Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: September 10, 2002
Publication Date: February 10, 2003
Citation: Kong, H.N., Blackwood, C.B., Buyer, J.S., Gulya, T.J., and Lydon, J. 2003. The genetic characterization of pseudomonas syringae pv. tagetis based on the 16s-23s rdna intergenic spacer regions. Weed Science Society of America Meeting Abstracts. 43:29. Technical Abstract: Pseudomonas syringae pv. tagetis, a plant pathogen being considered as a biological control agent of Canada thistle (Cirsium arvense (L.) Scop.), produces tagetitoxin, an inhibitor of RNA polymerase which results in chlorosis of developing shoot tissues. Although the bacteria is known to effect several Composite plant species and has been reported in several countries, little is known of its genetic diversity. Here we report the genetic relatedness of 18 strains of Ps. pv. tagetis with respect to each other and to other Pseudomonas syringae pathovars and two closely related species, Pseudomonas savastanoi, based on 16S-23S intergenic spacer (ITS) sequences. The 16S-23S spacer regions were amplified by PCR, the purified PCR products cloned in a pGEM vector, and the sequence data determined using an ABI 373A DNA Sequencer and Big Dye terminators. The size of the 16S-23S ITS region was 526 bp in length for all 18 Ps. pv. tagetis strains tested. Half of the 18 Ps. pv. tagetis strains tested had the identical 526 bp sequence, while the other half differed from these at only one to three base positions, all of which occurred in the ITS region downstream from the tRNAAla gene. Thus, based on the 16S-23S ITS regions, there is very little divergence within this pathovar (99.4% to 99.8% homology). The genetic differences that exist were not correlated with differences in host plant or geographical origin. The 16S-23S ITS sequences of the seven P. syringae pathovars and two P. savastanoi pathovars tested ranged in size from 530 bp to 545 bp and showed significant heterogeneity from the 16S-23S sequences of Ps. pv. tagetis. Including base differences from substitutions, deletions, and additions, sequence homologies of Ps. pv. tagetis and the other closely related species tested varied from 82.5% to 97.3%. Thus, while not useful in determining differences within the species, the use of the 16S-23S ITS region of Ps. pv. tagetis provides a method of distinguishing this species from other closely related Pseudomonas species.