Identification and Characterization of Chromosome Length Polymorphisms Among Strains Representing Fourteen Races of Ustilago hordei. Kevin McCluskey. Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331-2902 U.S.A. Dallice Mills. Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331-2902 U.S.A. MPMI 3:366-373. Accepted 15 June 1990. Copyright 1990 The American Phytopathological Society.

Electrophoretic karyotypes were determined for monosporidial strains that represent each of the 14 races of Ustilago hordei. A unique karyotype was observed for each strain; the number of chromosome-sized DNA bands varied from a minimum of 15 to a maximum of 19, and their approximate length distribution ranged from 170 to 3,150 kilobases. Strains were also obtained from one ordered and six unordered meiotic tetrads representing four of the races. Karyotype was typically conserved among members of individual tetrads and between tetrads representing the same race. The strains from one tetrad from race 14, however, showed 2:2 segregation for one chromosome-sized DNA band. Conversely, the total soluble protein from 14 of these strains fractionated by sodium dodecyl sulfate-PAGE did not vary to the same extent as the karyotypes. Southern hybridization was used to identify chromosome length polymorphisms and to map genomic fragments and heterologous conserved genes to the chromosomes.