DIGESTION KINETICS AND COMPOSITION OF NORMAL AND BROWN MIDRIB SORGHUMMORPHOLOGICAL COMPONENTS

The brown midrib (bmr) mutation has shown the potential to improve the nutritive quality of forage sorghum [Sorghum bicolor (L.) Moench]; ho wever, no study has been conducted to directly compare the effect of t he bmr gene in a sudangrass (sorghum x drummondii (Steudel) Millsp. an d Chase) and its hybrid with a grain sorghum. Research was conducted t o evaluate the relationship between cell wall composition and digestib ility within the morphological components of normal and bmr sorghum cu ltivars. Cell wall constituents, structural carbohydrates, alkali-labi le phenolic monomers, and in vitro digestion kinetics were determined for 'Piper' (normal sudangrass), 'S407 (Piper bmr-6 sudangrass), and ' F1006-8 x S407' (male sterile grain type bmr-6 sorghun x Piper bmr-6 s udangrass). Whole plants were harvested at the boot and hard dough gro wth stages and separated into leaf blade, leaf sheath, inflorescence, and stem components. Significant differences were found between cultiv ars in concentrations of cell wall constituents. Neutral detergent fib er (NDF) concentration was lower (P < 0.05) in the bmr cultivars than in Piper due to lower concentrations of cellulose and acid detergent l ignin (ADL). Concentrations of ADL averaged 45 g kg(-1) dry matter for Piper, 28 g kg(-1) for S407, and 25 g kg(-1) for F1006-8 x S407. The bmr cultivars had lower (P < 0.05) concentrations of p-coumaric acid a nd higher (P < 0.05) concentrations of vanillin than Piper. There were no differences (P > 0.05) among cultivars in ferulic acid concentrati on. p-Coumaric acid concentrations averaged 25 g kg(-1) of NDF for Pip er, 16 g kg(-1) NDF for S407, and 14 g kg(-1) NDF for F1006-8 x S407. Rate constants for in vitro digestion of NDF were similar (P > 0.05) a mong cultivars. The bmr sudangrass (S407) had a greater (P < 0.05) ext ent of NDF digestion than either Piper of F1006-8 x S407. Extent of ND F digestion averaged 0.596 for Piper, 0.623 for S407, and 0.597 for F1 006-8 x S407. Results of this study indicate that the bmr mutation can effectively be expressed in both sudangrass and sorghun x sudangrass hybrid backgrounds.