Lignin Concentration and Composition of Divergent Smooth Bromegrass Genotypes

Esterified phenolics of noncore lignin and core lignin concentration and composition are correlated with forage digestibility. In this study, divergent smooth bromegrass (Bromus inermis Leyss.) genotypes selected for high or low in vitro dry matter disappearance (IVDMD) were evaluated for genotypic variation of lignin concentration and composition. Primary growth of nine genotypes from each IVDMD selection group was harvested during 2 yrs and separated in to leaf blade and stem plus sheath fractions. Detergent fiber components, core lignin concentration and composition, and esterifled noncore lignin content were determined. Differences were observed between the IVDMD genotype groups for neutral detergent fiber (NDF), hemicellulose and cellulose concentration in leaf blade tissue, and NDF and hemicellulose concentration of stems. Core lignin concentration was greater in stem of the low IVDMD group but not leaves. Yield of core lignin products was greater for the low IVDMD group leaf blades but not stem plus sheath tissue. Genotypic variation existed between and/or within IVDMD genotype groups for molar proportions of vanillin, syringaldehyde, p-coumaric acid, and ferulic acid from core lignin nitrobenzene oxidation products. Esterified ferulic acid concentration of noncore lignin was consistently greater in the high IVDMD group, but esterified p-coumaric acid was only greater in stem tissue of the low IVDMD group. Differences observed between the IVDMD groups were generally consistent with previous reports of correlations between lignin fractions and IVDMD. Differential phenotypic correlation coefficients between lignin concentration and composition for the high and low IVDMD groups suggested some value to attempting divergent, independent selection for lignin concentration and composition. Resultant genetic materials would be valuable tools for addressing mechanistic questions about the role of specific lignin fractions as inhibitors of fiber fermentability.