Problems encountered during immunofluorescent diagnosis of fireblight.
An immunofluorescent (fluorescent antibody or FA) staining technique was used to detect Erwinia amylovora in plant tissue (Cotoneaster, Crataegus, Pyrus, Pyracantha and Sorbus). In preliminary trials it failed to do so in most preparations from fireblight-infected plants but differential centrifugation greatly improved the rate of detection. Cultures of E. herbicola spp. ananas [E. ananas], E. stewartii, E. rhapontici and 2 plant isolates (probably Pseudomonas fluorescens and E. herbicola spp. herbicola) cross-reacted with E. amylovora in the FA stain. Of these only the P. fluorescens isolated and a different plant isolate of E. herbicola spp. herbicola cross-reacted with E. amylovora antiserum in the slide agglutination test. Use of absorbed E. amylovora antiserum completely eliminated cross reactions in the slide agglutination test, but only partly removed cross reactions in the FA stain. Immunofluorescence appears to be more sensitive but less reliable than conventional plating methods for fireblight diagnosis.