Master of Science (MS)


Plant Pathology and Crop Physiology

Document Type



Four hundred and two bacterial isolates isolated on the semi-specific S-PG medium from diseased rice tissues showing symptoms of panicle blighting. These isolates were purified using serial dilution in sterile water and replating on S-PG medium. A total of 420 single isolates were obtained. These isolates were subjected to pathogenicity tests on rice (Oryza sative L. cv. Cypress). Based on these tests, 339 isolates were used in BiologTM tests and identified to the species level. Bacterial strains from 39 species in 16 genera were identified, including 52 isolates representing15 Pseudomonas species and 261 isolates representing six Burkholderia species. The remaining 26 isolates included 14 other genera. Of 261 Burkholderia strains, 103 isolates were B. gladioli, 68 isolates were B. glumae, 60 isolates were B. multivorans, 25 isolates were B. plantarii, three isolates were B.cocovenenans and three isolates were B. vietnamiensis. The pathogenicity tests revealed that 69% or 234/339 isolates were on Cypress rice, causing seedling infection, sheath rot and/or panicle blighting. Most of the pathogenic strains were in the genera Burkholderia and Pseudomonas. The four most common species, B. glumae, B. gladioli, B. multivorans, and B. plantarii, comprised 90% of all of the pathogenic bacteria, suggesting that a complex of Burkholderia species were causing the panicle blight/sheath rot syndrome recently found in Louisiana. Five Pseudomonas species, with total of 16 isolates, were found to associate with this disease, including two isolates of P. syringae pv zizanize, three isolates of P. fluorescens, three isolates of P. pyrrocinia, one isolate of P. spinosa and seven isolates of P. tolaasii. The symptoms of the disease on rice were only produced by the indicated bacterial strains. Symptoms included brown, margined flag leaf sheath lesions, grain rot, sterile florets, grain discoloration, and leaf and sheath rot on inoculated seedlings. It was impossible to distinguish among Burkholderia species based on symptoms and colony morphology. Pathogenic Burkholderia strains produced a yellow pigment in King’s B medium. Avirulent strains did not produce this pigment. The isolates from rice were grouped by species and pathogenicity. It appeared that B. glumae and B. gladioli were the most main pathogenic species.



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Committee Chair

Milton C. Rush