USE OF SPECIFIC REPETITIVE SEQUENCES IN PERONOSPORA-TABACINA FOR THE EARLY DETECTION OF THE TOBACCO BLUE MOLD PATHOGEN

A 232-bp DNA sequence was obtained from random amplified polymorphic D NA of Peronospora tabacina, the blue mold pathogen of tobacco. This se quence had homology to P. tabacina DNA but not to DNA of other downy m ildew or oomycetous fungi tested. The fragment was determined to be pa rt of a repetitive DNA sequence that was ubiquitous in a worldwide col lection of P. tabacina. Oligonucleotides were designed for amplificati on of this sequence by polymerase chain reaction. The fragment was rel iably amplified with amounts of DNA (1-10 fg) that are less than that contained in a single P. tabacina sporangiospore. Use of this techniqu e enabled the detection of P. tabacina DNA directly in local lesions, systemic vascular infections, and other infected parts of tobacco plan ts. The use of spore traps followed by amplification of this fragment facilitated the prediction of a local disease epidemic. Use of this hi ghly specific and reliable detection method could prove valuable for r egulatory agencies and for epidemiological and etiological studies.