Corynebacterium flaccumfaciens, causing bacterial wilt in bean, is a quarantine organism for Europe. This paper compares two methods for detecting C. flaccumfaciens in seed lots on the market. Experimentally contaminated bean seeds were homogenized and a standard extraction and concentration procedure was used. The final pellets were used for immunofluorescence staining and indirect isolation (through bean seedlings). The immunofluorescence staining sensitivity threshold was 1.23 × 107, corresponding to 1.82 × 104 fluorescent cells per ml of final concentrate. The risk of false negative reactions to immunofluorescence staining caused by serologically unrelated C. flaccumfaciens strains was also examined. The indirect isolation sensitivity threshold was 1.23 × 106 producing 43% symptomatic plants and 53% positive reisolation. There was no serious interference between C. flaccumfaciens and Pseudomonas syringae pv. phaseolicola in mixed inoculations and both pathogens were successfully reisolated. The comparative results are discussed in relation to the applicability of the methods to commercial lots of bean seeds.
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Calzolari et al. (1987) studied this question.