Genetic Interactions Between Erysiphe fischeri (Blumer) and Members of the Genus Senecio

Twelve single spore isolates of E. fischeri were made and each was shown to possess a different virulence phenotype when inoculated onto 47 lines of S. vulgaris. Three crosses were made between resistant and susceptible lines of S. vulgaris, and the resistance phenotypes of F1 and F2 plants recorded, using available samples from the 12 isolates of the pathogen. Resistance was shown to be under the control of one or two major genes, with resistance either dominant or recessive. In some of the cases of recessive resistance there was evidence of a separate locus containing a gene that inhibited the expression of resistance genes. In one cross, seven resistance genes were shown to be linked