Hannah Roden

Date of Award


Document Type



Environmental and Forest Biology

Thesis Advisor

Thomas R. Horton

Thesis Advisor

William M. Powell


American chestnuts have been genetically engineered to express an oxalate oxidase gene isolated from wheat, which allows the plants to degrade oxalic acid, the virulence factor produced by Cryphonectria parasitica, the pathogenic fungus that causes the chestnut blight. In this study, we investigated the effect of oxalate oxidase gene expression on rate of mycorrhizal colonization of American chestnut root tips. Six-month-old transgenic and wildtype plantlets were placed in a soil inoculant and cultured in a greenhouse for 7 months, then root tips were visually assessed to estimate how many were colonized (expressed as a percentage). Three genotypes were used: ELLIS 1 trees were a cloned wildtype, and Darling 54 and Darling 58 were ELLIS 1 genotypes transformed with the oxalate oxidase gene, differing only in where the gene construct was inserted into the genome. Of surviving trees, 100% of both ELLIS 1 and Darling 58 trees were >95% colonized. Ninety percent of Darling 54 were >95% colonized, and 10% were 90-95% colonized. A Fisher’s exact test of independence was used to reach the conclusion that expression of the oxalate oxidase gene has no effect on mycorrhizal colonization, a result consistent with similar studies.