Smut is a disease of cereals, corn, grasses, onions, and sorghum that can be caused by any of more than 700 species of parasitic fungi. Smuts generally have a negative economic impact on agriculture, because they affect so many food crops. An exception to this is corn smut, which is considered a delicacy in Mexico.

Corn infected with the fungus Ustilago maydis forms large, swollen, kernel-like globules with soft black flesh covered by a silvery gray skin. Called huitlacoche (pronounced wee-tlah-KOH-cheh), the native Nahuatl word, this dish is characterized by an inky, mushroom flavor and has apparently been eaten in central Mexico for thousands of years. In the United States, after decades of trying to eradicate corn smut, some farmers are attempting to grow corn with large corn smut infestations because the fungus is becoming a prized gourmet food item, garnering much higher prices than healthy corn.

The various smuts are characterized by masses of sooty spores that grow on or inside the plant during a fungus's last stage of growth. Many begin to grow in the plant embryo, feeding on maturing plant tissue through a network of filaments, or hyphae. To reproduce, a blister forms and breaks open, and the black, powdery fungus spores are borne away by air currents.

The specimen presented here was imaged with a Nikon Eclipse E600 microscope operating with fluorite and/or apochromatic objectives and vertical illuminator equipped with a mercury arc lamp. Specimens were illuminated through Nikon dichromatic filter blocks containing interference filters and a dichroic mirror and imaged with standard epi-fluorescence techniques. Specific filters for the corn smut fungus stained thin section were a B-2E/C and a Y-2E/C. Photomicrographs were captured with an Optronics MagnaFire digital camera system coupled to the microscope with a lens-free C-mount adapter.

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