Development of a quantitative immunodipstick assay for Phytophthora nicotianae

Monoclonal antibodies have been produced that are specific for the species, Phytophthora nicotianae, a plant pathogen which causes blackshank on tobacco and root rots in citrus. The antibodies react with the surface of P. nicotianae cysts but not with cysts of any other species of Phytophthora or Pythium tested. The antibodies have been used in a dipstick assay in which a colorimetric detection system gives a quantitative indication of the level of inoculum present. In this assay, one of the species-specific antibodies, Pn8E6, detected P. nicotianae spores at densities as low as 10 spores/ml. In preliminary tests, the assay was able to detect P. nicotianae in contaminated soil samples and the intensity of the reaction showed a correlation with results obtained from plating assays on selective media.