Molecular variation and restriction fragment length polymorphisms (RFLPs) within and between six species of Verticillium

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Molecular variation within and between six species belonging to the fungal genus Verticillium has been examined, either by direct visualization of strongly fluorescing bands in DNA digests or by probing Southern blots with rDNA, mtDNA or random genomic clones derived from an isolate of V. albo-atrum . The two main plant pathogenic species studied, V. albo-atrum and V. dahliae , could be differentiated from each other and from the other four species by the direct visualization approach, although the bands were not always easily seen against the background smear of single or low copy number fragments. Variation was also revealed by probing with rDNA or mtDNA but this variation was generally not correlated with identified interspecific or intraspecific taxonomic groupings. When Southern blots were probed with random genomic clones, all isolates of V. albo-atrum originating from lucerne were clearly differentiated from all other isolates of this species tested which originated from a range of other hosts. There was, however, little variation within these two groups of V. albo-atrum isolates. V. dahliae was clearly differentiated from V. albo-atrum by probing with random genomic clones and considerable variation within this species was evident. Only a few other taxon-specific polymorphisms were identified when using the limited set of probes tested but others may be located when more probes have been examined. The location of genes involved in important attributes such as pathogenicity will require the construction of linkage maps of molecular markers and genes of interest. The results suggest that for the analysis of V. albo-atrum the most useful parasexual cross would be between a lucerne and a non-lucerne isolate and that for the analysis of V. dahliae sufficiently disparate pairs of isolates exist.