Reducing lignin concentration in lignocellulosic biomass can increase forage digestibility for ruminant livestock and saccharification yields of biomass for bioenergy. In sorghum (<
i>
Sorghum bicolor<
/i>
(L.) Moench) and several other C4 grasses, <
i>
brown midrib<
/i>
(<
i>
bmr<
/i>
) mutants have been shown to reduce lignin concentration. Putative <
i>
bmr<
/i>
mutants isolated from an EMS-mutagenized population were characterized and classified based on their leaf midrib phenotype and allelism tests with the previously described sorghum <
i>
bmr<
/i>
mutants <
i>
bmr2<
/i>
, <
i>
bmr6<
/i>
, and <
i>
bmr12<
/i>
. These tests resulted in the identification of additional alleles of <
i>
bmr2<
/i>
, <
i>
bmr6<
/i>
,and <
i>
bmr12<
/i>
, and, in addition, six <
i>
bmr<
/i>
mutants were identified that were not allelic to these previously described loci. Further allelism testing among these six <
i>
bmr<
/i>
mutants showed that they represented four novel <
i>
bmr<
/i>
loci. Based on this study, the number of <
i>
bmr<
/i>
loci uncovered in sorghum has doubled. The impact of these lines on agronomic traits and lignocellulosic composition was assessed in a 2-yr field study. Most of the identified <
i>
bmr<
/i>
lines showed reduced lignin concentration of their biomass relative to wild-type (WT). Effects of the six new <
i>
bmr<
/i>
mutants on enzymatic saccharification of lignocellulosic materials were determined, but the amount of glucose released from the stover was similar to WT in all cases. Like <
i>
bmr2<
/i>
, <
i>
bmr6<
/i>
, and <
i>
bmr12<
/i>
, these mutants may affect monolignol biosynthesis and may be useful for bioenergy and forage improvement when stacked together or in combination with the three previously described <
i>
bmr<
/i>
alleles.