Morphological development of sclerotia by Sclerotinia sclerotiorum: a view from light and scanning electron microscopy

Abstract

Sclerotinia sclerotiorum is a worldwide pathogen with a broad host spectrum pathogenic to around 400 plant species. Sclerotia formed by S. sclerotiorum serve as resting structures that secure fungal survival in soil for prolonged periods in the absence of a host plant or may help to overcoming periods of unsuitable growth conditions. In the present study, the morphological development of sclerotia was examined by light and scanning electron microscopy of fungal microcultures. Observations from microscopy indicated that, during the first 4 days of culture, the sclerotial primordial originate by dichotomous branching of apical hyphae and from the 5th day mycelial clusters were also observed, indicating the initiation stage of sclerotia formation. From the 6th to the 8th day, sclerotia turned from white to dark color, and water drops (exudates) were observed on their surface. The process of sclerotia formation ended at the 9th day when they were easy to detach from the culture medium and had a black coloration. All the morphological processes involved in the formation of sclerotia by S. sclerotiorum were observed with both light and scanning electron microscopy.