Date of this Version
Published in Crop Sci. 43:782–789 (2003).
Brown-midrib genes increase digestibility due to reduced lignification in sudangrass, Sorghum bicolor subsp. drummondii (Nees ex Steud.) de Wet & Harlan. Brown-midrib lines are known to be low in forage yield potential, but this reduction in forage yield has not been previously quantified. The objectives of this study were to quantify the increase in forage quality and decrease in forage yield and to provide an economic assessment of this dichotomy. Piper and Greenleaf (normal leaves) were compared with their brown-midrib counterparts and four highly selected brown-midrib (FG) lines at two locations for 2 yr. Brown-midrib lines averaged 9.0% lower in lignin and 7.2% higher in in vitro fiber digestibility than normal lines. The reduction in first-harvest forage yield was highly variable across germplasms and locations. Greenleaf and the FG lines showed severe forage yield reductions in Wisconsin but not in Nebraska, whereas forage yield of Piper was uniformly reduced across locations. Reduced tillering and plant height of the brown-midrib plants appeared to be mechanisms for reducing forage yield. The brown-midrib phenotype of sudangrass, caused by the homozygous condition of the bmr-6 allele, appears to be environmentally sensitive, particularly limiting production in cooler and shorter growing seasons. Conversely, uniform reductions in second-harvest forage yield suggested a fundamental limitation to regrowth potential associated with the brown-midrib phenotype. Predicted net returns from feeding sudangrass hay were similar for first-harvest normal and brown-midrib lines, but severely depressed for brown-midrib lines in second harvest, due to the severe yield reductions.