BMR: How a Gene Mutation Became a Breakthrough in Digestibility

Over the course of the past decade, Brown Midrib, or BMR forages have become widely familiar as the elite of summer annual forages. The “cream of the crop,” these corn hybrids, sorghums, and pearl millets are distinguished by a genetic makeup that reduces their lignin content and can be visually evident as a light to dark brown tint in the stalk and leaf midrib. The BMR characteristic is actually caused by a natural genetic mutation that was discovered in the 1920s, which has the effect of increasing whole-plant fiber digestibility (usually expressed as NDFd and TTNDFD). BMRs do have some drawbacks, but these have been managed with better genetics and handling in the field. For one, the lower lignin content can mean reduced standability, since lignin is what gives structure to the plant to support its weight, and becomes more critical once the plant gets tall and top-heavy with heading. This has been addressed by breeding for a dwarf structure, resulting in a shorter plant with greater amounts of leaf material in proportion to stalk tissue. Shorter, leafier plants can rival traditional sorghums in yield and get the bonus of greater fiber digestibility from a higher leaf-to-stem ratio. A dwarf BMR combines the advantages of lower lignin with a greater leaf to stem ratio. Lowering nitrogen applications and seeding rates can also help alleviate standability issues. Yield drag is another concern that sometimes afflicts BMR products. Our trials generally show slightly