Date of Award

8-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Agronomy

Committee Chair

Christie E. Williams

Committee Member 1

Stephen B. Goodwin

Committee Member 2

Steven R. Scofield

Abstract

Wheat (Triticum aestivum) yield is limited by biotic stresses such as Hessian fly [Mayetiola destructor (Say)] attack which causes a significant annual loss. Previous studies have shown that Brachypodium distachyon is resistant to Hessian fly infestation. Since B. distachyon has advantages over wheat to be used as a model plant in genetic and genomics, we compared the response of 5 wheat lines (4 resistant lines, harboring different Hessian fly-resistance H genes, and 1 susceptible line to Hessian fly infestation) to B. distachyon at early stages [12 hours, 1 day, 3 days and 5 Days After Hessian fly egg-Hatch (DAH)] of Hessian fly infestation. Using q-RT-PCR, we studied the expression profile of some Hessian fly-responsive genes as well as genes involved in plant resistance/susceptibility to pathogens and insects. Based on the current data, we conclude that, for some genes, expression level and timing differ among wheat lines carrying different resistance H genes conferring resistance to Hessian fly. We also conclude that the gene-for-gene resistance of wheat and the non-host resistance of B. distachyon utilize a few different gene sets in defense against Hessian fly. We have also investigated the expression profiles of genes associated with Hessian fly resistance and susceptibility expressed in four tissues (leaf 2 base, leaf 2 blade, leaf 3 base and root) of wheat lines H9-Iris (resistant) and Newton (susceptible) at 1, 3 and 5 DAH to determine whether Hessian fly attack caused systemic or localized responses in wheat. qRTPCR data revealed that wheat response to Hessian fly resistance is localized. In contrast to resistance, wheat response to Hessian fly susceptibility is systemic. These results indicate that wheat resistance to Hessian fly is very efficient with less energy and resources consumed than if the entire plant produced defense molecules. Using light microscope, we conducted a study of Hessian fly larval body area on Hessian fly-resistant and -susceptible wheats to determine whether the Hypersensitive Response (HR) might play a role in Hessian fly resistance. Results revealed that sizes of larvae on a resistant wheat line utilizing the HR did not significantly differ from those of larvae on a resistant wheat line that did not express the HR.

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