Bacteria isolated from coriander and other umbelliferous herbs

Abstract

Thirteen bacterial isolates associated with leaf spotting symptoms of coriander (Coriandrum sativum Linn.), anise (Pimpinella anisum) and caraway (Carum carvi), were tested for pathogenicity to coriander. Inoculation of young plants showed that 10 isolates caused dark, water soaked lesions on the leaves.

The 13 isolates plus Pseudomonas syringae pv. syringae, Pseudomonas fluorescens (Pseudomonas marginalis) and Pseudomonas aeruginosa were tested for levan production, oxidase activity, ability to cause soft rot in potato, presence of arginine dihydrolase, tobacco hypersensitivity, ability to liquefy gelatin, ability to ice nucleate, ability to degrade pectate, poly-β-hydroxybutyrate accumulation, and ability to utilize more than 100 substrates as sole sources of carbon and energy.

The results of these tests were analyzed in a numerical taxonomy study. Results of using two association coefficients (simple matching coefficient and Jaccards coefficient) and two sequential, agglomerative, hierarchical, nonoverlapping clustering techniques (single linkage clustering and complete linkage clustering) were compared for all bacterial isolates which produced results that did not measure any characteristic that was also measured by another test, and that had discriminatory value between the isolates. This was repeated with a reduced set of data, produced by excluding 87 carbon source utilization results of questionable value, generated by a commercial diagnostic package. The numerical taxonomy analyses produced similar dendograms and showed that the 10 isolates capable of causing a pathogenic reaction in coriander formed two distinct clusters, particularly when a reduced number of tests were used in the analyses. These two clusters were most easily distinguished by the ability of the members of only one cluster to produce fluorescent pigments when grown on Kings medium B.

The two clusters were confirmed by the results of a restriction mapping analysis conducted on the 13 isolates and Pseudomonas syringae pv. syringae. DNA:DNA hybridization (slot blotting) analyses failed to support the clusters produced in the numerical taxonomy study, but this technique is not suitable for investigating relationships between bacterial strains.

It was concluded that there are two strains of bacteria pathogenic to coriander. One capable of producing fluorescent pigments when grown on Kings medium B, and the other without this characteristic. Although the fluorescent pigment producing strain appears to be in the Pseudomonas syringae group, it showed a closer resemblance to the nonfluorescent strain than to Pseudomonas syringae pv. syringae in a number of tests. This is consistent with the observation of other workers.