Infektion und Wirtsreaktion beim Gerstenmehltau : [Kommentar zum Tonfilm]

Abstract

An epidermal strip of the barley coleoptile (Hordeum 'Vulgare) was used to microscopically study infection and host responses following inoculation with powdery mildew (Erysiphe graminis f. sp. hordei). The conidiospores germinate during the first hour after inoculation and form a primary germ tube. A small cytoplasmic aggregate can be recognised at this time. It represents the earliest visible host response. The secondary, appressorial germ tube forms at 4-6 hours after inoculation and elongates to form an appressorium. From a lobe of this appressorium, host cell penetration is intitiated. Host responses are a prominent cytoplasmic aggregate and wall appositions (papillae). After successful formation of the first haustorium in the host epidermal cell, secondary hyphae grow out of the appressorium and colonise the leaf surface. The development of a small pustule is demonstrated by time lapse photography over three days. Defense reactions of incompatible host-parasite combinations are also shown: A large papilla, conditioned by the ml-o gene (cultivar Helena) and the hypersensitive response, conditioned by the Ml-a gene (cultivar Carina).