Diversity and variation in expression of resistance to <i>Erysiphe fischeri</i> in <i>Senecio vulgaris</i>

Abstract

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.