VIEW ARTICLE

A Fine-Structure Study of the Primary Infection Process during Infection of Barley by Erysiphe graminis f. sp. hordei. H. H. Edwards, Assistant Professor, Department of Biological Sciences, Western Illinois University, Macomb 61455; P. J. Allen, Professor and Chairman, Department of Botany, University of Wisconsin, Madison 53706. Phytopathology 60:1504-1509. Accepted for publication 8 May 1970. DOI: 10.1094/Phyto-60-1504.

The chronological events in the primary penetration process of germinating powdery mildew conidia (Erysiphe graminis f. sp. hordei) into the epidermal cells of barley (Hordeum vulgare 'Traill') primary leaf tissue are described. Observation of this process by electron microscopy shows that the penetration consists of (i) the enzymatic digestion of the cuticle and cellulose portion of the epidermal wall by enzymes apparently secreted by the developing mildew infection peg; and (ii) a mechanical pushing of the infection peg through a layer of material which has been deposited on the underside of the epidermal wall. This layer (papilla) is more electron-dense than the cellulose portion of the cell wall, and contains membranous material embedded in an amorphous matrix. The papilla is formed after the appressorium attaches to the outer surface of the host epidermal wall, but prior to the formation of the infection peg.