SEQUENCES OF THE INTERNAL TRANSCRIBED SPACERS OF THE RIBOSOMAL-RNA GENES AND RELATIONSHIPS BETWEEN ISOLATES OF VERTICILLIUM-ALBOATRUM AND V-DAHLIAE

The sequences of the internal transcribed spacers (ITS) 1 and 2 of the rRNA genes of 38 Verticillium alboatrum and V. dahliae isolates have been determined. The isolates represented RFLP groups of both species, V. dahliae vegetative compatibility groups and pathotypes, and V. alboatrum 'group 2' (the majority of the V. alboatrum isolates studied were in 'group 1'). The ITS sequences of a single V. tricorpus isolate were also determined. RFLP groups L and NL of V. alboatrum were distinct, with a maximum of three nucleotide differences between any isolate. Most haploid V. dahliae isolates were identical and separated from most L/NL V. alboatrum isolates by differences at five or six positions. A few haploid V. dahliae isolates, not forming any obvious grouping, differed from the majority, each at a single position. Diploid isolates of V. dahliae were identical but only one nucleotide difference separated them from some RFLP group L V. alboatrum isolates. At least six differences separated the diploid isolates of V. dahliae from the haploid ones. The 'group 2' V. alboatrum isolates were more distantly related to 'group 1' isolates (at least 17 positions different) than was V. tricorpus. The possibility of defining specific primers for use in PCR to discriminate species and subspecific groups is discussed.