Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Plants, Soils, and Insects

Major Professor

Fred L. Allen

Committee Members

Arnold M. Saxton, Robert Mee, Hem S. Bhandari, Mark T. Windham, Dennis R. West


Switchgrass (Panicum virgatum L.) is a perennial, warm season grass that can be used as a biofuel. A greater understanding of the relationship of biomass yield and ethanol yield with disease susceptibility and morphological traits, estimation of the underlying genetic parameters of these traits, and the efficacy of selection at different maturity and under different production conditions could help breeders more effectively develop improved biofuel switchgrass cultivars. To examine these issues, three studies were performed. The first examined switchgrass leaves exhibiting low, medium, and high severity of rust symptoms, caused by infection with Puccinia emaculata. Results indicate P. emaculata infection may negatively impact ethanol yield in biofuels switchgrass with predicted ethanol yield reductions of 10% to 34% in leaves exhibiting medium rust severity and 21% to 51% in leaves exhibiting high rust severity. The second study analyzed a diallel of eight parents selected from the cultivars ‘Alamo’, ‘Kanlow’, and ‘Miami’. Correlations of morphological traits to biomass yield indicate a high biomass yielding ideotype of a tall plant with a high number of thick tillers, wide leaves, and an open canopy density. Traits with moderate correlations to biomass yield showed significant, but weak, negative correlations to ethanol yield. Significant SCA effects, maternal effects, and high parent heterosis were found within all traits. Selection during the establishment year did not differ significantly from selection in subsequent years. The third study used the same diallel populations but compared evaluations under space planted conditions to simulated swards. Evaluation under sward conditions differed from evaluation under space planted conditions for estimates of mean production performance, characterization of morphological traits, estimates of genetic parameters, identification of high GCA and SCA in populations, and identification of potential maternal effects or high parent heterosis. If sward conditions are more representative of production conditions, evaluation under space planted conditions could lead to assessment and selection of plants that are less than optimal in production conditions. Results from these three studies should help breeders identify more efficient and effective methods for improving biofuel switchgrass cultivars.

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