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In Vitro dry Matter Disappearance of Brown Midrib Mutants of Maize (Zea Mays L.)¹

U. S. Department of Agriculture, University Park, Pennsylvania 16802 and and Purdue University, Lafayette, Indiana 47907

Abstract

Normal (non-mutant) and three brown midrib (mutant) genotypes of maize (Zea mays L.) in Tr background, bm₁/bm₁ (bm₁), bm₃/bm₃ (bm₃), and bm₁/bm₁:bm₃/bm₃ (bm₁:bm₃), were harvested at 10, 35 and 55 days post-silk. Plants were separated into leaf, sheath, stem, husk, kernel, cob and tassel tissue. In vitro dry matter disappearance (IVDMD) was determined on all parts and a whole composite using the two-stage in vitro rumen fermentation technique. IVDMD of the whole plant normal, bm₁, bm₃, and bm₁:bm₃ was 68.3, 72.0, 75.5 and 77.8%, respectively, for plants harvested 35 days post-silk. IVDMD values for leaf, sheath, cob, and tassel from the same harvest were higher (P<.05) for all mutants compared to the normal counterpart. The IVDMD of bm₃ and bm₁:bm₃ stem tissue from this harvest was higher (P<.01) than the stem tissue of bm₁ or the normal counterpart. The IVDMD of the bm₃ and bm₁:bm₃ whole plants was greater than the normal counterparts in all harvests. The higher IVDMD values of the brown midrib mutant genotypes compared to the normal were reflected in the reduced acid detergent lignin countents of the mutants. Regression and correlation analyses indicated that the altered lignin content of the mutants is the most important variable responsible for the alterations in IVDMD.

¹ Cooperative investigations of the Plant Science Research Division, Agricultural Research Service, U.S. Department of Agriculture; and the Purdue University Agricultural Experiment Station, Lafayette, Indiana. Journal Paper No. 4271 of the Purdue University Agricultural Experiment Station.

² Research Agronomist, Plant Science Research Division, Agricultural Research Service, U.S. Department of Agriculture, U.S. Regional Pasture Research Laboratory, University Park, Pa. 16802 (formerly at Lafayette, Indiana); Assistant Professor of Animal Science; Professor of Agronomy; and Associate Professor of Animal Science, Purdue University, Lafayette, Indiana 47907.