Inbreeding of the avirulent physiologic race 8 strains of Ustilago hordei was purported to have increased its pathogenicity in a stepwise manner that led to a highly pathogenic race, designated race 14. The analysis of electrophoretic karyotypes and restriction fragment length polymorphism profiles detected with a telomere-specific probe (TelomereRFLP) in races 8 and 14, and progeny obtained by selfing race 8 strains, revealed substantially changed patterns in the purported progeny of the second generation of selfing, and the race 14 strain. The telomereRFLP patterns in strains purported to be the progeny of the second generation of inbreeding of race 8, were unlike both race 8 and race 14 strains, and identical to those of U. hordei physiologic races 10 and 13. These data suggest that the progeny believed to have been derived from the second selfing of race 8 strains were clonal lineages from either race 10 or race 13 strains, rather than the products of meiosis of race 8 teliospores. The electrophoretic karyotypes resolved from race 8 and 14, revealed chromosome-length polymorphisms (CLPs) that were similar in magnitude to those reported among strains of the fourteen physiologic races of U. hordei, rejecting the postulate that race 14 is a lineage derivative from race 8. Electrophoretic karyotyping and ribosomal DNA (rDNA) sequence analysis of eight Ustilago species revealed that the four sporidium-forming species, U. avenae, U. hordei, U. kolleri, and U. nigra, form a coherent group. Ten probes detected a maximum of 15% CLPs among the putative homologous chromosomes of theses species, and the internal transcribed spacer (ITS) amplified from these species shared 97-99% sequence identity. The taxonomic distinctness of U. maydis from the rest of the smut fungi was evidenced by its divergence at 7 nucleotides in the 5.8S rDNA coding region. / Graduation date: 1996