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The Ustilaginomycetes comprises more than 1300 species in ca. 80 genera of basidiomycetous plant parasites. They occur throughout the world, although many species are restricted to tropical, temperate, or arctic regions. Some species of Usti-lago and Tilletia, e.g., the barley, wheat or maize smut fungi, are well known because they are of economic importance (Trione 1982; Thomas 1989; Valverde et al. 1995). For example, from 1983 to 1988, the barley smut fungi reduced annual yields by 0.7% to 1.6% in the prairie provinces in central Canada, causing annual losses of about US$8000000 (Thomas 1989). Tilletia contraversa Kühn is important in the international wheat trade (Trione 1982) and, 2-5% in a corn field are generally infected by Ustilago maydis (DC.) Corda, while up to 80% of a field can be infected if conditions are good for the smut fungus. On the other hand, the galls of U. maydis are …