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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.
Porter et al. (Wed,) studied this question.