Putative subgroups of Verticillium albo-atrum distinguishable by PCR-based assays
Robb, J. | Moukhamedov, R. | Hu, X. | Platt, H. | Nazar, R.N.
DNA assays based on polymerase chain reaction (PCR) amplification of the 18-25S rDNA internal transcribed spacer (ITS) regions in genes encoding ribosomal RNA are being developed for the identification of Verticillium species in potato. Routine screening of fungal cultures, isolated from infected plant material or soil, using V. albo-atrum. V. dahliae or V. tricorpus-specific oligonucleotide primers, identified a potato Verticillium isolate which had been classified previously as V. albo-atrum using common taxonomic criteria, but responded negatively with all three standard PCR assays. The corresponding ITS regions in this unusual isolate were sequenced and found to be substantially different from the anticipated V. albo-atrum sequence but very similar to that of V. tricorpus. A closer examination of morphological features also revealed an unusual bundling of the dark mycelium. A diagnostic primer set was developed for this unusual isolate and used to screen other V. albo-atrum cultures from North America and Europe. The assays indicate that this variant is present on both continents. These results further illustrate the effectiveness of PCR-based diagnostics for Verticillium and suggest that the V. albo-atrum species should be divided into two subgroups.
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