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A range of cultural and biochemical criteria have been compared to assess their value in distinguishing species of Sclerotinia. Twenty-seven isolates of Sclerotinia have been included, with representatives from all three species groups recognised in recent taxonomic treatments. When mycelial characteristics were compared, growth rate at 25 °C distinguished S. trifoliorum from S. sclerotiorum and S. minor, whilst assessments of relative hyphal densities and mycelial interactions yielded results with only limited taxonomic value. Comparison of sclerotial characteristics differentiated S. minor from the other two species on the basis of sclerotial size and pattern within the colony, but did not distinguish S. sclerotiorum from S. trifoliorum. Ascospore characteristics were not considered useful because the time factor and unpredictability involved in ascocarp production precluded their use for rapid identification. Comparison of major soluble proteins from sclerotia by polyacrylamide gel electrophoresis, or discriminant analysis of pyrolysis mass spectra of sclerotial preparations, added further support to species groupings constructed using traditional cultural criteria. It would be difficult to use these biochemical criteria alone to distinguish between the three species. Much closer similarities exist between S. sclerotiorum and S. trifoliorum than between either fungus and S. minor, and it is suggested that they may be better regarded as subspecies. |
