Evaluating the performance of low-lignin transgenic bioenergy feedstocks in the field

Lignin in the cell walls of lignocellulosic biomass limits the accessibility of carbohydrates for breakdown into fermentable sugars and subsequently biofuels. The resistance of plant biomass to enzymatic or microbial deconstruction, known as biomass recalcitrance, can be overcome by reducing lignin content or modifying its composition through genetic modification of the lignin biosynthetic pathway. However, few studies to date have assessed the performance of low-lignin biofuel feedstocks under field conditions. Because lignin plays a vital role in several developmental and stress-related processes, characterization of these plants under the appropriate agronomic conditions is necessary to confirm that the improved biofuel-related traits can be maintained under field conditions without compromising plant growth or susceptibility to stresses. The general goal of this thesis project was to gain a better understanding of how lignin-modified feedstocks might perform in the field. The first chapter provides an introduction on the use of lignocellulosic biomass for biofuel production, the significance of lignin engineering for improving biofuel yields, and the importance of field trials to validate greenhouse results in a more realistic environmental setting. Chapter two is a review of the consequences of altered lignin biosynthesis on plant susceptibility to biotic and abiotic stresses. Chapter three reports the results of a two-year field evaluation of reduced recalcitrance transgenic switchgrass for chemical composition, sugar release, ethanol yield, agronomic performance, and disease susceptibility.