Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/9/2002
Publication Date: 5/19/2003
Citation: CASLER, M.D., PEDERSEN, J.F., UNDERSANDER, D.J. FORAGE YIELD AND ECONOMIC LOSSES ASSOCIATED WITH THE BROWN-MIDRIB TRAIT IN SUDANGRASS. CROP SCIENCE. 2003. Interpretive Summary: Brown-midrib genes increase digestibility due to reduced lignification in sudangrass, Sorghum bicolor (L.) Moench. Brown-midrib lines are known to be low in forage yield potential, but this reduction in forage yield has not been previously quantified. We demonstrated that improved nutritional value of brown-midrib sudangrass offsets losses in forage yield for first harvest, but not for second harvest. Brown-midrib sudangrass is unable to produce sufficient regrowth to make a second harvest economical. Reduced tillering may be partly responsible for this. The brown-midrib phenotype of sudangrass appears to be associated with environmentally sensitive genes in some genetic backgrounds, suggesting that forage yield losses associated with the brown-midrib trait may be reduced in warmer and longer growing seasons. The research provides decision-support information for forage producers, allowing them to make informed choices between normal and brown-midrib sudangrass.
Technical Abstract: Brown-midrib genes increase digestibility due to reduced lignification in sudangrass, Sorghum bicolor (L.) Moench. 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 to their brown-midrib counterparts and to four highly selected brown-midrib (FG) lines at two locations for 2 years. 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.