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Serological Detection of Plasmodiophora brassicae by Dot Immunobinding and Visualization of the Serological Reaction by Scanning Electron Microscopy. L. Lange, Novo BioKontrol, Novo Nordisk Industri A/S, Novo Allé 1, DK-2880 Bagsværd, Denmark; M. Heide(2), L. Hobolth(3), and L. W. Olson(4). (2)(3)Institute of Plant Pathology, Danish Research Service for Plant and Soil Science, Lottenborgvej 2, DK-2800 Lyngby, Denmark; (4)Institut for Sporeplanter, University of Copenhagen, Ø. Farimagsgade 2 D, DK-1353 Copenhagen K, Denmark. Phytopathology 79:1066-1071. Accepted for publication 12 December 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1066.

An antiserum was made against Plasmodiophora brassicae, the causal agent of club root of cabbage. A semipurified suspension of spores of P. brassicae was used as antigen, obtained by filtration and Percoll gradient centrifugation of infected roots. Crude root suspension samples were bound to a nitrocellulose membrane and tested by a dot immunobinding assay. The individual steps of the serological procedure were examined with a scanning electron microscope. The surface of the resting spores of P. brassicae, race 7, appeared smooth, while the dot immunobinding processed spores had a heavy, irregular coating, which was demonstrated to originate from incubation in the primary antiserum. Normal serum did not give rise to a coating on the resting spores. The antiserum of P. brassicae did not react with surface antigens of resting spores of Polymyxa. Further, no cross reaction with other common root pathogens such as Pythium ultimum, Rhizoctonia solani, and Fusarium oxysporum was observed. With antiserum prepared against spore surface antigenic determinants the dot immunobinding technique can be used as a routine test for detection of infection of P. brassicae in host plants and in bait plants (used as indicators of soil infestation). The sensitivity obtained was within the range permissible for a routine test.