DIVERSITY AND VARIATION IN EXPRESSION OF RESISTANCE TO ERYSIPHE-FISCHERI IN SENECIO-VULGARIS

The reactions of 20 inbred lines of Senecio vulgaris (groundsel) to inoculation with up to 10 isolates of Erysiphe fischeri (powdery mildew) were investigated in a number of repeat experiments. There was considerable variation among isolate/plant line reaction phenotypes with examples of both isolate-specific complete resistance and isolate-specific partial resistance. Some plant lines possessed high levels of partial resistance to all isolates tested. Incubation temperature and plant age influenced the infection types of some isolate/plant line combinations. In this pathosystem, complete and partial resistance, together with age-dependent and temperature-dependent resistance, appear to have evolved to facilitate a defence strategy based on a complex mosaic of interacting factors.