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Genetic Characterization and Real-Time PCR Detection of Burkholderia glumae, a Newly Emerging Bacterial Pathogen of Rice in the United States

Panicle blight of rice (Oryza sativa), caused by the bacterium Burkholderia glumae, is one of the most important new diseases in rice production areas of the southern United States. In this study, pathogenic strains were isolated from diseased panicles in Arkansas rice fields and examined using the Biolog GN microplate system, whole cell fatty acid methyl ester analysis (FAME), rep-polymerase chain reaction (PCR) genomic DNA fingerprinting, and 16S--23S ribosomal DNA (rDNA) intergenic transcribed spacer (ITS) sequence analysis. The B. glumae isolates from Arkansas can be divided into two major groups, but their genetic diversity was relatively low as revealed by 16S--23S rDNA ITS sequence analysis. Since no practical method existed, up to now, for testing the presence of B. glumae in rice seeds, we have developed in this study a real-time PCR method that is effective in detecting and identifying the pathogen in seed lots and in whole plants. The specific PCR primers were designed based on the 16S--23S rDNA ITS sequence of several representative isolates from Arkansas and Japan. This method is highly sensitive, rapid, and reliable, and has great potential for analyzing large numbers of samples without the need for DNA extraction or agarose gel electrophoresis. Although vertical resistance has not been observed among tested rice cultivars, LM-1 and Drew exhibited considerable resistance to B. glumae infection based on disease lesion size and the bacterial growth in planta.