Serological Detection in Soil of Plasmodiophora Brassicaeresting Spores

Polyclonal antisera were raised to whole (coded: 16}2), and sonicated (coded: 15}2) resting spores of Plasmodiophora brassicae, and to soluble components prepared by ®ltration and ultracentrifugation (coded: SF}2). Cross-reactivity of all three antisera with a range of soil fungi, including Spongospora subterranea was low. Test formats including western blotting, dip-stick, dotblot, indirect enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence were assessed for their potential to detect resting spores of P. brassicae in soil. Dot-blot was least sensitive, with a limit of detection level of 10000000( resting spores /g in soil. With Western blotting the lower limit of detection with antiserum 15}2 was 100000. This antiserum showed the greatest sensitivity in a dip-stick assay, indirect ELISA and indirect immunofluorescence, for all of which there was a limit of detection of 100 spores. The indirect ELISA was successful only after the substitution of alkaline phosphatase by protein A conjugated horseradish peroxidase. Of the assays
tested, indirect immunofluorescence appears to be the most rapid and amenable assay for the detection in soil of low levels of resting spores of P. brassicae.