Use of Specific Repetitive Sequences inPeronospora tabacinafor the Early Detection of the Tobacco Blue Mold Pathogen

A 232-bp DNA sequence was obtained from random amplified polymorphic DNA of Peronospora tabacina, the blue mold pathogen of tobacco. This sequence had homology to P. tabacina DNA but not to DNA of other downy mildew or oomycetous fungi tested. The fragment was determined to be part of a repetitive DNA sequence that was ubiquitous in a worldwide collection of P. tabacina. Oligonucleotides were designed for amplification of this sequence by polymerase chain reaction. The fragment was reliably amplified with amounts of DNA (1-10 fg) that are less than that contained in a single P. tabacina sporangiospore. Use of this technique enabled the detection of P. tabacina DNA directly in local lesions, systemic vascular infections, and other infected parts of tobacco plants [...]