COMPARISON OF DIFFERENT SEROLOGICAL METHO DS FOR THE DETECTION OF THEFIRE BLIGHT PATHOGEN, ERWINIA-AMYLOVORA (BURRILL) WINSLOW ET-AL

1. Three serological methods (slide agglutination test for colonies is olated by a semiselective medium (Hahn agar), immunofluorescence techn ique (IFT) and enzyme-linked immunosorbent assay (DAS-ELISA) were comp ared for detecting Erwinia amylovora, the causal agent for fireblight, in fluids resp. on twigs contaminated and stored up for some days and by different temperatures. 2. By all techniques the causal agent coul d be surely detected in concentrations of 10(5) cells/ml; but by isola tion on the semiselective agar medium (Hahn agar), still 10(2) cells/m l of E. amylovora were to find out easily. In many cases isolates of E . herbicola, a frequent saprophytic inhabitant of plant surfaces, show ed cross reactions with antisera against E. amylovora, if agglutinatio n test was used, but such reactions could not be completely eliminated by employing the IFT, too. However, in ELISA cross reactions with E. herbicola strains were not observed. 3. In all experiments the results of IFT and DAS-ELISA essentially agreed. 4. After few days of storing by different temperatures a decrease of the cell concentration in sus pensions of E. amylovora could be demonstrated by the isolation method and by IFT. By short-time storing of suspensions (24 h) preservation by 22-degrees-C (laboratory) or 4 to 6-degrees-C (refrigerator) induce d smaller losses of cell concentration than freezing (-21-degrees-C). By storing longer than 24 hours in samples preserved in a refrigerator (4 to 6-degrees-C) the slightest reduction of pathogen density could be stated. 5. In contrast to, on twigs contaminated cell populations o f the causal agent persisted without diminishing.