Molecular characterization of the host-adapted pathogen Verticillium longisporum on the basis of a group-I intron found in the nuclear SSU-rRNA gene

Verticillium wilt of oilseed rape is caused by the host-adapted pathogen Ve rticillium longisporum comb. nov. With one set of nuclear SSU-rRNA gene pri mers, a PCR amplification product of ca. 2.5 kb was generated from all isol ates of V. longisporum tested (36 from Europe, Japan, and USA), with the ex ception of two recombinant isolates. On the contrary, all the other phytopa thogenic and non-phytopathogenic species of Verticillium tested (18 species , 46 isolates), with the exception of one isolate of V. lecanii and two of Cordyceps sp., generated a product of cn. 1.65 kb. Sequence analysis of the SSU-rRNA gene of two typical isolates of V. longisporum (wild radish, Japa n, and oilseed rape, Germany) revealed that this dimorphism was due to the presence of an identical 839-bp intron located in a highly conserved insert ion position (nt 1165 of Saccharomyces cerevisiae). The intron sequence was classified as group-I intron on the basis of conserved sequence and second ary structural elements. Primers designed from the 839-bp intron sequence a mplified only the V. longisporum. Phylogenetic analysis based on SSU-rDNA s equences showed that V. longisporum was closely related to the genera of ot her filamentous Ascomycetes with fruiting bodies.