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Abstract
One hundred and sixteen isolates of Sclerotinia homoeocarpa, the causal agent of dollar spot of turfgrass, were collected from golf courses at nine locations in southern Ontario and one location in Nova Scotia. Isolates were assessed for vegetative compatibility in culture, and four types of reactions were observed. These reactions were examined for transmission of hypovirulence-associated double-stranded RNA (dsRNA) and the results indicated that vegetative incompatibility in S. homoeocarpa ranged from fully to partially incompatible. The fully incompatible reaction strongly restricted transmission of hypovirulence-associated dsRNA whereas the partially incompatible reactions allowed limited spread between vegetative compatibility groups (VCGs), suggesting that vegetative incompatibility is not an absolute barrier to the transmission. Intra- and inter-location VCG tests detected vegetative incompatibility at 7 of the 10 locations, but there were only four unique VCGs among the 116 isolates. These VCGs were compared with representative isolates of six VCGs identified in Michigan, Illinois, and Wisconsin. Three VCGs in the present study correspond to VCG-A, -B, and -E, respectively, and one VCG, named VCG-G, was a new group. In southern Ontario, VCG-B was the most commonly recovered VCG, comprising 56.0% of the sampled isolates, and was present at nine locations. VCG-A and -G comprised 11.2 and 31.9% of the sampled isolates and were present at three and seven locations, respectively. VCG-E was only detected at one location. These results support the hypothesis that there is limited diversity among VCGs in S. homoeocarpa. The transmission of hypovirulence-associated dsRNA among VCGs and the relatively simple genetic structure, as reflected in the small number of VCGs within populations of S. homoeocarpa, is consistent and supportive of the use of hypovirulence as a biocontrol agent for dollar-spot management.Key words: Sclerotinia homoeocarpa, dollar spot, turfgrass, vegetative compatibility, hypovirulence, double-stranded RNA, dsRNA.