Efficacy of singular and stacked brown midrib 6 and 12 in the modification of lignocellulose and grain chemistry.

In sorghum, brown midrib (bmr) 6 and 12 impair the last two steps of monolignol synthesis. bmr genes were introduced into grain sorghum to improve the digestibility of lignocellulosic tissues for grazing or bioenergy uses following grain harvest. Near-isogenic grain sorghum hybrids (AWheatland x RTx430) were developed containing bmr6, bmr12, and the bmr6 bmr12 double mutant (stacked), and their impacts were assessed in a two-year field study. The bmr genes did not significantly impact grain or lignocellulosic tissue yield. Lignocellulosic tissue from bmr6, bmr12, and stacked hybrids had reduced lignin content and increased in vitro dry matter digestibility (IVDMD) compared to those of the wild type (WT). The lignin content of the stacked lignocellulosic tissue was further reduced compared to that of bmr6 or bmr12. Surprisingly, bmr12 modestly increased carbohydrates in lignocellulosic tissue, and bmr6 increased fiber and lignin content in grain. These data indicate that bmr6 and bmr12 have broader effects on plant composition than merely lignin content, which has promising implications for both livestock utilization and bioenergy conversion.