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Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

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Epicoccum purpurascens, also known as E. nigrum, is a common anamorphic fungus present in both outdoor and indoor environments. While a primary decomposer of plant tissues in nature, E. purpurascens also poses health risks for humans. Inhalation of its conidia (asexual spores) commonly causes allergic responses in humans. Conidia are produced in tremendous numbers from specialized sporogenous cells borne primarily on the surfaces of superficial cushion-shaped masses of hyphae termed sporodochia. This study examines ultrastructural details of sporodochium and conidium development using a combination of scanning (SEM) and transmission electron microscopy (TEM). Although some ultrastructural data are available on sporodochium and conidium in E. purpurascens from the early work of Griffiths [1], results of this study should provide a much more complete understanding of the formation of both these structures.In this study E. purpurascens was grown in culture plates on either potato dextrose or corn meal agar. Small block of agar bearing sporodochia in various stages of development were removed from culture plates and prepared for study with either SEM or TEM. For SEM, samples were fixed in glutaraldehyde and Os0 4 and prepared for examination using the procedures of Enkerli et al. [2]. Samples for TEM were prepared for study using either a conventional chemical fixation protocol [3] or high pressure freezing followed by freeze substitution [4].A developing sporodochium first appeared as a small loose aggregation of hyphae on the agar surface. These hyphae quickly proliferated to form a raised mass of branched and more densely packed hyphae (Fig. 1). Numerous short sporogenous cells then arose from the surfaces of these hyphae (Fig. 2). The tip of each sporogenous cell enlarged to form a single swollen conidium initial that soon became delimited from the sporogenous cell by a septum. Once delimited, the young conidium quickly enlarged and became divided into multiple cells as the result of the formation of both transverse and longitudinal septa (Fig. 3) within the developing conidium. Each conidium possessed a thick multilayered wall with very rough, irregular surface features (Fig. 3). Mature conidia were roughly spherical in shape and quite variable in size with some reaching 25 µm in diameter (Fig. 4). As evident in Fig. 4, conidia accumulated in large masses on the surface of a sporodochium.