Brown Midrib Mutants in Sudangrass and Grain Sorghum¹

Abstract

Three low lignin, brown midrib (bmr) sorghum (Sorghum bicolor L. Moench) mutants, designated bmr‐6, bmr‐12, and bmr‐18, were each backcrossed to normal grain‐ and grassy‐type sorghums. The objective was to determine if the effect of the brown midrib mutants on fiber composition would be expressed equally in both grain‐ and grassy‐type genetic backgrounds.Analysis for fiber composition and in vitro dry matter disappearance (IVDMD) was conducted on mature stem tissue of mutant and normal plants from the F2 generation Of the first and second backcross. The bmr‐6 mutant reduced lignin percentage from 10.3 to 8.5 (P < 0.01) and increased IVDMD percentage from 39.6 to 48.7 (P < 0.01). Mutant ✕ background and mutant backcross interactions were not significant (P > 0.10), indicating that the effect of the bmr‐6 mutant was expressed as well in grassy‐type as in grain‐type backgrounds. Similar results were obtained with the bmr‐12 and bmr‐18 mutants. These mutants, evaluated after only one backcross, reduced stem lignin from 8.3 to 6.1% (P < 0.01) and increased IVDMD from 44.0 to 55.5% (P < 0.01). The effects were expressed as well in grassy‐type as in grain‐type backgrounds.Results indicate that sudangrass sorghums containing brown midrib mutant genes are lower in lignin percentage and higher in digestibility than normal genotypes. Mutant sudangrasses of this nature should be higher in digestible energy percentage and should result in greater animal production than normal sudangrasses [Sorghum sudanense (Piper) Stapf] when fed to ruminant animals.

Chemical composition and in situ ruminal nutrient degradability of normal and brown midrib forage pearl millet grown in southwestern Québec

“…However, ADF was similar for both types of forage millet. Our results are consistent with other studies that showed lower NDF and ADL for bmr millet, sorghum and corn compared with their normal counterparts (Fritz et al 1981;Cherney et al 1988;Cherney et al 1990). Harvest had no effect on NDF, ADF, and ADL.…”

“…Cherney et al (1988) reported 10% higher in vitro DM digestibility for bmr than normal genotype pear millet. Similar improvement in in vitro DM digestibility was reported for bmr sorghum and sudangrass (Fritz et al 1981;Akin et al 1986;Cherney et al 1986). …”

The Present Status of C₄ Tropical Grasses Breeding and Molecular Approaches

“…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. Fritz et al (1981) reported that both grain sorghum and sudangrass (Sorghum sudanense (Piper) Staft), each of which backcrossed with bmr-6, bmr-12 and bmr-18, expressed brown midrib traits and had less lignin content and more digestibility than normal genotypes. Recently, several cultivars bred to contain brown midrib traits have been released (Table 4).…”

Genetic variation and breeding strategies for improved cell wall digestibility in annual forage crops. A review

“…Results were doubtless similar for lignin content. Using three chemically induced mutants, selected by Porter et al [151] for the further experiments, Fritz et al [99] showed an improvement in stem IVDMD ranging between 8 and 12% in brown midrib sorghum, compared to normal sorghum. From their results, the ADL/NDF was reduced by 1.3, 2.2 and 2.5 percent point in bmr6 (BC2), bmr12 and bmr18 (BC1) sorghum, compared to normal, respectively.…”