Genetic variability in Australian isolates of Puccinia coronata f. sp avenae assessed with molecular and pathogenicity markers

In a preliminary survey of genetic variability among 12 Australian isolates of Puccinia coronata f. sp. avenae Fraser and Led (Pca) collected from 196 6 to 1993, two relatively diverse (<76% similarity) clusters were found wit h selectively neutral DNA markers. Five US isolates included for comparison formed a third cluster, intermediate to the two clusters of Australian iso lates. The two Australian sub-populations may have resulted from exotic int roductions of genetically distinct isolates of Pca. Given that Pca does not undergo sexual recombination in Australia, these isolates may have acted a s 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 simil ar in virulence phenotype. The differences in pathogenicity observed within two of these pairs could have resulted from mutations to virulence for res istance genes present in Australian oat cultivars. A low overall correlatio n was found between pathogenic variability and variability in DAF banding p attern. This may be a reflection of host-directed selection of virulences i ndependent of an isolate's background genotype or an indication that mechan isms other than clonal propagation and random mutation contribute to geneti c 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 f or further detailed studies.