Comparison of polypeptides in Ustilago spp. pathogenic on wheat, barley, and oats: a chemotaxonomic study

Detergent-soluble polypeptides were extracted from spores of several isolates of Ustilago spp. pathogenic on wheat, barley, and oats: U. tritici, U. nuda, U. nigra, U. hordei, U. avenae, and U. kolleri. These polypeptides were then separated by two-dimensional isoelectric focusing – polyacrylamide gel electrophoresis. Despite large differences in virulence, the three isolates of U. tritici virulent on wheat gave almost identical polypeptide patterns; an isolate virulent only on Aegilops spp. differed from these three by nine polypeptides. In U. nuda, two isolates had identical patterns, and four polypeptides varied between two other isolates. There were five or fewer differences in polypeptides between two isolates of each of U. nigra, U. hordei, U. avenae, and U. kolleri. This low level of intraspecific variation and the variability between closely related isolates preclude use of the present technique to differentiate isolates of unlike virulence of these six fungi. However, the species U. tritici and U. nuda differed by 47 polypeptides; this high level of interspecific variation supports the concept of treating these two pathogens as separate taxa. In contrast, the seedling-infecting smuts of barley and oats, U. nigra, U. hordei, U. avenae, and U. kolleri, showed only a difference in 13 polypeptides overall, with the last two differing by only one polypeptide. This limited interspecific variation supports the view that these four pathogens are very closely related and should be united under one taxon.