Table 2.
A selection of diagnostic characters for the three core Sclerotinia species. These are some of the characters used by Kohn (1979) and Willetts and Wong (1980) to recognise and distinguish S. sclerotiorum, S. minor, and S. trifoliorum. Although representative, this list is not exhaustive.
| Character | S. sclerotiorum | S. minor | S. trifoliorum | |
|---|---|---|---|---|
| Number of nuclei per ascospore | 2 | 4 | 4 | |
| Haploid chromosome numbers (n) | 16* | 4 | 8 | |
| Ascospore dimorphism | No | No | Yes | |
| Sclerotia in culture | Fewer, large | Many, small | Fewer, large | |
| Sclerotial formation in culture | On growing tips of hyphae, at colony periphery | Laterally on hyphae, throughout colony | On growing tips of hyphae, at colony periphery | |
| Sclerotial rind | No tomentum hyphae | No tomentum hyphae | Tomentum hyphae extend beyond rind | |
| Sclerotial patterning in culture | One, two, or more concentric rings may be discernible. Single ring often near edge of petri dish | Irregularly arranged throughout cultures | As for S. sclerotiorum, but sometimes irregularly distributed | |
| Electrophoretic patterns | Distinctive for this fungus | Distinctive | Distinctive, intermediate in some respects between S. sclerotiorum and S. minor | |
| Ectal excipulum (apothecia) | Cell shape | Textura prismatica, sometimes bound in gel | Textura prismatica, sometimes bound in gel, but more often only cells at margin bound in gel | Textura prismatica |
| Orientation | Perpendicular to apothecial surface | Perpendicular to apothecial surface | Perpendicular to apothecial surface | |
| Outermost cells | Margin consists of textura porrecta, outermost excipular cells sometimes give rise to 1–2 celled tomentum hyphae | Outermost excipular cells often give rise to 1–2 celled tomentum hyphae | Margin consists of textura porrecta, outermost excipular cells often give rise to 1–2 celled tomentum hyphae | |
| Ectal excipulum (stipe) | Cell shape | Textura porrecta | Textura prismatica | Textura prismatica |
| Orientation | Turning out perpendicular to stipe axis | Oriented parallel to stipe axis | ||
| Outermost cells | Give rise to one-celled tomentum hyphae, which turn out perpendicularly to stipe axis | Give rise to 1–2 celled tomentum hyphae, which sometimes group in fascicles | Give rise to one-celled tomentum hyphae, which turn out perpendicularly to stipe axis | |
| Mycelial | Growth rate on solid agar media at 26 °C | Fast | Not documented | Slow – about half that of S. sclerotiorum |
| Formation of haptera at edges of petri dishes | Produced infrequently | Variable but usually produced infrequently | Produced frequently | |
| Mycelial | Aerial mycelia | Moderate to abundant amounts of aerial mycelium giving white appearance to plates | Moderate aerial mycelium | Sparse aerial mycelium |
*Although Kohn (1979) and Willetts and Wong (1980) list the haploid chromosome number as 8, genomic data has shown that this species possesses 16 chromosomes. This inconsistency is explained by a newly discovered phenomenon whereby S. sclerotiorum divides its haploid chromosomes between two nuclei (Tian et al. 2025).