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Molecular Plant Pathology

Detection of Andean Potato Virus X Isolates by Radioactive and Nonradioactive Nucleic Acid Spot Hybridization Tests. M. Querci,International Potato Center, Apartado 5969, Lima, Peru; L. F. Salazar, and E. N. Fernandez-Northcote. International Potato Center, Apartado 5969, Lima, Peru. Phytopathology 83:171-176. Accepted for publication 17 September 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-171.

A cDNA probe, pX61, prepared from the Andean potato virus X (PVX) cp strain was tested against a broad spectrum of Andean PVX isolates grouped in two serotypes: 1) the PVX^A Andean serotype detected only in Peru and Bolivia, which includes the cp and HB strains; and 2) the PVX^O common serotype, which contains isolates serologically similar to those occurring elsewhere in the world. In radioactive nucleic acid spot hybridization tests (R-NASH) of virus in crude sap using the ³²P-labeled RNA probe pX61, the PVX^A isolates showed stronger hybridization signals and a detectability usually from two to six threefold dilution steps higher than those shown for PVX^O isolates. The difference in the detectability of isolates from PVX^A and PVX^O serotypes was similar to that in nonradioactive nucleic acid spot hybridization tests (NR-NASH) with biotinylated DNA probe pX61. However, detectability in NR-NASH was lower than in R-NASH. When biotinylated DNA probes of pX61 (PVX^A-specific) and pPVX19 (PVX^O-specific), prepared from a British PVX isolate of the common European strain-group 3, were compared in NR-NASH, pPVX19 hybridized much more strongly to most isolates from the PVX^O serotype than to those from the PVX^A serotype. Several PVX^O isolates, mostly from Bolivia, reacted as weakly with pPVX19 as the PVX^A isolates. For R-NASH and NR-NASH tests, virus concentration in crude sap was checked by the double-antibody sandwich form of enzyme-linked immunosorbent assay, confirming that the differences obtained were not because of differences in virus concentration. These results were reconfirmed in R-NASH tests with DNA probes pX61 and pPVX19 using known concentrations of purified RNA from selected isolates. The differences shown between PVX^A and PVX^O isolates stress the importance of using the appropriate probes to detect PVX in breeding programs for resistance and quarantine purposes.