Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Plant, Soil and Environmental Sciences

Major Professor

Hem S. Bhandari

Committee Members

Fred L. Allen, Feng Chen, Vincent R. Pantalone, Arnold M. Saxton


Switchgrass is a warm-season C4 grass used for biofuel production. The primary goal of this study is biomass yield improvement for use as a bioenergy feedstock. The research plan was partitioned into three main objectives: (i) evaluate the genetic diversity among lowland switchgrass populations using microsatellite markers; (ii) assess genetic variation in an Alamo half-sib (AHS) population developed through phenotypic selection; (iii) and identify quantitative trait loci (QTL) associated with biomass yield and establishment related seed traits using a Nested Association Mapping (NAM) population. The genetic diversity study on lowland switchgrass showed significant phenotypic variations (P<0.05) among and within germplasm accessions. The Analysis of Molecular Variance (AMOVA) revealed that among genotypes within populations and among populations explained 84 and 16% of molecular genetic variations. The Principal Coordinate Analysis (PCoA) and cluster analysis separated switchgrass populations according to the ancestral background. The study on genetic variation showed significant variation (P<0.05) among AHS for biomass yield, tillering ability, and spring vigor, suggesting the importance of additive genetic variation in these traits. Results also showed great potential for biomass yield improvement through selection based on family performance. Using 10% selection intensity, parental control of two, and a narrow-sense heritability estimate of 0.11, gain per cycle selection from half-sib family selection is estimated to be 23%. The study on identification of QTLs associated with biomass yield and establishment related traits showed significant variation among NAM families and genotypes within families for biomass yield, seed weight, and germination (P<0.05). A total of 785 significant markers for biomass yield were detected (P<0.05) of which 176 were for seed weight and 131 for germination. Composite interval mapping revealed 21 QTLs for biomass yield across locations in 2 years the highest LOD score of 7.6 detected in chromosome Ia that explained a 12.5% of the phenotypic variation. Two QTLs located in chromosome VIIIb for seed weight explained 5.2% and 4.6% phenotypic variation. One QTL for germination located in chromosome IXa explained 5.2% of the phenotypic variation. The results of these studies will be useful for future breeding efforts in switchgrass and other perennial grasses.

Available for download on Thursday, August 15, 2019

Files over 3MB may be slow to open. For best results, right-click and select "save as..."