Coevolutionary patterns in theLinum marginale-Melampsora liniassociation at a continental scale

Abstract

Patterns in the distribution of virulence and resistance in the Linum marginale A. Cunn. ex. Planch – Melampsora lini (Ehrenb.) Lev. host–pathogen interaction that is endemic to Australia were examined in a 3500-km pancontinental comparison. Pathogen isolates derived from Western Australia were virulent on a much greater proportion of hosts from Western Australia than they were on a broad range of L. marginale lines collected throughout eastern Australia. In contrast, the physical isolation of Western Australia had no discernible effect on the distribution of the mean resistance of host lines. Within eastern Australia, isolates collected from Tasmania (isolated by 100 km of sea), southern New South Wales, and South Australia showed varying levels of response in terms of their virulence on host lines originating from the same or other eastern subregions. Finally, across the entire distribution of the pathogen, there was a significant effect of distance such that more distant pathogen isolates were generally less well adapted to host lines than more locally derived ones.Key words: coevolution, pathogen, resistance, rust, speciation, virulence.