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 ge netic diversity among 42 Australian and five American field isolates o f the rust fungus Uromyces appendiculatus var. appendiculatus, pathoge nic on cultivated bean Phaseolus vulgaris. Phenetic analysis of polymo rphisms generated by 10 arbitrary decanucleotide primers indicated tha t the Australian isolates represented two background genotypes, A and B (17% band dissimilarity), with a third group (genotype AB) represent ing putative hybrids and recombinants between A and B. This confirms a previous restriction fragment length polymorphism and RAPD study carr ied out on a subset of 12 Australian isolates. The American isolates, of unknown homology to the Australian isolates prior to this investiga tion, were selected to represent the two major genetic groups determin ed previously using isozymic markers. RAPDs confirmed the isozymic gro upings and revealed that one group, represented by one American isolat e, clustered with the Australian isolates of genotype B. However, the other four American isolates formed a divergent cluster, designated ge notype C, that showed an average band dissimilarity of 45% compared wi th genotypes A and B. A graphic display of polymorphic RAPD bands was used to compare genomic components common to different genotype cluste rs. 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 re combination between progenitors of genotypes B and C. Although genotyp e C is commonly found in North America, its absence from the 42 Austra lian isolates suggests that it is either uncommon or has not yet been introduced to Australia. Results are discussed in relation to the evol ution and possible mechanisms of generation of current genotypes of U. appendiculatus.