The soil-borne obligate pathogen Plasmodiophora brassicae causes clubroot disease in species of Brassicaceae , including Arabidopsis thaliana . The host-pathogen interaction was studied with respect to the age of the plant at the time point of inoculation and to different infection pressures in order to establish a standardization of infection parameters and evaluation of disease extent for A. thaliana lines. Spore number per root weight, root and shoot weight of inoculated and non-inoculated plants as well as infection rate and disease index (DI) were analysed and correlated. The disease extent of different lines was comparable as measured by the relation of root weight of inoculated and non-inoculated plants (R-i/R-ni index) and the DI. Most of the 71 screened A. thaliana lines turned out to be susceptible. However, the mutant lines tu8, tu3, det1-1, and rhd3-1 showed a certain degree of tolerance under specific culture conditions. The reactions of rhd3-1 indicate that hypertrophy is a prerequisite for maturation of the pathogen. The reactions of the tu3 and tu8 mutants indicate a role of indole glucosinolates and indole-3-acetonitrile/IAA in development of clubroot disease.