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Cloned DNA Probes for Identification of Phytophthora parasitica. P. H. Goodwin, Department of Plant Pathology, University of California, Davis 95616; B. C. Kirkpatrick, and J. M. Duniway. Department of Plant Pathology, University of California, Davis 95616. Phytopathology 79:716-721. Accepted for publication 13 February 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-716.

Chromosomal DNA of Phytophthora parasitica, digested with HindIII and EcoRI, was ligated to pUC8 and used to transform Escherichia coli. Three recombinant plasmids were identified that hybridized to P. parasitica DNA but not to DNA of other Phytophthora species, healthy tomato roots, and Pythium species. DNA from all isolates of P. parasitica tested, including P. parasitica var. nicotianae, hybridized strongly with the probes. Southern blot hybridizations revealed that the probes hybridized to multiple restriction fragments, suggesting that the cloned sequences recognize repetitive DNA. There was no homology between the three cloned DNA fragments of P. parasitica. A non-radioactively labeled DNA probe, chemically modified by sulfonation, was as sensitive as a 32P-labeled DNA probe for the detection of purified P. parasitica DNA. These species-specific DNA probes provide a sensitive new tool for the identification of P. parasitica.