RANDOM AMPLIFIED POLYMORPHIC DNA REVEALS RELATIONSHIPS AMONG DIVERSE GENOTYPES IN AUSTRALIAN AND AMERICAN COLLECTIONS OF UROMYCES-APPENDICULATUS

Random amplified polymorphic DNA (RAPD) markers were used to assess genetic diversity among 42 Australian and five American field isolates of the rust fungus Uromyces appendiculatus var. appendiculatus, pathogenic on cultivated bean Phaseolus vulgaris. Phenetic analysis of polymorphisms generated by 10 arbitrary decanucleotide primers indicated that the Australian isolates represented two background genotypes, A and B (17% band dissimilarity), with a third group (genotype AB) representing putative hybrids and recombinants between A and B. This confirms a previous restriction fragment length polymorphism and RAPD study carried out on a subset of 12 Australian isolates. The American isolates, of unknown homology to the Australian isolates prior to this investigation, were selected to represent the two major genetic groups determined previously using isozymic markers. RAPDs confirmed the isozymic groupings and revealed that one group, represented by one American isolate, clustered with the Australian isolates of genotype B. However, the other four American isolates formed a divergent cluster, designated genotype C, that showed an average band dissimilarity of 45% compared with genotypes A and B. A graphic display of polymorphic RAPD bands was used to compare genomic components common to different genotype clusters. This revealed a group of RAPD markers common to genotypes C and A but absent from B. The data were consistent with A being derived by recombination between progenitors of genotypes B and C. Although genotype C is commonly found in North America, its absence from the 42 Australian isolates suggests that it is either uncommon or has not yet been introduced to Australia. Results are discussed in relation to the evolution and possible mechanisms of generation of current genotypes of U. appendiculatus.