Master of Science (MS)


Plant Pathology and Crop Physiology

Document Type



Bacterial panicle blight, caused by Burkholderia glumae, is a major bacterial disease of rice in Louisiana. This bacterium contains several virulence factors required for disease development such as toxoflavin, lipase and flagella. In a genome-wide search for regulatory factors related to the virulence of B. glumae, tepR was identified as a negative regulator for toxoflavin production and found to encode a sigma 54-dependent response regulator. TepR is homologous to LuxO, a quorum-sensing signaling component of Vibrio spp. A markerless tepR deletion mutant of B. glumae 336gr-1, LSUPB401, produced more toxoflavin and showed higher lipase and protease activities compared to the wild type, 336gr-1. The phenotype of mutant LSUPB401 was complemented by a functional tepR clone, confirming that tepR is a novel negative regulator for toxoflavin production in B. glumae. In addition, LSUPB401 was more aggressive than the wild type in causing symptoms on rice panicles and onion bulb scales. However, LSUPB401 lost flagellar motility and hypersensitive reaction, suggesting positive roles of tepR in those phenotypes. These findings suggest that TepR promotes the cellular functions for initial host colonization. Ten bacterial strains showing antagonistic activities against B. glumae in an in vitro assay were detected from several thousand bacterial isolates obtained from the root region of rice grown at the Rice Research Station, Crowley, Louisiana. Those bacteria were identified as Bacillus, Paenibacillus and Pseudomonas based on the 16S rDNA sequences. Some isolates suppressed bacterial panicle blight significantly in both greenhouse and field conditions, therefore, are potential candidates for further biocontrol studies.



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Committee Chair

Ham, Jong Hyun