Effect of Sclerotial Water Content on Carpogenic Germination of Sclerotinia sclerotiorum.

The relationship between moisture content and carpogenic germination (CG) of Sclerotinia sclerotiorum sclerotia and the dynamics of sclerotial water imbibition were studied in a controlled environment. The study was conducted using laboratory-produced sclerotia from seven S. sclerotiorum isolates. The quantity and rate of water imbibition by three sizes of sclerotia was determined gravimetrically in silty clay, sandy loam, and sandy soils maintained at 100, 75, 50, and 25% of soil saturation and in distilled water. Smaller sclerotia imbibed water at a significantly faster rate (P = 0.05) than larger sclerotia in water and in soil at all saturation percentages. When buried in soil, small, medium, and large sclerotia were fully saturated within 5, 15, and 25 h, respectively, in all three soil types and moisture percentages. The effect of sclerotia moisture content on CG was evaluated on sclerotia maintained at 95 to 100, 70 to 80, 40 to 50, and 20 to 30% of their water saturation capacity using cool mist humidifiers. Sclerotial moisture content significantly influenced CG (P = 0.05). Maximum CG was observed on fully saturated sclerotia, while no CG was observed below 70 to 80% of saturation. These findings help explain S. sclerotiorum's ability to produce apothecia in soils with relatively low moisture levels.