SORI (sr) in spikelets, dark oliviaceous brown, first sticky and covered by a delicate, grayish membrane, later dusty, usually completely destroying all floral parts, remaining only naked stalks.

Most of the spores formed first occur in cylindrical conglomerations that later divide into smaller fragments and single spores. The spores germinate by formation of four-celled basidia (promycelium). The basidium produces no basidiospores, but its cells germinate and form short, uninucleate hyphae that fuse in pairs and produce dikaryotic mycelium, which is capable of infection.

PLANT HOST AND DISTRIBUTION. Ustilago nuda affects different plant species of the genus Hordeum (Vanky 1994).

The fungus has a worldwide distribution.

NOTES. Ustilago nuda causes loose smut of barley.

Many pathogenic races have been recognized in U. nuda (Smith et al. 1988).

Ustilago nuda infects its plant hosts systemically. Disease symptoms may be visible before heading, because leaves of infected plants become slightly discoloured.

Ustilago nuda is transmitted in the form of a dormant mycelium in any part of the embryo except the radicle. The hyphae grow intercellularly behind the growing point and penetrate into the leaves and the primordia of the ears, as well as into the roots. Some weeks before the ears emerge, the spores begin to form, usually completely replacing the tissues of the ovary. When dry, the spores are dispersed by wind to flowers of flowering plants and germinate to produce infective hyphae. These penetrate through the young ovary wall and establish themselves as a dormant mycelium in the embryo before the seeds mature.

REFERENCES

Vanky K. 1994. European smut fungi. Gustav Fischer Verlag. Stuttgard-Jena-New York, 570 pp.

Smith I. M., Dunez J., Lelliott R. A., Phillips D. H., Archer S. A. 1988. European handbook of plant diseases. Blackwell Scientific Publications.