Doctor of Philosophy (PhD)
Plant Pathology and Crop Physiology
Burkholderia glumae is a rice pathogenic bacterium that causes bacterial panicle blight. Some strains of this pathogen produce dark brown pigments when grown on the casamino-acid peptone glucose (CPG) agar medium. A pigment-positive and highly virulent strain of B. glumae, 411gr-6, was randomly mutagenized with mini-Tn5gus, and the resulting mini-Tn5gus derivatives showing altered pigmentation phenotypes were screened on CPG agar plates to identify the genetic elements governing the pigmentation of B. glumae. In this study, several positive and negative regulators, for the pigmentation of B. glumae were identified. During this study, a novel two-component regulatory system (TCRS) composed of the PidS sensor histidine kinase and the PidR response regulator was identiﬁed as an essential regulatory factor for pigmentation. Notably, the PidS/PidR TCRS was also required for the elicitation of the hypersensitive response in tobacco leaves, indicating the dependence of the hypersensitive response and pathogenicity (Hrp) type III secretion system of B. glumae on this regulatory factor. In addition, B. glumae mutants defective in the PidS/PidR TCRS showed less production of the phytotoxin, toxoﬂavin, and less virulence on rice panicles and onion bulbs relative to the parental strain, 411gr-6. In addition, the shikimate pathway genes aroA and aroB are required for the pigmentation of B. glumae in the CPG medium. This study revealed that aroA and aroB of B. glumae are also essential for virulence, growth in M9 minimal medium and tolerance to UV light but not required for the production of toxoflavin. Bacterial panicle blight and sheath blight of rice are the two most important diseases of Louisiana, and most of rice cultivars grown here are susceptible to these diseases. During this study, several rice lines showing superior phenotypes in disease resistance and agronomic traits were developed through plant breeding techniques. LB-33, a recombinant inbred line derived from Bengal and LM-1, was superior to the parents in terms of the disease resistance to bacterial panicle blight and sheath blight as well as other important agronomic characters associated with high yield. In addition, pre-treatment with non-pathogenic strains of B. glumae suppressed the development of bacterial panicle blight and sheath blight disease.
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Karki, Hari Sharan, "A Genetic Study on the Virulence Mechanism of Burkholderia glumae and, Rice Resistance to Bacterial Panicle Blight and Sheath Blight" (2013). LSU Doctoral Dissertations. 3491.