THE POPULATION GENETIC-STRUCTURE OF THE RUST FUNGUS MELAMPSORA-LINI AS REVEALED BY PATHOGENICITY, ISOZYME AND RFLP MARKERS

Isozyme and RFLP markers were used to investigate genetic variation un derlying the racial structure of populations of Melampsora lini occurr ing on the Australian endemic host species, Linum marginale. Previous studies of the pathogenicity of isolates occurring in a series of disc rete but interconnected populations detected an overall structure char acterized by linkage disequilibrium-indicative of a pathogen populatio n reproducing asexually as a number of clonal lines (Burden and Jarosz , 1992). Using samples from that study, we detected two isozyme multi- locus phenotypes. One of these was restricted to two closely related r aces which appear to be examples of recent migrants into the area. Var iation was also detected among and between races of the pathogen using two RFLP markers. Differences detected by one of these markers sugges ted the occurrence of a previous migrational event. Variation in the e ther marker detected two phenotypes within three common, widespread ra ces. However, not all possible phenotypes were recovered, suggesting t hat the variation detected was not generated by recent sexual recombin ation.