Plant Pathology: Extension: Plant Disease Library
How To Methods
Compound Microscope Use
The compound microscope typically has a total magnification range of 40-1000x. There are usually 3 to 4 objectives on each microscope. Objectives provide 4x, 10x, 40x, 100x (sometimes a 20x objective may replace the 4x) magnification. Another 10x magnification is gained through the eyepieces.
The compound microscope is used to view wet mount or stained slides for fine details of fungal fruiting structures and spores. It is usually not possible to identify a fungus solely on spore characteristics. Many fungi produce similar spores. An example is Cercospora and Septoria fungi. Both produce thin, elongated, multi-celled conidia and if only the spores are viewed, the fungi are virtually indistinguishable from one another. To accurately identify the fungus, you must see where the spores were produced. Cercospora conidia are produced on darkly pigmented naked conidiophores, whereas Septoria conidia are produce within a pycnidium.
Some fungi can be identified based upon spore characteristics such as pigmentation, shape, size, and ornamentation. A few examples are Entomosporium, Pestalotia, and Fusarium. Some fungi produce no spores such as Rhizoctonia and Sclerotium (cause of southern blight). These fungi are identified based on mycelial characteristics including hyphae septation, color, size, etc.
When viewing a slide of a disease sample, look through the eyepieces and focus your view using the coarse and fine focus control knobs while on the lowest power objective (usually 10x). To increase magnification move the 20x or 40x objective into place and focus your view while looking through the eyepieces using only the fine focus control knobs. Using the coarse focus control knobs can often raise the slide into the objective breaking the cover slip making viewing the slide difficult.
For most fungi the highest magnification needed is 400x which is obtained using the 40x objective. The 100x objective is an oil immersion objective and is only used for viewing bacterial stains.
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 Pestalotia |
