Comparative studies on myceliogenic germination of tan sclerotia of Sclerotinia sclerotiorum and Sclerotium rolfsii

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Abstract
Tan-colored sclerotia of Sclerotium rolfsii and of an aberrant strain of Sclerotinia sclerotiorum that were freshly harvested from 5-week-old cultures on potato dextrose agar or stored at room temperature in paper bags for 4 weeks germinated myceliogenically on moist field soil without exogenous nutrients. A comparative study by time-lapse photomicroscopy revealed similarity in the mode of myceliogenic germination of sclerotia of the two species. The germination appeared to be of the hyphal type in both species and was characterized by the emergence of individual hyphae through the rind. There was no evidence of eruptive type of germination in any of the strains tested. Although several hyphae often emerged through the same spot of the rind, these hyphae emerged singly, and the time-lapse photomicrographs showed no evidence of eruptive germination. While most of the germinated sclerotia of S. rolfsii developed into colonies within 4 days of incubation on moist soil, the development of colonies from germinating sclerotia of S. sclerotiorum appeared to be slow, taking up to 28 days. Results of the inoculation studies showed that mycelia from the germinated sclerotia of S. rolfsii were able to infect and cause seed rot and damping-off of canola and alfalfa, which were planted near the soil surface at a distance of at least 15 mm from the sclerotium, without providing exogenous nutrients.

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