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Genetic Variation for Response to Advancing Maturity of Smooth Bromegrass Forage Quality Traits¹

Genetic variation for quality of early headed forage is well documented, as is the decline in quality with advancing maturity of spring growth forage. The objectives of this research were to i) evaluate nine polycross families of the B8HD smooth bromegrass (Bromus inermis Leyss.) experimental synthetic for differences in response to advancing maturity (RTM) for the forage cell wall fractions neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), cellulose, hemicellulose, and insoluble ash on spring growth forage and ii) determine whether differences in RTM among the nine families were consistent across locations, years, and stand types (pure stands vs. alfalfa, Medicago sativa L., mixtures). Nine polycross families of B8HD were established in solid seeded plots, both with and without an alfalfa overseeding, at Hancock and Lancaster, WI in late August 1981. In 1982 and 1983, smooth bromegrass forage was sampled every 7 days for 7 weeks, beginning in early May. Quality of smooth bromegrass forage was reduced significantly in mixtures with alfalfa compared to pure stands. At most growth stages, polycross families in mixed stands averaged 10 to 15 g kg^–1 higher in NDF, ADF, and cellulose, as compared to pure stands. Average differences between stand types for ADL and hemicellulose were too small to be of practical value. Polycross families differed significantly in their linear RTM effects for NDF, ADF, ADL, cellulose, and hemicellulose, and in their quadratic RTM effects for NDF, ADF, ADL, and cellulose. Differences among families for RTM involved both changes in rank value at different growth stages and differences in the magnitude of response. For each trait, interactions of families with locations, years, and stand types were nonsignificant for RTM. Improved forage quality of B8HD would be expected as a result of selection for a slow RTM for NDF, ADF, or cellulose. Families selected for a slow RTM in pure stands should also have a slow RTM in mixed stands.

Key Words: Bromus inermis Leyss. • Orthogonal polynomials • Neutral detergent fiber • Acid detergent fiber • Acid detergent lignin

² Former graduate research assistant (presently plant breeder, Cal/West Seeds, Woodland, CA 95695) and assistant professor of Agronomy, Dep. of Agronomy, Univ. of Wisconsin.

Received for publication May 29, 1984.