Histological characterisation of the incompatible interaction between Arabidopsis thaliana and the obligate biotrophic pathogen Plasmodiophora brassicae

The obligate biotrophic pathogen Plasmodiophora brassicae induces cataplast ic galls in the roots of various species of the Brassicaceae. The ecotypes Ze-0, Tsu-0, and Ta-0 of Arabidopsis thaliana carry alleles of a dominant s ingle gene (RPB1) for resistance against this pathogen. The pathotype-speci fic resistance reactions in the roots were accompanied by a hypersensitive response. Infected cells were surrounded by necrotic boundaries and thereby the pathogen growth was restricted. The pathogen could induce hyperplasia and hypertrophy to a slight extent and develop spores within mini-galls sur rounded by the neurotic cells, if it was able to colonise meristematic tiss ue. Ecotype Ze-0 showed the highest level of resistance to P, brassicae iso late 'e' as indicated by the very limited number of infected cells, whereas the resistance of the ecotype Ta-0 was rated lower. The results are discus sed in relation to the interaction of the pathogen with Brassica crops.