Burkholderia andropogonis has a broad host range including 52 species of 15 families of unrelated monocot and dicot plants such as white clover, carnation, bougainvillea, and other ornamental plants (2). In October 2003, a severely diseased Bougainvillea sp. was found in Kowloon, Hong Kong. Diseased leaves had circular lesions with brown centers surrounded by dark, red-brown margins bordered by chlorotic halos. A bacterium consistently isolated from such lesions using peptone yeast extract agar plus glucose plates was compared with several B. andropogonis strains, including the type strain as well as a B. andropogonis-like strain previously isolated from white clover in Vancouver, BC, Canada in June 1995. Pathogenicity of the isolates was determined by infiltrating greenhouse-grown white clover and carnation leaves with bacterial suspensions of ≈106 CFU/ml. Inoculated leaves developed lesions typical of those caused by B. andropogonis. Koch's postulates were fulfilled by isolating bacteria from typical lesions on inoculated plants that were identical to inoculated strains in colony morphology and biochemical characteristics. Using transmission electron microscopy, the Canadian and Hong Kong isolates, as well as authentic strains of B. andropogonis, were shown to have a single, polar sheathed flagellum, a unique feature of this bacterium (4). The two new isolates were compared with authentic strains of B. andropogonis using the Biolog system (Biolog Inc., Hayward, CA), whole cell protein profiles, and polymerase chain reaction (PCR) with species-specific primers. The two new isolates and authentic B. andropogonis cultures, including the type strain, were all identified as B. andropogonis using the Biolog system. The similarity in protein patterns of the new strains to those of authentic B. andropogonis strains supported their preliminary identification on the basis of morphology, pathogenicity, and the Biolog identification system. PCR amplification using primer pair Pf/Pr (Pf: 5′-AAGTCGAACGGTAACAGGGA-3′, and Pr: 5′-AAAGGATATTAGCCCTCGCC-3′), which specifically targets B. andropogonis 16S rDNA (1), produced the expected 410-bp amplicon with genomic DNA templates from the two isolates, further confirming their identity. No sequence variation was observed between the amplicon and data (X67037) from GenBank, which confirmed the earlier observation that strains of B. andropogonis were phylogenetically homogenous (1). To our knowledge, this is the first report of B. andropogonis infection on Bougainvillea sp. in Hong Kong. The disease has been previously reported on this host only from Brisbane, Australia. This is also the first report of the isolation of B. andropogonis from clover in Canada, although the disease occurs on clover in other regions such as Australia and Hawaii. B. andropogonis has been previously reported in Canada only on greenhouse carnations (Dianthus sp.) (3). Usually, conditions of high humidity and high temperature are optimal for infection by B. andropogonis. On the basis of historical weather data, Hong Kong has tropical and subtropical coastal weather similar to Brisbane, Australia, while Vancouver, although mild, is cooler but has periods of high humidity.
References: (1) R. D Bagsic et al. Lett. Appl. Microbiol. 21:87. 1995. (2) E. J. Cother et al. Plant Pathol. 53:129, 2004. (3) D. W. Creelman. Can. Plant Dis. Surv. 44:146, 1964. (4) X. Li. Ph.D. diss. The University of Queensland, St. Lucia, Australia. 1993.
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