Potential of Brown-Midrib, Low-Lignin Mutants for Improving Forage Quality

Publisher Summary Brown-midrib (bmr) mutants differing in quality and quantity of lignin from normal genotypes offer an opportunity to increase the overall digestion of plant fiber. It is a simple recessive trait that phenotypically produces a reddish-brown pigmentation associated with lignified tissues. Several different genes have been identified in both maize and sorghum, which produce the characteristic bmr phenotype. Lignin concentrations in bmr genotypes are consistently lower than their normal counterparts. Besides differences between bmr and normal alkali-labile phenolics, the nitrobenzene oxidation of the two lignins yields different ratios of products. In vitro digestibility of bmr genotypes has been consistently higher than normal, but in vitro rate of digestion does not appear to be consistently affected by the mutation. Animal performance on bmr forage has not always produced better results than with normal genotypes but the tendency is for improved animal performance with bmr genotypes. Activities of several enzymes involved in lignification differed between bmr and normal genotypes. Differences in activities are not consistent across species, indicating that several different modifications of the lignifications pathway may result in a similar phenotypic bmr response. This chapter concludes that bmr provide an excellent system for examining and possibly modifying the lignifications process in plants.