Melampsora lini, the causal agent of rust disease on flax and linseed (Linum usitatissimum), also occurs on the indigenous Australian speciesLinum marginale. Forty-five isolates ofM.linicollected fromL.marginaleplants at 21 locations were tested for pathogenicity on 46 lines ofL.marginalethat originated from 22 sites spanning the same range (approximately 2000ensp;km) covered by the rust isolate collection sites. The results reveal the existence of extensive variation in both host and pathogen. Rust isolates originating from different sites possessed unique virulence patterns in all cases. Among the host lines, 21 different phenotypes were identified. Lines from six sites were susceptible to all isolates, but no line was resistant to all isolates. The results, together with those of a companion study, provide evidence of virulence-gene adaptation ofM.linito different host species and of adaptation on a broad geographic scale within a host species. The rust reaction data suggest that theNgene for resistance inL.usitatissimumalso occurs inL.marginale, but otherwise there is no evidence for commonality between the (presumptive) resistance genes inL.marginaleand those inL.usitatissimum.
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