Submitted to: International Symposium on Biological Control of Weeds
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2002
Publication Date: 4/27/2003
Citation: Zhang, W., Sulz, M., Mykitiek, T., Li, X., Yanke, J.L., Kong, H.N., Buyer, J.S., Blackwood, C.B., Lydon, J. 2003. A canadian strain of psuedomonas sp. causes white-color disease of canada thistle. International Symposium on Biological Control of Weeds. Interpretive Summary:
Technical Abstract: Patches of white-colored Canada thistle (Cirsium arvense) plants were recently found on roadsides, pastures, and market gardens in Devon, Mulhurst, Stony Plain, and Edmonton, Alberta, Canada. The diseased plants showed apical chlorosis, sometimes with dark and necrotic leaf spots. These symptoms were also associated with stunted growth, fewer shoots, inhibition of flowering, and/or sterility. A total of 101 bacterial strains were isolated from the leaves, stems, and flowers of white-colored Canada thistle plants. A bacterial species (one strain designated CT99B016C) was consistently isolated from diseased plants and was found to produce similar symptoms on Canada thistle under both greenhouse and field conditions. The organism was reisolated from inoculated, diseased plants, thereby fulfilling Koch's postulates. The disease severity of Canada thistle caused by CT99B016C was not affected by the relative humidity in the air, but was increased by the supplement of dew. The optimal bacterial cell concentration to achieve maximum disease was within the range of 108 ¿ 109 cfu/ml, while the optimal surfactant concentration was 0.15-0.3% Silwet L-77â. The CT99B016C strain also caused severe disease of annual and spiny sowthistle (Sonchus oleraceus and S. asper) and dandelion (Taraxacum officinale). The disease severity on these two weed species was even greater than that on Canada thistle. Results of biochemical and nutritional tests and fatty acid analysis clearly placed the CT99B016C strain within the P. syringae group, however, these determinants were not significant enough to separate the P. syringae strains at the pathovar level. Thus, the exact pathovar identification of CT99B016C remains to be determined. Attempts to characterize CT99B016C at the pathovar level using DNA analysis are in progress.