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Immunoenzymatic Detection of Phytophthora fragariae in Infected Strawberry Plants. Eugénie Amouzou- Alladaye, INRA—Station de Pathologie Végétale, Centre de Recherches de Bordeaux, BP 131, 33140 Pont de la Maye, France; Jean Dunez, and Michel Clerjeau, INRA—Station de Pathologie Végétale, Centre de Recherches de Bordeaux, BP 131, 33140 Pont de la Maye, France. Phytopathology 78:1022-1026. Accepted for publication 22 February 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-1022.

Antiserum obtained by injecting rabbits with mycelial protein extracts of one strain of Phytophthora fragariae had a dilution end point of 1/64 in double diffusion and 1/512,000 in indirect enzyme-linked immunosorbent assay (ELISA). This serum could detect 11 different strains of P. fragariae in pure culture and the pathogen in naturally infected or inoculated roots. Although the sensitivities of direct double antibody sandwich and indirect ELISA were comparable, the direct double antibody sandwich ELISA was more specific for the detection of P. fragariae in strawberry roots. The antiserum failed to react with 18 fungal species isolated from underground parts of strawberry but reacted with some strains of P. cactorum, which parasitized only rhizomes but not roots, and Pythium middletonii, which was isolated sometimes in association with P. fragariae from strawberry roots. In inoculated strawberry roots, P. fragariae was detected reliably by ELISA several days before oospores were found and before symptoms developed. Thus, direct double antibody sandwich ELISA may be useful for early detection of infection and for the detection of latent infections of strawberry plants by P. fragariae.