VIEW ARTICLE

Genetics

Induced Morphological and Virulence Variants of the Obligate Barley Pathogen Erysiphe graminis f. sp. hordei. J. E. Sherwood, Michigan State University (MSU)-Department of Energy (DOE) Plant Research Laboratory, Present address: Department of Plant Pathology, Montana State University, Bozeman 59717; B. Slutsky(2), and S. C. Somerville(3). (2)Michigan State University (MSU)-Department of Energy (DOE) Plant Research Laboratory, Present address: Environmental Protection Agency, Washington, DC 20460; and (3)MSU-DOE Plant Research Laboratory and Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 81:1350-1357. Accepted for publication 7 May 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1350.

A mutagenesis procedure designed to limit contamination was developed for Erysiphe graminis f. sp. hordei, an obligate pathogen that causes powdery mildew disease on barley. Gnotobiotic cultures of E. g. hordei were established on barley leaf sections placed on an agar medium in petri dishes. To mutagenize E. g. hordei, leaf sections with 3-day-old cultures were transferred to an agar medium containing ethyl methanesulfonate for 12–14 h. Seven days after mutagen treatment, the cultures were screened for morphological mutants. Among the classes of variants observed were those with red conidia and hyphae, round conidia, prematurely germinating conidia, and altered colony morphology. Based on the occurrence of red variants, the mutation frequency after exposure to ethyl methanesulfonate was estimated to be 1–2 × 10^–4. As a means of further analyzing host-pathogen interactions in the powdery mildew disease, mutants of E. g. hordei with increased virulence were generated with this mutagenesis protocol. A number of variants showing minor increases in virulence were recovered, but no fully virulent variants were observed. The mutation in one weakly virulent isolate was inherited as a simple, nuclear factor.