Forage Yield and Economic Losses Associated with the Brown-Midrib Trait in Sudangrass

associated with the brown-midrib phenotype average ≈20% for grain, 10 to 17% for stover, and 16% for Brown-midrib genes increase digestibility due to reduced lignificafodder (Miller et al., 1983; Lee and Brewbaker, 1984). tion in sudangrass, Sorghum bicolor subsp. drummondii (Nees ex Some brown-midrib lines may have stover yields as high 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 as the best normal lines, but grain yield is always depreviously quantified. The objectives of this study were to quantify the pressed (Miller et al., 1983). There is one report of increase in forage quality and decrease in forage yield and to provide similar fodder yields for two pairs of isogenic brownan economic assessment of this dichotomy. Piper and Greenleaf (normidrib and normal maize lines, but the brown-midrib mal leaves) were compared with their brown-midrib counterparts and lines were 3 d later in silking and had a lower ear-toto four highly selected brown-midrib (FG) lines at two locations for stover ratio than the normal lines (Weller et al., 1985). 2 yr. Brown-midrib lines averaged 9.0% lower in lignin and 7.2% Brown-midrib lines are generally shorter than normal higher in in vitro fiber digestibility than normal lines. The reduction counterparts, but not sufficiently so to account for all in first-harvest forage yield was highly variable across germplasms yield losses (Miller et al., 1983; Lee and Brewbaker, and locations. Greenleaf and the FG lines showed severe forage yield 1984). Brown-midrib lines have reduced stalk mass per reductions in Wisconsin but not in Nebraska, whereas forage yield of Piper was uniformly reduced across locations. Reduced tillering and unit length (Zuber et al., 1977) and increased stalk lodgplant height of the brown-midrib plants appeared to be mechanisms ing (Miller et al., 1983). While there are no reports for reducing forage yield. The brown-midrib phenotype of sudangrass, of yield differences between normal and brown-midrib caused by the homozygous condition of the bmr-6 allele, appears sorghums, sudangrasses, or hybrids, the effect of bmr to be environmentally sensitive, particularly limiting production in loci in Sorghum is generally believed to be similar to cooler and shorter growing seasons. Conversely, uniform reductions that in maize, an important impediment to commercialin second-harvest forage yield suggested a fundamental limitation ization (Kalton, 1988). to regrowth potential associated with the brown-midrib phenotype. The objectives of this study were to quantify the inPredicted net returns from feeding sudangrass hay were similar for crease in forage quality and decrease in forage yield first-harvest normal and brown-midrib lines, but severely depressed associated with the brown-midrib trait in sudangrass, to for brown-midrib lines in second harvest, due to the severe yield reductions. determine if selection for yield and vigor can overcome the negative association between yield and quality, and to provide an economic assessment of this negative association. B mutations, when present in the homozygous recessive state, result in reduced lignificaMATERIALS AND METHODS tion, reduced cell-wall concentration, increased digestibility, and increased voluntary intake of feed by The germplasm for this study consists of two cultivars with ruminants. These single-locus mutations represent the normal leaf-blade phenotype, Piper and Greenleaf, and their single most rapid and effective mechanism of genetically brown-midrib counterparts. Piper-bmr and Greenleaf-bmr were created by three generations of backcrossing the bmr-6 modifying nutritional value of forage crops. As singleallele from grain sorghum into Piper and Greenleaf (Fritz et locus recessive mutations, they can be backcrossed al., 1981; J.D. Axtell, 1994, personal communication). readily into elite lines. Lignin concentration of brownFour additional brown-midrib lines were generated from midrib lines has been reduced by 5 to 50%; a 10 g the pedigree selection and backcrossing program of the late kg 1 decrease in lignin generally resulted in a 40 g kg 1 Dr. R.R. Kalton working in collaboration with Forage Genetincrease in digestibility (Cherney et al., 1991). As a ics, Inc., and Cal/West Seeds, Inc. These four lines derived result, voluntary intake and animal performance may from 684 lines that had been selected for vigor, disease resisincrease by up to 30% (Cherney et al., 1991). tance, and regrowth potential near Ames, IA, between 1965 Despite these advantages, and the discovery of the and 1990. The 684 lines from this program were tested for brown-midrib trait as early as 1931, brown-midrib muinitial and regrowth forage yield, establishment, and disease resistance at Arlington or West Salem, WI, between 1992 and tants were not used in commercial germplasm until the 1995. Both selfand open-pollinated seed were produced on 1990s. Brown-midrib phenotypes suffer from reduced one to four plants per line in each year. Open-pollinated seed vigor and yield. In maize (Zea mays L.), yield reductions was used for testing, while self-pollinated seed was used to advance selected lines to the next generation. M.D. Casler, USDA-ARS, U.S. Dairy Forage Research Center, 1925 In February 1996, seeds from Piper, Greenleaf, Piper-bmr, Linden Dr. West, Madison, WI 53706-1108; D.J. Undersander, Dep. Greenleaf-bmr, and the best four lines from the Iowa/Wisconof Agronomy, Univ. of Wisconsin-Madison, Madison, WI 53706-1597; sin selection program (hereafter called FG lines) were germiJ.F. Pedersen, USDA-ARS, Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583-0937. Received 21 Feb. 2002. *Corresponding auAbbreviations: ADF, acid detergent fiber; ADL, acid detergent lignin; thor ([email protected]). DM, dry matter; FG, Forage Genetics, Inc.; NDF, neutral detergent fiber; NDFD, neutral detergent fiber digestibility. Published in Crop Sci. 43:782–789 (2003).