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Laboratory and in vitro Evaluation of Inbred and F₂ Populations of Brown Midrib Mutants of Zea mays L.¹

The purpose of this research was to determine the effect of brown midrib mutants on the lignln percentage and in vitro dry matter disappearance (IVDMD) of corn (Zea mays L.) stover. F₂ populations of corn carrying the brown midrib mutants bm¹, bm², and bm³, were grown under field couditions and harvested at 35 and 55 days post-silking. Plants harvested at 35 days post-silking were separated into several parts. Samples were analyzed for structural composition and in vitro dry matter disappearance using detergent solution and rumen fermentation techniques, respectively. Stover, harvested 55 days postsilking, contained 8.15, 8.07, 4.96, and 8.81% acid detergent lignin for genotypes bm¹, bm², bm³, and F₂ normal, respectively. The IVDMD percentages were 49.9, 47.6, 56.3, and 46.2, respectively. At 95 days post-silking, the lignin content was lower and the IVDMD higher in bm³ than in the other genotypes for all plant parts except the kernel. The structural composition and IVDMD of normal corn was similar to that of a commercial hybrid included in the study.

Mutant inbred lines (Tr background) of bm¹, bm³, bm²bm³, and bm⁴ were also evaluated. Mutants bm³ and bm¹bm³ were lowest in lignin and highest in IVDMD. In both the inbred and F² populations, structural components other than acid detergent lignln did not differ appreciable among the genotypes.

Since lignin limits the digestion and utilization of fibrous feeds by ruminant animals, the possible use of brown midrib mutants for improving the nutritional quality of corn stover and silage appears promising. Mutant bm³ appears to have the most potential for this purpose.

Key Words: Lignin • Structural composition • In vitro dry matter disappearance

² Assistant Professor of Agronomy, Purdue University; Assistant Professor of Dairy Science, South Dakota State University (formerly at Purdue University); Professors of Agronomy, Purdue University; and Research Agronomist, Plant Science Research Division ARS, USDA, U.S. Regional Pasture Research Laboratory, University Park, Pa. (formerly at Purdue University).

Received for publication January 21, 1972.