Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 2003
Publication Date: March 1, 2005
Citation: Kong, H.N., Blackwood, C.B., Buyer, J.S., Gulya Jr, T.J., Lydon, J. 2005. The genetic characterization of pseudomonas syringae pv. tagetis based on the 16s-23s rDNA intergenic spacer regions. Biological Control. 32:356-362. Interpretive Summary: Pseudomonas syringae pv. tagetis, a bacterial disease of Canada thistle, is being developed as a biological control agent for this invasive weed. As the disease is known to effect other plants, and the bacterial group Pseudomonas syringae is widespread, we analyzed a region of the genes from several strains of the disease to determine if the strain isolated from Canada thistle was unique. The gene region analyzed contained sufficient variation such that it was useful in distinguishing P. syringae pv. tagetis from other closely related bacterial plant diseases. The results also indicated that a strain of P. syringae that infects sunflower is probably a form of P. syringae pv. tagetis. It was also determined that the 24 P.syringae pv. tagetis strains examined varied very little genetically. The genetic analysis of the Canada thistle pathogen indicated that the strain is probably not unique to this weed. The results of this study will be useful to researchers developing biological control agents of weeds.
Technical Abstract: Pseudomonas syringae pv. tagetis, a plant pathogen being considered as a biological control agent of Canada thistle (Cirsium arvense), produces tagetitoxin, an inhibitor of RNA polymerase which results in chlorosis of developing shoot tissues. Although the bacteria is known to affect several Asteraceae plant species and has been reported in several countries, little is known of its genetic diversity. The genetic relatedness of 24 strains of P. syringae pv. tagetis with respect to each other and to other P. syringae and P. savastanoi pathovars was examined using 16S-23S rDNA intergenic spacer (ITS) sequence analysis. The size of the 16S-23S rDNA ITS regions ranged from 508 bp to 548 bp in length for all 17 P. syringae and P. savastanoi pathovars examined. The size of the 16S-23S rDNA ITS regions for P. syringae pv. helianthi and all the P. syringae pv. tagetis strains examined were 526 bp in length. Furthermore, the 16S-23S rDNA ITS regions of both P. syringae pv. tagetis and P. syringae pv. helianthi had DNA signatures at specific nucleotides that distinquished these from the 15 other P. syringae pv. pathovars examined. These results provide strong evidence that P. syringae pv. helianthi is a nontoxigenic form of P. syringae pv. tagetis. The results also demonstrated that there is little genetic diversity among the known strains of P. syringae pv. tagetis. What genetic differences that do exist were not correlated with differences in host plant, geographical origin, or the ability to produce toxin. While not useful in distinguishing between strains of P. syringae pv. tagetis, the use of the 16S-23S rDNA ITS analysis provides an affective method for distinguishing P. syringae pv. tagetis from other closely related Pseudomonas pathovars.