Coronatine-producing and non-producing strains of Pseudomonas syringae pv. glycinea have been examined. We found a connection between copper resistance and synthesis of coronatine. Published data implied that these properties may be encoded on different plasmids. Production of coronatine and copper resistance were also found to be correlated for pv. glycinea in 19 field-isolates from leaf spots of plants in a soybean field and in 28 strains of a bacterial culture collection. Genomic diversity within pv. glycinea was investigated by plasmid profiling, DNA hybridization studies and PCR analysis. All strains unable to produce coronatine (cor-) were sensitive to copper ions and showed no homology to DNA from plasmid pSAY1, which carries a gene cluster for steps in coronatine production. In addition, cor- strains could be distinguished from coronatine-producing strains by a single unique band when amplified by random primer PCR. Plasmid profiles of strains isolated from field-populations during 1983, 1985 and 1990 showed that coronatine-producing and non-producing strains were present. The plasmid patterns also varied in 28 strains examined from a culture collection. No correlation between plasmid patterns and race specificity was observed. Cosmid pSAY1 proved to be an effective probe for detection of the coronatine synthesis genes and also revealed polymorphisms in coronatine producing strains of pv. glycinea.