S.V. Beer, D.W. Bauer, E.M. Steinberger
Although fire blight was the first disease shown to be caused by a bacterium, the mechanism by which Erwinia amylovora causes the disease is still unknown. In the past, several materials (e.g. ammonia, cell wall degrading enzymes, amylovorin) were suggested as pathogenicity determinants of E. amylovora. However, conventional physiological and biochemical techniques so far have failed to demonstrate clearly that these materials are involved in pathogenesis.

In 1980, Buchanan and Starr (Curr. Micro. 4:63–68) described the isolation and activity of a necrotoxin from pear cell suspension cultures (PCSC) inoculated with E. amylovora. Necrotoxin preparations inhibited the further growth of PCSC and caused necrosis of pear seedlings. This necrotoxin recently has been studied in our laboratory. Based on the results of gel permeation chromatographic studies and ultrafiltration studies and its stability to acid, base and ashing, Bauer and Beer concluded that the necrotoxin activity is due to inorgánic salts that were concentrated from the tissue culture medium during purification [Phytopathology 73:362 (1983)].

Repeated failures to detect and ascribe functions to determinants of pathogenicity by conventional analysis called for a fresh approach. During the last decade, questions of pathogenicity by other phytopathogenic bacteria have been addressed successfully using techniques of molecular biology. We are now taking a similar approach to the study of the mechanisms of pathogenicity of E. amylovora. Our goal is to isolate and characterize genes of the bacterium that are responsible for its pathogenic capabilities, including differential virulence and the induction of hypersensitivity.

Mutants of E. amylovora that are altered in these pathogenic functions are being produced by transposon mutagenesis. The mutants will be complemented with cloned DNA fragments from wild-type (pathogenic) strains of E. amylovora. Steinberger and Beer have made progress in developing transposon mutants [Phytopathology 73:1347 (1983)]. The transposon Tn5 has been inserted into the genome

Beer, S.V., Bauer, D.W. and Steinberger, E.M. (1984). STUDIES ON THE MECHANISM OF PATHOGENESIS OF ERWINIA AMYLOVORA. Acta Hortic. 151, 233-234
DOI: 10.17660/ActaHortic.1984.151.30

Acta Horticulturae