The population genetic structure of the rust fungus Melampsora lini as revealed by pathogenicity, isozyme and RFLP markers

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Abstract
Isozyme and RFLP markers were used to investigate genetic variation underlying the racial structure of populations of Melampsora lini occurring on the Australian endemic host species, Linum marginale. Previous studies of the pathogenicity of isolates occurring in a series of discrete but interconnected populations detected an overall structure characterized by linkage disequilibrium—indicative of a pathogen population reproducing asexually as a number of clonal lines (Burdon & Jarosz, 1992), Using samples from that study, we detected two isozyme multi‐locus phenotypes. One of these was restricted to two closely related races which appear to be examples of recent migrants into the area. Variation was also detected among and between races of the pathogen using two RFLP markers. Differences detected by one of these markers suggested the occurrence of a previous migrational event. Variation in the other marker detected two phenotypes within three common, widespread races. However, not all possible phenotypes were recovered, suggesting that the variation detected was not generated by recent sexual recombination.