Verticillium dahliae is an asexually reproducing soil-borne fungal pathogen that causes vascular wilt to hundreds of economically important crops globally.  Most host plants are dicots, while monocots are generally considered to be non-hosts since no disease has been reported on them in the field.  As a result, monocots (ex. cereal crops) have been used in crop rotations with host plants in efforts to manage the pathogen even though associations between V. dahliae and non-host plants have not been well explored.   
We had a unique opportunity to sample for V. dahliae in both symptomatic potato plants and asymptomatic oat plants at a farm in Schuylkill County, PA, where the two crops were in alternate rotation with each other in side-by-side fields.  We found that 30% of oat plants were colonized by V. dahliae.  One objective was to assess whether isolates collected from oats were genetically related to those collected from potatoes in neighboring fields.  Another objective was to investigate how these oat isolates relate to others collected from a wider diversity of host plants.  The newly collected isolates were compared to an extensive, global collection of V. dahliae associated with dozens of plant hosts, comprising a wide geographic range.   Using our large fungal culture collection and several highly polymorphic and reproducible molecular markers, we examined the genetic diversity among V. dahliae isolates.  Molecular markers used include the intergenic spacer (IGS) region and several other anonymous polymorphic sequences. 

Results/Conclusions

Maximum parsimony analysis revealed that the newly collected oat and potato isolates of V. dahliae grouped together and they were genetically similar to isolates that cause disease from other hosts.  Our preliminary sampling suggests that the potential role of non-hosts as alternative refuges for V. dahliae in the absence of host plants deserves further attention.