Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

Document Type



This research was conducted to enhance utilization of the Liberty herbicide resistance transgene in rice. Non-lethal methods to determine the sensitivity of transgenic rice plants to hygromycin B and Liberty were developed, tested and used in this research. Four homozygous transformed plants were selected to make reciprocal crosses with their non-transformed parent cultivars Taipei 309 and Nipponbare. Their resistances to Liberty and hygromycin B were controlled by the closely linked single dominant genes bar and hpt. Some non-resistant phenotypes in the F2 populations were due to gene silencing. The bar gene in some of these plants were allelic and some were non-allelic. When seven independently transformed homozygous transgenic plants with bar and hygromycin genes from Taipei 309 and Nipponbare were crossed reciprocally, progeny evaluations showed five allelic locations among the seven transgenic plants. Twenty additional homozygous transgenic plants from independent transformation events were crossed reciprocally with the previous seven transgenic plants. Evaluation of F1, F2, and F3 populations showed that some of the genes were allelic, but most of them were non-allelic with two or more pairs of genes being expressed. The functional foreign gene (bar) appeared to be restrictively inserted into the rice genome in some cases and was not randomly inserted and expressed. Three to five repeated backcrosses were made using transgenic plants as the donor and current cultivars as the recurrent parents. The results from selected progeny rows, and two-years of yield tests with selected lines, indicated that the target bar gene could be transferred to lines similar to commercial cultivars from homozygous transformants in 4-5 years of backcrossing, giving lines similar to the recurrent parents based on phenotype and yield potential. Liberty herbicide has antibiotic characteristics and suppressed growth of several rice fungal pathogens and Burkholderia glumae in in vitro tests. Liberty had a short residual activity against Rhizoctonia solani in field tests, but single applications of Liberty after disease development had started in the field significantly reduced sheath blight ratings and yield loss. Control of sheath blight by Liberty was equal to or better than that given by the registered fungicide Quadris.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Milton C. Rush