| Abstract: | Resistance induced by microbial metabolites against powdery mildew on barley always proved to be highly effective particularly under practical conditions in field. The results obtained in the present study demonstrate that the successful induction of resistance requires a conditioning of plants by the environmental conditions acting prior to the application of the inducer. If plants were grown in the greenhouse or outdoors, the infection densities were efficiently reduced after the treatment with the inducer. In contrast to this the disease intensities were not reduced on plants grown at constant temperature, light and humidity conditions. Frequently changing temperatures and the daily courses of temperature, normally occurring in greenhouse or outdoors, were substantiated as the most important factors for a successful induction of resistance. The conditioning of the plants under these temperature conditions depended on light energy, especially in just developing leaves. The dependence of the induced resistance on the environmental conditions was proved with other host-pathogen-relationships as well as with barley and powdery mildew. |
