Phenotype, Fiber Composition, and in vitro Dry Matter Disappearance of Chemically Induced Brown Midrib (bmr) Mutants of Sorghum¹

Abstract

Chemically induced brown midrib (bmr) mutants sorghum (Sorghum bicolor (L.) Moench) were characterized with regard to phenotype, fiber composition, and in vitro dry matter disappearance (IVDMD). The recessive bmr genes produced brown pigmentation in the leaf midrib and stem of mature plants. Pigmentation varied among mutants in intensity, time of appearance, and degree of fading as plants matured.Stem and leaf samples of mutant and normal plants were analyzed in the laboratory to determine percent cell wall constituents (CWC), acid detergent fiber, (ADF), cellulose, hemicellulose, permanganate lignin (PL), vitro dry matter, and in vitro cell wall constituent disappearance (IVDMD and IVCWCD). Ten of the 13 mutants had significantly less stem lignin than the normal counterparts. Reductions in lignin ranged from 5 to 51% in stems and from 5 to 25% in leaves. In the case of other fiber components, only occasional differences were observed between normal and mutant plants. Increases in IVDMD and IVCWCD of as much as 33 and 43%, respectively, were associated with the presence of bmr genes.Variation among mutants in lignin concentration probably indicates that several different bmr genes were involved. Similarities between the bmr genes of sorghum and the bm genes of maize (Zea mays L.) suggest the possible existence of similar genes in other grasses, although their identification may be more complicated because of polyploidy.

Free Phenols in Maize Pith and Their Relationship with Resistance to <I>Sesamia nonagrioides</I> (Lepidoptera: Noctuidae) Attack

“…Previous studies have indicated impairing different steps in monolignol biosynthesis results in reddish brown to tan stem and stalk pigmentation, including the CAD and COMT mutants examined in this study (Mackay et al 1997, Tsai et al 1998, Sibout et al 2005, Zhang et al 2006). There are differences in pith and midrib (leaf vein) coloration between bmr6 and bmr12 (Porter et al 1978, Saballos et al 2009), probably because bmr6 and bmr12 block different steps of the monolignol biosynthetic pathway. However, the increased mortality of both H. zea and S. frugiperda on both bmr mutant pith types suggests a common chemical or biochemical resistance factor(s), yet to be identified, which is not related to differences in pith color.…”

The Present Status of C₄ Tropical Grasses Breeding and Molecular Approaches

“…However, effort to improve forage quality through traditional breeding have been hindered by the complexity of this trait and its regulation by many genes, although the sorghum brown midrib (bmr) mutants induced by Porter et al (1978) sparked a major breakthrough in breeding for forage sorghum quality. Forage digestibility, one of the major limitations of ruminant productivity, is negatively correlated with lignin content and is affected by the lignin composition in plant cell walls, whereby lignin causes forage quality to decline (Barrière et al 2003).…”

“…In addition to their biochemical properties, these mutants show a reddish-brown pigment in the leaf midrib and stem. Porter et al (1978) reported that three of the mutants (bmr-6, bmr-12, and bmr-18) appeared most promising to improve forage quality. Since the brown midrib trait is inherited as a simple recessive trait and is closely associated with improved forage digestibility (Barrière & Argillier 1993, Bittinger et al 1981), forage quality can be improved by fixing bmr alleles.…”

A Genomewide Analysis of the Cinnamyl Alcohol Dehydrogenase Family in Sorghum [Sorghum bicolor(L.) Moench] IdentifiesSbCAD2as theBrown midrib6Gene

“…Genetic complementation experiments demonstrated that expression of the wild-type OsCAD2 gene was sufficient to restore normal cell wall composition of gh2 plants (Zhang et al 2006). The brown midrib (bmr) mutants of sorghum (Porter et al 1978) are similar to the bm mutants of maize. The abbreviation bmr was adopted to distinguish it from bm, already in use for the sorghum bloomless mutants (Ayyangar and Ponnaiya 1941).…”