Observations on the Comparative Morphology and Taxonomic Relationships of Certain Grass Smuts in Western North America

SUMMARY

This paper deals with the comparative morphology and taxonomic relationships of the smuts of barley grasses, brome grasses, and wheat grasses in the Northwest heretofore known under the names Ustilago Lorentziana, U. bromivora, and U. bullata, respectively.

Examination of 19 current collections, and 41 herbarium specimens of these three smuts revealed that they are morphologically similar. There is more variation in the morphology of the spores of collections of U. bromivora, than exists between U. bromivora, as a species, and either U. bullata or U. Lorentziana.

The modes for the diameter of the spores of various collections of U. bromivora ranged from 6 μ in collection M-K to 10 μ in collections M-J and M-H. The mode for spore diameter of U. bullata was 7 μ in 3 collections and 8 μ in a fourth; for U. Lorentziana it was 8 μ in all collections.

In U. bromivora the epispore also varied according to collection from very minutely echinulate-verrucose in collection M-K to rather coarsely verrucose in collection M-L. Most collections were distinctly echinulate-verrucose. U. bullata and U. Lorentziana showed less variation, from finely echinulate-verrucose to minutely verrucose.

It is considered that the smuts under the names Ustilago bromivora, U. bullata, and U. Lorentziana really represent one composite species, probably containing numerous well-defined physiologic races. Since U. bullata has priority over the other two names and is descriptive of the sori, it is proposed that that name apply to this species.

An emended description of Ustilago bullata is accordingly given, with a list of the hosts in North America. Thus, 5 species of Agropyron, 23 species of Bromus, 1 of Elymus, 7 of Hordeum, and 1 of Sitanion are recognized as hosts to U. bullata, in the new concept of this species. Ten of this total of 37 grasses are herein reported for the first time.