Mating and Progeny Isolation in the Corn Smut Fungus Ustilago maydis

The corn smut pathogen, Ustilago maydis (U. maydis) (DC.) Corda, is a semi-obligate plant pathogenic fungus in the phylum Basidiomycota (Alexopoulos et al., 1996). The fungus can be easily cultured in its haploid yeast phase on common laboratory media. However, to complete its sexual cycle U. maydis strictly requires its specific plant host, maize (Zea mays). The fungus is an interesting and important model organism for the study of the interactions of fungal biotrophic pathogens with plants. In this protocol, we describe the process of plant inoculation, teliospore recovery, germination, progeny isolation and initial mating type analysis. The primary purpose of this protocol is to identify individual progeny strains of U. maydis that can be used for downstream genetic analyses. Generation of targeted mutants to study various processes is a common approach with this and many plant pathogenic fungi. The ability to generate combinations of mutations is facilitated by sexual crossing without the need for additional selectable markers.