Vegetative compatibility and seasonal variation among isolates of Sclerotinia homoeocarpa

Dollar spot of amenity turf, caused by Sclerotinia homoeocarpa, occurs in two seasonal epidemics in the northern United States, one from May to late July and a second from mid-August through October. It is not known whether these seasonal epidemics are the result of multiple species or due to seasonal variation within a single species. Isolates of S. homoeocarpa were collected from dollar spot lesions obtained from golf courses in Michigan, Illinois, and Wisconsin. Vegetative compatibility reactions between isolates identified six vegetative compatibility groups (VCGs) among more than 1,300 isolates collected from the eight locations. Most VCGs were present throughout the season, but one was generally recovered only in the late epidemic. Sequences of the nuclear ribosomal internal transcribed spacer 1 (ITS1) were identical among VCGs, indicating that the VCGs represent a single species. The results of this study suggest that the seasonal dollar spot epidemics observed in the northern United States are caused by a single species.