DNA-FINGERPRINTING OF PERONOSPORA-PARASITICA, A BIOTROPHIC FUNGAL PATHOGEN OF CRUCIFERS

The fungus Peronospora parasitica (Pers. ex Fr.) Fr. is an obligate bi otroph infecting a wide range of host species in the family Cruciferae . Isolates from different hosts are morphologically similar, and patho types are usually distinguished on the basis of host range. Random Amp lified Polymorphic DNA (RAPD) fingerprints were generated from a range of P. parasitica isolates from different Brassica species. Reaction c onditions, in particular DNA template, primer and Mg2+ concentrations, were optimized to ensure that amplifications were reproducible. Possi ble artefacts arising through host plant DNA were assessed by includin g such DNA in control reactions. Confirmation that diagnostic RAPD ban ds were generated from fungal DNA was also obtained by Southern hybrid ization of a RAPD band to genomic fungal DNA. By screening 20 decamer primers, 2 were found to detect sufficient genetic variation to allow complete differentiation between pathotypes. These results illustrate the potential value of RAPDs for detecting polymorphisms between isola tes of a non-culturable plant pathogenic fungus.