COMPARISON OF NUCLEAR RIBOSOMAL DNA-SEQUENCES FROM ALTERNARIA SPECIESPATHOGENIC TO CRUCIFERS

The sequences coding for the nuclear 18s rRNA, 5.8s rRNA, and the inte rnal transcribed spacers (ITS1 and ITS2) were amplified by the polymer ase chain reaction and sequenced for one isolate each of Alternaria br assicae, A. brassicicola, A. raphani, A. alternata and Pleospora herba rum. The 5.8s rDNA sequences from the four Alternaria species were ide ntical and differed at only one base pair from that of P. herbarum. Th e internal transcribed spacer sequences, especially ITS1, were very va riable in both base composition and length. The 18s rDNA sequences wer e highly conserved, but enough variability was present to distinguish genera clearly. Phylogenetic analysis of the sequence data sets by bot h parsimony and maximum likelihood methods clearly separated genera an d species. AU of the Alternaria species were closely related. Pleospor a also appeared to be more closely related to Alternaria than to Lepto sphaeria.