Corn smut fungus (Ustilago maydis), SEM

Coloured scanning electron micrograph (SEM) of Ustilago maydis, a pathogenic fungus that causes corn (maize) smut disease. Shown here is the budding yeast stage (laboratory grown) and its mucilaginous matrix. When grown in the lab on very simple media, Ustilago maydis behaves like baker's yeast, forming single cells, commonly named sporidia. These yeast cells multiply by budding off daughter cells (shown here). The fungus damages the corn plants and reduces yields by forming galls on the ears, stalks and leaves. When the galls mature (dikaryotic phase) their interior turns into a mass of powdery, dark, olive-brown spores. The grey membrane of the gall then ruptures releasing the millions of teliospores. These spores overwinter in the soil before germinating the next year on a new corn crop. Corn smut occurs wherever corn is grown in the world. Magnification: x1,335 when shortest axis printed at 25 millimetres.