Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/12/2005
Publication Date: 9/23/2005
Citation: Oliver, A., Pedersen, J.F., Grant, R., Klopfenstein, T. 2005. Comparative effects of the sorghum bmr-6 and bmr-12 genes i: forage sorghum yield and quality. Crop Sci. 45:2234-2239. Interpretive Summary: Brown midrib forage sorghum has been shown to contain less lignin is therefore more digestible than normal forage sorghum. This is due to two different modifications in biochemical pathways by which lignin is produced in the plant. The gene bmr-6 causes a decrease in the activity of the enzyme cinnamyl alcohol dehydrogenase. Either of a pair of alleles, bmr-12 or bmr-18, causes a decrease caffeic acid O-methyl transferase activity. There has been speculation, but little research done to determine the relative value of the different genes. The objective of this study was to determine the impact of the bmr-6 and bmr-12 on yield and quality of the forage sorghum lines Atlas, Rox Orange, Kansas Collier, and Early Hegari-Sart. The bmr-6 gene generally resulted in a shorter plant and less yield, but did not reduce lignin compared to 'normal' forage sorghum. The bmr-12 gene generally resulted in reduced lignin, later maturity, and reduced or equivalent yield when compared to normal sorghum. There is a more digestible fiber fraction in both bmr-6 and bmr-12 forage sorghums. When all data are considered in aggregate, the bmr-12 gene appears superior to the bmr-6 gene in terms of less negative impact on yield performance and greater reduction in lignin content and fiber digestibility.
Technical Abstract: Brown midrib (bmr) forages usually contain less lignin and exhibit increased digestibility. Recent research has identified the modifications in biochemical pathways resulting from bmr mutations. In sorghum [Sorghum bicolor (L) Monech.], bmr-6 has been linked to a decrease in cinnamyl alcohol dehydrogenase (CAD) activity. The allelic bmr-12 and bmr-18 genes decrease caffeic acid O-methyl transferase (OMT) activity. There has been only limited research comparing bmr genes to each other and wild-type in isogenic sorghum. The objective of this study was to determine the impact of the bmr-6 and bmr-12 on yield and quality in near-isogenic versions of 'Atlas', 'Early Hegari-Sart', 'Kansas Collier', and 'Rox Orange.' Height, lodging, neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), in vitro NDF digestibility (IVNDFD) and dry matter (DM) yield were measured in replicated complete block experiments with gene nested within line in four environments. Brown midrib genes generally had negative agronomic impact, but these were not uniformly expressed across backgrounds. The bmr-6 gene generally resulted in a shorter plant and less dry matter yield, but did not reduce ADL. The bmr-12 gene generally resulted in reduced ADL, later maturity, and reduced or equivalent DM yield when compared with the wild-type. There is a more digestible NDF fraction in both bmr-6 and bmr-12 forage sorghums. When all data are considered in aggregate, the bmr-12 gene appears superior to the bmr-6 gene in terms of less negative impact on agronomic performance and greater positive impact on ADL content and fiber digestibility.