pBR322 provided a recombinant plasmid named pPPV9A. This plasmid was labeled by nick translation and used in dot-blot hybridization assays. As little as 100 pg of purified virus was detected. This is equivalent to about 5 pg of PPV RNA. The enzyme-linked immunosorbent assay (ELISA) applied to the same purified virus solution allowed the detection of about 1 ng of virus per assay and was therefore 10 times less sensitive. When the respective sensitivities of the two methods were compared with crude sap samples, molecular hybridization was again more sensitive as far as actual amounts of virus or of infected tissues were concerned. The usefulness of this technique for routine detection work is discussed.