FORAGE YIELD AND QUALITY OF A BROWN MID-RIB MUTANT IN PEARL-MILLET

Pearl millet (Pennisetum glaucum L.) is used extensively as forage for livestock, and any improvement in forage digestibility may enhance feeding value. The effect of a pearl millet brown mid-rib gene (bmr) on forage quality and yield was evaluated using near-isogenic lines. An F-1 and two backcrosses were made to an inbred line (T85DB) to incorporate the bmr gene into a non-bmr background. From this crossing scheme, random F-2 plants were selfed to produce F-3 lines that were planted in a randomized complete-block yield trial in Tifton, GA, during 1990 and 1991. Random F-2 plants from the same cross were planted in 1989 and 1991 to evaluate forage yield and quality differences of leaf sheath, leaf blade, and stem fractions from normal and brown mid-rib plants. Brown mid-rib lines yielded 77% as much forage as normal F-3 lines. Forage in vitro dry matter digestibility was 5 percentage units greater for brown mid-rib lines compared with normal lines. Brown mid-rib F-2 plants produced 73% as much stem biomass as the normal phenotype. Stem fraction digestibility of brown mid-rib plants was 11 percentage units greater than that from normal plants. The digestibility of leaf blade, leaf sheath, and head fractions were only 2.4, 3.6, and 3.6 percentage units, respectively, greater for brown mid-rib plants vs. normal plants. Negative pleiotrophic effects attributed to the bmr gene on forage yield for the genotype in this study mag offset any advantages gained in forage digestibility.