MITOCHONDRIAL-DNA RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS IN-FIELD ISOLATES OF THE ASPERGILLUS-NIGER AGGREGATE

The mitochondrial DNAs (mtDNAs) and the ribosomal repeat unit (ribosom al DNA, rDNA) of black Aspergillus isolates collected in various parts of the world were examined. Wide-ranging mtDNA variation was observed in natural populations of the Aspergillus niger aggregate. Most isola tes were classifiable as A. niger or Aspergillus tubingensis according to their rDNA and mtDNA patterns. The mtDNA variation was distributed unevenly in the populations studied. The mtDNAs of most of the isolat es collected in Australia were of the A. tubingensis type, with an une xpectedly high degree of variation, while the rDNA of these isolates e xhibited the same A. tubingensis pattern as that of isolates from othe r locations. Some other local populations displayed very little polymo rphism in their mtDNA and rDNA. Hybridization experiments in which clo ned A. niger and Aspergillus nidulans mtDNA fragments were used reveal ed that the two main mtDNA groups corresponding to A, niger and A. tub ingensis are more distantly related than concluded earlier. Six of the 13 Brazilian isolates examined exhibited mtDNA and rDNA types differe nt from those of all the other strains and could not be classified int o the above species. Classical taxonomic examination of these strains is in progress.