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Specific Identification of Clavibacter michiganense subsp. sepedonicum by DNA-Hybridization Probes. I. E. Johansen, Danish Research Service for Plant and Soil Science, Lottenborgvej 2, DK-2800 Lyngby, Denmark; O. F. Rasmussen(2), and M. Heide(3). (2)Genetic Engineering Group, Building 227, The Technical University of Denmark, DK-2800 Lyngby, Denmark; (3)Danish Research Service for Plant and Soil Science, Lottenborgvej 2, DK-2800 Lyngby, Denmark. Phytopathology 79:1019-1023. Accepted for publication 14 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1019.

Three DNA sequences specific for the causal agent of bacterial ring rot of potatoes, Clavibacter michiganense subsp. sepedonicum, have been isolated from a library prepared from total DNA. One of the DNA probes is a PstI fragment of 2.6 kilobases (kb), which contains a region that is repeated numerous times. By using a probe labeled with ³²P-dCTP, 0.5 ng of total DNA could be detected. The same detection limit was obtained with a biotinylated probe, whereas a sulphonated probe was only about one-third as sensitive. The presence of large amounts of nonhomologous DNA affected the signal considerably, especially when the homologous DNA constituted less than 5%.