Abstract

In a preliminary survey of genetic variability among 12 Australian isolates of Puccinia coronata f. sp. avenae Fraser and Led (Pca) collected from 1966 to 1993, two relatively diverse (< 76% similarity) clusters were found with selectively neutral DNA markers. Five US isolates included for comparison formed a third cluster, intermediate to the two clusters of Australian isolates. The two Australian sub-populations may have resulted from exotic introductions of genetically distinct isolates of Pca. Given that Pca does not undergo sexual recombination in Australia, these isolates may have acted as founding isolates from which new genotypes arose via mutation. Within the Australian isolates, three pairs of isolates that possessed identical DNA Amplification Fingerprints (DAF) or phenotypes were also identical or similar in virulence phenotype. The differences in pathogenicity observed within two of these pairs could have resulted from mutations to virulence for resistance genes present in Australian oat cultivars. A low overall correlation was found between pathogenic variability and variability in DAF banding pattern. This may be a reflection of host-directed selection of virulences independent of an isolate’s background genotype or an indication that mechanisms other than clonal propagation and random mutation contribute to genetic variability in Pca in Australia. The results obtained indicated that DNA-based marker systems are useful in revealing information about the genetic backgrounds of Australian Pca isolates, and provide an experimental basis for further detailed studies.